Host-parasite relatedness in wood ducks: patterns of kinship and parasite success

We investigated the role of kinship in intraspecific nest parasitism of wood ducks (Aix sponsa). Among waterfowl, female philopatry creates the potential for female relatives to nest in proximity. Costs of intraspecific nest parasitism to host females may be reduced if parasites lay eggs with kin. However, previous observations of marked wood ducks indicated that females avoided parasitizing clutch mates or the female that incubated them. To further examine the role of kinship, we determined the genotypes of 27 host-parasite pairs at five microsatellite loci. Average relatedness between hosts and all females laying parasitic eggs was only 0.04 +/- 0.03. Parasites appeared to choose hosts randomly with respect to kinship from among females with nests in the neighborhood and those within the entire study area. However, host relatedness to the parasite with the greatest number of young leaving the nest was 0.11 +/- 0.03, which was greater than expected if eggs were accepted randomly from neighboring females or from females present on the entire study area (p = .03 and p = .02, respectively). These patterns may reflect parasitism of randomly selected nests followed by differential acceptance by hosts, differential hatching success of related parasites (e.g., due to greater laying synchrony), or a mixture of parasitic strategies, one with a focus on related hosts and the other on unrelated hosts. Genetic data revealed that social relationships did not always reflect true relatedness and that success of primary parasites was associated with kinship to hosts.