OXYGEN-CONSUMPTION AND CARBON-DIOXIDE PRODUCTION IN MALE PRAIRIE DEERMICE (PEROMYSCUS-MANICULATUS BAIRDII) IN DIFFERENT REPRODUCTIVE CONDITIONS AND GROUP DENSITIES

Natural and laboratory populations of Peromyscus exhibit a profound bu t reversible reproductive inhibition related to population density. Ou r earlier studies described the endocrine physiology oi inhibited anim als which resembles a condition of delayed puberty, but they did not r eveal a primary mechanism for the induction and maintenance of the inh ibition. These studies indicated that reproductive inhibition could be associated with an overall change in general metabolism To test this hypothesis, oxygen consumption (VO2) and carbon dioxide production (VC O2) were measured in three groups of Peromyscus maniculatus males that were: 1) reproductively-proven, 2) reproductively-inhibited, or 3) re covered from inhibition. We found that the mean of the 2-hr period wit h the lowest VO2 (the Resting Metabolic Rate, or RMR) was significantl y lower, and the mean Respiratory Exchange Ratio (RER) was significant ly higher in reproductively-inhibited males compared with reproductive ly proven males. In addition, previously inhibited males allowed to re cover reproductive function had a significantly higher mean VO2, while the mean RER was not different from reproductively-proven males. More over, and contrary to some studies with other species, increasing the ambient carbon dioxide concentration or the caging densities to as hig h as six animals did nor: significantly affect oxygen consumption when compared with the corresponding values for individuals. Taken togethe r, these findings indicate that the reproductive inhibition observed i n P. maniculatus laboratory populations is causally associated with a significant reduction in general metabolism and that this metabolic re duction which is associated with reproductive-inhibition is not induce d by a CO2 signal or induced by absolute density, per se. (C) 1998 Els evier Science Inc.