The Burden of Reproduction in Lizards: Changes in Respiratory Physiology Associated with Reduced Lung Volume at the Sevilleta National Wildlife Refuge

Previous morphological work on lizards suggests that the volume of growing eggs may result in a significant decrease in lung volume during gravidity. Iguanid lizard lungs are located within continuous thoracic and abdominal cavities and are highly distensible. Because of their distensible nature and lack of a diaphragm, both naturally occurring and introduced structures within the abdominal and thoracic cavities (i.e. organs, food, eggs) compress them and potentially reduce available lung volume for gas exchange. During reproduction, this decrease comes at a time of increased energetic demands, due to the cost of provisioning eggs and the physical burden of transporting the extra mass before laying. This means that females must increase the oxygen/carbon dioxide exchange with effectively smaller lung capacity than when they are not reproductive. Therefore, the way species compensate for this decrease affects performance, and ultimately the survival of individuals and their offspring.既往针对蜥蜴的形态学研究表明，怀卵期（gravidity）内，发育中的卵的体积可能会导致肺体积显著降低。鬣蜥科蜥蜴（Iguanid lizard）的肺位于连续的胸腔与腹腔内，且具有高度可扩张性。由于其具备可扩张特性且缺乏膈膜，胸腔与腹腔内天然存在的结构以及外来结构（即器官、食物、卵）均会压迫肺部，进而可能缩减用于气体交换的有效肺容积。在繁殖阶段，肺容积的这种缩减恰好发生在能量需求上升的时期——这源于为卵提供营养的代谢成本，以及产卵前携带额外体重带来的生理负担。这意味着，相较于非繁殖状态，雌性个体在肺有效容积更小的情况下，必须提升氧气与二氧化碳的交换效率。因此，物种应对该肺容积缩减的补偿策略，会影响个体的生理机能表现，最终决定个体及其后代的存活情况。