Brain form and foraging behaviour in a stream fish

Brain form (i.e., brain size and morphology) has been linked to variation in foraging behaviour among species of fishes in lakes and oceans, such as larger brains associated with fish foraging higher in the food chain. However, much less is known about these relationships across habitats, or in stream fishes. Therefore, we explore relationships between foraging behaviour and brain form in the omnivorous creek chub (Semotilus atromaculatus) across different streams of Southwest Ontario, Canada. We assessed foraging behaviour variables (i.e., trophic position, proportion of terrestrial energy in diet and foraging flexibility on aquatic and terrestrial resources) against brain form (i.e., relative brain size and the proportional size of the cerebellum, hypothalamus, olfactory bulbs, optic tectum, and telencephalon). Principal component analysis was used to extract covariation patterns among the size of brain regions. We found that creek chub brain size is positively associated with trophic position and proportion of terrestrial energy in diet, but not foraging flexibility. The first principal component, explaining 91% of size covariation among brain regions, was also positively associated with trophic position but not with proportion of terrestrial energy in diet suggesting that brain regions outside of those measured contribute to the association between brain size and proportion of terrestrial energy in diet. Our results suggest that a relationship between brain size and trophic position may be common among fishes, and that foraging on resources from the terrestrial energetic pathway in streams may present a novel, yet to be characterized cognitive challenge for fish.