title: Spatial patterns of extra-pair paternity in a waterbird colony: separating the effects of nesting density and nest site location.
abstract: Centres of avian colonies are usually associated with reduced predation risk and, thus, attract individuals of high quality, while poor-quality individuals are relegated to peripheral zones. Assuming that the incidence of extra-pair paternity (EPP) is dependent on individual quality, we could expect lower incidence of extra-pair offspring in the central parts of colonies. On the other hand, central pairs often nest in higher densities, which might increase EPP rate. To test these hypotheses, we sampled 124 great cormorantPhalacarocorax carbo sinensischicks from 30 broods from different zones of a colony and genotyped them at seven highly polymorphic microsatellite loci. Sibship reconstruction confirmed the presence of at least one extra-pair chick in 30.0 % of broods. We found that EPP varied significantly between the zones of the colony, with higher incidence of extra-pair broods in the peripheral zone (53.3 vs. 6.7 % of broods). Centre-edge difference in EPP was consistent with the expected distribution of pair quality and suggested that poor-quality peripheral females were more likely to solicit extra-pair interactions, possibly to gain 'good genes' for their offspring. By contrast, we found no evidence for density dependence in EPP rate, indicating that likelihood of raising extra-pair offspring was not constrained by limited availability of local males. The results indicate that spatial randomization of sampling within avian colonies is critical to obtain robust estimations of EPP for non-solitary species. To our knowledge, this study provides the first evidence for the centre-edge difference in EPP within a breeding colony of birds.
authors.affiliation: Department of Teacher Training and Biodiversity Studies, University of Łódź, Banacha 1/3, 90-237 Łódź, Poland.
authors.forename: Piotr
authors.initials: P
authors.lastname: Minias
authors.affiliation: Department of Vertebrate Ecology and Zoology, University of Gdańsk, Wita Stwosza 59, 80-308 Gdańsk, Poland.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Wojczulanis-Jakubas
authors.affiliation: Department of Molecular and Biometrical Techniques, Museum and Institute of Zoology PAS, 00-679 Warsaw, Poland.
authors.forename: Robert
authors.initials: R
authors.lastname: Rutkowski
authors.affiliation: Medical University of Łódź, Sterlinga 1/3, 91-425 Łódź, Poland.
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Kaczmarek
authors.affiliation: Department of Teacher Training and Biodiversity Studies, University of Łódź, Banacha 1/3, 90-237 Łódź, Poland.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Janiszewski
keywords: Coloniality; Great cormorant; Microsatellites; Phalacrocorax carbo sinensis; Sibship reconstruction