MORPHOMETRIC ANALYSIS REVEALS THE EVOLUTION OF BEHAVIOR-CONTROL REGIONS IN THE MEXICAN CAVEFISH

Behaviors are complex processes that are constantly evolving. Although little is known about the genetic and neuronal mechanisms underlying the evolution of behavior, studying the brain may be useful in addressing this. The Mexican Cavefish, Astyanax mexicanus, is a species with populations that inhabit surface rivers as well as caves. A. mexicanus populations are excellent models for convergent and parallel evolution. Using morphometric analysis software, we investigated the differences in brain morphology between the two morphs. The cave populations exhibit a smaller optic tectum volume, which is consistent with their loss of eyes, a larger hypothalamus, and an increased size of the olfactory bulb volume. Each of these regions have known roles in different behaviors, which differ between cave and surface fish. These findings provide insight into how evolution can affect behavior by changing neuroanatomical structure.