The elephant in the family: Costs and benefits of elder siblings on younger offspring life-history trajectory in a matrilineal mammal

1. 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.

2. 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 five years old, body condition, reproductive success (i.e. age at first reproduction and lifetime reproductive success), and long-term survival of subsequent offspring.

3. We find that elder siblings have heterogenous effects on subsequent offspring life-history traits depending on their p...