You are here

Daily body temperature rhythms persist under the midnight sun but are absent during hibernation in free-living arctic ground squirrels

TitleDaily body temperature rhythms persist under the midnight sun but are absent during hibernation in free-living arctic ground squirrels
Publication TypeJournal Article
Year of Publication2011
AuthorsWilliams, CT, Barnes, BM, Buck, LC
JournalBiology Letters
VolumeOnline
Abstract

In indigenous arctic reindeer and ptarmigan, circadianrhythms are not expressed during theconstant light of summer or constant dark ofwinter, and it has been hypothesized that a seasonalabsence of circadian rhythms is common toall vertebrate residents of polar regions. Here,we show that, while free-living arctic groundsquirrels do not express circadian rhythmsduring the heterothermic and pre-emergenteuthermic intervals of hibernation, they displayentrained daily rhythms of body temperature(Tb) throughout their active season, whichincludes six weeks of constant sun. In winter,ground squirrels are arrhythmic and regulatecore body temperatures to within +0.28C for upto 18 days during steady-state torpor. In spring,after the use of torpor ends, male but notfemale ground squirrels, resume euthermiclevels of Tb in their dark burrows but remainarrhythmic for up to 27 days. However, onceactivity on the surface begins, both sexes exhibitrobust 24 h cycles of body temperature. Wesuggest that persistence of nycthemeral rhythmsthrough the polar summer enables groundsquirrels to minimize thermoregulatory costs.However, the environmental cues (zeitgebers)used to entrain rhythms during the constantlight of the arctic summer in these semi-fossorialrodents are unknown.

DOI10.1098/rsbl.2011.0435
Username Tag: