Effects of testosterone on contractile properties of sexually dimorphic forelimb muscles in male bullfrogs (Rana catesbeiana, Shaw 1802)

Abstract

SummaryThis study examined the effects of testosterone (T) on the contractile properties of two sexually dimorphic forelimb muscles and one non-dimorphic muscle in male bullfrogs (Rana catesbeiana, Shaw 1802). The dimorphic muscles in castrated males with testosterone replacement (T+) achieved higher forces and lower fatigability than did castrated males without replaced testosterone (T0 males), but the magnitude of the differences was low and many of the pair-wise comparisons of each muscle property were not statistically significant. However, when taken as a whole, the means of seven contractile properties varied in the directions expected of masculine values in T+ animals in the sexually dimorphic muscles. Moreover, these data, compared with previous data on male and female bullfrogs, show that values for T+ males are similar to normal males and are significantly different from females. The T0 males tended to be intermediate in character between T+ males and females, generally retaining masculine values. This suggests that the exposure of young males to T in their first breeding season produces a masculinizing effect on the sexually dimorphic muscles that is not reversed between breeding seasons when T levels are low. The relatively minor differences in contractile properties between T+ and T0 males may indicate that as circulating T levels rise during breeding season in normal males, contractile properties can be enhanced rapidly to maximal functional levels for breeding success.

Population density and structure drive differential investment in pre- and postmating sexual traits in frogs

“…In these species, males aggressively defend territories and attract females with courtship calls, with relatively large and strong males typically having the greatest mating success (Mallick 1986;Liao and Lu 2011b;Mi 2012). Testosterone has also repeatedly been shown to increase the size and strength of male forelimb muscles that are involved in amplexus (Regnier and Herrera 1993;Dorlöchter et al 1994;Kampe and Peters 2013). Although we cannot currently draw any firm conclusions as to the exact reasons for these positive associations, there are at least three potential and nonmutually exclusive explanations.…”

“…Because testosterone is secreted by the Leydig cells in the interstitial tissue of the testes (Jorgensen 1992), relatively large testes may be able to produce more testosterone. Testosterone has also repeatedly been shown to increase the size and strength of male forelimb muscles that are involved in amplexus (Regnier and Herrera 1993;Dorlöchter et al 1994;Kampe and Peters 2013). A positive association between forelimb muscles and testes mediated by androgens could thus be predicted, although to our knowledge a conclusive link remains unexplored empirically.…”

Developmental, physiologic and phylogenetic perspectives on the expression and regulation of myosin heavy chains in mammalian skeletal muscles

“…Androgen exposure stimulates laryngeal specific MyHC in female Xenopus laryngeal muscles (Catz et al 1995 ). Androgens are also involved in controlling the contractile properties of muscles belonging to a different allotype, the forelimb muscles of male amphibians involved in amplexus, though the likely basis that these properties are due to MyHC changes has yet to be determined (Kampe and Peters 2013 ). In mammals this androgen sensitivity of MyHC expression is found in muscles of yet another allotype, the jaw muscles of rodents (Lyons et al 1986 ; Eason et al 2000 ; Reader et al 2001 ).…”

Exploring sexual differences in external morphology and limb muscles of Hylarana guentheri (Anura: Ranidae) during non‐breeding season

“…Dorlöchter et al (1994) has reported that experimental manipulation or seasonal changes in androgen levels could lead to hypertrophy or atrophy of androgen-sensitive forelimb muscles in anurans. Testosterone is responsible for large muscle mass of vertebrate skeletal muscles, and commonly results in sexual dimorphism (Kampe & Peters, 2013). The presence of intersexual differences in anuran limb muscles outside the breeding season may reflect organizational effects of androgens on the muscles during development (Blackburn & Bernardo, 1998).…”