Morphological variation of taxa frequently is correlated with local environmental variation. We tested for covariation in morphology and environmental variables in bluntnose minnow Pimephales notatus from 10 sites in central Indiana. We used principal components analysis (PCA) to summarize local environmental variation and geomorphic morphometrics (procrustes method and relative warp analysis) to summarize morphological variation among individuals. We used MANCOVA to test for variation in morphology attributable to environmental variation, body size, and sexual dimorphism. Additionally, we used linear discriminant analysis (LDA) to identify if morphology varies with sexual dimorphism. Individual relative warp scores were separated by sex and tested for covariation with habitat PC axes using Pearson's correlations. We identified shape variation that was correlated with environment irrespective of body size or sex. Individuals with deeper-bodies tended to occur in deeper and wider streams with increased discharge. Individuals with fusiform body shape (e.g., slender elongated snouts) tended to occur at sites with increased current velocity. Although the morphology of male and female individuals covaried similarly with environmental variation, LDA significantly distinguished females, which had distended abdomens, narrower caudal peduncle and dorsal fin bases, and slightly upturned head shapes compared to males. We suggest that shape variation may be a product of phenotypic plasticity and may contribute toward the success of species with broad physicochemical tolerances by enhancing their ability to occupy a wide range of hydrological conditions.
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