Physiology of the sternoradialis muscle: Sexual dimorphism and role in amplexus in the leopard frog (Rana pipiens)

SUMMARY Reproductive success in thermally varying environments will depend on maintaining metabolic capacity of tissues that are important in mating behaviours. Here we test the hypothesis that cold acclimation will occur in those tissues that are important for reproduction, and that acclimation will be sex specific, reflecting behavioural differences between the sexes. We used the frog Limnodynastes peronii as a model because anurans engage in energetically demanding reproductive behaviour, and many species, including L. peronii, are reproductively active across seasons. Additionally,reproductive behaviours such as calling and amplexus are sex specific. We acclimated animals to naturally occurring autumn (15°C, N=10) and summer (25°C, N=10) temperatures. Whole-animal resting oxygen consumption decreased with lowered temperature, but there was no difference in oxygen consumption between acclimation treatments or sexes. However, the respiratory control ratio (RCR) of mitochondria from the liver and external oblique calling muscle increased with cold acclimation. The increase in RCR with thermal acclimation was due to upregulation of state 3 respiration, and not to a decrease in state 4 respiration. Males had higher activity of citrate synthase, β-hydroxyacyl CoA dehydrogenase and cytochrome coxidase than females in the calling (external oblique) muscle, and males also showed thermal acclimation of these enzymes while females did not. Additionally, males had greater activity of metabolic enzymes in the principal muscle (extensor carpi radialis) used during amplexus. However, there were no differences in metabolic capacity between sexes in the gastrocnemius muscle and in liver, and both sexes showed significant acclimation of lactate dehydrogenase and cytochrome c oxidase in the former and latter,respectively. In L. peronii, thermal acclimation of metabolic capacities is linked to reproductive success, and reversible phenotypic plasticity therefore confers a selective advantage by extending the temporal and spatial extent of the animals' fundamental niche.

Section: Discussionmentioning

confidence: 99%

Beneficial acclimation: sex specific thermal acclimation of metabolic capacity in the striped marsh frog (Limnodynastes peronii)

Rogers

Thompson

Seebacher

2007

“…As a result, many of their forelimb muscles are larger than those in the females. This sexual size dimorphism is specific to those muscles that control elbow flexion, wrist flexion and thumb extension (Kirby, 1983;Melichna et al, 1972;Oka et al, 1984;Peters and Aulner, 2000;Yekta and Blackburn, 1992).…”

Section: Introductionmentioning

confidence: 99%

Isometric contractile properties of sexually dimorphic forelimb muscles in the marine toad Bufo marinus Linnaeus 1758: functional analysis and implications for amplexus

Clark

Peters

2006

It has been shown in the bullfrog, Rana catesbeiana Shaw 1802, that certain forelimb muscles in males have different contractile properties when compared with females, which may result from adaptation for amplexus. We extended this study to a distantly related species, Bufo marinus Linnaeus 1758, by testing the isometric contractile properties of three muscles, abductor indicus longus (AIL), and flexor carpi radialis (FCR) (both dimorphic muscles), and extensor carpi ulnaris (ECU) (nondimorphic control). In males the dimorphic muscles had greater wet mass and cross-sectional area than in the females, and also produced significantly greater isometric force. As in bullfrogs, however, the maximum tetanic force per cm 2 of muscle cross-section did not differ between the sexes. In spite of this similarity in maximum force, the two dimorphic muscles were much less fatigable in the males than in the females. Lower fatigability in males correlated with exceptionally elongated relaxation times that maintained high levels of force between stimulus trains. This sustained force was negligible in the females, suggesting that this feature may allow males to maintain amplexus for prolonged periods. The same sustained force response was observed in the earlier study of Rana catesbeiana. Because this response is similar in Bufo and Rana, muscular properties correlated with amplexus may be shared across anurans by inheritance of this response from a common ancestor.

“…Some forelimb muscles such as extensor carpi radialis, flexor carpi radialis, sternoradialis and abductor indicus longus that are involved in amplexus have been found to be larger in mass and cross-sectional area in male than in female frogs (Clark and Peters, 2006;Kirby, 1983;Oka et al, 1984;Peters and Aulner, 2000;Yekta and Blackburn, 1992) and to have more oxidative fibers and/or higher oxidative capacity in males than in females (Kirby, 1983;Melichna et al, 1972;Peters, 2001;Rubinstein et al, 1983) (but see Oka et al, 1984). Such differences in muscle morphology have been found to lead to higher absolute isometric force in male muscles, without a difference in isometric stress (force per cross-sectional area) between sexes in two distantly related species, Rana catesbeiana and Bufo marinus (Clark and Peters, 2006;Peters and Aulner, 2000).…”

Section: Introductionmentioning

confidence: 99%

“…However, throughout the year sexual dimorphism was evident with higher FCR ATPase activity and faster twitch activation and relaxation rates in females than in males. Resting membrane potential of sternoradialis increased during the breeding season, such that very little stimulation was required to elicit muscle force (Kirby, 1983).…”

Section: Introductionmentioning

confidence: 99%

Sexual dimorphism of extensor carpi radialis muscle size, isometric force, relaxation rate and stamina during the breeding season of the frogRana temporariaLinnaeus 1758

Navas

James

2007

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.