Life with fur and without: experimental field energetics and survival of naked meadow voles

Abstract

Hair is considered to be a basic mammalian feature that provides protection and insulation, promoting energy conservation and survival. To quantify the functional significance of mammalian pelage, we tested the short-term experimental effects of fur removal in a natural population of the California vole, Microtus californicus, in winter. The daily energy expenditure (DEE) of seven voles was directly measured in the field using stable isotopes, first with the animals in their natural condition and then again after experimental removal of pelage by shaving. The initial mean±SD DEE of 96.0±23.1 kJ/day increased by only about 10%, to 106.3±21.4 kJ/day, following shaving. The voles showed a body mass loss of 5%, about half of which was due to fur removal. Comparing slightly larger samples of all animals whose local survival could be documented, we found 100% survival over the 5 initial days of the experimental manipulation in 16 control animals and nine shaved animals; over the following 3 weeks the survival of shaved mice did not differ significantly from that of controls. We were surprised that the average increase in energy expenditure of voles without fur was so modest, though the range of individual values was great, and likewise we were surprised that shaved voles survived as well as they did. M. californicus survives naturally in winter under conditions of social aggregation that include huddling together of individuals in nests; this situation probably provided our experimentally shaved voles an opportunity to minimize the energetic disadvantages of pelage loss. They may also have employed a variety of compensatory physiological and behavioral responses, including reduction in activity time and food intake, and perhaps a related small decline in body mass. Our limited sample sizes made it difficult to detect subtle differences that may have been biologically significant in the system we studied. Nonetheless, we can reaffirm that fur has an insulative value that promotes energy economy and survival. However, we also conclude that mammalian physiology and behavior are sufficiently complex and flexible that a variety of responses can be deployed to promote survival under unusual circumstances such as those of our experimental test.

Ambient temperature shapes reproductive output during pregnancy and lactation in the common vole (Microtus arvalis): a test of the heat dissipation limit theory

“…Whether the effects reported here are also present in a field situation remains to be investigated. A recent non-breeding study that focused on survival of shaved versus non-shaved Microtus californicus in the field found no effects (Kenagy and Pearson, 2000).…”

Shaving increases daily energy expenditures in free living root voles

“…Independent of shaving treatment, larger individuals lost more weight (F 1,67 =19.16, P<0.0001, interaction body mass × treatment was not significant and therefore not included in the final model). The decrease in body mass was most likely caused by increased energy expenditure, which was also observed in shaved golden-mantled squirrels in laboratory conditions (Kauffman et al, 2004) and in shaved meadow voles in the field (Kenagy and Pearson, 2000).…”

“…To our knowledge this is the first successful demonstration of the effectiveness of such manipulation of mammalian DEE. In freeranging meadow voles (Kenagy and Pearson, 2000), elephant shrews and rock mice (Boyles et al, 2012) there was no significant influence of shaving treatment on DEE or on the heterothermy index (Boyles et al, 2012). However, those studies relied on small samples sizes (7, 12 and 13 individuals, respectively) and may therefore have been insufficiently powered to detect a significant effect.…”

“…Meadow voles had only a small and statistically insignificant increase of DEE in shaved compared with unshaved individuals (Kenagy and Pearson, 2000). These studies were based on a very small sample size.…”

Social thermoregulation and torpor in the Siberian hamster

“…As a consequence, the increase in metabolic rate in response to low T a may be smaller (Gębczynski, 1969;Kenagy and Pearson, 2000;Kauffman et al, 2003;Scantlebury et al, 2006). Although we did not measure nest temperature, it is plausible that the local temperature in the nest with four animals inside was higher than that of the nest of single hamsters.…”