Date Published: February 4, 2019
Publisher: Public Library of Science
Author(s): Kahoko Tochigi, Yukino Aoki, Tetsuya Maruyama, Koji Yamazaki, Chinatsu Kozakai, Tomoko Naganuma, Akino Inagaki, Takashi Masaki, Shinsuke Koike, Cyril Charles.
Cementum annuli widths in mammals are is influenced by the nutrition of mammals. Reproductive stress has been is suggested to reduce the width of lead to narrower cementum annuli widths in female Asian black bears (Ursus thibetanus); however, food availability in autumn strongly impacts bear nutrition and likely impacts cementum widths as well. This study aimed to test how cementum annuli widths and the formation of false annuli were influenced by hard mast production. We established two hypotheses: (1) cementum annuli widths become narrower in poor mast years owing to inadequate nutritional conditions and (2) false annuli occur more frequently in poor mast years. We used teeth samples from male bears to avoid reproductive influences and separated width data into “adult” and “subadult” groups. We calculated the proportional width index (PWI) and used linear mixed models to estimate the masting effects on PWI. Generalized linear mixed models estimated the masting effects on false annuli frequency. True annuli widths and false annuli formation showed no significant relationship with mast production in adults. In subadults, poor mast production weak negative influence on false annuli formation. These new data resolve previous questions, allowing us to deduce that cementum annuli widths are a reliable index of reproductive success in female bears.
For some organisms, banded growth lines on specific body parts document periodic growth . For example, the growth line, or annual ring, is produced in the xylem of some woody plant species representing a single year’s growth and often is used as an estimate of tree age. Like woody plants, some mammal species have growth lines that form in a periodic manner on the cementum of their teeth called cementum annuli . Cementum is connective tissue that grows in incremental layers surrounding the roots of teeth, becoming thick with mineral deposition . These bands consist of both thick light-stained bands (hereafter, light band) and narrow, dark lines (hereafter, dark band) (Fig 1).
Until September, light bands were formed in the teeth of all individuals, and no dark bands were formed. Formation of dark bands was observed in October (in 8 of 24 bears), November (0 of 3), and January (1 of 1) (Table 1).
Our results showed that there were decreasing width patterns and periods of light- or dark-band formation in the cementum annuli of premolar teeth of Asian black bears, similar to other mammals. In addition, we found that hard mast production had no impact on cementum patterns for adult period, but a small impact on subadult period.