DEVELOPMENTAL AND MATERNAL THERMOREGULATORY ADAPTATIONS TO HIGH ALTITUDE IN THE NORTH AMERICAN DEER MOUSE, PEROMYSCUS MANICULATUS

Abstract

Altricial mammals develop the capacity to independently thermoregulate during the first few weeks of postnatal development. This shift in performance is driven by the maturation of the two primary thermo-effector organs, brown adipose tissue (BAT) and skeletal muscle which are non-functional at birth. In wild rodent populations this is also a time of high mortality (50-95%), making the physiological systems that develop during this period potential targets for natural selection. High altitude is a particularly challenging environments for small endotherms due to unremitting low O2 availability and consistently low ambient temperatures. As a result, some high-altitude taxa have evolved a superior adult thermogenic capacity. However, it is unclear if selection has occurred to survive these unique challenges early in development. The goal of my thesis is to address this gap in knowledge and assess developmental thermoregulatory adaptations in an altricial high altitude endotherm. I used deer mice (P. maniculatus) native to high and low altitude population, and a strictly low altitude species (P. leucopus), all raised under common garden conditions to assess how high altitude adaptation has altered the onset of endothermy, developmental plasticity of thermogenic capacity and maternal care. I have shown that selection has fundamentally delayed the maturation of the BAT and skeletal muscle in high altitude natives and has altered their capacity for developmental plasticity. High altitude pups are able to maintain growth rates and body composition under cold hypoxic conditions despite receiving less maternal care than their low altitude counterparts. These data suggest that high altitude adapted mice have evolved to suppress energetically costly thermogenesis during development.