Morphological diversity within the O zark minnow ( Notropis nubilus : L euciscidae)

The Ozark minnow, Notropis nubilus , is a small stream fish that has a disjunct distribution in the Ozark Plateau and upper Mississippi River basin. Three reciprocally monophyletic and deeply divergent lineages have been hypothesized within the species based on molecular data. These lineages are allopatric and isolated from each other. The objective of this study was to test the hypothesis that these lineages and the disjunct population in the upper Mississippi River basin are morphologically distinct. Meristic and geometric morphometric data were used to identify and quantify morphological diversity within the Ozark minnow. Analyses of the meristic data and a principal component analysis of the morphometric data were unable to find any noticeable differences in morphology among groups. However, canonical variates analyses of the morphometric data and linear models were able to define statistically significant differences in shape. Analyses of all‐individuals were able to identify shape differences between all groups. Males‐only analyses were less conclusive, but there was some indication that males may be diverging more quickly than all‐individuals. The detection of subtle variation in shape implies selection is not a strong factor in morphological divergence and observed differences are most likely due to morphological drift. This indicates that the lineages within the Ozark minnow are likely on the trajectory for speciation. The allopatric nature of these clades makes the Ozark minnow an interesting model for the study of morphological drift and speciation.