Department of Biology, University of Turku, Turku, Finland.
Institute of Biodiversity, Animal Health & Comparative Medicine, University of Glasgow, Glasgow, UK.
J Anim Ecol. 2021 Nov;90(11):2663-2677. doi: 10.1111/1365-2656.13573. Epub 2021 Sep 20.
Many mammals grow up with siblings, and interactions between them can influence offspring phenotype and fitness. Among these interactions, sibling competition between different-age offspring should lead to reproductive and survival costs on the younger sibling, while sibling cooperation should improve younger sibling's reproductive potential and survival. However, little is known about the consequences of sibling effects on younger offspring life-history trajectory, especially in long-lived mammals. We take advantage of a large, multigenerational demographic dataset from semi-captive Asian elephants to investigate how the presence and sex of elder siblings influence the sex, survival until 5 years old, body condition, reproductive success (i.e. age at first reproduction and lifetime reproductive success) and long-term survival of subsequent offspring. We find that elder siblings have heterogeneous effects on subsequent offspring life-history traits depending on their presence, their sex and the sex of the subsequent offspring (named focal calf). Overall, the presence of an elder sibling (either sex) strongly increased focal calf long-term survival (either sex) compared to sibling absence. However, elder sisters had higher impact on the focal sibling than elder brothers. Focal females born after a female display higher long-term survival, and decreased age at first reproduction when raised together with an elder sister rather than a brother. Focal males born after a female rather than a male showed lower survival but higher body weight when both were raised together. We did not detect any sibling effects on the sex of the focal calf sex, survival until 5 years old and lifetime reproductive success. Our results highlight the general complexity of sibling effects, but broadly that elder siblings can influence the life-history trajectory of subsequent offspring. We also stress the importance of considering all life stages when evaluating sibling effects on life trajectories.
许多哺乳动物在成长过程中都有兄弟姐妹，它们之间的相互作用会影响后代的表型和适应度。在这些相互作用中，不同年龄的后代之间的竞争会对年幼的后代产生生殖和生存成本，而合作则会提高年幼后代的生殖潜力和生存能力。然而，对于兄弟姐妹效应对年幼后代的生活史轨迹的影响，尤其是在长寿哺乳动物中，我们知之甚少。我们利用来自半圈养亚洲象的大型、多世代人口数据集，研究了年长兄弟姐妹的存在和性别如何影响后续后代的性别、5 岁前的生存、身体状况、生殖成功（即首次繁殖年龄和终生生殖成功）以及长期生存。我们发现，年长兄弟姐妹对后续后代的生活史特征有不同的影响，这取决于它们的存在、性别以及后续后代（称为焦点小牛）的性别。总体而言，与没有兄弟姐妹相比，年长兄弟姐妹（无论性别）的存在强烈增加了焦点小牛的长期生存（无论性别）。然而，姐姐对焦点兄弟姐妹的影响大于哥哥。与哥哥相比，与姐姐一起长大的雌性焦点小牛的长期生存更高，首次繁殖年龄更小。与哥哥相比，与姐姐一起长大的雄性焦点小牛的存活率较低，但体重较高。我们没有检测到兄弟姐妹效应对焦点小牛的性别、5 岁前的生存和终生生殖成功的影响。我们的结果突出了兄弟姐妹效应对生活史轨迹影响的一般复杂性，但总体而言，年长的兄弟姐妹可以影响后续后代的生活史轨迹。我们还强调了在评估兄弟姐妹对生活轨迹的影响时，考虑所有生命阶段的重要性。
