natural selection Sexual selection favors large males and females. Males choose females based on their readiness to spawn and their size in order to maximize their breeding opportunities. Larger bodies allow females to reproduce larger and more numerous eggs, better nest choice and ability to defend it, and the ability to bury eggs deeper and provide more protection. Females vary their breeding rate depending on the size of the courting male, mating more quickly with larger males. This increases the likelihood that larger males will displace attending, smaller males. Male sockeye salmon social status and greater reproductivity are directly associated with larger body size and more extreme body shapes; Larger bodies provide males with advantages when it comes to intrasexual competition and being selected for by females during reproduction. Males preferentially spawn with females who are red, which is the usual color of females. Even small changes in wavelength, saturation, and brightness can affect preference. Both sexually naïve males and experienced males showed the same preferences, which illustrates that preference for a red hue may be innate. Some traits that lead to reproductive success, such as body size and sexual dimorphism can affect one's survival. This leads to opposing pressures of natural selection and sexual selection. Larger males are favored, unless the risk of predation is very high. Sockeye salmon that die prematurely from predation are typically the larger ones in a population. This shows natural selection against large bodies. Populations with higher levels of predation tend to evolve smaller body size. Without the threat of predation, salmon that breed early in the season live longer than those that breed late in the season. Other ecological factors like stranding effect select for smaller body size in sockeye salmon when present in a habitat. Stranding is when salmon swim into dry land or shallow water during their migration for spawning and die from suffocation. In fact, studies show that the Sockeye salmon with the largest bodies are most susceptible to stranding mortality. Energy cost Reproduction is marked by depletion in energy stores. Fat, protein, and somatic energy stores decrease from the final moments in marine migration through freshwater entry, spawning, and death. Sockeye salmon do not feed during reproduction. Feeding ends once they enter into freshwater, which can be several months before spawning. Embryos are maintained with only endogenous food supplies for about 3–8 months. Reproduction in the sockeye salmon has