Brain size affects responsiveness in mating behavior to variation in predation pressure and sex-ratio

Despite ongoing advances in sexual selection theory, the evolution of
mating decisions remains enigmatic. Cognitive processes often require
simultaneous processing of multiple sources of information from
environmental and social cues. However, little experimental data exist on
how cognitive ability affects such fitness-associated aspects of behavior.
Using advanced tracking techniques, we studied mating behaviors of guppies
artificially selected for divergence in relative brain size, with known
differences in cognitive ability, when predation threat and sex-ratio was
varied. In females, we found a general increase in copulation behavior in
when the sex-ratio was female biased, but only large-brained females
responded with greater willingness to copulate under a low predation
threat. In males, we found that small-brained individuals courted more
intensively and displayed more aggressive behaviors than large-brained
individuals. However, there were no differences in female response to
males with different brain size. These results provide further evidence of
a role for female brain size in optimal decision-making in a mating
context. In addition, our results indicate that brain size may affect
mating display skill in male guppies. We suggest that it is important to
consider the association between brain size, cognitive ability and sexual
behavior when studying how morphological and behavioral traits evolve in
wild populations.