Reproductive Histories of Asian Black Bears Can be Determined by Cementum Annuli Width

Abstract

Very little is known about the cementum annuli of Asian black bears (Ursus thibetanus). We collected the first premolar tooth from adult female bears in central Japan to investigate whether reproductive history was reflected in cementum annuli width; previous studies have indicated that this is possible in other bear species. We calculated the proportional width index (PWI) value as an index of annular cementum growth, and we confirmed reproductive status by direct field observations (females with cubs, with yearlings, or without offspring). We compared both PWI and reproductive status among 10 females to determine whether PWI was correlated with reproduction. In years when females were accompanied by cubs, PWI was significantly smaller than in years when females were with yearlings or without offspring. Our results indicate that reproductive success (parturition and lactation) in female Asian black bears decreases cementum annulus width, which appears to be a useful index of past reproductive history. These data will improve our ability to determine this life-history parameter as we monitor and manage Japan's bear population. Linking other factors (e.g., food availability) to PWI could increase the accuracy of detection of cub survival by this reproductive success index.