Abstract
The southern alligator lizard (Elgaria multicarinata) exhibits a courtship behaviour during which the male firmly grips the female's head in his jaws for many hours at a time. This extreme behaviour counters the conventional wisdom that reptilian muscle is incapable of powering high-endurance behaviours. We conducted in situ experiments in which the jaw-adductor muscles of lizards were stimulated directly while bite force was measured simultaneously. Fatigue tests were performed by stimulating the muscles with a series of tetanic trains. Our results show that a substantial sustained force gradually develops during the fatigue test. This sustained force persists after peak tetanic forces have declined to a fraction of their initial magnitude. The observed sustained force during in situ fatigue tests is consistent with the courtship behaviour of these lizards and probably reflects physiological specialization. The results of molecular analysis reveal that the jaw muscles contain masticatory and tonic myosin fibres. We propose that the presence of tonic fibres may explain the unusual sustained force properties during mate-holding behaviour. The characterization of muscle properties that facilitate extreme performance during specialized behaviours may reveal general mechanisms of muscle function, especially when done in light of convergently evolved systems exhibiting similar performance characteristics.
Highlights
IntroductionMany lizards exhibit mate-holding behaviour (e.g. skinks, lacertids, iguanians, etc.) in which the male uses his jaws to grasp the female’s neck, typically by a fold of skin, or at another part of the body [1,2,3,4]
Many lizards exhibit mate-holding behaviour in which the male uses his jaws to grasp the female’s neck, typically by a fold of skin, or at another part of the body [1,2,3,4]
The objective of the current study was to characterize the contractile properties of the jaw-adductor muscle complex of the southern alligator lizard (E. multicarinata), with a primary focus on simulating in situ the natural in vivo function of the muscles
Summary
Many lizards exhibit mate-holding behaviour (e.g. skinks, lacertids, iguanians, etc.) in which the male uses his jaws to grasp the female’s neck, typically by a fold of skin, or at another part of the body [1,2,3,4]. Few male lizards perform mate-holding behaviour by grasping the entire head of the female for extended periods, as is the case with the southern alligator lizard (Elgaria multicarinata). During courtship in this species of anguid lizard, the male firmly grips the female’s head in his jaws for many hours at a time. Online searches reveal images of limbless anguids (e.g. Pseudopus apodus and Anguis fragilis) showing mate-holding behaviour identical to that documented in E. multicarinata and E. coerulea, suggesting that the behaviour may be typical of the Anguidae. It is unknown whether mate-holding behaviour by anguid lizards represents mate guarding, a demonstration of strength or endurance to the female, and/or is associated with other aspects of reproductive biology
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