Ontogenetic and Comparative Morphology of Clinch Dace (Chrosomus sp. cf. saylori)
Clinch Dace (Chrosomus sp. cf. saylori) is a rare species of minnow with fragmented populations occurring in the upper Clinch River watershed in Virginia. Major morphological and life history characteristics have not been described for Clinch Dace, and evidence that Clinch Dace is a new species is largely anecdotal. Here, we compare Clinch Dace morphometric and meristic characteristics to those of closely related congeners and test for sexual and ontogenetic changes in morphology. We also determined diet preference through gut content analysis. We conclude that Clinch Dace are morphologically distinct from congeners, and that there are changes in morphology attributable to sex and ontogenetic development. This study suggests that Clinch Dace is a distinct species, and isolation of Clinch Dace from congeners has led to distinct, measurable differences in morphology. Furthermore, digestive anatomy of Clinch Dace combined with a diet high in macroinvertebrates suggests that Clinch Dace occupy a trophic niche that is atypical for Chrosomus.
Photographs of Laurel Dace (A) and Clinch Dace (B). The only discernible difference in external morphology between the two congeners is in the upper lateral band, which ends before the caudal fin in Laurel Dace and is complete in Clinch Dace, and two yellow spots at the base of the caudal fin in Clinch Dace. Photograph of Laurel Dace by D. Neely and Clinch Dace by C. Skelton.
Length frequency histogram for Clinch Dace captured in fall/winter (black, n = 23) and spring/summer (gray, n = 40). Otolith ages are shown above bars with vertical lines segregating age classes.
Regression of standard length (mm) on age (months) for Clinch Dace (n = 63). Inner black line is the fitted line, middle dark gray bars 95% confidence intervals, and outer light gray bars 95% predictive intervals.
Standard length and weight (A) and log standard length and log weight (B) for Clinch Dace (n = 82). The resulting fitted lines from regressions are shown. The slope of the regression of the log transformed data is significantly greater than 3 (P < 0.001).
Sheared PCA of Clinch Dace (black, n = 42) and Laurel Dace (gray, n = 29). The significant (by MANOVA, P < 0.0001) separation is strongest on SPCA axis 2, which was positively correlated to head depth and negatively correlated to length of the anal-fin base.
Sheared PCA of year-1 males (gray squares), year-2 males (white triangles), young-of-year females (black crosses), year-1 females (gray diamonds), and year-2 females (black circles).
Contributor Notes
Associate Editor: T. Grande.