Much our research uses comparative approaches to answer fundamental questions about how organisms adapt and evolve to better cope in challenging environments. What are the integrative mechanisms of adaptive evolution and phenotypic plasticity? To what extent do interacting and integrated traits (e.g., steps in the O2 transport pathway) evolve in concert? Are changes in some traits more likely to constitute the first steps of adaptation? Do evolved changes in some traits alter the adaptive value of changes in other traits? Does the evolution of organismal performance arise via similar underlying mechanisms across different lineages? Our research examines these questions in different vertebrate groups.
Evolution and Plasticity in High-Altitude Deer Mice
High-altitude environments are among the most challenging environments experienced by terrestrial animals. Temperatures are much colder at high altitude than at sea level, increasing the O2 demands of thermogenesis, but high altitude also has thin air with low O2 availability (hypoxia) to support these high O2 demands. In fact, O2 levels atop the highest mountains in the world are scarcely sufficient to support life in many species – they are so low that unacclimatized lowland animals can be rendered comatose within minutes. However, every mountain range contains animals that have overcome this challenge and thrive at high altitudes.
The emphasis of much of our current work in this area focusses on deer mice (Peromyscus maniculatus), the species with the broadest altitudinal distribution of any North American mammal. In high-altitude populations, natural selection favours a high capacity to produce body heat (‘thermogenic capacity’), a key performance trait that is underpinned by several intersecting areas of physiology (cardiorespiratory physiology and the O2 transport pathway, mitochondrial metabolism, thermoregulation, etc.). We maintain lab colonies of mice derived from wild populations at high altitude (4300m in the Rocky Mountains) and low altitude (Great Plains) to study these processes in captivity.
Mice can be held in control conditions reflective of sea level, and can also be exposed to conditions that simulate the cold and hypoxic conditions at high altitude. Comparisons between environments are used to uncover mechanisms of phenotypic plasticity, which we examine during adulthood (acclimation), early life (developmental plasticity), and even across generations (trans-generational plasticity, epigenetics). Comparisons between high-altitude and low-altitude populations are used to elucidate the mechanisms underlying evolutionary adaptation and the evolution of phenotypic plasticity.
Evolutionary Physiology of High-Altitude Birds
The Andes of South America contain a great diversity of species that have adapted to high-altitude environments. Many high-altitude lakes contain several species of ducks, geese, and other waterbirds that have independently colonized high altitude. Some of these taxa are well established and endemic to high altitude, whereas some others are relatively new colonists of the high-altitude environment. We compare these high-altitude taxa to their close low-altitude relatives to uncover mechanisms of high-altitude adaptation that are conserved across species, to examine how time at high altitude affects high-altitude phenotypes, and to understand how and why differences between species may alter the responses to high-altitude in different lineages.
Phylogenetic relationships of bird taxa used in the comparative analyses of the O2 transport pathway and mitochondrial physiology in high-altitude natives (Dawson et al. 2020). Multiple pairs of high- and low-altitude taxa are used to evalute whether common physiological changes have arisen across high-altitude birds (e.g., convergent evolution), or whether birds in different lineages exhibit distinct changes at high altitude.
Scott Lab @ McMaster 