Sexual dimorphism in histological characteristics and contractility of the iliofibularis muscle in the lizard Sceloporus torquatus

Our results and observations support the idea that muscle characteristics are coadaptations of organisms and environment, as noted by Bonine et al. (2001). What we need to know now is whether and how the environment affects the relationship between muscle phenotype and fitness. Therefore, studies on habitat, behavioural patterns, morphological characteristics and locomotor performance are needed to better understand the plasticity of the locomotor muscles.The iliofibularis is a hindlimb muscle used in lizard locomotion that is composed of at least three types of fibres: fast-twitch-glycolytic (FG), fast-twitch-oxidativeglycolytic fibre (FOG) and slow-twitch-oxidative (SO). The striated skeletalmuscle is a highly plastic tissue undergoing phenotypic change in response to activity. The lizard Sceloporus torquatus has sexual differences associated with microhabitat use, which can be reflected in the physiology and anatomy of the muscle, and thus, in our study, we analysed the morphological and contractile characteristics of the iliofibularis muscle (IF) of S. torquatus males and females. We found a larger prevalence of FOG compared with FG and SO fibres in the muscle of both sexes. We also found that males show larger areas of the three types of fibres, develop greater strength but also faster fatigue than females, suggesting that strength is a key functional feature that enables males to perform faster movements (but for shorter periods), associated with the demands of territoriality.CONACYT 226935/21266