Ontogeny and allometry of body shape in the Blacktail Shiner, Cyprinella venusta

Ontogenetic changes in body shape and its associated allometry were studied in the Blacktail Shiner, Cyprinella venusla, using geometric morphometric methods. We used a single, large sample (n = 397; 182 males, 215 females), collected in Catahoula Creek, Jourdan River drainage, Hancock County Missis sippi. Ten body landmarks were digitized from each specimen, which yielded partial warp scores that were used as shape variables to describe body shap e change during ontogeny, assess sexual dimorphism, and investigate the rel ationship between reproductive states and ontogenetic body shape change. We also assessed the effect of sexual dimorphism on size and body shape. The null hypothesis of isometry during ontogeny was strongly rejected by multiv ariate regression of shape on size for both sexes (males, P < 0.0001, F = 2 1.970; females, P < 0.0001, F = 16.238). We found large, highly significant sexually dimorphic differences in the body shapes of males and females (MA NOVA for overall shape, P < 0.0001, F = 7.535, Wilks' lambda, 0.758), which remained significant using MANCOVA with size as a covariate (lag SL, P < 0 .0001, F = 34.872, Wilks' lambda, 0.438; log CS, P < 0.0001, F = 34.829, Wi lks' lambda, 0.439). Moreover, the ontogeny of body shape differs between m ales and females. There were highly significant shape differences among, re productive classes within males and females. These finding suggest that cha nge in reproductive status may occur in concert with body shape change.