Behaviour 2019
Evolution of sexual dimorphism in brain size and brain region volumes across wild guppy populations
Angie S. Reyes, Natasha I. Bloch, Amaury F. Bittar, Natalia P. Esmeral. Universidad de Los Andes, Bogotá, Bogota DC, Columbia

Brain size is known to vary greatly in response to selection on cognitive abilities and the cost of developing a larger brain. In guppies, the evolution of brain size and anatomy relative to diverse environmental factors and sexual traits has been extensively studied in the laboratory. However, we still lack a good understanding of brain evolution in the wild. Here, we study brain anatomy and its relationship with sexual traits across 18 wild guppy populations in diverse environments. We found extensive variation in female and male relative brain size, as well as the degree of sexual dimorphism in brain size across populations. Moreover, the main brain regions do not scale allometrically with brain size, suggesting different brain regions are responding to different selective pressures across this system. In line with previous laboratory studies, our findings show males with larger brains have longer genitalia and longer tails. We also found there is a strong association between the size of brain regions and the primary sexual traits we measured. Our results suggest that varying selective pressures are driving differences in brain anatomy across populations and between sexes