Fatigue resistant jaw muscles facilitate long-lasting courtship behavior in the southern alligator lizard (Elgaria multicarinata)

The southern alligator lizard (Elgaria multicarinata) exhibits a courtship behavior during which the male firmly grips the female’s head in his jaws for many hours at a time. This extreme behavior counters the conventional wisdom that reptile muscles are fast to fatigue and incapable of powering high endurance behaviors. We conducted in situ experiments in which the jaw-adductor muscles of lizards were stimulated directly while bite force was measured simultaneously with a force transducer. Fatigue tests were performed by supramaximally and bilaterally stimulating the muscles for several minutes with a series of tetanic trains. Our results show that a substantial sustained force gradually develops during the first few minutes of 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 natural courtship behavior of these lizards and lik...