Zbyszek Boratyński

Animals inhabiting high altitudes are exposed to low ambient temperatures and hypobaric hypoxic conditions. Such dual environmental pressure reinforces mechanisms to counteract demanding thermal environment and, at the same time, physiological constraints of reduced partial oxygen pressure. We investigated how a community of rodents inhabiting the Ethiopian Highlands responded to such dual pressure. We measured internal organ masses (spleen, kidney, liver, heart, and interscapular brown adipose tissue) and fur properties (length and density of hairs) in Arvicanthis blicki , Lophuromys flavopunctatus , Otomys helleri , Stenocephalemys albocaudatus , S. sokolovi , and S. albipes . Phylogenetic vector and mixed regression analyses showed that all species, except for A. blicki , had large internal organs and long and/or dense fur, indicative of high internal heat production and good insulation properties. Instead, A. blicki had the largest interscapular brown adipose tissue, but the poorest fur insulation. The link between organ masses and fur insulation suggests different physiological heat economics among the rodent species. Furthermore, O. helleri had the most similar lengths of hind and forelimbs, indicative of cursorial locomotion, that coincides in this species with large spleen. Cursorial species, which depend on endurance running, may require large spleens to secure a storage and on‐demand release of red blood cells for aerobic physiology during prolonged exercise in high altitudes. Altogether these findings suggest different mechanisms of maintaining thermal and exercise performance under inseparable hypoxic‐thermal conditions of the high‐altitude environment among the studied rodents.

The use of energy is universal to all life forms and all levels of biological organization, potentially linking processes operating at variable scales. Individual and species ranges might be energetically constrained, yet divergent metabolic limitations at both scales can disassociate these individual and species traits. We analysed comparative energetic and range data to unravel the mechanistic basis of the dissociation between individual and species range sizes observed among mammalian species. Our results demonstrate that basal, or maintenance, metabolism negatively correlates with individual ranges, but, at the same time, it positively correlates with species ranges. High aerobic capacity, i.e. maximum metabolic rate, positively correlates with individual ranges, but it is weakly related to species range size. These antagonistic energetic constraints on both ranges could lead to a disassociation between individual and species traits and to a low covariation between home and species range sizes. We show that important organismal functions, such as basal and maximum metabolic rates, have the potential to unravel mechanisms operating at different levels of biological organization and to expose links between energy-dependent processes at different scales.