Spatial separation from family in the mobile young of a biparental fish: risks and dynamics of returning home

In species with extended parental care, mobile dependent young are potentially more vulnerable to predators when they stray and become separated from their parents. We would expect that the likelihood of, and latency time for, a separated young to safely return to its ‘family unit’ (i.e. parents and brood mates) to be, respectively, inversely and positively related to the initial distance of separation and potentially mediated by its age or body size. Using the biparental convict cichlid fish (Amatitlania siquia), we tested these predictions by capturing individual young and displacing them at varying distances from their family unit in both the field and laboratory. As expected, displaced fish were less likely, and took longer, to return to their family with increasing separation distance from the family unit. The body length of displaced young mediated these relationships and their antipredator behaviour; larger young refuged more than smaller ones and were also less likely to be eaten by predators. These results suggest that selection should favour strong affiliative behaviour in mobile young animals towards their brood mates and protective parents because straying from the family unit leads to increased exposure to predation and a reduced likelihood of returning home with increasing separation distance.