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.

中文翻译：

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抗疲劳的下颌肌肉促进了南方短吻鳄蜥蜴（Elgaria multicarinata）的持久求爱行为

南方短吻鳄蜥蜴 (Elgaria multicarinata) 表现出一种求偶行为，在此期间，雄性将雌性的头部一次牢牢地夹在下巴中数小时。这种极端行为违背了爬行动物肌肉无法为高耐力行为提供动力的传统观点。我们进行了原位实验，其中直接刺激蜥蜴的下颌内收肌，同时测量咬合力。通过用一系列强直训练刺激肌肉来进行疲劳测试。我们的结果表明，在疲劳测试过程中会逐渐产生大量的持续力。这种持续的力量在峰值强直力量下降到初始强度的一小部分后仍然存在。在原位疲劳测试中观察到的持续力与这些蜥蜴的求偶行为一致，可能反映了生理特化。分子分析结果表明，颌部肌肉含有咀嚼肌球蛋白和强直肌球蛋白纤维。我们建议强直纤维的存在可以解释在配偶保持行为期间不寻常的持续力特性。在特定行为期间促进极端表现的肌肉特性的表征可能揭示肌肉功能的一般机制，尤其是在根据表现出相似表现特征的收敛进化系统进行时。我们建议强直纤维的存在可以解释在配偶保持行为期间不寻常的持续力特性。在特定行为期间促进极端表现的肌肉特性的表征可能揭示肌肉功能的一般机制，尤其是在根据表现出相似表现特征的收敛进化系统进行时。我们建议强直纤维的存在可以解释在配偶保持行为期间不寻常的持续力特性。在特定行为期间促进极端表现的肌肉特性的表征可能揭示肌肉功能的一般机制，尤其是在根据表现出相似表现特征的收敛进化系统进行时。