Incisor growth rate in rodents and the record of the entire annual cycle in the incisors of Marmota baibacina centralis

Abstract

The lower incisors of 80 specimens of Marmota baibacina of 1–10 years old killed in spring in the highland of the Tien Shan Mountains were investigated. On the surface of all the incisors, regular daily increments and “hibernation zones” were revealed. The mean width of increments was used as an indicator of the incisor growth rate before hibernation. We found that the mean width did not depend on the sex of animals, locality, and incisor length, but depended on animal age. The increment width significantly decreased, and the number of the increments formed before hibernation significantly increased with age. This means that the growth rate of the incisors and the intensity of their attrition decrease with the animals’ age. The decrease in the incisor growth rate with age is a manifestation of the well-known decrease with age in the intensity of all growth processes in mammals. As a result of this decrease, in the majority of old marmots under study, zones of hibernation were revealed in the basal as well as in the apical parts of the incisor. The zone in the basal part formed during the latest hibernation and the zone in the apical part corresponded to the previous one. Thus, the incisor preserved the record of the entire year of animal life.