Maximizing survivorship in cold: thermogenic profiles of non-hibernating mammals

Abstract

2002. Maximizing survivorship in cold: thermogenic profiles of non-hibernating mammals. [In: Theriology at the turn of a new century. J. Gliwicz, ed]. Acta Theriologica 47, Suppl. 1: 221-234.Winter-active small mammals residing in seasonal environments employ many different behavioral, anatomical and physiological mechanisms to cope with cold. Herein we review research on survival mechanisms in cold employed by small mammals with emphasis on the families Soricidae, Muridae and Sciuridae. The focus of this review is on research delineating the role of seasonal changes in resting metabolic rate (RMR), nonshivering thermogenesis (NST), body mass, and communal nesting in enhancing winter survivorship of six species of small mammals (masked shrew Sorex cinereus, short-tailed shrew Blarina brevicauda, southern red-backed vole Clethrionomys gapperi, white-footed mouse Peromyscus leucopus, deer mouse P. maniculatus, and southern flying squirrel Glaucomys volans) residing in the Appalachian Mountains of Pennsylvania, USA. Each species shows good over-winter survivorship but exhibits a different suite of mechanisms to maximize survival in cold. B. brevicauda, S. cinereus, and G. volans show slight increases in RMR during winter, whereas Peromyscus and C. gapperi exhibit decreased RMR overwinter. All six species experience elevated NST in winter. The comparatively low RMR and NST of G. volans during winter was attributable to a decreased energy expenditure due to a larger body mass, coupled with communal nesting in cavities of trees that provided insulation from low ambient temperatures. Squirrels nesting singly experienced a longer period of elevated NST in winter and higher mean NST year-round than did squirrels nesting communally. Energy conservation in the form of growth retardation in winter was exhibited by C. gapperi and S. cinereus but not the other species.

Geographic and temporal correlations of mammalian size reconsidered: a resource rule

“…The question that arises from this pattern is why this response is so limited: it has been clearly seen only in Sorex, Myodes (=Clethrionomys), and Microtus (Dehnel 1949;Merritt and Zegers 2002), but may also occur in other cold-climate arvicoline rodents. The decisive requirements for the use of this reduction in size appear to be that the species must live in seasonally cold environments, have a small mass, and be committed to continuous endothermy.…”

Habitat selection drives dietary specialisation inSorex minutus

“…Common adaptive strategies seen in other small mammals, such as huddling [20], cannot be adopted by Sorex shrews due to their territoriality, particularly in winter when little to no contact is observed between individuals [21]. Several adaptations have developed in order to survive during the winter, both behavioural and physiological [22]. Nests are used throughout the year, allowing a reduction in thermogenic cost whenever the ambient temperature is lower than approximately 24 °C, above which point the effects are negligible as thermoneutrality is reached [18].…”

Social thermoregulation in least shrews, Cryptotis parva

“…Avoidance involves energy conservation and can be accomplished via a number of tactics, including heterothermy, seasonal reduction in body mass (Dehnel Effect), reduction in level of activity, changes in microclimatic regime (e.g., communal huddling or construction of elaborate nests), adjustment in foraging zone, food hoarding, or adaptation in body size, insulation, appendages or coloration (Merritt 2010). Small mammal species rarely depend upon a single mechanism to survive cold but exhibit a suite of adaptive strategies, a metabolic-behavioral profile, that has evolved in response to the specific habitat, basic attributes and lifestyle of the species (Merritt and Zegers 2002).…”