RUSSELL, GA*; CHAPPELL, MA; HAMMOND, KA; Univ. of California, Riverside: Effects of high altitude development and cold acclimation on summit metabolism and organ mass in the deer mouse, Peromyscus maniculatus

A key to understanding putatively adaptive changes in metabolic rate is identifying causative changes in organ or organ system mass. Changes in summit metabolism (maximum oxygen consumption induced by cold; VO_2sum) that result from cold acclimation have been well documented, and seem intuitively adaptive in cold habitats. However, little attention has been paid to changes in organ mass (other than brown adipose tissue, BAT) that result from cold acclimation. In several vertebrates in utero development in a hypoxic environment (e.g. high altitude, HA) can alter organ growth and hence metabolic rate. To examine if visceral organ mass is correlated with VO_2sum and whether development at HA affects VO_2sum after subsequent acclimation to low altitude (LA), we studied three groups of deer mice, Peromyscus maniculatus: one born at LA (380 m) and two born at HA (3800 m) and acclimated to 380 m for several months. One group of HA-born mice was acclimated to 5°C for 8 weeks; control mice were housed at 23°C. After 8 weeks, VO_2sum was determined and each mouse was dissected. We used previously collected VO_2sum data from LA-born, cold-acclimated mice as a comparison. VO_2sum was 12-43% higher in cold-acclimated mice than controls, but was not affected by birth altitude (p < 0.05). VO_2sum was 28% higher in HA-born control mice than LA-born mice (p < 0.05). No organ mass was correlated with VO_2sum except testicle mass in cold-acclimated, HA-born males (r² = 0.98, p = 0.02). We can conclude that site of development influences metabolism to some degree and that no organ or organ system mass, other than BAT, appears to be strongly involved in regulating acclimatory changes in summit metabolism.