Navas Carlos A, James Rob S
Departamento de Fisiologia, Instituto de Biociências, Universidade de São Paulo, Rua do Matão-Travessa 14 No 321, CEP 05508-900, São Paulo, SP, Brasil.
J Exp Biol. 2007 Feb;210(Pt 4):715-21. doi: 10.1242/jeb.000646.
Mating success of individual male frogs within explosive breeding species can depend on their ability to compete for a mate and to hold onto that mate during amplexus. Such importance of amplexus has resulted in the evolution of sexual dimorphism in the morphology and contractile characteristics of the anuran forelimb muscles used during amplexus. The aims of our study were to use an explosive breeding frog (Rana temporaria) during the breeding season to compare extensor carpi radialis (ECR) muscle length, mass, isometric activation times, relaxation times, absolute force, relative force (stress) and fatigue between male and female frogs. We found that ECR muscle mass and length were greater (tenfold and 1.4-fold, respectively), absolute tetanic muscle force and relative tetanic force (stress) were greater (16-fold and 2.2-fold, respectively) and relaxation times were slower in males than in females. Male ECR muscles incompletely relaxed during fatigue tests and showed less fatigue than female muscles. These sex differences are likely to be beneficial to the male frogs in allowing them to produce relatively high absolute muscle forces for prolonged periods of time to hold onto their mate during amplexus.
在爆发性繁殖物种中，单个雄性青蛙的交配成功率可能取决于它们竞争配偶以及在抱对期间留住配偶的能力。抱对的这种重要性导致了在抱对期间使用的无尾目动物前肢肌肉的形态和收缩特性出现了两性异形进化。我们研究的目的是在繁殖季节利用一种爆发性繁殖的青蛙（林蛙）来比较雄性和雌性青蛙的桡侧腕伸肌（ECR）的肌肉长度、质量、等长激活时间、松弛时间、绝对力、相对力（应力）和疲劳情况。我们发现，雄性青蛙的ECR肌肉质量和长度更大（分别为雌性的10倍和1.4倍），肌肉强直收缩的绝对力和相对力（应力）更大（分别为雌性的16倍和2.2倍），并且雄性的松弛时间比雌性慢。在疲劳测试中，雄性ECR肌肉不能完全松弛，且比雌性肌肉表现出更少的疲劳。这些性别差异可能对雄性青蛙有利，使它们能够在抱对期间长时间产生相对较高的绝对肌肉力量以留住配偶。
