Thermal acclimation and non-shivering thermogenesis in three species of South American rodents: a comparison between arid and mesic habitats

Non-hibernating mammals that live in seasonal and arid environments change their non-shivering thermogenesis (NST) capacity to maintain homeothermy. Metabolic capabilities of animals, such as NST, are considered adaptive plastic traits because they have a broad range of possible phenotypes with different ambient temperatures (i.e. the reaction norm). Consequently, we determined the reaction norm for NST in Octodon degus (Bennett, 1832; mb=189 g) andPhyllotis darwini (Waterhouse, 1837; mb=61 g) from the mesic habitat of central Chile, and inPhyllotis xanthopygus (Waterhouse, 1837; mb=67 g) from the high Andean plains of northern Chile, an arid and seasonal habitat. Octodon degus showed a 22% increase in NST with thermal acclimation, whereas P. xanthopygus showed a 112% increase, and P. darwini showed a 117% increase in NST, being the largest change observed. These results are in agreement with our hypothesis of evolutionary inertia, which states that observed metabolic plasticity in Phyllotis species is consequence of their high Andean origin, in spite of the fact the actual habitat ofP. darwini is the less seasonal central valley of Chile.