Interspecific and intraspecific comparisons reveal the importance of evolutionary context in sunfish brain form divergence

Habitats can select for specialized phenotypic characteristics in animals. However, the consistency of evolutionary responses to particular environmental conditions remains difficult to predict. One trait of great ecological importance is brain form, which is expected to vary between habitats that differ in their cognitive requirements. Here we compared divergence in brain form and oral jaw size across a common littoral-pelagic ecological axis in two sunfishes at both the intraspecific and interspecific levels. Brain form differed between habitats at every level of comparison, however divergence was inconsistent, despite consistent differences in oral jaw size. Pumpkinseed and bluegill species differed in cerebellum, optic tectum, and olfactory bulb size. These differences are consistent with a historical ecological divergence because they did not manifest between littoral and pelagic ecotypes within either species, suggesting constraints on changes to these regions over short evolution...