Data from: Higher relatedness mitigates mortality in a nematode with lethal male fighting

According to kin selection theory, individuals show less aggression
towards their relatives. Limited dispersal promotes interactions among
relatives but also increases competition among them. The evolution of
cooperation in viscous populations has been subject of mainly theoretical
exploration. We investigated the influence of relatedness on aggression in
males of entomopathogenic nematode Steinernema longicaudum that engage in
lethal fighting. In a series of in vitro experiments, we found that both
competitor male group size and relatedness influence male mortality rates.
Higher relatedness led to progressively lower rates of male mortality. In
experimentally infected insects, wherein large numbers of males and
females interact, the proportion of dead and paralysed (= terminally
injured) males was higher when infection was established by infective
juveniles originating from a mixture of three lines than in those infected
by a single line. The results collectively show that Steinernema
longicaudum males recognize their kin and consequently male mortality
rates are lower in groups consisting of more related males. Furthermore,
this monotonic negative relationship between aggression and relatedness
suggests that kin selection benefits are still substantial even under
extreme competition. Our experiments also suggest that kin recognition in
entomopathogenic nematodes has a genetic basis rather than being strictly
based on environmental cues. We discuss our findings within the
theoretical context of the evolution of altruistic/cooperative behaviour
in structured populations.