No sexual dimorphism in limb muscles of a frog not engaging in amplexus

Abstract

Sexual dimorphism in limb muscles is widespread among anurans, with males having stronger limbs than females. This phenomenon has been interpreted in the context of intrasexual selection: 1) the robust forelimb muscles in males are associated with amplexus, in which the male tries to grasp the female tightly, and also with rejection of rivals' attempts at taking over, and 2) massive hindlimb muscles favor the ability to kick away rivals during scramble competition. However, in a few species, fertilization occurs without any form of amplexus and in these species the hmb muscle dimorphism is expected to be absent. We tested this prediction in Feirana taihangnicus: a species without amplexus. As expected, we detected non-significant sexual differences in the mass of both forelimb and hindlimb muscles after accounting for body size and age. Our findings represent an interesting example of coevolution of form and function.

Sexual Dimorphism in the Limb Bones of Asiatic Toad (Bufo gargarizans) in Relation to Sexual Selection

“…Males have longer and heavier muscles, more muscle fibers, higher muscle forces, longer and heavier humeri and radioulnas, and larger areas for muscle attachment on the humerus than females [ 11 , 12 , 13 , 14 , 15 , 16 ]. Previous studies found that the relative or absolute weight of males’ forelimb muscles associated with amplexus and hindlimb muscles, which are related to the scramble competition, are larger than that of females; however, the weight of the forelimb muscles, which is unrelated to the clasping action, does not differ between sexes [ 12 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. According to the sexual selection theory, such secondary sexual dimorphism in limbs is attributed to adaptation for amplexus, which is a behavior used in male–male competition [ 15 , 21 , 22 ].…”