Spatial patterns of extra-pair paternity in a waterbird colony: separating the effects of nesting density and nest site location.

Piotr Minias,Katarzyna Wojczulanis-Jakubas,Robert Rutkowski,Krzysztof Kaczmarek,Tomasz Janiszewski

doi:10.1007/s00265-015-2056-0

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 cormorant Phalacarocorax carbo sinensis chicks 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.

Highlights

Extra-pair paternity (EPP) has been recorded in about 90 % of all bird species, demonstrating that a large majority of socially monogamous birds show varying degrees of promiscuity (Griffith et al 2002; Neudorf 2004)
We confirmed the occurrence of the centre-edge difference in extra-pair paternity (EPP) within a colony of great cormorants
Most of the broods with extra-pair offspring were recorded in the peripheral part of the colony, while incidence of EPP in the central zone was negligible

Summary

Introduction

Extra-pair paternity (EPP) has been recorded in about 90 % of all bird species, demonstrating that a large majority of socially monogamous birds show varying degrees of promiscuity (Griffith et al 2002; Neudorf 2004). The ‘good genes’ hypothesis assumes that females seek extra-pair copulations (EPCs) with males of higher genetic quality than their mates to gain indirect genetic benefits (viability genes or genes for attractiveness) for their offspring (Kempenaers et al 1992; Strohbach et al 1998). Under this scenario, poor-quality females, which usually mate assortatively with poor-quality males (Andersson et al 1998; García-Navas et al 2009), would be more likely to raise extra-pair offspring. As poorquality pairs are likely to occupy low-quality nest sites (Sergio et al 2009), we might expect more EPP in less attractive territories or nest sites, providing that high-quality males are available in the neighbourhood as potential extra-pair sires (Schlicht et al 2015)

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