Heterozygosity and fitness benefits of extrapair mate choice in White-rumped Swallows (Tachycineta leucorrhoa)

David W Winkler,Irby J Lovette,Viviana Massoni,Valentina Ferretti,Florencia Bulit

doi:10.1093/beheco/arr103

David W Winkler, Irby J Lovette + Show 3 more

Open Access

https://doi.org/10.1093/beheco/arr103

Copy DOI

Abstract

Female birds that engage in extrapair mating may choose extrapair mates that are genetically compatible, increasing their fitness through genetic benefits, such as increased heterozygosity, to their offspring; or choose mates that are heterozygous at one or more loci. Here, we describe the extrapair mating system, explore the fitness benefits of extrapair mating and test the heterozygosity hypothesis in White-rumped Swallows (Tachycineta leucorrhoa) breeding in Argentina using a panel of microsatellite loci. Extrapair offspring accounted for 56% of the nestlings and 77% of the broods in our population. Within broods, 1–4 males fathered extrapair offspring, and in 29% of nests, all offspring were from extrapair sires. We found that broods with extrapair offspring fledged overall more young than broods with no extrapair offspring but that the young that died were more heterozygous than the ones that fledged. Although extrapair offspring had a higher probability of surviving than within-pair offspring, these 2 groups did not differ in their level of heterozygosity. Neither the heterozygosity of the social mate nor the genetic similarity of the social pair predicted the presence of extrapair young. Instead, females chose social mates that were significantly less genetically similar to them. Our results do not support the heterozygosity hypothesis and contradict 2 of its main predictions.

Highlights

Since the first application of molecular techniques to studies of parentage in birds in the late 1980’s (Burke and Bruford 1987) much progress has been made in our understanding of avian mating systems and their variation
White-rumped Swallows engage in extrapair matings that result in a high proportion of EPY, at least half of which are sired by males within the colony
We did not find fitness benefits associated with extrapair behavior, the relationship between reduced heterozygosity and increased fitness of offspring, as well as the reduced genetic similarity between the social pair, are topics that will benefit from further study and might provide a better insight to the study of mating systems and sexual selection

Summary

Introduction

Since the first application of molecular techniques to studies of parentage in birds in the late 1980’s (Burke and Bruford 1987) much progress has been made in our understanding of avian mating systems and their variation. Matings outside the pair bond may clearly be advantageous for males by directly increasing the number of offspring sired in a given season (reviewed in Birkhead and Møller 1992). Fitness benefits of extrapair mating for females, have been more difficult to identify due to the indirect nature of most such benefits (Jennions and Petrie 2000; Arnqvist and Kirkpatrick 2005; Akxcay and Roughgarden 2007). It has been proposed that females that choose their mates can obtain 2 types of benefits: 1) direct benefits in the form of nesting sites, access to resources, parental care, etc.; or 2) indirect benefits through an increase in their offspring’s genetic quality (see review in Andersson 1994).

Methods

Results

Discussion

Conclusion