“…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 ].…”