Is There a Record of Hibernation on the Surface of Incisors in the Common Hamster (Cricetus cricetus, Rodentia, Cricetidae)?

Abstract

As was shown earlier, in some hibernating rodents the patterns of hibernation are recorded by tooth dentine and can be revealed in stained or ground sections of the incisors, as well as on the incisor surface. Hibernation in the common hamster, Cricetus cricetus, can be described as facultative with great individual variability of the body temperature dynamics during the winter. To investigate the records of hibernation on the incisor surface of this species, we studied the lower incisors of hamsters that had wintered with implanted temperature data loggers under natural conditions in a city park of Simferopol, Crimea (two animals); in semi-natural conditions in the village of Khunzakh, Dagestan (two animals); and using 19 hamsters from a natural population found dead in Simpferopol or its environs during late winter or early spring. Previous studies of eight hamsters that were kept under laboratory conditions and that had received tetracycline injections confirmed the daily formation of the increments on the incisor surface. This data allowed us to find the part of the incisor that could have been formed during hibernation in the hamsters with implanted loggers. In three of four of them, the typical pattern of daily increments was disrupted in the parts presumably formed during hibernation. The patterns of disruption varied in different animals, and it was impossible to interpret them as a record of hibernation. Those hamsters revealed no sequences of narrow and clearer increments characteristic of the records of hibernation on incisors. Such a sequence was seen on incisors of only one of 19 hamsters from the natural population. Consequently, no unambiguous record of the periods of hypothermia was found on the surface of incisors in the common hamster. According to the data published earlier, hibernation records on incisors were found in other hamsters of the subfamily Cricetinae (the genera Allocricetulus and Mesocricetus, in particular). A comparison of the dynamics of body temperature during hibernation in these hamsters and in the common hamster allow us to surmise that the formation of narrow increments can be determined in part by the depth and duration of hypothermia, but it mainly depends on the duration of normothermia and the feeding habits of animals during hibernation.