Brain size evolution in the frog Fejervarya limnocharis supports neither the cognitive buffer nor the expensive brain hypothesis

Variable environmental conditions affect brain size evolution. To explain inter‐ and intraspecific brain size variation among vertebrates, two adaptive hypotheses – the expensive brain hypothesis ( EBH ) and the cognitive buffer hypothesis ( CBH ) – have been proposed. The EBF proposes that relative brain size is reduced in animals that experience longer periods of low food availability in fluctuating environments. Alternatively, the CBH states that a major advantage of a relatively large brain is to enhance cognitive abilities in fluctuating environments. We found considerable variation in brain size and the sizes of brain structures in the Asian grass frog ( Fejervarya limnocharis ) among populations. Inconsistent with the predictions of the EBH and the CBH , individuals living in habitats with medium variation in temperatures and length of growth seasons at middle latitude and/or altitude had a relatively large brain, suggesting that environmental habitat‐induced energetic constraints do not play an important role in shaping brain size evolution. Moreover, we also detected a significant intersexual difference in telencephalon size. Specifically, none of relative size of brain structures was correlated with variation in temperature and growth season related to environmental habitats, although latitude strongly affected the relative sizes of telencephalon and cerebellum. Our findings decline both the EBH and the CBH to explain brain size variation in the Asian grass frog. Furthermore, our results also suggest the sex‐specificity of the environmental‐induced brain size evolution in adult frogs associated with reproductive behaviors and spawning site selection.