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Are there any animals that are unable to hear the human voice?
Humans and animals have different hearing ranges. The frequency range of a human, for example, is stated with 20 Hz to 20 kHz, whereas the fundamental voice frequency is stated with 125 Hz for men, 250 for women and 440 for children.
Now if I understand correctly, the hearing range of bats, for example, is commonly stated with 1 kHz to 200 kHz (depending on species). The hearing range of mice is stated with 1 kHz to 70 kHz.
Are there (apart from those with no sense of hearing at all) any animals that are unable to hear human voices at all?
(Edited in reaction to the first and the second comment below. Humans can obviously realise speech with energy at much higher frequencies. My examples are in this respect misleading.)

In your background information you may be misinterpreting the meaning of fundamental frequency; human speech includes substantial energy at much higher frequencies than the ones you mention, centered around about 1 kHz on a log scale.

There are plenty of animals that don't have a sense of hearing. E.g. I don't think sponges or jellyfish have a sense of hearing

Thank you, Mr Krause, for your remark. I have indeed misinterpreted the meaning of fundamental frequency and insofar given misleading examples. I do realise that humans are able to realise speech at much higher frequencies than at fundamental level. My original question, however, if there are animals that  do have a sense of hearing and yet are unable to hear the human voice, remains. Thank you,

Are there (apart from those with no sense of hearing at all) any
  animals that are unable to hear human voices at all?

I don't know of any examples off the top of my head, but let's think about this systematically.
The voiced speech of a typical adult male will have a fundamental frequency from 85 to 180 Hz, and that of a typical adult female from 165 to 255 Hz.
These are fundamental tones, and DO NOT include overtones (harmonics) of higher frequencies, that are actually responsible for the timbre of the voice, i.e. its characteristic sound and full content sonic content.
Here is a Fourier transformation of an audio clip of a female voice (a plot of frequency vs. amplitude, whereby the original recording was broken down into its constituent sine waves).

As you can see, the vocal cords produce overtones up to - and beyond - 7.5kHz. These overtones theoretically go to infinity in frequency, but are very negligibly quiet past around 10kHz in our case. Certainly very low in terms of decibels (though do not confuse real decibels with the -70dB sensitivity on the graph; with audio processing gear, 0dB is at which the signal is maximally saturated, or 'clips'). Let's assume 10kHz is the upper limit for normal female speech.
Keep in mind this does NOT mean that one could not perhaps sing a high note, and produce overtones past 10kHz - this is in fact doable. But let's stick with regular speech in our case.
Below you'll find the hearing ranges of some animals (source).

You'll find that all animals listed (save one) can hear some significant range of a regular (female) human voice. The little brown bat would not be able to hear the upper harmonics of a typical female speaker, given that they speak in a monotone.
Lastly, please keep in mind the difference between decibels ('loudness') and frequency (ability to sense a pitch). Some of the extreme high overtones are very quiet, so even if an animal would be able to sense them, they may not have a sensitive enough ear to pick up how quiet these sounds would be.
And really lastly, remember that sound produces vibrations and resonates through objects that sound waves hit. These resonate at different frequencies, so your voice can be sensed indirectly too through these resonating frequencies.

I hate to upvote an answer to what I consider a poor question, but I congratulate you on the evidence you have brought to bear on this.


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How to generate electrical current from biological decomposition
I'm working on a project to generate and store small amounts of electrical current by means of decaying organic matter and would like to know:
a) Is it possible to generate electrical current from biological decomposition ("decay of organic matter") i.e as a result of the naturally occurring chemical reactions that result from decay?
b) If so, how can this be demonstrated in a lab?
I've found this article on the subject so far and am looking for more accessible information on the topic:
https://www.livescience.com/63569-gut-bacteria-produces-electricity.html

Welcome to Biology.SE! Please take the [tour] and then go through the help pages starting with [Ask] questions effectively on this site and [edit] your question accordingly. In particular, please clarify and focus your question — the article you linked to (and the original research article) seems to answer part a) of your question. If you have some reason to doubt that result please elaborate on why in your post. If not, then convert part a) into a statement (and reference the original paper as evidence). Note: you can probably answer b) by reading the Methods of that paper. Thanks!

What I was looking for is called a "Microbial Fuel Cell":
https://en.wikipedia.org/wiki/Microbial_fuel_cell

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

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DNA methylation and the validity of the definition of epigenetics
I am currently studying a textbook that presents the following definition of epigenetics:

Epigenetics is defined as heritable changes in gene expression without changes in the DNA sequence.

The authors then claim the following:

DNA methylation is a stable and inheritable epigenetic mark. This genetically programmed modification is almost exclusively found on the 5' position of the pyrimidine ring of cytosines (5mC) adjacent to a guanine.

Given these two excerpts, it seems somewhat contradictory to define epigenetics as heritable changes in gene expression without changes in the DNA sequence. After all, the DNA sequence is comprised of nucleotides, and it is these nucleotides that are modified during methylation (for instance, the addition of the methyl group on the 5' position of the pyrimidine ring of cytosines adjacent to a guanine), right? So, is it not technically true that the DNA sequence is changed? Or is what they're saying that, although the nucleotide is changed (such as in DNA methylation), the base pairs are unchanged (I'm unsure if this is true, just hypothesising)?
I would greatly appreciate it if people would please take the time to clarify this.

A methylated nucleotide is the same nucleotide, for the purposes of base-pairing events. The methylated base will be paired with its Watson-Crick opposite after replication, for instance (and methylation will even persist after replication).

The Methylation will change the individual nucleotide(s) and persist after replication. However the order of the base pairs does not change, so the information in the DNA will still remain , and the base pairs remain with their same partners.For an analogy consider a hardcover book as the DNA . Then the author of the book signs the cover. The signature is like the methylated nucleotide. There is now more information on the book cover but the message inside remains the same.

Most of the DNA methylation in gametes is erased. However, not all the histone codes or DNA methylation patterns are completely erased and that may provide some transgenerational inheritance.

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question about cat's claws?
ok so I went and read this website:
https://www.yourpetsbestfriend.com/your_pets_best_friend/2010/03/why-cats-sharpen-their-claws.html
So I have some questions to ask:

how many times does a cat has use its claw to lose its razor-sharpness and become like this?

when a cat scratch a tree or any hard objects, it sheds its worn outer sheaths and will become like this: (the big one is before it sharpen, the small one is after). I heard that there claws have layers like an onion, so how many layers does it has on its claw? how many times can it do this in one day, i mean can it do this sharpening method everytime or it has a limit?

this question could use of clarity and research.

New horn sheathes continually grow throughout a cat's life. The mechanism is described in depth in the following:

The structure of the cornified claw sheath in the domesticated cat (Felis catus): implications for the claw‐shedding mechanism and the evolution of cornified digital end organs (2009)

The highly complex architecture of the cornified claw sheath is generated by the living epidermis that is supported by the dermis and distal phalanx. The latter is characterized by an ossified unguicular hood, which overhangs the bony articular base and unguicular process of the distal phalanx and creates an unguicular recess. The dermis covers the complex surface of the bony distal phalanx but also creates special structures, such as a dorsal dermal papilla that points distally and a curved ledge on the medial and lateral sides of the unguicular process. The hard‐cornified external coronary horn and proximal cone horn form the root of the cornified claw sheath within the unguicular recess, which is deeper on the dorsal side than on the medial and lateral sides. As a consequence, their rate of horn production is greater dorsally, which contributes to the overall palmo‐apical curvature of the cornified claw sheath. The external coronary and proximal cone horn is worn down through normal use as it is pushed apically. The hard‐cornified apical cone horn is generated by the living epidermis enveloping the base and free part of the dorsal dermal papilla. It forms nested horn cones that eventually form the core of the hardened tip of the cornified claw. The sides of the cornified claw sheath are formed by the newly described hard‐cornified blade horn, which originates from the living epidermis located on the slanted face of the curved ledge. As the blade horn is moved apically, it entrains and integrates the hard‐cornified parietal horn on its internal side. It is covered by the external coronary and proximal cone horn on its external side. The soft‐cornified terminal horn extends distally from the parietal horn and covers the dermal claw bed at the tip of the uniguicular process, thereby filling the space created by the converging apical cone and blade horn. The soft‐cornified sole horn fills the space between the cutting edges of blade horn on the palmar side of the cornified claw sheath. The superficial soft‐cornified perioplic horn is produced on the internal side of the unguicular pleat, which surrounds the root of the cornified claw sheath. The shedding of apical horn caps is made possible by the appearance of microcracks in the superficial layers of the external coronary and proximal cone horn in the course of deformations of the cornified claw sheath, which is subjected to tensile forces during climbing or prey catching. These microcracks propagate tangentially through the coronary horn and do not injure the underlying living epidermal and dermal tissues. This built‐in shedding mechanism maintains sharp claw tips and ensures the freeing of the claws from the substrate.

is it possible to put your answers on the numbers of my question, please


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Has a walrus ever been filmed catching a seal under water?
Walruses have been long thought to be grazing feeders, scooping up clams from the sea floor. However, when walruses bodies have been examined by scientists, frequently the remains of seals are found in their stomachs. This has led to the speculation that walruses hunt seals, however, apparently this behavior has not been observed because it would take place under water, if it occurred. The Wikipedia merely says that the "importance of seals in the walrus diet is under debate". Has anyone ever filmed a walrus hunting, catching and eating a seal under water?

If you can attach a camera to the head of a giant walrus, it's perhaps the best way to film it. You can send the filming suggestion to the bbc or to sir-dave's office which is well connected with nature cinamatographers. Strangely, I only found this: https://edition.cnn.com/2018/12/07/americas/seals-eels-nostril-hawaii-intl-scli/index.html

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Damselfly identification
Can somebody identify this damselfly? Found near a stream about 15 miles west of Boston.

I would have called that a Blue Darner, but apparently that's been a local Missouri name and not a real name this whole time, so I don't know what the real name would be. It was even called Blue Darner on the official FFA entomology exams.

It be an Argia anceps, but the shade of blue is a little off. The pattern of black marks looks close though. Wikipedia points out that many damselfly species have very similar appearances.

@user137 is it September 19th already?

@arboviral What does September 19 have to do with it?

@user137 https://en.wikipedia.org/wiki/International_Talk_Like_a_Pirate_Day ("It be [...]"). :)

@arboviral You mean you don't talk like that every day?

Just got word from a biologist from State of Mass......“Violet Dancer” (Argia fumipennis)

It looks to me like a male Argia fumipennis violacea

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Can you identify this animal?

It was in the bathroom, 2cm in lenght (or so). It has two small antenas on the head. I live on Balkan peninsula, inland.

Looks like a millipede, maybe a centipede. I can't count the legs.

That is a European Millipede.

I found this picture by searching European Millipede. Obviously there are different types - and this is the one you have.
Here is a wiki link I found: https://en.wikipedia.org/wiki/Cylindroiulus
I think your specifically is a Cylindroiulus britannicus
.

do you have any reference to add; what made you think that this is a european millipede?

Sure. I will edit the post.

Why would C. britannicus be in the Balkans? I couldn't find a habitat range for the species, but its name would suggests otherwise.

@MarchHo- I think they were imported somehow. I am not sure, but I can look that up.

It is certainly a millipede, but I doubt it is C. britannicus. They live in natural habitat, like forest floors. In the balkan, greece and cyprus, there is a millipede that commonly lives near and in houses, I have encountered it often. Unfortunately, I haven't been able to find the name (yet).

@RHA, same - but it looked very, very similar so I assumed that that was it...


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Plant growing inside a fruit
Today after cutting open a papaya , a plant was found in it:

How is it possible for a plant to grow in a fruit? How does it gets $CO_2$ and light for photosynthesis?

That is a papaya seed showing vivipary, or premature sprouting. The plant is getting all the sugar it needs from the nutrients stored in the seed so it does not photosynthesize. If it were to run out, the plant would die.


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Help ID this South Indian fruit-bearing tree
So there's this fruit-bearing tree near my house in Kerala, South India. A senior neighbor of mine tells me that this fruit is edible. I tried it out, and it tastes alright. I want to ID this plant, know its botanical name, as well as whether it has any medical/commercial/culinary application.

The fruit is green when tender and red when ripe.

This looks like Muntingia calabura, the Jamaica Cherry.

pic source

pic source
It is indigenous to tropical America and often planted in Asia.
It is edible and used in jam, cake and fruit drinks. The bark is sometimes used as rope. Source: "Tropische vruchten, Nowak&Schulz 1999"

Googled it and confirmed. This is what I was lookin' for. Thanks again!


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Why Is Action Potential Propagation Not Described by Telegrapher's But Cable Equation?
In modelling the propagation of action potential in an axon, why is the partial differential equation the cable equation rather than the telegrapher's equation? The difference between the two is that the former does not have inductance while the latter has. Does an axon not have inductance whether it is myelinated or unmyelinated? This is related to my previous question. There the only answer I obtained attributes this choice not to experimental evidence but the deficiency on the part of biologists in mathematical sophistication in dealing with the complication of electromagnetism arising from including inductance.

I am the individual who answered your earlier question.  The answer remains much the same.  The Cable Equation is inappropriate.  It was developed originally as the Heat Equation of Thomson,  While Thomson disowned its application to the axon as a cable, Herman continued to promote the solution within the Biology community.  The problem is the Cable Equation requires as an initial condition that the stimulation of the cable continues until the signal reaches the terminus of the axon by conduction (diffusion).
When exploring the myelinated axon, the Telegrapher's equation must be used.  The formal name for this equation is the General Wave Equation, GWE, of Maxwell. It involves an initial condition that is much more lenient.  The stimulus must only be applied to the axon for long enough to ensure the desired full waveform is represented. Thus the GWE involves propagation and not conduction (or diffusion).  See section 7.4 of Chapter 7 of "Processes in Biological Hearing," PBH, on my website.
Cole & Baker, "Longitudinal Impedance of the Squid Giant Axon", Journal of General Physiology, (1941) vol 24(6) pp 771-783 present their initial measurements of inductance within the large axon of a small squid.  This axon generated "swim waveforms" and not "Action Potentials" as currently defined.  The inductance is much smaller in a non-myelinated axon than in a myelinated axon.  It remains calculable in either case.
I have reviewed the two papers by Lieberstein & Mahrous you cited for my benefit.  The authors are apparently two very good mathematicians without much knowledge of biophysics or the biophysics literature.  They quote a diffusion velocity from Hodgkin & Huxley (1952) that is several orders of magnitude slower than the phase velocity along an axon that is very well documented by Cole and more recently by Smith et al.  I have uploaded a more complete analysis in Section 9.1.1.4.3 of the above citation to chapter 9 of my work, 9SignalTransmission.pdf.
These two papers should not be relied upon until reviewing Section 9.1.1.4.3

Thank you, again, for your answer. Here are two more papers that suggest the existence of induction in an axon, http://jgp.rupress.org/content/jgp/22/5/649.full.pdf,
http://sciencedirect.com/science/article/pii/0025556470900416 and http://jgp.rupress.org/content/jgp/25/1/29.full.pdf. Feel free to incorporate these references into your answer.


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How should the interval between serial dilutions be expressed?
The interval between simple dilutions is a constant value added to the preceding dilution to get the next. How should a factor for serial dilutions be mentioned? As there is no common difference between successive serial dilutions, rather a common ratio.

That depends strongly on your experimental needs. Sometimes 1:10 between two steps is necessary, sometimes 1:100 fits better.

I apologise, but I actually meant to ask how would you mention the interval. Like, interval for a simple dilution is 2% so how would the interval be stated for a serial dilution with concentration reduction by 1/10th every successive dilution?


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Why does spiral or annular thickening occur in water conducting plant vessels?
From what I behold, spiral and annular thickening of xylem and trachied cell walls leaves a lot of not thickened regions of cell wall. Lignin is the material which prevents water from escaping these water conduits. If lignin is absent from certain regions, does not that mean that water flows out of the xylem vessels and trachieds through their cell walls? If so, is not this disadvantageous to a plant? Why can't a plant simply thicken the cell walls with uniform lignin deposition, only sparing pits to allow lateral flow into the required tissue? I would appreciate your kind response.

Exactly, if pits have the function of lateral flow then why is not lignin deposition uniform? That is what I am curious about.

Non uniform lignification of xylem vessels is beneficial to a plant in that it enables growth. It is at the unlignified parts of plants that growth occurs since fully lignified tissues are dead and so can not grow. Spiral and annular thickening allows for vessels to elongate and thus allows tissues to expand without breaking the vessel walls.
Water cannot just go on flowing from plant cells because they are not lignified, plant cells have cellulose cell walls and cell membranes which prevent water loss. In addition, water in the xylem is not under pressure so I do not think water would be able to flow out of the xylem vessels except in cases where water is forced to move to adjacent phloem tissues by osmosis during phloem translocation.

Welcome to Biology.SE! Your answer sounds reasonable, however, it is likely to receive a more favorable response if you include supporting references (primary literature is best, but a textbook available online would seem sufficient for this question).  You also should be able to easily remove the pictures by editing your post ...——— Please take the [tour] and then consult the help pages for additional advice on [Answer] effectively on this site and then edit your answer accordingly. Thanks!


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Goodwin oscillator explained
Hello I have been reading papers about the Goodwin oscillator and I found that the equations are kind of tricky. Specially the part of the hill coefficient. In his paper "An entrainment model for timed enzyme synthesis in bacteria" from 1966, in the part of the differential equation of the mRNA concentration Xi, there is the term Zi and this term also exists in other books that talk about this oscillator. However, I don't know what it means. Goodwin never mentioned what this term means. I'm guessing it is about the hill coefficient, but still I do not quite understand well.
I share the link of a chapter book that explains the equations of this oscillator (page 244):
Biochemical Oscillations
Thanks for your help.

Adding a link to the paper and including the section in question would improve this question a lot.

I can´t put the link of the paper because you need a subscription to download it. But i can share the link of the chapter of a book that explains this oscillator.

A link to pubmed is fine. Many folks here have Uni library access.

The ODEs for the Goodwin oscillator are:
$$\begin{align}
\frac{dX}{dt}=&\ k_1\frac{K_i^n}{K_i^n+Z^n} -k_2X\\[1em]
\frac{dY}{dt}=&\ k_3X-k_4Y\\[1em]
\frac{dZ}{dt}=&\ k_5Y-k_6Z\end{align}$$
If you assume $X$ to be mRNA and $Y$to be protein then $Z$ can be thought of as an activated form of the protein (lets for instance assume a phosphorylated form).
The Hill coefficient, $n$ roughly tells you how many monomers of the activated protein co-operatively bind to the promoter or the number of protein monomers that form a multimeric repressor complex which inhibits the production of $X$. $K_i$ is a measure of how strongly would $X$ be inhibited by $Z$. To be precise it is equal to the concentration of $Z$ at which the production of $X$ is half its maximum rate. (Similar to Michaelis constant)
What the model says is that at higher values of $n$ (>8) there are sustained oscillations (which are called limit cycles). At lower values the oscillations damp. Note that even for low values of $n$ sustained oscillations (but not limit cycle types) can arise if there is substantial delay in the loop. However these oscillations are not as stable as limit cycles to perturbations.
Have a look at this post.
These are some advanced concepts and you may start by reading this book by Steven Strogatz called Non-linear Dynamics and Chaos*.

*Strogatz, Steven H. Nonlinear dynamics and chaos: with applications to physics, biology, chemistry, and engineering. Westview press, 2014. (latest edition);  ISBN-13: 978-0813349107; ISBN-10: 0813349109


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Why do people remove excess solution after they put on a coverslip?
Today, my classmate and I stained a slide of cheek cells. After we put on a coverslip, our teacher said that we are supposed to remove excess solution using a tissue.
Why should we do this? I am so confused

If I understood the question, it's just because otherwise the solution would flow out and stain the microscope.

If you leave it is messy, it can obscure the image when the stuff is on top of your sample, if it sticks to the sides the slip may float on it. If you press the slip slightly you push out bubbles and excess liquid. then by carefully removing any excess fluid you will get a stably fixated slip on a clean prep that is ready to watch.

Well, from personal experience, whenever there was excess solution on the glass slide, our teacher always commented that our slides were messy. So I guess the entire idea is to keep the slide neat, clean and to make it look presentable for observation. Also, in case the excess solution flows out to the entire surface of the glass slide, the stage clips may not be able to hold the slide in place when it is kept on the stage of the microscope (since it would be all slippery). Usually, only such little things go wrong, nothing huge. It is actually more of a basic etiquette or precaution that is followed while preparing a slide, like wiping your mouth after eating. Your observation is not affected in any way.

Neither of the current answers fully answer the question.
The amount of liquid underneath a coverslip should be just sufficient to hold the coverslip and sample onto the slide. If there is too much water, the surface tension would become reduced, allowing the coverslip to fall off the slide.
Additionally, minimising the amount of water between the coverslip and the slide would ensure that the z-axis variation in your sample is minimised, therefore reducing the likelihood that your sample will have different focal points across the sample.
This UCLA guide on microscopy slide mounting explains it (emphasis mine):

Small pieces of filter paper (Whatman #1) are placed around the edge of the coverslip to absorb excess mounting medium. If your specimen is tissue culture cells or frozen tissue sections, this should not harm them. This does two things: a) it allows the coverslip to come as close to the specimen as possible and reduces the depth of the field. You will get less focus aberration if you do this judiciously. b) the coverslip will be a lot less likely to float around on the slide and move which could specimen damage. The surface tension between the coverslip and slide will be much higher. You will also be much better able to seal your coverslip to the slide.

March Ho is right: when viewed at any magnification, that tiny amount of fluid between slide and coverslip is an ocean, where all those things are present that are present... well in an ocean: fluid currents and those critters once just underneath the surface, than again "in the deep". As March put the later: "z-axis variation".
Those involved in studying live critters, pond dipping and such (everyone should do it at least a few times!) know the phenomenon all too well.


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What is the population limit that makes consanguinity an issue?
A recent incident brought in the news one of the last uncontacted people - the Sentinelese:

the Sentinelese appear to have consistently refused any interaction
  with the outside world.
There is significant uncertainty as to the group's size, with
  estimates ranging between 40 and 500 individual

If I understood correctly, the Sentinelese have a rather small population for dozens if not hundreds of generations and I am wondering if consanguinity is not issue (e.g. serious childhood effects) for them.
Question: What is the population limit (lower bound) that makes consanguinity an issue?

Yes, inbreeding depression can be a big problem for very small populations (It's also a big problem for conservation efforts of critically endangered species, such as the Kakapo). Unfortunately, I can't really answer your specific question regarding lower bound.

I don't have a great knowledge in population genetics but I think your question can be answered by the relationship between loss of heterozygosity and the effective population size.
For an ideal asexually reproducing genetically diploid population, the heterozygosity is lost with increasing generations according to this equation:
$$H_t=\left(1-\frac{1}{2N}\right)^t H_0$$
where $H_t$ is the heterozygosity at the generation $t$, $H_0$ is the heterozygosity of initial population and $N$ is the population size.
If you analyse this equation then you'll note that heterozygosity exponentially reduces at rate inversely proportional to the population size.
For real populations you have to replace the population size with effective population size. Effective population size for a sexually reproducing population would be:
$$\frac{1}{N_e} = \frac{1}{4N_m} + \frac{1}{4N_f}$$
Where $N_e$ is effective population size, $N_m$ is number of males and $N_f$ is number of females.
You can find the derivation of these formulas in Principles of Population Genetics by Hartl and Clark.
Other than that, the probability of extinction is also higher, the smaller the population is.
When would consanguinity be an issue depends on other factors too such as initial heterozygosity, presence of deleterious alleles in the gene pool and other environmental factors. I don't think there is some kind of mathematical/practical lower bound. The minimum viable population is approximated using simulations.


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Are peanut proteins similar to chicken meat proteins?
I'm studying amino acids content in vegetable food. I was looking at peanut protein and noticed its similarity with chicken meat, as you can see in the table below (quantities are measured in grams). Third column is first column minus second column. Green amino acids are the essential ones.
The biggest difference (-1.11) happens for Lysine, but Lysine quantity (0.901) is still bigger than the lowest one, which is Tryptophan (0.2445). So in this case, is Tryptophan the limiting factor in protein synthesis? (Tryptophan amount is < than any other amount).

The table below lists the optimal profile of the essential amino acids (first column). Second column is obtained by dividing the values in table 1, first column, by 25.3055 and multiplying by 1000.
Notice that Lysine is the only one amino acid less than the reference (36<51).

So the questions are:
1) Have peanut proteins a limiting factor (if yes what is and why?) or can be considered a complete protein?
2) If the answer to 1) is "yes it has a limiting factor" what vegetable foods rich in lysine can be eaten with peanut in order to obtain all the amino acids? And how to calculate the ratio of peanut and the complementary foods to eat in order to get the proper profile of the essential amino acids?

Source for first table (first and second columns) https://ndb.nal.usda.gov
Source for second table (first column) http://nutritiondata.self.com/help/analysis-help

I'm not sure if biology is the correct site to post this question, so if you know a better one let me know, thanks.

I posted an answer to a similar question here: https://health.stackexchange.com/questions/9124/is-all-protein-the-same/9130#9130

You're not using protein as it is to maintain your body. It's first
  broken down to the individual amino acids, which your body can then
  use to build new stuff.
If you're lacking one of the essential amino acids, you can only build
  as much new protein until that runs out, and all the other amino acids
  are just excess. A protein that contains all the necessary amino acids
  is called a complete protein, and you could calculate the differences
  in the so-called quality of the protein.
A perfect protein (i.e. from egg/milk/soy) will contain amino acids in
  exactly the ratio you need, some protein contains so little of a
  certain amino acid that you'd need to eat twice as much of that
  protein (for example rice or peanuts).
In your case, if beef is making you recover fastest, you'd need to eat
  30*0.92/0.70 = 39g of peas for the same effect.
You could get around this by combining different sources of protein.
  For example grains are limited in lysine, while beans are limited in
  cysteine/methionine.

thanks for the answer, but could you explain the calculus 30*0.92/0.70 ?

It's from this link: https://en.wikipedia.org/wiki/Protein_Digestibility_Corrected_Amino_Acid_Score. The questioner wanted to know how much pea-protein they needed to eat to get the equivalent of 30g of beef protein. Beef has a "quality factor" of 0.92, pea has 0.70.

Mm I don't know then if that calculus is correct. If you eat 30g of soy protein you get all the essential amino acids. To have the same result with beef you have to eat 30/0.92=32.6g of beef protein, and with pea you have to eat 30/0.7=42.9g of pea protein. This is what I understood from reading about PDCAAS.

You're correct, but the poster was talking about the consumption of 30g beef protein.

Ah I understand now

Firstly, here are many types of proteins in both peanuts and chicken, so it is a little ambiguous to say "peanut proteins" or "chicken proteins". Secondly, proteins are proteins. "Complete" and "incomplete" are simply nonsensical terms for describing these macromolecules. Each protein performs a certain task, be it structural, like keratin, or functional, like enzymes. The purposes, as well as the abundances and characteristics of the proteins in say, a piece of chicken define its traits. The amino acid content, though related to these things about proteins, do not imply them. Proteins in different food items are simply made up differently.
To answer the question, no, there is no inert limiting factor on the synthesis of proteins in peanuts, and yes, these proteins are "complete".
I hope this helps!

I think sound wave is talking about nutrition, and the use of protein as a food. In nutrition, the terms complete and incomplete protein are widely used.

Ah ok I was unaware of that


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Are there two different senses of the word 'heritability' in use?
Target Height as Predicted by Parental Heights in a Population-Based Study states:

The heritability value was taken as the regression coefficient between
final height and midparental height

Is this the same sense of the word 'heritability' that is in use in https://en.wikipedia.org/wiki/Heritability and in answers on this site, namely Var G/Var P? Or are there two different senses in use simultaneously?
Edit: see https://www.jstor.org/stable/2531017 ... heritability h^2 is defined as follows:

Note the superscript (1/2) in the equation, indicating a square root. So the slope of the regression does not seem to be a ratio of variances.
FWIW, Wikipedia cites the S.E.P., which cites Behavioral Genetics by Plomin.

Possible duplicate https://biology.stackexchange.com/questions/59053/heritability-in-population-genetics, https://biology.stackexchange.com/questions/112552/is-heritability-just-slope

Does this answer your question? Why does the slope of parent-offspring regression equals the heritability in the narrow sense?

Actually this question answers your question. Basically if you do a bunch of math, the slope reduces to the (narrow-sense) heritability. Var(G)/Var(P) is usually broad-sense heritability, but it's hard to do infinitesimal math with the broad sense heritability.

@MaximilianPress I'm not sure that it does answer my q. It cites https://web.archive.org/web/20210420073545/http://userwww.sfsu.edu/efc/classes/biol710/heritability/heritability.htm#Oosterhout, which states (without proof or reference) that "The slope of regression of offspring on parents will tell you about resemblance between relatives, h^2". The maths in the Q/A don't add anything to that assertion.

The page you cite https://en.wikipedia.org/wiki/Heritability expresses the general concept in the first sentence:

Heritability is a statistic used in the fields of breeding and genetics that estimates the degree of variation in a phenotypic trait in a population that is due to genetic variation between individuals in that population.

This is a conceptual definition, not a mathematical one. Variance is only one statistical measure of variation; see also https://stats.stackexchange.com/questions/88348/is-variation-the-same-as-variance
I would consider a statement like "Heritability = H2 = Var G/Var P" to be not a different sense but rather an operational definition that says "in this context, we'll use this mathematical representation of the concept".
There are multiple ways to estimate or compute heritability, some of them addressed in that same article under the heading "Estimating heritability", including methods based on correlations and regression. For a simple, univariate relationship, the Pearson correlation r and the coefficient of determination are related, in that the coefficient of determination is r2 and the same as R2 and the same as the "variance explained".

So... when you see in a paper a statement like "___ has a heritability of 0.7", how on earth are you meant to make sense of that? What about meta-analyses which look at the heritability of different traits?

@Mohan In a paper producing numbers, they should be clear about what the number means; in a sense, it's a lot like how you could say something "weighs 60", but this isn't really something you can make sense of, they need to provide the units, too, so you know they're talking about 60 kg or 60 g or 60 lbs. In this case, there are no units, but you still need to know what the quantity is to make sense of it, and especially if some people are giving you a square-root version of what other people are giving you (e.g., r rather than r^2).

Thank you. Having looked into this further, I think what's confusing in this case is that not just the term 'heritability' but also the specific expression h^2 is being used to denote two different quantities, one of which is the square of the other.  [See my edit to my Q.] Sometimes a single paper seems to use both senses -- see e.g. the Plomin textbook I cited. I almost wonder whether someone looked at eq(5) in the paper I quoted and missed the square root symbol, and then that error has propogated through the literature?

@Mohan I don't know enough about the history of the term to know why h^2 is used; on the statistics side, R^2 is useful because it's interpretable as the fraction of variance explained, and also because it doesn't make sense for sign to enter into it; a squared quantity will always be positive, when you take a square root it's ambiguous whether you started with positive or negative numbers.

Another place it comes up a lot for some overlapping reasons is in variances versus standard deviations; standard deviations are useful because they are on the measurement scale. Variances are useful because that's the scale on which variation sums.


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What do we know about "continence" in animals?
What do we know about continence in animals? In particular, what do we know about the development of continence in animals?
By "continence", I'm referring specifically to whether or not a wild animal, free from human influences, appears to exhibit discrimination in when and where it relieves itself, and to what extent. For example, rats are allegedly incontinent, at least by this definition. (The article would seem to imply they are physically unable to control themselves, but other sources state that rodents can learn continence, which would imply that they normally just don't bother, which is what I want to know about.) Conversely, cats can be quite fastidious, and kittens are reportedly "unable" to void themselves without their mother's assistance. In fiction, we have an example of a species which is said to uncontrollably void when they eat.
Based on what we know from studying real animals, is it plausible that an animal would be unable to control its voiding out of a habit of not trying to do so (I'm ignoring physical problems, here), or is the cited source, if you'll excuse the highly apropos expression, full of sh--? If it is plausible, what types of animals, generally speaking, would exhibit this, and to what extent? Also, how does this change from birth to maturity?
Ultimately, what I am looking for is a set of guidelines that would allow me to predict an animal's voiding habits and the extent to which the animal is able to control the same given the animal's age/maturity and other general information (e.g. dietary tendencies). I am not worried about outliers, unless the answer is that it is not possible to make a prediction with any reasonably accuracy, in which case I would still like to know what range of variation I might expect.

Edit: I'm increasingly suspect of the cited source on rats. If that's bunk, I would still like to know; are there any examples of animals (perhaps excluding humans, because that can turn into quite the argument) who, at any life stage, do not exhibit continence and/or exhibit feline-like "hyper-continence" (i.e. inability, or at least instinctive disinclination, to void on their own) absent physiological abnormalities? (Alternatively, am I also wrong about cats?)

Please don't disrespect what folks on another SE forum have offered to you in the way of criticism, whether you "buy" it or not.

@elemtilas, to be fair, you're saying that the question, even as I have posed it here, cannot be answered because no one knows? No one has done any studies in this area? Because I really do find that hard to believe. (Conversely, I'd readily believe that the WB question has failed to attract anyone with the requisite knowledge, which is what I'm hoping to rectify by asking here instead.) FWIW, I attempted to reword that statement.

The (limited) answers there are somewhat light on details (especially with respect to how things change during maturation) and examples. To wit, so far the examples cited in the question (baby cat, adult rat) are the only "hard" facts I have. Surely someone must know more? Most of what I've gotten is instead "this is a bad question, we can't answer". BTW, feel free to suggest edits. I've tried very hard to be clear about what I'm asking.

You likely can't have it both ways: you want a general answer but you also want it to be specific enough to cover multiple life stages? It does seem like you've gotten good worldbuilding-style answers over there. Have you also tried simple searches such as: https://scholar.google.com/scholar?hl=en&q=rat+continence to better inform your question?

(elemtilas) Eh, fair enough. Done. (Bryan) Well, what I'm looking for may not be a short answer. My guess would be something like "rats are the only species that are actually incontinent, and den-residing animals need a parent's help until they're old enough to move around"... but I don't know if that's accurate? (I suspect "only rats" isn't; I'm using that as an example of where I could use help!) Also, most of my attempts to do research (including your suggestion) keep running into incontinence due to physiological problems, which is not what I'm after.

@Matthew The search I linked is full of discussion of continence (rather than incontinence) in rats; it seems a bit unusual, then, to consider them incontinent. I think probably the reference you used to refer to rats as incontinent is not meaning what you think it is, I think they're just referring to pest rodents not utilizing human toilet facilities.

@BryanKrause, the page explicitly claims that "[rats and mice] have no control over their bladders". If your claim, however, is that that's bunk, well, I'm increasingly inclined to believe you. So, are there any (non-human) examples of animals which are incontinent (absent physiological abnormalities) at any life stage?


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identify some kind of vine
I have found this plant in Trabzon, a city in Turkey. I found it near the highway. I assume it isn't planted intentionally, but maybe left after previous ornamantel plantings. It smells good I think. I am interested in it because of the nice scent. Please could you help me to find what species is this.

edit: and I forgot to add its fruits. I want to plant this vine, but if there are better varieties, I can plant them instead.
Sadly flowers lost their conditions because i collect them 2days ago. and i transported them in a plastic bag.

i can provide photos from different angles, if thoese arent clear enough

Please add the location where you found it and if you found it in the wild or in a garden.

This is a clematis, probably clematis vitalba.
This plant is native to Europe and Turkey. It also occurs on the westcoast of the USA and Australia/New Zealand, but it is probably introduced there. Source occurences
Picture from Dutch wiki:

Many clematis species have a very nice smell, and both the flower and the fruit are also nice to look at. That is why clematis species are grown in garden often, with countless varieties. They differ in color (most are white, pink or purple), in flower size and in flower time (spring/summer).

this answer is great, i was planning to plant it but i see there were better varieties with more spectacular fruits. but i dont accept this answer yet. because maybe you could want to improve your answer after i edited my question.

It's a very un-remarkable clematis, the wild type. it looks like a bush. children smoked the stalks in old times. There are much more suitable garden varieties. clematis can develop a stalk 5cm wide after enough time, they are my favourite climber along with yellow clematis, passion fruit and wisteria. clematis seeds grow very easily.


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What kind of spider is this (reddish spider)?
I just saw this spider on my door and was wondering what kind of spider this is.
information

Country: The Netherlands (Europe)
Color: quite reddish (maybe an idea why this one is reddish?)

pictures

This most likely is Microlinyphia pusilla. Note that this is a male, females look quite different. A picture that closely resembles yours can be found here

https://www.ispotnature.org/node/402405
And in case you want to know, the Dutch name is 'kleine heidehangmatspin'


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What wasp like insect breeds in clay pots with dead spiders?
I found several small clay pots of oval/cigar shape roughly 2cm long in a rarely used window in the house, because a wasp like insect was flying into a small cavity of the window.
I removed one and found dead spiders inside.

I let the rest of the nest alone and closed the window again. I guess I don't have to bother them if they aren't bothering me.
I'm wondering what type of insect is that building such nests? It looked like a cross between a wasp and a hornet.
As far as I know, wasps and hornets build their nests from wood, which gives them a paper like material. This one however is made from soil/dirt.
I'm also not sure if spiders are the only food. But given the street lamps outside, I suspect that spiders are very available and easy to catch.
The region is central Europe.

You might be interested in the answer to my question: https://biology.stackexchange.com/questions/62724/which-organism-built-this-2-cm-long-sandy-tube

They are mud daubers. Rarely sting humans and hunt spiders. Seem like a pretty helpful hornet to me!!

It's some sort of potter wasp/mason wasp (Eumeninae). The spiders are paralyzed and brought there as food for its larvae.
Here is an example of an opened nest I found on Bugguide.net that looks similar to yours:

I don't know if it's possible to say what species it is from the nest.

Please note another family does similar things: the Sceliphron which is also common in Europe (some species are also invasive). After by the pictures and the victimology, I cannot say which type of family/genus/species.

Oh i didn't know their nests were so similar! Since the author of the question saw the animals, and described them as "like a cross between a wasp and a hornet" they should be able to tell of it was a potter wasp or Sceliphron since the latter is much more slender.


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What kind of flying insect is this?
What kind of flying insect is this? It kinda resembles a dragonfly but it had what looked like a stinger on the end of it's tail. It was found in Franklin, Ohio.

Better provide some visuals, else it will be very difficult to identify.


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What kind of larve is this? Found in shed on terracotta pot in Northwest Oregon
Found this on a terracotta pot in my shed

They look like the nest and pupae of a mud dauber wasp; the black and yellow mud dauber is a common species to your area and elsewhere, though I can't personally identify the species clearly from the larvae themselves they certainly are consistent.
A nice view of the nest building process

These wasps have a characteristic very skinny abdomen, and they pack their nests with spiders before laying an egg there. They aren't typically a bother to people because they don't have any communal nest to defend, except for building nests on troublesome places like airplanes.

@Charles Those nests are pretty distinctive, though I see the blue variety more often than the black and yellow where I am (OP's nest could easily be a blue mud dauber as well).


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Trees growing around objects vs pushing them away. Where is the threshold?
If a tree grows against a taut wire then the tree will grow around it, eventually enveloping the entire wire. This often scars the tree, and if the wire is thick enough, it will interrupt nutrient flow and cause more significant damage.
But if the tree grows against a larger obstacle, such as a wide board, the tree displaces the obstacle as it grows.
As a real-life example of this, I have a large pine tree on my property next to an old wooden building. The tree, as it grew, pushed hard enough against the building's eaves to bend a 2x4 piece of lumber five inches out of the way. When that 2x4 finally met the rest of the building, the tree could no longer move the board and started growing around it.
Where is this threshold? I assume it can be described as a simple pressure (force over area), and that it is dependent on the specific type of tree. Is this tabulated somewhere?
Specifically, I wish to hang a 40lb (18kg) weight, permanently, from a branch of an ~80ft (~25m) lodgepole pine. I intend to use some sort of wider material in between the cord and the branch. It would be great if I could simply run the cord through a larger-diameter pipe and position this pipe over the top of the branch. But if this wouldn't be sufficient then I'll use boards (or similar) to distribute the weight. I won't be constricting the entire circumference of the branch.
I know that mounting a bolt into the tree would be better, but that isn't an option for me in this case.
I don't want to do this: (!)
image source

I'd have checked a forestry forum for experience there.

@com.prehensible Yeah, I also considered the gardening stack. But I'm more interested in the science behind it :)

No matter what it is is it is solidly mounted to the tree or against the tree, it will try to grow around it. your best bet is to drill into the tree and use a stainless steel bolt or screw. Just don't mount it flush and don't use anything that can corrode. wire tends to cut off a large section, it is essentially partial girdling. but a screw disturbs very little of the living portion of the plant.

Thanks, @John, the bolt is a good idea. Unfortunately I can't use one in this case. I've modified my question a bit.

its not hard to imagine that every tree has its own unique behavior...

Since you asked for the science I'll try to give a scientific but simple explanation.
Trees (and plants) become wider and taller over time. This growth is due to cell division and cell elongation from meristematic cells (analog to stem cells in animals).
The stem (upper part of a plant) becomes wider because is it constantly creating new vascular tissue from the cambium. The cambium creates xylem to the center of the tree and phloem to the outer parts. The bark that peels off is the phloem and other tissues irrelevant for the explanation. Here you can find a good illustration.
Since the tree adds new xylem all the time the, cambium gets further away from the center of the tree.
When the tree pushes against a wire, the wire cuts and kills the phloem cells and after that the cambium cells. But the plant has mechanism to regenerate the cambium ring and that's why the tree continues to grow there. In the photo the wire is already in the xylem section.
When the tree pushes against a wall there is a barrier in the whole section. Either the wall collapses (or, more commonly seen, the sidewalk rises) or growth in that sections stops.
I saw graphs of cells having up to 3MPa of turgur pressure but the actual pressure you should check is that of the bark which can be higher or lower. It changes between plants species, sections of plants and plants itself so the best is to simply check.
I wouldn't hang a weight from a tall tree. Trees get diseases and many times you only see that they are rotten from the inside when it is too late.


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Species identification - what kind of worm is this?
I am finding these worms in my bathroom since summer arrived. I have been finding these on floor, walls and damp towel I left hung overnight in bathroom couple of times. When these worms are squished, a bang like sound is produced. Can you help me identifying this, is it something to be taken seriously & requires immediate action? Average length of these worms is ~ 1-1,5 inches.  Please find a closeup picture I managed to capture with mobile camera.
I moved into this house last winter so don't know previous summer history. Anyways I think I should get bathroom drain cleaned.
Edit: Just noticed it has very tiny hair thin, white/ transparent legs, many of them. These legs are barely seen with naked eye. May be they are just hair like things not legs (I don't know proper terminology).
Edit2: origin is Lahore, Pakistan. It's far from sea, open agricultural terrain. Climate is hot.
About movement, no they don't move like earth worms (shortening in length and then stretching). Neither it's snake like. It kinda straight. They also don't have legs as centipedes do, on their sides.

It might be helpful to include what kind of climate/what region you live in

Do they move by shortening in length and then extending OR in a snake-like motion moving side to side. This could tell us whether they are a worm or closer to a millipede. Also do they have a hard or slimey exterior

definitely looks like a millipede (or some other myriapod) with lots of legs. are they really 3 inches long? (my experience is that things crawling in your house often feel bigger than they really are) i don't know about millipedes being problematic, but i don't really know much about pest control. i think you need a better picture for proper identification.

@hamilthj, origin is Lahore, Pakistan. It's far from sea, open agricultural terrain. Climate is hot. It usually gets as high as 48 degree Celsius in summer. Rains have less frequency (fortnightly, monthly).
About movement, no they don't move like earth worms (shortening in length and then stretching). Neither it's snake like. It kinda straight. They also don't have legs as centipedes do, on their sides.

@picapica, yes you're right. They are shorter than 3 inches, way shorter. It has max length of maybe ~1-1.5 inches. I misperceived it's length before. Didn't have a ruler.

Well, I don't think we'll get much further without much better photos. But my guess is that they just like the damp areas in your bathroom. I doubt they do any harm (other than possibly scaring humans), but if you make it dryer they'll probably leave. Also, you should add the new information to the question to make it easier to find.

It's some sort of millipede. Look closely and you will see hundreds of small white legs sticking out of its sides. Also, you said it goes "Bang" when stepped on; that suggests it has a rigid jointed exoskeleton, something that all millipedes have but, as far as i'm aware, cannot be found in any surviving annelid worm.

This is almost certainly not a millipede as it has no antennae and moves by compressing its body. My money is on insect larva, possibly a drain fly (which would make sense if you regularly see them in the bathroom).
It would be interesting if you could put one in a jar and see what it develops into.


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What is this insect from Brasil?

SE Brazil Atlantic rainforest Oct 2017. I'm assuming this is an early stage of an insect. It was crawling around a tree in the moss and was about 6-7mm.

SE atlantic rainforest brazil

I thought maybe a young stage cicada


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What is this plant, and is it edible?

After I planted some spring mix lettuce a couple of years ago, nothing survived except for this plant.  It doesn't look like any of the leaves that I am used to.  Does anyone know what it is?  Is it edible?  I am located in East Tennessee.
Thank you for any help you can give!
I just posted some more photos with measurements. The total length from base of the plant to the end of the leaf is about one foot. These plants have no flower growing from the base, however there is a separate plant nearby in the mix that does have flowers. I included a photo of it in case it is related. The original plant in question has leaves that are mostly smooth (some have tiny white or clear hairs on the backside or stem...some are smooth). They are almost as thick as spinach leaves.

Welcome to SE Biology. Can you edit your question to include where you are? It will help with the identification.

Thank you!  I just updated to include area... Chattanooga, Tennessee area / Southeast United States.

At first glance, I was thinking some species of plantago, but the leaf veins are wrong. Please provide more info: size of leaves, texture (hairy/fuzzy, smooth, waxy, thin/thick, etc), and any info on a flower if you have it

My guess would be Asteraceae, but species I don't know. Someone more familiair with the American flora might know.

BTW: lettuce is also Asteraceae.

Thank you all for your responses!  I just posted some more photos with measurements.  The total length from base of the plant to the end of the leaf is about one foot.  These plants have no flower growing from the base, however there is a separate plant nearby in the mix that does have flowers.  I included a photo of it in case it is related.  The original plant in question has leaves that are mostly smooth (but very few of them have tiny white or clear hairs on the backside or stem).  They are almost as thick as spinach leaves.  I hope this helps.  Thank you again for your help!!

This is a leaf vegetable called Cichorium, Endive in English. There are several closely related species, Cichorium endivia (also called endive), Cichorium pumilum (also called wild endive), and Cichorium intybus (also called common chicory). I think it looks most like common chicory, but if it comes from your seeds, Cichorium endivia is more likely.
Flower from Cichorium intybus

Flower and leaves of Ch. pumilium

https://en.m.wikipedia.org/wiki/File:Cichorium_pumilum.jpg
(source pictures:wikipedia)

Oh wow! That is very helpful...Thank you for your response, RHA!!

So looking again at the other leaves in the other photos, are you thinking that those are chicory too?

@steve I've added a second picture, from Ch. Pumilium, on which you can see leaves resembling yours.


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Identification of Bird feather, probably from a predatory bird

Found in Berlin,Germany
Area of Charlottenburg
I want to know the species of this bird, someone please tell me.
Approximate size 19 cm

Have you seen this (German) page: http://www.greifvogelhilfe.de/artenbestimmung/gefieder-greifvoegel/ ? That might help to narrow down the number of candidates.

This is a Common Kestrel (Falco tinnunculus) primary wing feather, so it is indeed from a predatory bird. The orange hue suggests that this came from a juvenile and/or female individual. Featherbase provides a good reference here.
For future feather identification questions, you may wish to post them to the Found Feathers project on iNaturalist.

Welcome to Biology.SE! This looks like a good answer, but you are more likely to get a positive response if you explain why your identification is correct. Specifically, please [edit] your answer to add discussion of key features that led you to this conclusion and supporting references or at least validated images. Without this your answer is indistinguishable from opinion. (Note that answers must stand on their own — i.e not require us to follow links.) ——— Please also take the [tour] and then consult the help pages for additional advice on [Answer] effectively on this site. Thank you!


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What culturing process / experiment needs a "grid" petri dish (one with a vertical division)
You can buy petri dishes with separations in them like this:

I have studied biology and biochemistry and never come across one of these before.  What cell culturing / experiment would this be used in?
** Edit: **
Perhaps it's not cell culturing but instead used for containing different macroscopic organisms like woodlice or something?  But then I'd have thought they'd climb over the divisions.

I am not sure about 'vertical' division. But in general there is article describing use of Divided Petri Dishes

We grow plant explants on petri dishes. They grow paifully slowly, so having several on one dish is major space-saver. Howewer, I wouldnt use prefabricated divider. Drawing marker lines on the bottom is usually enough to keep track of what is what.


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How are the first mammary glands thought to have functioned?
I happened upon a book (not about biology) containing this text:

A life-changing birth occurred on the planet about 190 million years ago [...] the first tiny shrew like creature brought forth an infant and began suckling her young. [...] this furry little mammal embodied a huge leap in biological evolution

The description is nicely dramatic, but it doesn't ring true for me. While I know that evolution likely wasn't as gradual as high school books represent it, the thought that a non-mammal bore a daughter with fully functional mammary glands who actively suckled her young is a bit too much for me to swallow. For other body systems, I have read stories how they emerged gradually, for example the oldest species having a few nerve cells, then new ones having a whole nervous "network" with a few ganglions, before actual brains emerged. Or similarly, worms having a patch of photosensitive cells on the skin evolved into animals with eyes. I know that platypuses have mammary glands without nipples, but presumably even they are already much more sophisticated than the first mammary glands.
So what are proto-mammary glands thought to have been like? Did they evolve de novo especially for feeding babies, or were they maybe repurposed sweat glands or something like that? What are they supposed to have functioned like?

the production of liquids to nourish offspring has evolved separately in several lineages, mammals have simply taken it further than any other group. it is pretty easy to see how it could evolve, any way of providing even trace nutrients or nourishment to young will have an advantage in organisms that are already engaged in child rearing. it means exposing the young to predators less often.
Mammary glands are modified sweat glands.
Monotremes do not have nipples what they have is a cluster of mammary glands on a patch of skin. the young have to suck the milk of the a cluster of hair.
The exact sequence of how lactation evolved is not well known since lactation leaves no fossil evidence.

Sources:
Lefèvre, C.M., Sharp, J.A. and Nicholas, K.R., 2010. Evolution of lactation: ancient origin and extreme adaptations of the lactation system. Annual review of genomics and human genetics, 11, pp.219-238.
Capuco, A.V. and Akers, R.M., 2009. The origin and evolution of lactation. Journal of Biology, 8(4), p.37.


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What kind of insect is it?
I found it hanging on the wall at night. It was approximately an inch long. Near my dormitory there is a lot of birch trees. The photo was taken in Prague, Czech Republic.

It is a moth in the family Noctuidae. I don't know the species.

This is the heart and dart moth (Agrotis exclamationis). Its name refers to the special black spots, which have shape of dart and heart.

This moth is one of the most common in the Paleoarctic ecozone. It has a wingspan of 35-44 mm. The larva of this moth is brown above and grey below. It is capable of feeding itself on a variety of plants.


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How to safely conserve my current DNA methylation marks?
I read the Wikipedia article on DNA methylation
Let's say I want to extract and then stock my current DNA methylation marks somewhere so that I can use it safely 20 years in the future for a medical procedure that doesn't exist yet.
What method should I use?

Welcome to Biology.SE. Your DNA will be the same in 20 years from now.

@Remi.b Sorry for the misconception. I have reformulated the question.

To record the current methylation state of your DNA, you can use bisulfite sequencing. Basically, you take half of your DNA sample and treat with bisulfite, which deaminates cytosines (C->U) , so they read as T instead of C. Methylated cytosines are protected, so they still read as C. You run two sequencing reactions, one with bisulfite-treated and the other with untreated DNA, so you can tell where the true Cs are in the genome. See the below diagram:

Wikimedia commons
Note that if you're thinking of doing this from a longevity point of view, that there are hugely different methylation patterns in different cell types; I'm not sure which cell type you'd want to pick. Also, methylation is not the only covalent modification of DNA that exists, there's also hydroxymethylation, and I'd bet there are more that we haven't discovered yet. There certainly are in bacteria and phage (glucosyl-hydroxymethylcytosine, for one). The hard thing about saving things for the future is that we really don't understand the full picture of what's happening now epigenetically, and as such, we don't have assays to detect things we don't know about.

I believe the DNA is going to be as stable in native form as it should be after bisulfite treatment. You can use commercially available methods of storing DNA samples and safely assume it will be intact in 20 years time.


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What is a rough estimate of CO₂ saturation for high-yield or high growth rate plants?
Naturally, plants have individual photosynthesis capacities, but it would still be interesting to get a general picture of CO2 saturation levels for some common cultures. Where lies the optimal yield, growth rate, etc compared to the 0.04% in the atmosphere? What is this specific field of research called?
My first assessment is that there is no saturation level for individual plants, that each plant consumes CO2 according to its species' respiration level, and culture density is adapted to the species and practical circumstances such as the greenhouse construction. Is there a field of expertise in planning greenhouse constructions, and if so, what is it called?
It seems to me plants have already or can be genetically modified for heightened respiration. I'm not familiar with this field, further reading would be appreciated.
Would plants genetically modified for heightened respiration require nightly venting/oxygen infusion to support it?
Are there examples of cultures treated as respiration machines that are completely optimized for the capacity of their DNA?

I am a horticultural consultant for 36 years. I can add that in some enclosed greenhouse situations, growers will artificially increase atmospheric CO₂ in the greenhouse to 1000-1200 PPM, about 3 times normal ambient CO₂.

Related: http://biology.stackexchange.com/questions/26231/can-plants-grow-under-extreme-1-carbon-dioxide-concentrations


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Vectors for genetic engineering
Well can a bacterium be used as a vector?I have learnt that Agrobacterium tumifacian can be used to deliver a gene of interest in plant cells but on a book in a multiple choice question it says that only plasmid and bacteriophage can be used and not the bacteria to deliver a gene of interest to a host cell.

It's a matter of semantics. Some would want 'vector' to be used strictly for plasmids, viruses and the like (see, for instance, the Wikipedia page). Others, like @physics12 below, would include whole bacteria since they can act as carriers of foreign DNA.

Yes, Agrobacterium is indeed a very widely used vector in plants. So it wouldn't be wrong to consider bacteria as vectors. Just to add, it's worth noting that in recent times, bacterial vector options have been explored in the case of humans also, especially in the case of gene therapy for cancer treatment, though its success hasn't been demonstrated yet. Refer https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3056088/ for more information on this.
To conclude, bacteria can be considered as a vector undoubtedly.

Welcome to Biology.SE!  This is a good answer, and it would greatly benefit from inclusion of a few citations for the things you claim (i.e. bacteria as a vector in plants, bacteria as vectors for gene therapy in cancer treatment).  If you haven't yet, please check out the tour.

Well 'Twinkle sheen' if the bacterium just tranfers its plasmid into the cell and the plasmid is responsible for introducing the gene of interest and not the bacterium itself then can't we apply the same logic to bacteriophages.Bacteriophages do not act as a vector but only their genetic material does.

Thank you Dirigible. I've added a link for reference.

Agrobacterium tumefaciens and Agrobacterium rhizogenes  are soil-based plant pathogenic bacterial strains containing plasmid. This plasmid is known as Ti plasmid and is responsible for inducing tumor. Part of this plasmid called T-DNA can be integrated into the host chromosomes. So, this bacterium plasmid act as vector, but not the whole bacterial cell.
(Via: https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/agrobacterium-tumefaciens)
This is true with all the pathogenic bacterial strains, as they can transfer their DNA material to cause pathogenicity. So, these pathogenic strains can be used in genetic engineering to transfer particular gene to host/mammalian cell.
Using bacteria as a vector to treat cancer or various other pathological conditions is still at developmental stage.
(Via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3056088/
https://www.ncbi.nlm.nih.gov/pubmed/16362987/)


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Do men have more extreme variations than women?
This question was considered unsuitable for Skeptics and I think it is more suited to BIology than Cognitive Sciences
I was reading this article which I found interesting. It is not supported with references but was an invited address for the American Psychological Association.
It makes the claim that men go to more extremes than women.
People can point to plenty of data that the average IQ of adult men is about the same as the average for women. So to suggest that men are smarter than women is wrong. No wonder some women were offended.

There are more males than females with really low IQs. Indeed, the
  pattern with mental retardation is the same as with genius, namely
  that as you go from mild to medium to extreme, the preponderance of
  males gets bigger.

[...]

Almost certainly, it is something biological and genetic. And my guess
  is that the greater proportion of men at both extremes of the IQ
  distribution is part of the same pattern.

[...]

Nature rolls the dice with men more than women. Men go to extremes
  more than women. It’s true not just with IQ but also with other
  things, even height: The male distribution of height is flatter, with
  more really tall and really short men.

Another notable example of a similar claim was Lawrence Summer's speech regarding the possible reasons for dearth of women in tenured positions in science and engineering at top schools.
Summers outlined 3 possible reasons, with a major kerfuffle erupting - resulting in his firing from the job as a Harvard University President - over his presented second reason [ quotes from Wiki ]:

The second hypothesis, different availability of aptitude at the high end, caused the most controversy. In his discussion of this hypothesis, Summers said that "even small differences in the standard deviation [between genders] will translate into very large differences in the available pool substantially out [from the mean]
Summers referenced research that implied differences between the standard deviations of males and females in the top 5% of twelfth graders under various tests. He then went on to argue that, if this research were to be accepted, then "whatever the set of attributes... that are precisely defined to correlate with being an aeronautical engineer at MIT or being a chemist at Berkeley... are probably different in their standard deviations as well".

QUESTION: Are there any studies or evidence to support the claim that men have more extreme variations than women (in other words, that the trait's distribution in males have fatter tails) in a variety of traits?
Possible areas of research can be:

Intelligence (general IQ or specific linguistic or spacial abilities)
Physical attributes (strength, height, weight)
personality traits

for lack of anything better, let's take the FFM's Five:
openness
conscientiousness
extroversion
agreeableness
neuroticism

In order for the answer to be "yes", the research needs to show fat tails in at least 5-6 traits from all 3 of the buckets above (intelligence, physical, and personality), although precise trait mix may be arbitrary and not necessarily limited to my examples, as long as 5-6 somewhat independent traits fit.
In order for the answer to be "no", at least 8 of the 11 traits above should have no fatter tails in men.
Anything else means "inconclusive".

The first article referenced has been taken down (possibly due to controversy). The latest available snapshot can be found at https://web.archive.org/web/20131002194704/http://www.psy.fsu.edu/~baumeistertice/goodaboutmen.htm

Having a less oppressive environment increases variance in many phenotypes. The IQ variance of (less-oppressed) whites is greater than (more-oppressed)  blacks despite less genetic diversity. Since women are on average more oppressed (i.e. outcasted more for a given deviance from the norms and given norms that take more effort to conform to) their traits would be narrower.

keep in mind even in the studies showing the largest difference the effect is incredibly minor (1.5% max) and cannot be shown to be independent of cultural factors. The wiki actually has a decent review and set of references, this question pops up over and over in my class. https://en.wikipedia.org/wiki/Sex_differences_in_intelligence#Researchers_in_favor_of_males_in_g_factor

First of all for the first 22 chromosomes (and the mitochondrial chromsome) are the same between women and men. The X and the Y together are something like 1.5% of the total DNA in the human cell.  The X chromosome is also in common, so it has the same chromosomal (genetic) variations the same as women and men.
While I am not sure about the differences you point out, its for sure there are lots of differences between the biology of men and women!  The reason that women's traits might have different variances than men comes from the fact that in women there are 2 X chromosomes and in men there is only one, as well as the additional Y chromosome.
If there are any singular defects in the X chromosome a man carries, it will not be balanced out in the human male.  (other organisms have different sex chromosome schemes).  For instance because there is a cluster of genes that help the eye see in color, women's sense of color (i.e. from their cone cells) is sometimes better than men.  With 2 X chromosomes there is even the possibility of a woman who has four different color receptors in their cones.
On the other hand, why men see better in the dark (i.e. greater sensitivity in the rod cells), is possibly due to an extra Blue Rod pigment gene that remains on the Y chromosome (see above reference).  This is both an accident of genetics, but also an adaptive 'choice' that men would have different visual acuities than women.
Its also known that woman and men may have different epigenetic patterns, with some epigenetic modifications coming from the mother and others from the father.  This is adaptive and also not the direct result of the XY chromosomes.
Interestingly, it turns out that for the most part women's 2 X chromosomes are mosaic.  That is, in each cell only one of the randomly selected X chromosomes are active.  Recessive/dominant X genes are often not the case.
This could result in a greater observed genetic variance for women because when you have two chromosomes, often one of the genes is completely silenced.  Women display all of the alleles of their X chromsomes, whereas men have only one X chromosome entirely, the Y chromosome being much smaller.
So in other words, I would say that while men and women actually have the same variation in their DNA sequences, there are different patterns in the X and Y Chromosomes that might create more variance in terms of what we see in women's displayed genetic traits.

My question is not about the difference between the sexes, but the degree of variance.

The biggest problem with this question, (not just here, but for everyone who asks it,) is drawing on our culturally constructed definition of maleness to look for mechanisms of genetic inheritance of what are considered "male" traits.  We could measure frequency distributions of height, but we don't have a way to accurately probe any of the other qualities you listed on a genetic level.  Since we can't make these mechanistic connections, any conclusions we draw would be confounded by the nature vs nurture debate.
That said, I don't know of any studies to this effect.  So this isn't much of an answer to your question.
EDIT: I've been thinking about this question all day.
The sources of heritable variation within genders that could be attributed to gender differences are (1) X and Y chromosome mutations and expression profiles, and (2) heritable epigenetic gender differences.
(2) might be more difficult to argue, since the currently known mechanism for epigenetic inheritance is the same in men and women.
One way to make this problem tractable is to look at transcriptome analysis -- it's an indirect approach to this question that gets from genome to phenotype quickly.
A cursory pubmed search led me to a study in Drosophila that takes a different approach to this question.  They sought out previously undetected levels of gender difference.  Most current studies (and there are a lot of them, including for humans) look to quantify differences in expression between genders for specific tissues. This is a prerequisite for estimating this within-genders variation, standardized against the number of genes expressed.

+1 because I agree that there are too many confounding factors due to the environment/society for the specific phenotypes considered.

-1 It's more a comment rather than answer.

@MartaCz-C: I think it is a good answer, as it points out why the question cannot have a correct answer for the specific characteristics listed (things like oppenness, or extroversion, are too ill-defined to link them to a specific genetic mechanism).

@nico And that would make it a great comment. Still it's not the answer. I'm quite irritate about amount of answers like "I don't know the answer but still I want to say something" on this site.

@Marta, I had put this as a comment, but I switched it to an answer because if I had left it as a comment, it would really be saying that I'm interested in moving to close the question as off-topic.  I think it's not enough off topic to close. Besides, if the questioner doesn't know enough to know that the scope of their question is too narrow, a strict interpretation of the rules forcee all feasible answers into the comments section. I am reasonably certain that, as asked, this question has no good answer.

This isn't an issue of  a culturally constructed definition. It is about differences between biological sexes. The cultural fluff on top is irrelivant to my question. Dealing only with hard data, do males tend to have a greater range of variance in most areas when compared to females?

At least for physical data (heigth, weight etc) you can have a look of the DINED Anthropometric database http://dined.io.tudelft.nl/dined/.  Here you can find mean and standard deviation data for Dutch population studies on numerous anthropometric measures, and you can stratify the results by sex.

that would make a great comment but not much of an answer.

So far as we can tell any difference in variability (standard deviation) in humans is cultural not genetic and thus not consistent across the species.
You are talking about something called the Variability Hypothesis, which is most often referred to in intelligence. Variability hypothesis has long been criticised for being unsupported by evidence, or in the rare cases it has been supported, it is likely to be entirely cultural since it changes drastically with culture.  It also quickly runs into the problem of defining intelligence, since different skills show different distributions with large influence by culture.
There have been no studies showing a difference in variability in any physical characteristics in humans across gender that I am aware of although males and females often have different means (height for instance). Keep in mind if men have a higher average height then their variability will appear to be higher just due to boundary effects (IE you cannot have negative heights)
In biology there is the Bateman's hypothesis that males will often show more variability than females, but this is unproven and largely untested. This study also shows numerous flaws in the original work. Don't get me wrong their are species where males show much higher variability in some characters but there are also plenty where females show higher variability, meaning this is likely a situational outcome and not a general principle.
source 1
source 2
Source 3
Source 4


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Biological contamination from ground
I took samples of tapwater in order to examine concentrations of escherichia coli and enterococcus, in a rural area. I was told, by the analytical lab, to take samples in four sterilized vessels bought from pharmacy. The problem is that at the completion of the last vessel, its cap fell frοm my hand down to the soil and some grains of sand stack on the inner surface of the cap. As fast as I could, I picked it up and washed it off totally with the water of the sampling tap. After that I closed my last sampling vessel with it and this was the completion of the sampling. How great is the possibility my sample has a serious contamination of these twο biological pollutants after this incident?
Thanks and sorry for the long story and bad english

Document the incident and notify your supervisor. For environmental testing where SOP is involved, this would count as an incident, i.e. anything that falls outside SOP. Whether the incident is a non-conformance, deviation or nothing at all is up to your quality team. You can always take another sample, supplies withstanding, too.

I would say there is a pretty big chance that you sample is contaminated. Maybe by washing most of the bacteria or fungi are removed. It would be very difficult to stick on the lid when you washed it but still. Wash the sampling tap distillate water or just tap water. If so you don't have to worry much normally it has to be free from bacteria. But, At school we did an experiment to demonstrate the present from bacteria in this water and we found bacteria. Because you took it with you and bottle opening isn't sterile. There is a big chance on contamination. But the greatest contamination would probably be the air. I think it's best to not use the data you will gain from this sample. It wouldn't be representative for you experiment. My English isn't that good either so don't worry about that.


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Can someone ID this moth seen in Bellandur, Bangalore?

Picture taken near Saul Kere. You may need to zoom in.

It's the Indian Lily Moth
(https://en.m.wikipedia.org/wiki/Polytela_gloriosae).

That looks like a plausible ID. The site generally prefers the key details of the answer to be contained in the answer itself, not just at the link. What are the distinguishing features of the Indian Lily Moth, and how would you tell it apart from similar moths?


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Help me to identify this stream insects

this insect I found on a stream in the southern region of Bangladesh. Its dorsal part is fully black and head and thorax is yellowish with black spot. Body size approx. 5-6mm, limbs 8-10mm

Where (what country, what region, what kind of stream, ...) did you find it? What is its approximate size? Was it alive when you got it? What can you tell us about its behaviour?

If I'm interpreting what I'm seeing correctly, you have some sort of Water Strider (Order Hemiptera, Family Gerridae) here; which one will depend on where you found it (and your name suggests that you might not be from the United States -- which means that I at least cannot go further).

Hey I am sorry I didn't give the details... I found it in Bangladesh southern region. Its body length is around 5-6 mm and it limbs are approximately 8-10 mm

Attempt at an answer
I think it is a water strider. There are 1700 species of water strider. Some of them are easy to eliminate (the marine ones typically) but I am not really able to give you more info from your picture.
To make sure, it is a water strider, can you please tell us
- How long are the legs (hard to tell form the picture)?
- If it was alive, was it standing on water? What can you tell us about its behaviour?
What insects live in the water?
If it is a stream insect, it could be...

a mosquito larvea
a mayfly larvea
a odonate (dragonfly or damselfly) larvea
a water strider

Here are my thoughts for each of them

a mosquito larvea

No, mosquito larvea don't any limbs

a mayfly larvea

I can't see the long cerci

a odonate (dragonfly or damselfly) larvea

Again I can't see the cerci
Also, although, it is often hard to see, it does not appear to have a fancy detachable mouth piece.

a water strider

We can't tell the length of the limbs from the picture. Were they really long?
If it was alive, was it standing on the water?

Thanks a lot. I think the above information will help me to find out the species

Although you may be right about it being a water strider, your answer is incomplete. There are a lot more water insects. Coleoptera, Trichoptera, other Hemiptera than water striders, other Diptera than mosquitos, etc.


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What kind of Caiman is this and what is on it's nose?
I was able to snap a good picture in the Manù Parque Nacional in Peru. When I reviewed the pictures in more details I noticed something on it's nose, that resemble insects. What are those? Is it a known symbiosis? What do they gain?
Also our guide called it a "white river caiman", is this accurate?
And lastly: It seems one teeth is sticking out on top of it's mouth. By looking at the shape of the jaw it looks pretty natural. Is this common for caimans?
Picture for reference:

I took the picture around here:

Nose only:

Photo taken around May 2018.


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What insect is this? I saw it in my house in Kolkata on 2 April 2018, at 8:00 p.m

I saw this insect in my house in Kolkata (India) on 2 April, 2018 after a storm at around 8:00 p.m.  I would like to know what insect it is.  Thanks in advance.

Is Kolkata the same as Calcutta, India? Also, that looks like some sort of fly to me, but I can't tell you exactly what kind of fly.

I highly suspect it to be Austrosciapus proximus

Yes, Kolkata is the new name for Calcutta, India.

Is Austrosciapus proximus found in India?

@Joyoti I'm not so sure about that, not so much information about them. However I also found out the species of the Condylostylus genus are found in India. They seem to be very similar to the one in the picture, but I'm yet to confirm: http://nathistoc.bio.uci.edu/diptera/Condylostylus2.JPG

It is a species of fly, or of the insect order Diptera, insect family Dolichopodidae.  The exact genus and species is uncertain as there are many hundreds of species. See the link below.  You can also search Google images for these names where many similar fly photos can be seen.
https://en.wikipedia.org/wiki/Dolichopodidae

More specific identification will be helpful

I would concur with user22542 --> order Diptera: family Dolichopodidae
Supporting evidence outside of wikipedia is on an Australian website. http://www.bowerbird.org.au/observations/35021
I don't suggest them to be the same species, however potentially related as they seem to live in grassy places across the globe.


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Can somebody identify this species of spider?
I ran into this cool looking spider in my yard in Banjaluka, Bosnia and Herzegovina.  It's about the size of a fingernail and unusually shaped (spherical). Could it be poisonous?

Location and size would help.

About the size of a finger nail. In Europe / Bosnia and Herzegovina. City Banjaluka.

The white cross on the body makes me think it could well be an Araneus diadematus. It is quite common and not dangerous for humans. It paralyzes its preys using some venom, though.

I agree with Araneus diadematus.  It's a fairly variable spider, but there aren't too many other options that I know of in the area.  Caveat - I'm not completely familiar with European spiders, and it's possible that there is another, similar Araneid in the area that I have not come across.  It's venomous, but like all known orbweavers, it's quite harmless to humans (and, indeed, to anything too large to get caught in the web).
Here's a comparison photo from Bug Guide - the spider in the photo is from the US, but the species is found all across the northern hemisphere.  The link goes to some information, and I've included another link to a good website on European spiders.

https://bugguide.net/node/view/3376
https://ednieuw.home.xs4all.nl/Spiders/spidhome.htm


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Exponential growth equation and bacteria
I'm a microbiologist, but I'm teaching some ecology in my intro-level course, so when we got to population growth, I thought I'd use the example of a microbial population. But, I hit a strange problem that I thought maybe an ecologist could help me understand:
Imagine a population of bacteria that can divide every 30 minutes. In one hour, every cell produces four cells. Since no one really dies, the intrinsic growth rate (r) is 4. The exponential growth equation, dN/dt = rN works fine to show the growth of the population: starting with one cell, in one hour it's 4, then in two hours rN = 4*4 = 16, in three hours rN = 16*4 = 64 and so on. At 16 hours, we get to about 4 billion bacteria, which is exactly what the microbiologist expects.
But, we then tell the students that to make it easy to predict future numbers, we can do some math and get N(t) = N(0) e^rt. If N(0) = 1, t = 16 hours and r = 4 bacteria/hour/cell, this gives e^64 which is about 6x10^27. Yikes! Kinda far from 4 billion.
So...why doesn't this work? I feel like either I'm not understanding r correctly (it would have to be down around 0.6 for this to work out, I think) or maybe there's a limit on the equation and it just doesn't work for the absurdly high r of bacteria?
Thanks for the help...

Considering your assumption:

I'm just looking at the exponential part, where the simple exponential
  equation works. If we assume there's sufficient nutrients for bacteria
  to grow unchecked for a number of hours (more-or-less true in a real
  culture)

In your original model you are using discrete states and fixed time steps. So, if 30 min is one time step then after n-steps you have $2^n$ or $4^{(n/2)}$ cells. You are basically counting double steps, which is fine. For a continuous approximation you should estimate the rate like this.
You have the first-order growth equation:
$$\frac{dN}{dt}=rN$$
When you integrate this equation (definite integral) you'll get:
$$ln\left(\frac{N_f}{N_i}\right)=r\tau$$
Where $N_f$ is final number of cells, $N_i$ is initial number of cells and $\tau$ is the time interval.

When the cell number doubles then $\dfrac{N_f}{N_i}=2$ and $\tau=30\ \text{min}$ (doubling time).
 Then your rate constant would be: $\dfrac{ln(2)}{30}\approx0.023\text{ min}^{-1}$
After 16 hours (16×30min) your number of cells would be: $e^{0.023\times16\times60}\approx 4.27\times10^9$ (approx 4 billion).
So what is basically wrong? You haven't rescaled your rate. Since the exponent is $e$ and you know that $a^x=e^{x.ln(a)}$, all you need to do is scale the rate constant with $ln(a)$ (a=2). Moroever, in a continuous model, you don't have fixed time steps. So you scale the constant with the doubling time as well.

@Jon If this answer addressed your problem, please consider accepting it by clicking on the check mark/tick to the left of the answer, turning it green. This marks the question as resolved to your satisfaction, and awards reputation both to you and the person who answered.

Real bacteria population will likely reach some carrying capacity that will prevent them to grow exponentially. As a consequence, the exponential model will be a good fit for early growth only but after a while, one will need to use some other model (typically a logistic model).
Logistic model
Here, I quickly present one standard model of logistic growth for countinuous (and not discrete) time.
$$\frac{dN}{dt} = r N(t) \left(1-\frac{N(t)}{K}\right)$$
, where $K$ is the carrying capacity. From the above model, you can see that when $N(t)$ is low compared to $K$, then the differential equation is well approximated by the exponential model you described $\frac{dN}{dt} \approx r N(t)$. Setting $\frac{dN}{dt}=0$ shows that an equilibrium is reached when $N(t)=0$ (unstable equilibrium) or $N(t)=K$ (stable equilibrium).
The equivalent model in discrete generation can yield to all kind of behaviour when $r$ reaches high enough values including cyclic variation and chaos.
More advanced models
There are other more realistic models. For example, real bacteria populations could as well consume their resource at a rate that is higher than the rate at which resources are produced and population size would then decay to eventually reach extinction.
You will here the description of a model of population growth that includes predation populations.
Build your own model of population growth
These models are not so hard to build up t fit your needs. The first chapters of A Biologist's Guide to Mathematical Modeling in Ecology and Evolution (by Otto and Day) will help you to build and analyze your own models of population biology if you are interested.

This is helpful in terms of understanding the bigger picture, and I appreciate the reference to what looks like a really helpful book. But for this example, I'm just looking at the exponential part, where the simple exponential equation works. If we assume there's sufficient nutrients for bacteria to grow unchecked for a number of hours (more-or-less true in a real culture), then I think the dN/dt equation and the e^rt equation should give the SAME approximation of population size at a given time. Why do they give such different results?

Either your $r$ is too big (but I think it is not too a bad approximation) or the assumptions that there is no competition for access to resource is violated.

The quantity $r$ must be a frequence, measured in hours $^{-1}$. So it cannot be measured in bacteria/hour/cell. If the number of bacteria is multiplied by 4 each hour, this means that $\exp r= 4, $ or $r= \ln 4 $ , or 1, 39 per hours.


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miRNA_ID to GENE_SYMBOL conversion
I have a list of miRNA IDs and a list of mRNA IDs and they are from Mus musculus species. I have converted the list of mRNA IDs to gene symbols by a list of data that was exist in NCBI and miRNA IDs list to gene symbols using Diana but I got in trouble because gene symbols on NCBI didn't match with the gene symbols that exist in Diana site. I think the problem is that naming of gene symbols doesn't follow a specific rule in different databases and are not standardized. Can anyone tell me a good way to transform both mRNA & miRNA lists to a platform for example unigene that would be unique in all kinds of databases?

As far as I know, the gene names also in NCBI changes often. Did you have a look on the synonyms listed in NCBI? This may help you. You can also look here. Here you can search for your NCBI number and the species and also get a variety of synonyms for this gene.

For mouse gene names and other details you should refer to the mouse genome informatics database (it is a standard organism-specific database like flybase [Drosophila], SGD [yeast], etc).
However, it is much better to work with RefSeq IDs. Moreover, miRNAs are seldom referred to, using their gene names. Always stick to the miRNA naming convention that is described in miRbase.
I am not sure what you are actually interested in. If you intend to map miRNAs to their targets then you can use one of the standard gene names along with the RefSeq ID. If you are using miRanda or TargetScan to predict the targets then these programs return different identifiers for the target gene including its official gene name.
In general, for ID conversion, I would prefer BioMart.

Can you please tell me how can I use BioMart for mapping miRNAs to their targets ?  I used Diana but It returned me Ensemble gene ID and their own gene symbol and not Refseq ID, How can I convert miRNAs to their targets as refseq ID ?@WYSIWYG

@minoo Sorry for the late reply. BioMart cannot be used for mapping miRNA to their targets. Use the abovementioned tools for that. If you want a different ID corresponding to the one that miRNA target prediction tools return, then use BioMart for ID conversion.