Carranza Juan, Alarcos Susana, Sánchez-Prieto Cristina B, Valencia Juliana, Mateos Concha
Biology and Ethology Unit, Universidad de Extremadura, 10071 Cáceres, Spain.
Nature. 2004 Nov 11;432(7014):215-8. doi: 10.1038/nature03004.
Senescence may result from an optimal balance between current reproductive investment and bodily repair processes required for future reproduction, a theoretical prediction difficult to prove especially in large, long-lived animals. Here we propose that teeth that have fixed dimensions early in life, but that wear during chewing, can be taken as a measure of total lifetime 'repair', and their wear rate as a measure of current expenditure in performance. Our approach also considers the sexual selection process to investigate the advance of senescence in males compared with females, when selection favouring competition over mates reduces the reproductive lifespan of males. We studied carcasses of 2,141 male and 739 female red deer (Cervus elaphus) of different ages, finding that male molariform teeth emerged at a far smaller size than expected from body size dimorphism. This led to higher workload, steeper wear rate and earlier depletion of male teeth than in females, in concordance with sex-specific patterns of lifetime performance and reproduction. These findings provide the empirical support for the disposable-soma hypothesis of senescence, which predicts that investment in bodily repair will decrease when the return from this investment may not be realized as a result of other causes that limit survival or reproduction.
衰老可能源于当前生殖投入与未来生殖所需身体修复过程之间的最佳平衡，这一理论预测很难得到证实，尤其是在大型长寿动物中。在此，我们提出，牙齿在生命早期尺寸固定，但在咀嚼过程中会磨损，可将其作为一生总“修复”的衡量指标，而牙齿磨损率可作为当前性能消耗的衡量指标。我们的方法还考虑了性选择过程，以研究与雌性相比雄性衰老的进程，此时有利于争夺配偶的选择会缩短雄性的生殖寿命。我们研究了2141头不同年龄的雄性马鹿和739头雌性马鹿的尸体，发现雄性臼齿出现时的尺寸远小于根据体型差异预期的尺寸。这导致雄性牙齿的工作量更大、磨损率更高且比雌性更早耗尽，这与特定性别的一生性能和生殖模式一致。这些发现为衰老的“一次性体细胞”假说提供了实证支持，该假说预测，当由于其他限制生存或生殖的原因而无法实现这种投资回报时，对身体修复的投入将会减少。
