Parentage analysis across age cohorts reveals sex differences in reproductive skew in a group-living cichlid fish, Neolamprologus multifasciatus.

Group-living animals are often faced with complex reproductive decisions, namely how to partition within-group reproduction, how to obtain extra-group reproduction and how these two means of reproduction should be balanced. The solutions to these questions can be difficult to predict because ecological conditions can affect the scopes for within-group and extra-group reproduction in complex ways. For example, individuals that are restricted from moving freely around their habitats may have limited extra-group reproductive opportunities, but at the same time, groups may live in close proximity to one another, which could potentially have the opposite effect. The group-living cichlid fish Neolamprologus multifasciatus experiences such ecological conditions, and we conducted an intensive genetic parentage analysis to investigate how reproduction is distributed within and among groups for both males and females. We found that cohabiting males live in "high-skew" societies, where dominant males monopolize the majority of within-group reproduction, while females live in "low-skew" societies, where multiple females can produce offspring concurrently. Despite extremely short distances separating groups, we inferred only very low levels of extra-group reproduction, suggesting that subordinate males have very limited reproductive opportunities. A strength of our parentage analysis lies in its inclusion of individuals that spanned a wide age range, from young fry to adults. We outline the logistical circumstances when very young offspring may not always be accessible to parentage researchers, and present strategies to overcome the challenges of inferring mating patterns from a wide age range of offspring.