Seasonal investigation of fallow deer cellular cementum from Mediterranean ecosystems and its implications for reliable cementochronology applications

Abstract

We aim to extend our understanding of the seasonal formation of cellular cementum, and its functional relationships in fallow deer (Dama dama) from Mediterranean ecosystems, in order to achieve reliable cementochronology applications. We provide a specific reference for fallow deer in a specific ecosystem, as needed for forensic, paleontological and wildlife ecology research. A semi-quantitative rating of the last outermost increment deposited in the cellular cementum interradicular pad of the lower first molar (M1), together with the knowledge of the animal's date of death, provided the methodological basis of this study. We also analyzed the occurrence of each cementum state by season, as well as the influence of the photoperiod and seasonal diet quality variations, using indices such as cell wall digestibility (CWD), protein (N), and carbohydrate (C). In adults more than 4 years old we detected a significant seasonal cementum growth pattern in spring-summer, whereas the formation of rest lines took place mainly from October to February. All of our findings show a photoperiod control of cementum seasonal growth patterns, linked to the organism's annual growth cycle, whereas N and C probably do not influence seasonal deposition patterns. The deposition of the cementum begins to stop when the photoperiod begins to decrease, i.e. when the days begin to be shorter, which in the Mediterranean ecosystems of southern Spain takes place in the autumn and winter months. At this time, the amount of dry matter in food consumed increases, and voluntary food intake decreases. The amount of dietary protein and carbohydrate seems to influence the amount of cementum deposited each year, rather than the seasonal deposition pattern, at least in adults. No significant seasonal pattern was found for the younger fallow deer. Until this seasonal pattern is clarified, young specimens should be excluded from cementochronology applications, such as season-at-death estimations. Studies on the quantitative thickness of cementum increments should also be performed in order to confirm cementochronology as a useful tool for studying climatic variations and their biological impacts.