Geographic Variation of Sexual Dimorphism in the Raccoon Procyon lotor

Abstract

-Geographic variation of sexual dimorphism for 22 cranial characters was investigated in raccoons (Procyon lotor) from 87 localities. Geographic variation in the degree of sexual dimorphism occurred only for canine width and the degree of sexual dimorphism in canine width was significantly less for raccoons from W of the Continental Divide than those from E of the Continental Divide. The lack of geographic variation in sexual dimorphism of greatest length of skull indicates that sexual dimorphism in body size of raccoons also does not vary geographically (skull length is highly correlated with body size). Thus, it appears that selection pressures responsible for sexual dimorphism in raccoons are acting uniformly throughout much of the range of the species. Geographic variation in the degree of sexual dimorphism for canine width may be the result of geographic variation in the intensity of intrasexual selection (i.e., variation in the intensity of male-male competition for mates during the breeding season). If so, the apparent lack of geographic variation in sexual size dimorphism of raccoons may indicate that male body size is not under the same kinds of selection pressures (e.g., intrasexual selection) as canine size.