Yekta, N., and D.G. Blackburn (1992). Sexual dimorphism in mass and protein content of the forelimb muscles of the northern leopard frog, Rana pipiens. Canadian Journal of Zoology 70: 670-674.

Abstract:In certain frogs and toads, forelimb muscles that are used by the male to clasp the female during mating differ structurally and functionally between the two sexes. Sexual dimorphism in musculature of the northern leopard frog, Rana pipiens, was quantified with respect to wet mass, lyophilized dry mass, and total protein content of the major muscles of the adult forelimb. Of the 19 muscles studied, most were significantly heavier in males than in females in terms of dry mass (13 muscles) and wet mass (14 muscles), although females were larger in body mass and snout-vent length. Muscles exhibited a gradient of sexual dimorphism; mean dry mass of dimorphic muscles in females ranged from 8.8% to 90.9% of the mean mass of corresponding male muscles. The most dimorphic muscles were those that adduct the forearm, flex the elbow, flex the wrist, and abduct the first digit. Muscles that were sexually dimorphic in dry mass differed significantly between the sexes in total protein content, but not in concentration of protein or water.

[]Rana pipiens