Department of Biology, Concordia University, Montreal, QC, Canada.
Oecologia. 2010 Jan;162(1):261-71. doi: 10.1007/s00442-009-1443-5.
Two different processes can lead to a change in individual reproductive output with age in long-lived iteroparous vertebrates. The senescence hypothesis predicts a decline of performance in old age, whereas the terminal allocation hypothesis predicts an increase. Using long-term (>30 years) individually based data of female reindeer, we first assessed age-specific variation in body mass and different components of reproductive output. Then we investigated the contribution of senescence and terminal allocation (the increase in components of reproductive output) processes for shaping observed patterns. We found that female reindeer body mass increased up to about 11.5 years of age, and decreased afterwards, supporting the senescence hypothesis. Calf birth mass, both in absolute terms or for a given female mass, first increased and then declined with female age, also supporting the senescence hypothesis. The female mass gain (June-September) decreased with increasing age, and female change in mass between 2 consecutive years decreased with female age, all patterns again supporting the senescence hypothesis. However, the autumn calf mass did not change with age. Calf body mass in autumn tended to be positively related to female mass gain, supporting a quality effect. Raising a calf had a marked negative effect on female mass gain, indicating energetic reproductive costs of raising a calf. Calf body mass in autumn did not influence yearly female mass change. Overall, our results provided consistent evidence for general effects of senescence on most components of reproductive output and highlighted that both individual heterogeneity and reproductive costs shape female reindeer reproductive tactics.
在长寿的多次生殖的脊椎动物中，有两种不同的过程可以导致个体生殖输出随年龄的变化。衰老假说预测老年时表现能力下降，而终末分配假说则预测增加。使用雌性驯鹿的长期（>30 年）个体基础数据，我们首先评估了体重和生殖输出不同组成部分的年龄特异性变化。然后，我们调查了衰老和终末分配（生殖输出组成部分的增加）过程对观察到的模式的贡献。我们发现，雌性驯鹿的体重增加到约 11.5 岁，然后下降，支持衰老假说。绝对初生牛犊体重或给定雌性体重的初生牛犊体重首先增加，然后随雌性年龄下降，也支持衰老假说。雌性体重增加（6 月至 9 月）随年龄增加而减少，雌性在连续两年间的体重变化随雌性年龄而减少，所有这些模式再次支持衰老假说。然而，秋季牛犊体重没有随年龄变化。秋季牛犊体重与雌性体重增加呈正相关，支持质量效应。养育小牛对雌性体重增加有显著的负面影响，表明养育小牛的能量生殖成本。秋季牛犊体重不影响女性每年的体重变化。总的来说，我们的研究结果提供了衰老对生殖输出大多数组成部分的普遍影响的一致证据，并强调了个体异质性和生殖成本对雌性驯鹿生殖策略的影响。
