Aggression and spatial positioning of kin and non-kin fish in social groups

Group-living animals are faced with the challenge of sharing space and
local resources amongst group members who may be either relatives or
non-relatives. Individuals may reduce the inclusive fitness costs they
incur from competing with relatives by either reducing their levels of
aggression towards kin or by maintaining physical separation between kin.
In this field study, we used the group-living cichlid Neolamprologus
multifasciatus to examine whether within-group aggression is reduced among
group members that are kin and whether kin occupy different regions of
their group’s territory to reduce kin competition over space and local
resources. We determined the kinship relationships among cohabiting adults
via microsatellite genotyping and then combined these with spatial and
behavioural analyses of groups in the wild. We found that aggressive
contests between group members declined in frequency with spatial
separation between their shelters. Female kin did not engage in aggressive
contests with one another, whereas non-kin females did, despite the fact
these females lived at similar distances from one another on their groups’
territories. Contests within male-male and male-female dyads did not
clearly correlate with kinship. Non-kin male-male and male-female dyads
lived at more variable distances from one another on their territories
than their corresponding kin dyads. Together, our study indicates that
contests among group members can be mediated by relatedness in a
sex-dependent manner. We also suggest that spatial relationships can play
an important role in determining the extent to which group members compete
with one another.