Meeting Abstract

P3-71   -   Inter- and intraspecific comparisons reveal the importance of historical evolutionary context in sunfish brain form divergence Axelrod, CJ*; Laberge, F; Robinson, BW; Washington University; University of Guelph; University of Guelph a.caleb@wustl.edu

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, a morphological proxy for foraging ecology, 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, but divergence was inconsistent, despite consistent differences in oral jaw size. Pumpkinseed and bluegill species, which differ in their historical ecological specialization, 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 evolutionary time scales. There were also differences in brain form between conspecific ecotypes, but they were inconsistent between species. Littoral pumpkinseed had larger brains than their pelagic counterpart, and littoral bluegill had smaller telencephalons than their pelagic counterpart. Inconsistent brain form divergence between conspecific ecotypes of pumpkinseed and bluegill sharing a common littoral-pelagic habitat axis suggests that contemporary ecological conditions and historic evolutionary context interact to influence evolutionary changes in brain form in fishes.