EXTRAPAIR PATERNITY AND SEXUAL SELECTION IN SOCIALLY MONOGAMOUS BIRDS: ARE TROPICAL BIRDS DIFFERENT?

Abstract

The Auk, Vol�� 125, Number 4, pages 769–777�� ISSN 0004-8038, electronic ISSN 1938-4254��  2008 by The American Ornithologists’ Union�� All rights reserved�� Please direct all requests for permission to photocopy or reproduce article content through the University of California Press’s Rights and Permissions website, http://www��ucpressjournals�� com/reprintInfo��asp�� �OI: 10��1525/au���2008��11008 Sexually elaborate traits, such as bright plumage and courtship signals, are generally thought to evolve through sexual selection (Andersson 1994), which requires variance in male mating success to operate (Arnold 1994)�� More than 90% of all birds are socially monogamous (Lac� 1968) and, therefore, are expected to exhibit low variance in mating success and wea� sexual selection; yet, paradoxically, many socially monogamous birds show the stamp of strong sexual selection in such traits as exaggerated plumage ornamentation and courtship displays�� Although �arwin (1871) suggested alternatives (Webster et al�� 2007), numerous recent genetic studies have suggested that extrapair paternity (EPP) may be the most li�ely resolution of this apparent paradox: if copulations outside of the pair bond are common, then variance in mating success may be far larger, and sexual selection much stronger, than suggested by social pairing success alone (Webster et al�� 1995)�� Indeed, <25% of birds studied to date are genetically monogamous (Griffith et al�� 2002), and studies have shown that EPP can generate strong sexual selection in socially monogamous systems (e��g��, Albrecht et al�� 2007, Webster et al�� 2007)�� However, despite two decades of wor�, we have only rudimentary understanding of the factors that lead to variation in EPP rates across populations (Griffith et al�� 2002, Westneat and Stewart 2003, Neudorf 2004)�� Conclusions regarding the role of EPP in sexual selection, however, must be ta�en with a large and important caveat, the so-called “temperate zone bias” (Stutchbury and Morton 2001): most studies have focused on temperate-zone birds, only a handful loo�ing at tropical species�� Given that most birds, by far, live and breed in the tropics, this omission is critical (see Martin 1996, 2004)�� Without a better understanding of the prevalence of factors contributing to EPP in tropical species, our ability to generalize about EPP and its role in sexual selection among socially monogamous species will remain limited�� �espite the widely recognized lac� of empirical data, tropical species are generally considered to have lower rates of EPP than temperate species�� For example, Stutchbury and Morton “Studies of temperate species