Data from: Distinguishing between determinate and indeterminate growth in a long-lived mammal

Background: The growth strategy of a species influences many key aspects of its life-history. Animals can either grow indeterminately (throughout life), or grow determinately, ceasing at maturity. In mammals, continued weight gain after maturity is clearly distinguishable from continued skeletal growth (indeterminate growth). Elephants represent an interesting candidate for studying growth because of their large size, long life and sexual dimorphism. Objective measures of their weight, height and age, however, are rare. Results: We investigate evidence for indeterminate growth in the Asian elephant Elephas maximus using a longitudinal dataset from a semi-captive population. We fit growth curves to weight and height measurements, assess sex differences in growth, and test for indeterminate growth by comparing the asymptotes for height and weight curves. Our results show no evidence for indeterminate growth in the Asian elephant; neither sex increases in height throughout life, with the majority of height growth completed by the age of 15 years in females and 21 years in males. Females show a similar pattern with weight, whereas males continue to gain weight until over age 50. Neither sex shows any declines in weight with age. Conclusions: These results have implications for understanding mammalian life-history, which could include sex-specific differences in trade-offs between size and reproductive investment.

研究背景：物种的生长策略对其生活史诸多关键方面具有显著影响。动物的生长模式可分为两类：终生持续的不定生长（indeterminate growth），以及成熟后即停止的确定生长（determinate growth）。在哺乳动物中，成熟后持续的体重增长与持续性骨骼生长（即不定生长）具有明确区分。大象凭借体型庞大、寿命悠长且存在性二态性的特点，成为探究生长模式的优质研究对象。然而，目前关于其体重、身高及年龄的客观实测数据仍较为匮乏。研究结果：本研究依托半圈养种群的纵向数据集，针对亚洲象（Elephas maximus）是否存在不定生长展开探究。我们通过体重与身高的实测数据拟合生长曲线，评估生长过程中的性别差异，并通过对比身高与体重生长曲线的渐近值，检验不定生长是否存在。结果显示，亚洲象并无不定生长的相关证据：两性个体的身高均不会随年龄增长持续增加，雌性个体约15岁、雄性个体约21岁时便完成了绝大多数身高生长。雌性个体的体重增长模式与身高一致，而雄性个体则会持续增重至50岁以上，且两性个体的体重均未随年龄增长出现下降趋势。研究结论：本研究结果对理解哺乳动物生活史具有重要参考价值，其或可揭示体型与繁殖投入之间权衡关系的性别特异性差异。