Testing Hamilton's rule with competition between relatives

Hamilton's(1,2) theory of kin selection suggests that individuals should sh ow less aggression, and more altruism, towards closer kin. Recent theoretic al work has, however, suggested that competition between relatives can coun teract kin selection for altruism(3-11). Unfortunately, factors that tend t o increase the average relatedness of interacting individuals-such as limit ed dispersal-also tend to increase the amount of competition between relati ves. Therefore, in most natural systems, the conflicting influences of incr eased competition and increased relatedness are confounded, limiting attemp ts to test theory(4,8-10). Fig wasp taxa exhibit varying levels of aggressi on among non-dispersing males that show a range of average relatedness leve ls. Thus, across species, the effects of relatedness and competition betwee n relatives can be separated. Here we report that-contrary to Hamilton's or iginal prediction(1,2,12) but in agreement with recent theory(5-11) - the l evel of fighting between males shows no correlation with the estimated rela tedness of interacting males, but is negatively correlated with future mati ng opportunities.