Consistent changes in muscle metabolism underlie dive performance across multiple lineages of diving ducks

Diving animals must sustain high activity with limited O2 stores to
successfully capture prey. Studies suggest that increasing body O2 stores
supports breath-hold diving, but less is known about metabolic
specializations that underlie underwater locomotion. We measured maximal
activities of 10 key enzymes in locomotory muscles (gastrocnemius,
pectoralis) to identify biochemical changes associated with diving in
pathways of oxidative and substrate-level phosphorylation and compared
them across three groups of ducks — the strong diving sea ducks (Mergini,
8 spp.), the mid-tier diving pochards (Aythyini, 3 spp.), and the
non-diving dabblers (Anatini, 5 spp.). Relative to dabblers, both diving
groups had increased activities of succinate dehydrogenase and cytochrome
c oxidase, and sea ducks further showed increases in citrate synthase (CS)
and hydroxyacyl-coA dehydrogenase (HOAD). Both diving groups had relative
decreases in capacity for anaerobic metabolism (lower ratio of lactate
dehydrogenase to CS), with sea ducks also showing a greater capacity for
oxidative phosphorylation and lipid oxidation (lower ratio of pyruvate
kinase to CS, higher ratio of HOAD to hexokinase). These data suggest that
the locomotory muscles of diving ducks are specialized for sustaining high
rates of aerobic metabolism, emphasizing the importance of body O2 stores
for dive performance in these species.

潜水动物需在有限氧气储备的前提下维持高强度活动，方能成功捕获猎物。已有研究证实，提升机体氧气储备可支持屏气潜水行为，但针对支撑水下运动的代谢特化机制，目前尚缺乏充分认知。本研究检测了运动肌肉（腓肠肌（gastrocnemius）、胸肌（pectoralis））中10种关键酶的最大活性，以识别与潜水相关的氧化磷酸化及底物水平磷酸化通路中的生化变化，并对3组鸭类展开比较：强潜水型海鸭族（Mergini，共8个物种）、中等潜水能力的潜鸭族（Aythyini，共3个物种），以及非潜水型钻水鸭族（Anatini，共5个物种）。相较于钻水鸭族，两类潜水鸭群的琥珀酸脱氢酶（succinate dehydrogenase）与细胞色素c氧化酶（cytochrome c oxidase）活性均显著升高；海鸭族还进一步表现出柠檬酸合酶（citrate synthase, CS）与羟酰基辅酶A脱氢酶（hydroxyacyl-coA dehydrogenase, HOAD）活性的提升。两类潜水鸭群的无氧代谢能力均相对下降（乳酸脱氢酶（lactate dehydrogenase）与柠檬酸合酶的比值更低）；此外，海鸭族还具备更强的氧化磷酸化与脂质氧化能力（丙酮酸激酶（pyruvate kinase）与柠檬酸合酶的比值更低，羟酰基辅酶A脱氢酶与己糖激酶（hexokinase）的比值更高）。本研究数据表明，潜水鸭的运动肌肉特化为维持高水平有氧代谢速率，凸显了机体氧气储备对该类群潜水表现的重要性。