Meeting Abstract
The Southern Alligator Lizard (Elgaria multicarinata) exhibits an unusual courtship behavior in which the male firmly grips the female’s head in his jaws for several hours at a time. This behavior counters the conventional wisdom that the muscles of non-avian reptiles are fast to fatigue and incapable of sustaining high endurance behaviors. To quantify the contractile properties of the jaw adductors of E. multicarinata, we conducted in situ experiments in which the muscles of euthanized lizards were stimulated directly while bite force was simultaneously measured with a double-cantilever beam force transducer. Fatigue tests were performed by supramaximally and bilaterally stimulating the jaw-adductor muscles (internal adductor mandibulae complex) for several minutes with a series of tetanic trains (pulse duration = 0.2 ms, stimulation rate = 60 Hz, train duration = 150 ms, 1 train per 3 s). Our results show that a substantial residual force (approximately 15-20% of initial peak tetanic force) gradually develops during the first few minutes of the fatigue test, and this residual force persists after tetanic peak forces have declined to a fraction of the residual force (approximately 5 min into fatigue test). The observed residual force is consistent with the natural courtship behavior of these lizards, and it likely reflects physiological specialization related to the behavior. We propose that the presence of large populations of tonic fibers and/or a delayed Ca2+ reuptake mechanism may explain the unusual fatigue resistant properties of the jaw-adductor muscles.
