Sexual Dimorphism in Head Shape, Relative Head Width, and Body Size of Eurycea aquatica and Eurycea cirrigera

We examined variation in body size, head width, and head shape between males and females of two ecologically distinct species of plethodontid salamanders, Eurycea aquatica (Brownback Salamander) and Eurycea cirrigera (Southern Two-lined Salamander). Female-biased sexual dimorphism in body size occurred in E. cirrigera but not in E. aquatica. Male-biased sexual dimorphism in relative head width occurs in both species. Furthermore, male E. aquatica had larger heads than did male E. cirrigera. We also found significant differences in ventral and lateral head shape between male and female E. aquatica (sexual dimorphism in head shape), but male and female E. cirrigera did not differ in head shape. Males of the two species also significantly differed in both ventral and lateral head shape, while females of the two species differed in ventral head shape but not in lateral head shape. Because sexual dimorphism differed between the two species in different characteristics (body size, relative head width, and head shape), we concluded that these species experience dissimilar levels of sexual selection, ecological selection, or both, possibly as a result of their divergent habitat preferences. Our study represents one of the few reported examples of sexual shape dimorphism in salamanders.