Sexual dimorphism in the limb muscles of the dark-spotted frog, Pelophylax nigromaculata

It has been shown in many anurans that males with larger body size have a mating advantage. However, robust forelimb muscles rather than large body size per se might increase the likelihood of mating. To this end, we investigated sexual dimorphism of nine forelimb muscles and nine hindlimb muscles of Pelophylax nigromaculata. We found that three forelimb muscles involved in axillary amplexus were heavier in males compared to females, whereas five forelimb muscles not involved in axillary amplexus showed no sexual differences in muscle mass. The observed muscle dimorphism was allometric, and could be the result of sexual selection. The analysis on hindlimb muscle mass revealed a largely female-biased sexual dimorphism, likely related to females being heavier. There was a positive correlation between forelimb and hindlimb muscle mass and SVL for both sexes. There was no significant sexual difference in the contents of water in musculature except for the extensor carpi radialis.