Shared paternity revealed by genetic analysis in cooperatively breeding tropical wrens

POSTPONEMENT of dispersal and breeding to assist in rearing others' young may be favoured if helpers' contributions to the production of close kin exceed their likely reproductive success had they dispersed^1,2. Young adult stripe-backed wrens (Campylo-rhynchus nuchalis) remain in natal groups and greatly enhance reproductive success of close kin. Long-term behavioural observations suggest that only the dominant male and female in a group breed³; however, extra-pair parentage has been confirmed biochemically in apparently monogamous birds^4,5, including some social species^6,7. DNA fingerprinting of wren groups shows that behaviourally dominant males sometimes share paternity with auxiliary males previously thought to be nonproductive, whereas dominants are the only reproductives among females. Reproduction by auxiliary males (but not females) helps explain the long tenure of males in helper status and the contrasting combativeness of females in competition for breeding positions outside the natal group^8,9, but reproduction by auxiliaries cannot alone explain helping behaviour.