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Extra-group mating increases inbreeding risk in a cooperatively breeding bird.
X A Harrison1, J E York, D L Cram
1Institute of Zoology, Zoological Society of London, Regent's Park, London, NW1 4RY, UK; Centre for Ecology & Conservation, University of Exeter, Tremough Campus, Penryn, Cornwall, TR10 9EZ, UK.
Molecular Ecology
|October 15, 2013
Summary
In white-browed sparrow weavers, females engage in extra-group mating, but not to increase offspring heterozygosity. Instead, mating decisions appear influenced by male heterozygosity and competition, not relatedness.
Area of Science:
- Behavioral Ecology
- Evolutionary Biology
- Genetics
Background:
- Extra-group mating is common in cooperatively breeding species, yet its adaptive significance is unclear.
- A leading hypothesis suggests females seek genetically dissimilar extra-group mates to enhance offspring heterozygosity.
- The white-browed sparrow weaver (Plocepasser mahali) provides a model system to investigate these mating behaviors.
Purpose of the Study:
- To test the hypothesis that females engage in extra-group mating to increase offspring heterozygosity.
- To examine the factors influencing extra-group mating decisions in dominant female white-browed sparrow weavers.
- To assess the genetic relatedness and heterozygosity of social versus extra-group mates and their offspring.
Main Methods:
- Analysis of life history and genetic data from 36 white-browed sparrow weaver groups.
- Quantification of female relatedness to social and extra-group mates.
- Comparison of heterozygosity levels between dominant females, their social mates, and extra-group sires.
Main Results:
- Contrary to the heterozygosity hypothesis, females did not preferentially mate with more dissimilar extra-group partners.
- Females were more related to extra-group sires than their social mates.
- Extra-group mating was more likely when paired with less heterozygous social males; extra-group males were more heterozygous than social mates.
Conclusions:
- The genetic benefits of increased offspring heterozygosity do not appear to drive extra-group mating in this species.
- Male-male competition and the heterozygosity of social partners may influence extra-group mating decisions.
- Local kin structure in cooperative breeders may increase inbreeding risk, potentially negating benefits of extra-group mating.
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