Context-dependent genetic benefits of extra-pair mate choice in a socially monogamous passerine
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Extra-pair paternity is common in socially monogamous passerines; however, despite considerable research attention, consistent differences in fitness between within-pair offspring (WPO) and extra-pair offspring (EPO) have not been demonstrated. Recent evidence indicates that differences between maternal half-siblings may depend on environmental conditions, but it is unclear whether the influence of paternal genetic contribution should be most apparent under comparatively poor or favourable conditions. We compared phenotypic characteristics of WPO and EPO in 30 mixed-paternity broods of the tree swallow (Tachycineta bicolor) in relation to experimentally increased nest temperature (n = 13 heated nests; 17 control nests) and natural abundance of haematophagous parasites (Protocalliphora spp.). This allowed us to test the hypothesis that genetic benefits of extra-pair mating are environment dependent. EPO grew their ninth primary feathers faster than WPO regardless of nest temperature or parasite load and had significantly longer ninth primary feathers at fledging when parasite abundance was low, and when they were positioned early in the hatching sequence relative to WPO. In contrast, WPO under similar conditions did not differ from EPO in any phenotypic trait measured. These results indicate that the fitness benefits of extra-pair mating are likely to be context dependent, and that genetic effects on some phenotypic traits may be more apparent when conditions are relatively favourable.
KeywordsExtra-pair paternity Good genes Context dependence Fitness consequences Tachycineta bicolor
We thank Stephen Pruett-Jones and two anonymous reviewers for comments on a previous version of the manuscript. Anita Castle and Greg Sanders granted property access, and Dan Baxter, Pierre-Paul Bitton and Ben Schonewille provided assistance in the field. We are grateful to Brent Murray for providing access to lab space and equipment, as well as the UNBC molecular genetics lab and Mary Stapleton for advice and discussions concerning genetic analyses. Funding was provided by a Discovery Grant to Russell D. Dawson from the Natural Sciences and Engineering Research Council of Canada. Additional funding was provided by the Canada Foundation for Innovation and British Columbia Knowledge Development Fund. Our research protocols were approved by the Animal Care and Use Committee of UNBC.
- Crossman CC (1996) Single locus DNA profiling in the tree swallow Tachycineta bicolor: a comparison of methods. MSc thesis, Queen’s University, CanadaGoogle Scholar
- Gebhardt-Henrich SG, Richner H (1998) Causes of growth variation and its consequences for fitness. In: Starck JM, Ricklefs RE (eds) Avian growth and development. Oxford University Press, Oxford, pp 324–339Google Scholar
- Jamieson A (1994) The effectiveness of using codominant polymorphic allelic series for (1) checking pedigrees and (2) distinguishing full-sib pair members. Anim Genet 25:19–23Google Scholar
- McCarty JP (2002) The number of visits to the nest by parents is an accurate measure of food delivered to nestlings in tree swallows. J Field Ornithol 73:9–14Google Scholar
- Norušis MJ (2000) SPSS 11.0 Guide to data analysis. Prentice Hall, Upper Saddle RiverGoogle Scholar
- Robertson RJ, Stutchbury BJ, Cohen RR (1992) Tree swallow (Tachycineta bicolor). In: Poole A, Stettenheim P, Gill F (eds) The birds of North America, no. 11. The Academy of Natural Sciences, Philadelphia, PAGoogle Scholar
- Rogers CA, Robertson RJ, Stutchbury BJ (1991) Patterns and effects of parasitism by Protocalliphora sialia on tree swallow nestlings. In: Loye JE, Zuk M (eds) Bird-parasite interactions: ecology, evolution and behaviour. Oxford University Press, Oxford, pp 123–139Google Scholar