03. Sexual dimorphism in the forelimb muscles of the Asiatic toad Bufo gargarizans

TLDR: The aims of the present study are to Quantify the differences in body size and mass of selected forelimb muscles between female and male B. gargarizans and compare body sizes and mass between amplectant and non-amplectant males.

Abstract: A exhibit a variety of secondary sexual dimorphisms such as body size, vocal apparatus, head dimensions and colouration (Duellman & Trueb, 1986). With regard to muscle dimorphisms, studies have focused on muscles mass (Kirby, 1983; Yekta & Blackburn, 1992; Lee, 2001; Lee & Corrales, 2002; Liao et al., 2012a, b), muscle fibre types and their sizes (Muller et al., 1969; Melichna et al., 1972; Oka et al., 1984; Dorlochter et al., 1994), and muscle isometric contractile properties (Peters & Aulner, 2000; Girgenrath & Marsh, 2003; Clark & Peters, 2006; Navas & James, 2007). Sexual dimorphisms of muscles can for example be associated with sound production (Schmidt, 1965; Kelley, 1986; Emerson & Boyd, 1999) or amplexus (Kirby, 1983), and have been interpreted as the result of sexual selection (Duellman, 1992; Lee, 2001). Previous studies have shown that forelimb muscles involved in amplexus, such as pectoralis series, coracobrachialis series, deltoideus, triceps branchii, extensor carpi radialis, flexor carpi radialis, sternoradialis and abductor indicus longus, are larger and heavier in males than in females. Larger forelimb muscles in males produce enhanced force for amplexing females, and to resist attempted take-overs by competing males (Kirby, 1983; Oka et al., 1984; Duellman, 1992; Yekta & Blackburn, 1992; Peters & Aulner, 2000; Lee, 2001; Clark & Peters, 2006; Navas & James, 2007; Liao et al., 2012a). These muscles are also less fatigable in males than in females, which may allow male frogs to maintain amplexus for prolonged periods (Peters & Aulner, 2000; Clark & Peters, 2006; Navas & James, 2007). However, forelimb muscles not involved in amplexus have not received much attention so far. In this study, I compared the mass of forelimb muscles between males and females depending on whether they are used during amplexus, considering amplectant and non-amplectant males. The Asiatic toad, Bufo gargarizans, is widely distributed in China, Russia and Korea (Fei & Ye, 2001). In Nanchong City, the species hibernates in midNovember, and reproduction takes place in December or January (Yu et al., 2009). It is an explosively breeding species, with a breeding season lasting 6–24 days (Yu & Lu, 2010). Males do not discriminate potential mates with respect to body size (Yu & Lu, 2010). The aims of the present study are to: (i) Quantify the differences in body size and mass of selected forelimb muscles between female and male B. gargarizans; (ii) Compare body size and selected forelimb muscles mass between amplectant and non-amplectant males.