Evidence of morphological and functional variation among Bluegill Lepomis macrochirus

A myriad of factors have been shown to influence the morphology of freshwater fish. However, studies that parse out where variation is coming from (e.g. body size, sex, and habitat) as well as what potential these changes have to influence function (e.g. swimming performance) are understudied. Therefore, the objectives of this study were to describe morphological variation of Bluegill Lepomis macrochirus across the Grand Lake St Mary's watershed area (northwest OH, USA) and test for covariation of morphology with size, sex, and habitat as well as to assess swimming performance to discern whether any differences in habitat (and morphology) correspond with functional aspects related to critical swimming velocity. Geometric morphometric methods were used to assess shape variation among individuals and general linear models were used to test for covariation of morphology with size, sex, and habitat. Analyses indicated that body size was the strongest driver of morphological variation followed by sex, habitat, and interactions – indicating the presence of allometry, sexual dimorphism, and the potential for habitat induced plasticity. In general, more robust morphologies tended to correspond with larger individuals, males, and/or individuals from lentic habitats. Swimming performance trials supported functional differences as individuals from lotic habitats demonstrated significantly higher Ucrit swimming performance values (∼+20%) than lentic individuals. Broader applications of these findings can link to evolutionary ecology, management, and conservation