TESTING REPRODUCTIVE SKEW MODELS IN A COMMUNALLY BREEDING BIRD, THE PUKEKO, PORPHYRIO-PORPHYRIO

Recent attempts to explain variation among social species in the degre e to which reproduction is shared among group members have focused on what are known as reproductive skew models. Reproduction within social groups can vary from an even distribution among all adults (i.e. low skew) to complete monopolization by a dominant individual (high skew). Three critical predictions derived from these models have remained la rgely untested: (1) reduced chances of independent breeding due to str ong ecological constraints results in high reproductive skew; (2) the lower the genetic relatedness within social groups the lower the skew; and, counter-intuitively, (3) dominance-related aggression will be mo re prevalent in social groups composed of close kin where reproductive skew is predicted to be high. Here I test these predictions by compar ing two populations of the communally breeding pukeko (Porphyrio porph yrio), which show extremes in social organization, namely social group s consisting of close kin versus groups made up of unrelated breeders. I report evidence from both cobreeding males and females in support o f the above predictions. The results also indicate that low reproducti ve skew among unrelated group members may be prevalent in social speci es that possess weapons that can inflict serious injury in situations where reproductive competition may escalate to fighting. The consisten cy between these results and those from studies of social insects sugg ests that reproductive skew models may represent a unifying framework for understanding the factors shaping complex animal societies.