Integrating macroecology and quantitative genetics: evolution of body size and brain size under island rule
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2018
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Resumo
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 ± 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.
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Adaptive evolution, Ecogeographic rule, Evolutionary genetics, Microevolution, Island dwarfism
Citação
DINIZ-FILHO, José Alexandre Felizola; SANTOS, Wanderson; JARDIM, Lucas. Integrating macroecology and quantitative genetics: evolution of body size and brain size under island rule. Oecologia Australis, Rio de Janeiro, v. 22, n. 2, p. 201-209, 2018.