Torrent ducks inhabit fast-flowing rivers in the Andes from sea level to altitudes up to 4500 m. We examined the mitochondrial physiology that facilitates performance over this altitudinal cline by comparing the respiratory capacities of permeabilized fibers, the activities of 16 key metabolic enzymes and the myoglobin content in muscles between high- and low-altitude populations of this species. Mitochondrial respiratory capacities (assessed using substrates of mitochondrial complexes I, II and/or IV) were higher in highland ducks in the gastrocnemius muscle – the primary muscle used to support swimming and diving – but were similar between populations in the pectoralis muscle and the left ventricle. The heightened respiratory capacity in the gastrocnemius of highland ducks was associated with elevated activities of cytochrome oxidase, phosphofructokinase, pyruvate kinase and malate dehydrogenase (MDH). Although respiratory capacities were similar between populations in the other muscles, highland ducks had elevated activities of ATP synthase, lactate dehydrogenase, MDH, hydroxyacyl CoA dehydrogenase and creatine kinase in the left ventricle, and elevated MDH activity and myoglobin content in the pectoralis. Thus, although there was a significant increase in the oxidative capacity of the gastrocnemius in highland ducks, which correlates with improved performance at high altitudes, the variation in metabolic enzyme activities in other muscles not correlated to respiratory capacity, such as the consistent upregulation of MDH activity, may serve other functions that contribute to success at high altitudes.
The authors declare no competing or financial interests.
Conceptualization: N.J.D., K.G.M., G.R.S.; Methodology: N.J.D., K.G.M., G.R.S.; Formal analysis: N.J.D.; Investigation: N.J.D.; Resources: N.J.D., C.M.I., L.A., R.C., J.M.Y., B.C., W.K.M., K.G.M., G.R.S.; Writing - original draft preparation: N.J.D.; Writing - review and editing: N.J.D., C.M.I., L.A., R.C., J.M.Y., B.C., W.K.M., K.G.M., G.R.S.; Visualization: N.J.D.; Supervision: W.K.M., K.G.M., G.R.S.; Project administration: N.J.D., C.M.I., L.A., R.C., J.M.Y., B.C., W.K.M., K.G.M., G.R.S.; Funding acquisition: K.G.M., G.R.S.
The equipment and operational costs of this research was supported by funds from McMaster University, the Canada Foundation for Innovation, the Ontario Ministry of Research and Innovation, and Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grants to G.R.S. and W.K.M. This research was also supported by a National Science Foundation (NSF) grant (IOS-0949439) to K.G.M. G.R.S. is supported by the Canada Research Chairs Program. N.J.D. is supported by the James A. Kushlan endowment (awarded to K.G.M.) from the University of Miami.
- Received May 5, 2016.
- Accepted September 7, 2016.
- © 2016. Published by The Company of Biologists Ltd