Seasonal Acclimatization to Temperature in the Prairie Vole, Microtus ochrogaster

Abstract

Existence energy at different ambient temperatures, and assimilation efficiencies were determined for the prairie vole, Microtus ochrogaster, during summer and winter. Seasonal hair length, hair density and thermal conductance were also measured. Winter existence energy was significantly lower and was correlated with significantly greater hair length and hair density. The large proportional change in seasonal hair density indicated that it may be a more important thermal adaptation than generally recognized. Seasonal thermal conductance did not vary significantly. Winter voles also showed lower assimilation efficiency which was correlated with a higher caloric value per gram dry weight of feces excreted. Energy lost via urine became increasingly important with increasing ambient temperature. Body temperatures remained constant at 5, 12 and 20 C, but were significantly higher at 32 C. INTRODUCTION Temperature regulation has been studied more intensively in rodents than in any other group of mammals in recent years. This interest has stemmed partly from convenience in methodology, but primarily from the great diversity of regulatory responses within the group (Hart, 1971). Thermoregulation is significant ecologically since it is the main avenue of energy loss in homoiothermic animals (McNab, 1963). Thus, the measurement of energy expended for thermoregulation is fundamental both to calculating population energetics and to understanding seasonal acclimatization of free-living rodents. Metabolic thermoregulation has been determined in various microtine rodents. These include Microtus pennsylvanicus (Wiegert, 1961), M. arvalis (Trojan and Wojciechowska, 1967), M. montanus (Packard, 1968), M. oeconomus (Gebczynska, 1970) and M. longicaudus (Smith, 1969; Beck and Anthony, 1971). However, virtually no information is available on the energetics of the prairie vole, Microtus ochrogaster. The objectives of this study were to examine summer and winter acclimatization of the prairie vole to temperature and to provide preliminary data from which population energetics of freeliving voles may be calculated. METHODS Metabolic studies.-Prairie voles were captured in live traps during August 1971 and January 1972 in Effingham Co., Illinois. Less than 3 days elapsed from field capture until the voles were placed into individual metabolism cages located in constant temperature cabinets. Photoperiod was maintained at 15 light-9 dark hr for summer voles and 9 light-15 dark hr for winter voles to, simulate natural seasonal photoperiods. One half of the voles was tested first at 20 C and then