The low oxygen levels at high altitude are a potent and unavoidable physiological stressor to which highland mammals must adapt. One hypothesized adaptation to high altitude is an increased reliance on carbohydrates to support aerobic activities. Based on stoichiometries of combustion, ATP yield per mole of oxygen from carbohydrates is approximately 15% higher than from lipids (observed difference closer to 30%), and increased carbohydrate use represents an important oxygen-saving strategy that may be under high selective pressure. Although this hypothesis was first proposed nearly 30 years ago, the in vivo patterns of whole-body fuel use during exercise remain undefined for any highland mammal (including humans). Here we use a powerful multispecies approach to show that wild-caught high-altitude (4,000-4,500 m) native species of mice (Phyllotis andium and Phyllotis xanthopygus) from the Peruvian Andes use proportionately more carbohydrates and have higher oxidative capacities of cardiac muscles compared to closely related low-altitude (100-300 m) native counterparts (Phyllotis amicus and Phyllotis limatus). These results strongly infer that highland Phyllotis have evolved a metabolic strategy to economize oxygen when performing energy-demanding tasks at altitude. This study provides compelling evidence of adjustments in fuel use as an adaptation to high-altitude hypoxia in mammals.

BackgroundUnderstanding the forces that shaped Neotropical diversity is central issue to explain tropical biodiversity and inform conservation action; yet few studies have examined large, widespread species. Lowland tapir (Tapirus terrrestris, Perissodactyla, Tapiridae) is the largest Neotropical herbivore whose ancestors arrived in South America during the Great American Biotic Interchange. A Pleistocene diversification is inferred for the genus Tapirus from the fossil record, but only two species survived the Pleistocene megafauna extinction. Here, we investigate the history of lowland tapir as revealed by variation at the mitochondrial gene Cytochrome b, compare it to the fossil data, and explore mechanisms that could have shaped the observed structure of current populations.ResultsSeparate methodological approaches found mutually exclusive divergence times for lowland tapir, either in the late or in the early Pleistocene, although a late Pleistocene divergence is more in tune with the fossil record. Bayesian analysis favored mountain tapir (T. pinchaque) paraphyly in relation to lowland tapir over reciprocal monophyly, corroborating the inferences from the fossil data these species are sister taxa. A coalescent-based analysis rejected a null hypothesis of allopatric divergence, suggesting a complex history. Based on the geographic distribution of haplotypes we propose (i) a central role for western Amazonia in tapir diversification, with a key role of the ecological gradient along the transition between Andean subcloud forests and Amazon lowland forest, and (ii) that the Amazon river acted as an barrier to gene flow. Finally, the branching patterns and estimates based on nucleotide diversity indicate a population expansion after the Last Glacial Maximum.ConclusionsThis study is the first examining lowland tapir phylogeography. Climatic events at the end of the Pleistocene, parapatric speciation, divergence along the Andean foothill, and role of the Amazon river, have similarly shaped the history of other taxa. Nevertheless further work with additional samples and loci is needed to improve our initial assessment. From a conservation perspective, we did not find a correspondence between genetic structure in lowland tapir and ecogeographic regions proposed to define conservation priorities in the Neotropics. This discrepancy sheds doubt into this scheme's ability to generate effective conservation planning for vagile species.

No abstract available

No abstract

No abstract