INTEGRATING MACROECOLOGY AND QUANTITATIVE GENETICS: EVOLUTION OF BODY SIZE AND BRAIN SIZE UNDER ISLAND RULE
Keywords:adaptive evolution, ecogeographic rule, evolutionary genetics, island dwarfism, microevolution
Island rule proposes that a negative correlation between ancestral body size in continents and the descendent body size in islands exists, and this pattern have been widely studied in a macroecological and comparative perspectives. However, there are doubts about what mechanisms underlie body size evolution in islands. Here we review methodological and theoretical framework on evolutionary quantitative genetics, showing their application on body and brain size evolution in islands, using Hippopotamus dwarfism as example. In our analyses we started by generating 10,000 combinations of model parameters (generation time, effective size and heritability) and tested by Mutation-Drift Equilibrium model if body size dwarfism is a consequence of neutral drift or directional selection. We found that 99.9 % of simulations rejected neutral model. Then, we estimated the strength of directional selection necessary to differentiate the island species and found that a relatively low proportion of population (0.01 - 0.2%) should be selectively killed to decrease body size. Our results also showed that one unit decrease in body size would increase, on average, fitness by 4% in each generation, so directional selection is a plausible explanation to island rule. Finally, we also simulated the evolution of brain size of dwarfed Hippopotamus as a consequence of body size evolution alone. Our estimates of Expected Brain Size (EBS = 484 À 64 cc) were larger than the observed brain size (equal to 380 cc), which suggests the need to estimate directional selection acting on brain size independently of body size evolution. This supports the overall idea that brain size reduction is advantageous in island environments under a scenario reduction in resources, due to the high energetic budget of brain. Our analyses using evolutionary quantitative genetic support that Island Rule as a parsimonious adaptive explanation for the reduction in brain and body sizes and illustrates how to couple evolutionary analyses at population level to better understand macroecological patterns.
"Kutokana na utafiti wa ""maumbile ya binadamu"" na ""maumbile ya binadamu"" katika jamii ya binadamu, kuna uwezekano mkubwa wa kuonekana kwa njia ya maumbile ya binadamu, kwa sababu ya maumbile ya binadamu katika jamii ya binadamu." Hata hivyo, kuna shaka kuhusu utaratibu unaoongoza mabadiliko ya ukubwa wa mwili katika visiwa. Katika makala hii, tutakujulisha juu ya nadharia ya maumbile ya binadamu na jinsi ya kuitumia katika kuendeleza ubongo na mwili wa binadamu, kwa kutumia mfano wa hipopotamus. Katika uchambuzi wetu, tulianza kwa kuzalisha mchanganyiko wa vipimo 10,000 vya mfano (wakati wa kizazi, ukubwa wa ufanisi na urithi) na kukagua kwa mfano wa usawa wa mabadiliko ya mwelekeo ikiwa dwarfism ya ukubwa wa mwili ni matokeo ya mwelekeo wa kutofautisha au uteuzi wa mwelekeo. Kwa mfano, 99.9% ya simulations zilizochukuliwa zilikataa mfano wa neutral. "Kisha, tulikadiria nguvu ya uteuzi wa mwelekeo muhimu kutofautisha spishi za kisiwa na tukagundua kwamba sehemu ndogo ya idadi ya watu (0.01 - 0.2%) inapaswa kuuawa kwa kuchagua ili kupunguza ukubwa wa mwili.""" "Hata hivyo, matokeo ya utafiti huo yanaonyesha kuwa ""kupungua kwa kipimo kimoja katika ukubwa wa mwili kutaongeza, kwa wastani, uwezo wa mwili kwa asilimia 4 katika kila kizazi,"" na kwa hivyo uteuzi wa mwelekeo ni ufafanuzi wa kuaminika wa utawala wa kisiwa." Mwishowe, tulifanya simulation ya ukuaji wa ukubwa wa ubongo wa hippopotamus dwarfed kama matokeo ya ukuaji wa ukubwa wa mwili peke yake. Uwezo wa ubongo wa kutarajia (EBS = 484 - 64 cc) ulipimwa kwa kiwango cha juu zaidi kuliko ukubwa wa ubongo uliotarajiwa (kama 380 cc), na hivyo kuashiria umuhimu wa kukadiria uteuzi wa mwelekeo unaofanya kazi kwenye ukubwa wa ubongo bila kujali mabadiliko ya ukubwa wa mwili. Hii inasaidia wazo la jumla kwamba kupunguza ukubwa wa ubongo ni faida katika mazingira ya kisiwa chini ya hali ya kupunguzwa kwa rasilimali, kwa sababu ya bajeti ya juu ya nishati ya ubongo. Uchambuzi wetu wa chembe za urithi wa kiasi cha mageuzi unasaidia sheria ya kisiwa kama ufafanuzi wa kubadilika kwa kupunguza ukubwa wa ubongo na mwili na unaonyesha jinsi ya kuunganisha uchambuzi wa mageuzi katika kiwango cha idadi ya watu ili kuelewa vizuri mifumo ya ikolojia.