Extra-pair paternity in waved albatrosses: genetic relationships among females, social mates and genetic sires

Interactions among close relatives are expected to be common in colonially breeding species, species with limited geographic distributions such as island endemics, or those with limited natal or breeding dispersal. The waved albatross, Phoebastria irrorata, a colonially nesting, endemic seabird in Galapagos, Ecuador, presents an opportunity to closely examine relationships between genetic similarity of parents and extra-pair paternity. This species' mating system is characterized by high year-to-year social mate and nest site fidelity as well as an unexpectedly high level of extra-pair paternity. The probability of hatching was lower for social pairs with high genetic similarity, suggesting an apparent cost of inbreeding. Despite this apparent cost, analyses of multilocus minisatellite band-sharing coefficients revealed that genetic similarity was somewhat negatively associated with EPF probability, inconsistent with the pattern predicted by the Genetic Similarity Hypothesis (GSH) that social pairs with extra-pair offspring would be more similar than those with within-pair offspring. We found that a model with no effect of the type of dyad the female was in (female social mate compared to female genetic sire) on genetic similarity was as heavily weighted as one incorporating an effect, also inconsistent with the GSH. Evidence from our analyses suggested that cuckolded males were more genetically similar to randomly drawn males than to the genetic sire of their extra-pair offspring, a finding in contrast to the main prediction of our novel EPF tolerance hypothesis that males might tolerate extra-pair offspring if the actual sire is closely related. We discuss these findings in light of information about dispersal and we present some alternative explanations for extra-pair paternity in the waved albatross.