Abstract：
In cyclic climate variations, including seasonal changes, many animals regulate their energy demands to overcome critical transitory moments, restricting their high-demand activities to phases of resource abundance, enabling rapid growth and reproduction. Tegu lizards (Salvator merianae) are ectotherms with a robust annual cycle, being active during summer, hibernating during winter, and presenting a remarkable endothermy during reproduction in spring. Here, we evaluated whether changes in mitochondrial respiratory physiology in skeletal muscle could serve as a mechanism for the increased thermogenesis observed during the tegu\'s reproductive endothermy.
We performed high-resolution respirometry and calorimetry in permeabilized red and white muscle fibers, sampled during summer (activity) and spring (high activity and reproduction), in association with citrate synthase measurements.
During spring, the muscle fibers exhibited increased oxidative phosphorylation. They also enhanced uncoupled respiration and heat production via adenine nucleotide translocase (ANT), but not via uncoupling proteins (UCP). Citrate synthase activity was higher during the spring, suggesting greater mitochondrial density compared to the summer. These findings were consistent across both sexes and muscle types (red and white).
The current results highlight potential cellular thermogenic mechanisms in an ectothermic reptile that contribute to transient endothermy. Our study indicates that the unique feature of transitioning to endothermy through nonshivering thermogenesis during the reproductive phase may be facilitated by higher mitochondrial density, function, and uncoupling within the skeletal muscle. This knowledge contributes significant elements to the broader picture of models for the evolution of endothermy, particularly in relation to the enhancement of aerobic capacity.
We performed high-resolution respirometry and calorimetry in permeabilized red and white muscle fibers, sampled during summer (activity) and spring (high activity and reproduction), in association with citrate synthase measurements.
During spring, the muscle fibers exhibited increased oxidative phosphorylation. They also enhanced uncoupled respiration and heat production via adenine nucleotide translocase (ANT), but not via uncoupling proteins (UCP). Citrate synthase activity was higher during the spring, suggesting greater mitochondrial density compared to the summer. These findings were consistent across both sexes and muscle types (red and white).
The current results highlight potential cellular thermogenic mechanisms in an ectothermic reptile that contribute to transient endothermy. Our study indicates that the unique feature of transitioning to endothermy through nonshivering thermogenesis during the reproductive phase may be facilitated by higher mitochondrial density, function, and uncoupling within the skeletal muscle. This knowledge contributes significant elements to the broader picture of models for the evolution of endothermy, particularly in relation to the enhancement of aerobic capacity.
摘要：
目标：在周期性气候变化中，包括季节性变化，许多动物调节它们的能量需求以克服关键的瞬间，将他们的高需求活动限制在资源丰富的阶段，促进快速生长和繁殖。Tegu蜥蜴（Salvatormerianae）是具有强劲年周期的外温动物，在夏季活跃，冬天冬眠，在春天的繁殖过程中表现出非凡的吸热。这里,我们评估了骨骼肌线粒体呼吸生理的变化是否可以作为在tegu的生殖吸热过程中观察到的产热增加的机制。
方法：我们在透化的红色和白色肌纤维中进行了高分辨率呼吸测定和量热法，在夏季(活动)和春季(高活动和繁殖)采样，与柠檬酸合成酶测量相关。
结果：在春季，肌纤维表现出增加的氧化磷酸化。它们还通过腺嘌呤核苷酸转位酶（ANT）增强了非偶联的呼吸和热量产生，但不是通过解偶联蛋白（UCP）。柠檬酸合酶活性在春季较高，表明与夏季相比线粒体密度更大。这些发现在性别和肌肉类型（红色和白色）中都是一致的。
结论：目前的研究结果强调了在放热爬行动物中潜在的细胞产热机制，该机制有助于短暂的吸热。我们的研究表明，在生殖阶段通过非颤抖的产热过渡到吸热的独特特征可能是由较高的线粒体密度促进的，函数,和骨骼肌内的解耦。这些知识为更广泛的吸热演化模型提供了重要的元素，特别是与增强有氧能力有关。
方法：我们在透化的红色和白色肌纤维中进行了高分辨率呼吸测定和量热法，在夏季(活动)和春季(高活动和繁殖)采样，与柠檬酸合成酶测量相关。
结果：在春季，肌纤维表现出增加的氧化磷酸化。它们还通过腺嘌呤核苷酸转位酶（ANT）增强了非偶联的呼吸和热量产生，但不是通过解偶联蛋白（UCP）。柠檬酸合酶活性在春季较高，表明与夏季相比线粒体密度更大。这些发现在性别和肌肉类型（红色和白色）中都是一致的。
结论：目前的研究结果强调了在放热爬行动物中潜在的细胞产热机制，该机制有助于短暂的吸热。我们的研究表明，在生殖阶段通过非颤抖的产热过渡到吸热的独特特征可能是由较高的线粒体密度促进的，函数,和骨骼肌内的解耦。这些知识为更广泛的吸热演化模型提供了重要的元素，特别是与增强有氧能力有关。
