Lawrence, K.A.; Strange, R.M.: Allometric neuroanatomy among percids: correlation with adaptive trends?

Adaptation to small headwater streams and a concomitant reduction in overall size is a major evolutionary trend in percid fishes. Changes in behavior, such as habitat preferences and life history attributes, are often linked with changes in the proportionate sizes of corresponding regions of the brain. We examined the neuroanatomy among primitive percids (Perca and Stizostedion), primitive darters (Percina spp.), and more specialized darters (Etheostoma spp.) for evidence of simple scaling effects, correlation with adaptive changes in behavior, and phylogenetic legacy. A negative allometric relationship exists between body mass and brain mass in percids, indicating that darters have proportionately larger brain mass than either Perca or Stizostedion. This may be a scaling effect. Changes in cerebellum and optic lobes are isometric. A positive allometric relationship exists between both the cerebellum and optic lobes and the olfactory regions. Differing proportions among brain regions in percids may prove to be adaptive and not a phylogenetic effect if it can be shown that darters rely more on vision and agility in foraging and avoiding predators than do Perca or Stizostedion.