title: Cold acclimation in Peromyscus: individual variation and sex effects in maximum and daily metabolism, organ mass and body composition.
abstract: We studied metabolic and organ mass responses to thermal acclimation (7 weeks at 5 degrees C or 23 degrees C) in deer mice, Peromyscus maniculatus. Cold acclimation resulted in significantly higher maximal oxygen consumption in thermogenesis (V(O(2)max)) and daily mean oxygen consumption (V(O(2)mean)), an increase in the mass of most visceral organs, a lower absolute body fat and a marginally significant increase in hematocrit. The mass of digestive organs and body fat content differed significantly between sexes. Acclimation effects on fat content were more pronounced in females. Variation in heart and lung mass was positively correlated with V(O(2)max) and V(O(2)mean), while body fat content was negatively correlated with both traits. Nonetheless, a large fraction of the metabolic difference between cold- and warm-acclimated groups remained unexplained. Associations between traits at lower levels of biological organization measured here and whole-organism energetics remained consistent across acclimation temperatures, except for the correlation between kidney mass and V(O(2)mean), which was positive and significant in cold acclimation and negligible following warm acclimation. We conclude that: (1) V(O(2)max) and V(O(2)mean) share a common physiological basis that remains overall the same across acclimation regimes; (2) changes in these traits are associated primarily with changes in heart mass; and (3) male and female deer mice respond differently to thermal acclimation, possibly due to differences in reproductive allocation.
authors.affiliation: Departament de Genètica i de Microbiologia, Facultat de Biociències, Universitat Autònoma de Barcelona, Bellaterra 08193, Spain. enrico.rezende@uab.cat
authors.forename: Enrico L
authors.initials: EL
authors.lastname: Rezende
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Hammond
authors.forename: Mark A
authors.initials: MA
authors.lastname: Chappell
mesh_terms: D000064:Acclimatization; D000818:Animals; D001823:Body Composition; D003080:Cold Temperature; D004734:Energy Metabolism; D005260:Female; D007668:Kidney / Q000033:anatomy & histology; D008297:Male; D009929:Organ Size; D010542:Peromyscus / Q000033:anatomy & histology / Q000502:physiology*; D012727:Sex Characteristics; D012737:Sex Factors