Specific features of the record of hibernation on the incisor surface in Allocricetulus hamsters

Abstract

To evaluate how the course of irregular winter hibernation is recorded in the incisor teeth of Allocricetulus hamsters, an analysis was performed of the incisor surface in seven A. curtatus and two A. eversmanni hamsters and stained section of the incisors in one A. curtatus hamster. The animals were kept in cages at natural temperature and photoperiod. Five hamsters were implanted with a temperature data logger, and another five received tetracycline injections (5–20 days before death). In addition, the incisor surface was examined in eight A. curtatus and eight A. eversmanni hamsters trapped in the field. In hibernating hamsters, the duration of alternating periods of hypothermia (torpor bouts) and normothermia (arousals) and their ratio varied irregularly and randomly within and between individuals. Increments on the incisor surface were of two types: wide and poorly defined or narrow and distinct. The increments in hamsters trapped in the field were slightly more distinct than in experimental captive animals, and those in two hamsters that failed to hibernate were similarly wide and indistinct. In hibernating hamsters, wide increments proved to correspond to long periods of normothermia, while narrow increments were formed when torpor bouts alternated with short arousals. More distinct narrow increments formed when torpor bouts followed by short (no more than 1.5-days) arousals occurred in a series rather than singly. Although the number of narrow increments was approximately similar to that of short arousals, in was impossible to localize the record of each particular hypo/normothermia episode on the incisor surface. Dentin layers in stained preparations had no definite pattern and corresponded to these episodes no better than the increments on the incisor surface. In general, the narrow and distinct increments in a given Allocricetulus hamster is evidence that the animal did hibernate, and the number of such increments indicates the approximate minimum number of torpor bouts followed by arousals. The record of winter hibernation on the incisors of Allocricetulus hamsters has a pattern similar to that in Mesocricetus brandti (Batavia et al., 2013) but significantly differs from the pattern described in M. raddei (Klevezal et al., 2012).