Brain morphological adaptations of Gambusia affinis along climatic gradients in China

Many studies have confirmed the impact of the environment on the brain. However, it is still controversial whether the cause of the change is phenotypically plastic or heritable. In this study, we studied morphological variations of the brain among Gambusia affinis obtained from 10 different populations in China. We found that the sizes of total brain and brain regions were affected by climatic gradients. For instance, there was a decrease in the volume of olfactory bulbs, optic tectum, corpus cerebelli, and total brain from north to south. Common-garden experiments indicated that the variations in the sizes of the hypothalamus and the total brain were heritable, while that of other brain regions were phenotypically plastic. Variation in brain morphology of wild fish supports the mosaic hypothesis. The common-garden experiments provide a reference for heritability estimates and phenotypic plasticity of brain volumes. In addition, our study has laid the foundation for in-depth research on the adaptive evolution of the brain of G. affinis.