Genetic evidence for mixed parentage in nests of the emu (Dromaius novaehollandiae)

Parentage in emus (Dromaius novaehollandiae) was examined by microsatellite analysis using four independent loci. Of 106 chicks sampled in one breedin g season from 18 nests, 54 (51%) were not fathered by the nesting male, 12 (11%) were not from the observed mate of the sitting male, and 9 (8%) repre sented intra-specific brood parasitism, having no alleles in common with ei ther nest parent. Some males (11%) fathered all chicks in their nests, but the majority showed high levels of cuckoldry. Those males commencing incuba tion earliest in the season tended to have the highest levels of paternity in their own nests. These results reveal a high frequency of extra-pair fer tilisations and resultant cuckoldry in a predominantly socially monogamous bird and support recent reports which have described the emu mating system as a complexity of polyandrous, promiscuous and monogamous behaviour. Paren tage assignment of chicks resulting from extra-pair fertilisations revealed an evenly scattered pattern of paternity that did not show any particular male dominance in reproductive success. These results lead to a reassessmen t of behavioural observations of emus, the consequences of parentage distri bution, and theories about mating systems and sexual selection. The frequen cy of extra-pair copulations and intra-specific brood parasitism suggests p atterns of descent that differ greatly from those implied by social monogam y.