Low thyroxine serves as an upstream regulator of ecophysiological adaptations in Ansell’s mole-rats

About 10% of all rodent species have evolved a subterranean way of life, although life in subterranean burrows is associated with harsh environmental conditions that would be lethal to most animals living above ground. Two key adaptations for survival in subterranean habitats are extraordinarily low resting metabolic rate (RMR) and core body temperature (Tb). However, the upstream regulation of these unique traits was unknown thus far. Previously, we have reported exceptionally low concentrations of the thyroid hormone (TH) thyroxine (T4), and peculiarities in TH regulating mechanisms in two African mole-rat species, the naked mole-rat and the Ansell’s mole-rat. In the present study, we provided the first experimental evidence that the unique TH phenotype of Ansell’s mole-rats is the upstream regulator of low RMR and Tb. Thus, our study adds a novel aspect to the understanding of TH biology and contributes to a better understanding of the ecophysiological evolution of the subterranean lifestyle.