Philopatry yields higher fitness than dispersal in a cooperative breeder with sex-specific life history trajectories

Abstract

Social evolution is tightly linked to dispersal decisions, but the ecological and social factors selecting for philopatry or dispersal often remain obscure. Elucidating selection mechanisms underlying alternative life histories requires measurement of fitness effects in the wild. We report on a long-term field study of 496 individually marked cooperatively breeding fish, showing that philopatry is beneficial as it increases breeding tenure and lifetime reproductive success in both sexes. Dispersers predominantly join established groups and end up in smaller groups when they ascend to dominance. Life history trajectories are sex specific, with males growing faster, dying earlier, and dispersing more, whereas females more likely inherit a breeding position. Increased male dispersal does not seem to reflect an adaptive preference but rather sex-specific differences in intrasexual competition. Cooperative groups may thus be maintained because of inherent benefits of philopatry, of which females seem to get the greater share in social cichlids.

Early social complexity influences social behaviour but not social trajectories in a cooperatively breeding cichlid fish

“…However, both sexes will improve their social rank by dispersing, as they will occupy either the first or second rank in the hierarchy of a small social unit. Males were the more explorative sex and had a higher propensity to disperse than females, which is in line with natural dispersal patterns in this species [40] and findings from the laboratory [31]. It is also the general pattern in mammals and other fish species [51][52][53].…”

“…At 1 year of age (±2 weeks), we tested the focal fish for their propensities to show exploration, helping behaviour and dispersal, over a 3 week testing period ( figure 1 ). We waited until the fish were 1 year old, as older fish engage more readily in defence behaviour [ 39 ] and fish only start to disperse after sexual maturity [ 40 ]. All tests were done in a 1000 l tank partitioned into different areas, depending on the task.…”

How to prime your offspring

“…As this species is socially monogamous, this implies there is no shortage of potential partners per se, but rather a shortage of available territories. This result is congruent with recent findings indicating the relationship between dispersal and cooperation need not be straightforward, and dispersal in cooperative breeders is likely to be strongly influenced by intrasexual competition (Jungwirth et al 2023). Dispersal propensity of cooperatively breeding species displays strong intrasexual variation (Trochet et al 2016), which may be strongly dictated by demographic composition.…”

“…Additionally, ASR is an important demographic driver of inter-and intraspecific behavioural variability across the sexes (McNamara et al 2000;Jennions and Kokko 2010;Liker et al 2013;Rosa et al 2017;Zheng et al 2021). Dispersing individuals are often, but not always, changing their status from subordinate to dominant breeder (Kutsukake and Clutton-Brock 2007;Nelson-Flower et al 2011;Groenewoud et al 2018;Jungwirth et al 2023), meaning availability of mates often dictates the opportunities of successful dispersal. Males are less likely to search for additional female mates and increase parental care when the ASR is male-biased compared to when it is female-biased (Fromhage and Jennions 2016;Eberhart-Phillips et al 2018).…”

Executive functions and brain morphology of male and female dominant and subordinate cichlid fish

“…The first explanation is based on N. pulcher ’s strategic growth pattern that depends on its status. Subordinates remain smaller than dominants to avoid aggression and eviction from the group (Hamilton et al., 2005 ; Jungwirth et al., 2023 ). This suggests they might also be strategic in their energy expenditure on expensive tissues such as the brain and would only start investing in the brain once they become dominants.…”