Interrelationships Among Timing of Hibernation, Reproduction, and Warming Soil in Free-Living Female Arctic Ground Squirrels

Abstract

The effects of climate change on hibernating species will depend, in part, on their responsiveness to environmental cues used to adjust the seasonal timing of annual events of hibernation and reproduction. Using long-term data collected from two arctic ground squirrel populations living 20 km apart in northern Alaska, we investigate the relationships between the timing of hibernation and reproduction and, in addition, the potential for change in soil temperatures to act as a proximate cue. Previously, we found that female ground squirrels living at the southern-most site, Atigun River, emerge from hibernation and give birth 13 days earlier than females at Toolik Lake. Here we show that timing of parturition was tightly linked to the termination of heterothermy and subsequent emergence from the hibernacula at both sites, whereas timing of entrance into hibernation was only weakly correlated with date of parturition in Toolik Lake females. Females ended heterothermy in spring coincident with rising soil temperatures from winter minima, but since average soil temperatures did not differ between the two sites, a single threshold in warming cannot explain the differences in timing of spring emergence and reproduction between the two populations. Earlier reproduction at Atigun is associated with earlier snowmelt, yet, how this is achieved and the relative importance of phenotypic plasticity versus genetic differences between the two populations will require further investigation.