Spatial relatedness and brood parasitism in a female-philopatric bird population

Abstract

The spatial structure of relatedness between individuals in a population can be crucial for social selection and evolution. Here we analyze a female alternative reproductive tactic, conspecific brood parasitism, in relation to spatial relatedness among females in a Baltic Sea population of the common eider Somateria mollissima. The role of relatedness in brood parasitism is debated: some models predict parasite avoidance of related hosts, others predict host–parasite relatedness. We estimate pairwise relatedness from protein fingerprinting of egg albumen in 156 nests, with pairwise nest distances ranging from 1 to 6 km. Relatedness increases significantly from the longest distances to an average of r ’ 0.09 below 20 m. Brood parasitism is common, and average pairwise relatedness between host and parasite is estimated at 0.18–0.21. Parasites thus do not avoid relatives, and combined with the findings of a similar study in another eider population, the results show that mean host–parasite relatedness is higher than that among close neighbors. High host–parasite relatedness is therefore not an effect of natal philopatry alone; some other form of kin bias is also involved. Recognition and association between birth nest mates is a candidate mechanism for further study. Key words: joint nesting, kinship, local genetic structure, protein fingerprinting, spatial trend analysis. [Behav Ecol]