Abstract
Exercise is an important performance trait in mammals and variation in aerobic capacity and/or substrate allocation during submaximal exercise may be important for survival at high altitude. Comparisons between lowland and highland populations is a fruitful approach to understanding the mechanisms for altitude differences in exercise performance. However, it has only been applied in very few highland species. The leaf-eared mice (LEM, genus Phyllotis) of South America are a promising taxon to uncover the pervasiveness of hypoxia tolerance mechanisms. Here we use lowland and highland populations of Andean and Lima LEM (P. andium and P. limatus), acclimated to common laboratory conditions, to determine exercise-induced maximal oxygen consumption (O2max), and submaximal exercise metabolism. Lowland and highland populations of both species showed no difference in O2max running in either normoxia or hypoxia. When run at 75% of O2max, highland Andean LEM had a greater reliance on carbohydrate oxidation to power exercise. In contrast, highland Lima LEM showed no difference in exercise fuel use compared to their lowland counterparts. The higher carbohydrate oxidation seen in highland Andean LEM was not explained by maximal activities of glycolytic enzymes in the gastrocnemius muscle, which were equivalent to lowlanders. This result is consistent with data on highland deer mouse populations and suggests changes in metabolic regulation may explain altitude differences in exercise performance.
Highlights
Published: 29 October 2021Exercise is an important performance trait that can significantly impact fitness and survival in wild mammals [1,2]
Significant differences in mass were seen between lowland and highland populations of Lima leaf-eared mice (LEM)
These data show that submaximal exercise substrate use varies in a highland popula
Summary
Exercise is an important performance trait that can significantly impact fitness and survival in wild mammals [1,2]. Substrate use during submaximal aerobic exercise has been much less studied, but rates of oxidation of carbohydrates and lipids, the two major fuels used by exercising mammals, varies directly with differences in aerobic capacity [4]. A mammal with an elevated aerobic capacity would be expected to use glucose and fatty acids at a higher rate when at the same relative submaximal exercise intensities (as % of maximal oxygen consumption, VO2 max) as a more sedentary species. Mammals living in extreme environments may deviate from this predictable pattern of fuel use to improve exercise performance. There is surprisingly few studies examining how exercise metabolism in wild mammals varies across environments
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