In this paper we provide the first molecular genetic data on extra-pair paternity in a simultaneously polyandrous, sex-role-reversed avian species, the wattled jacana (Jacana jacana). Female jacanas often copulated with multiple mates, provided that the mates were not actively incubating eggs or tending young chicks. Both the presence of multiple 'available' mates, and the copulation behaviour of the female near the time of nest initiation, significantly predicted the probability of extra-pair fertilizations. A male's risk of being cuckolded was 0% in monandrous pairings, rose to 41% of broods (17% of chicks) in polyandrous associations where an additional mate was 'available', and increased to 74% of broods (29% of chicks) where the female was observed to copulate with multiple mates. Unlike findings from several sequentially polyandrous bird species, few if any fertilizations resulted from sperm stored from a previous nesting. We conclude that lost paternity can constitute a very real cost of polyandry for male wattled jacanas. The source of this cost is sexually active males simultaneously paired to the same female.
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