Larger female brains do not reduce male sexual coercion

Abstract

Sexual conflict generates a reproductive arms race that often involves behavioural adaptations of females to avoid male sexual coercion. Given the cognitive demands underlying behavioural adaptations, it is surprising that there has been little exploration of whether sexual conflict plays an important role in the evolution of female brain size. Here we used a livebearing fish, Gambusia holbrooki, from a natural population to examine the influence of female and male traits, including female brain size, on mating behaviours. Female body size was the best predictor of avoidance of attempted copulations, and the primary result suggesting an effect of female brain size indicated that females with smaller, not larger, brains displayed greater avoidance. Male coloration (silver or melanic) and female approaches to males were the primary determinants of interactions between the sexes. Melanic males directed more attention to females than did silver males. The positive association between female and male attention highlights the intriguing possibility that females may exert more control on male mating behaviour than previously acknowledged in this species. Overall, our results indicate that female brain size may have little impact on reducing male sexual coercion. Additional studies across taxonomic groups are needed to understand the generality of this pattern.