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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.
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