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Natural and sexual selection against hybrid flycatchers
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Animal Ecology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Animal Ecology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Animal Ecology.
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2008 (English)In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 275, no 1635, 735-744 p.Article in journal (Refereed) Published
Abstract [en]

While sexual selection is generally assumed to quickly cause or strengthen prezygotic barriers between sister species, its role in causing postzygotic isolation, through the unattractiveness of intermediate hybrids, is less often examined. Combining 24 years of pedigree data and recently developed species-specific molecular markers from collared (Ficedula albicollis) and pied (Ficedula hypoleuca) flycatchers and their hybrids, we were able to quantify all key components of fitness. To disentangle the relative role of natural and sexual selection acting on F1 hybrid flycatchers, we estimated various fitness components, which when combined represent the total lifetime reproductive success of F1 hybrids, and then compared the different fitness components of F1 hybrids to that of collared flycatchers. Female hybrid flycatchers are sterile, with natural selection being the selective force involved, but male hybrids mainly experienced a reduction in fitness through sexual selection (decreased pairing success and increased rate of being cuckolded). To disentangle the role of sexual selection against male hybrids from a possible effect of genetic incompatibility (on the rate of being cuckolded), we compared male hybrids with pure-bred males expressing intermediate plumage characters. Given that sexual selection against male hybrids is a result of their intermediate plumage, we expect these two groups of males to have a similar fitness reduction. Alternatively, hybrids have reduced fitness owing to genetic incompatibility, in which case their fitness should be lower than that of the intermediate pure-bred males. We conclude that sexual selection against male hybrids accounts for approximately 75% of the reduction in their fitness. We discuss how natural and sexual selection against hybrids may have different implications for speciation and conclude that reinforcement of reproductive barriers may be more likely when there is sexual selection against hybrids.

Place, publisher, year, edition, pages
2008. Vol. 275, no 1635, 735-744 p.
Keyword [en]
postzygotic isolation, hybrid fitness, speciation, reinforcement, extra-pair paternity, assortative mating
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:uu:diva-95232DOI: 10.1098/rspb.2007.0967ISI: 000252764900017PubMedID: 18211878OAI: oai:DiVA.org:uu-95232DiVA: diva2:169365
Available from: 2006-11-24 Created: 2006-11-24 Last updated: 2016-04-15Bibliographically approved
In thesis
1. Natural and Sexual Selection in a Natural Hybrid Zone of Ficedula Flycatchers
Open this publication in new window or tab >>Natural and Sexual Selection in a Natural Hybrid Zone of Ficedula Flycatchers
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Speciation can be viewed as the formation of reproductive barriers between different populations. This thesis investigates patterns of natural and sexual selection shaping reproductive barriers between two hybridizing flycatchers (i.e. collared – and pied flycatchers). Behaviorally driven sexual isolation depends on both the availability of conspecific mates and on discrimination ability of individuals. My results demonstrate that these two factors may also interact. Discrimination abilities may change in response to the relative frequency of two interbreeding species. The underlying reason appears to be that male pied flycatchers have a song that incorporates more elements of the song characteristics of male collared flycatchers into their own song repertoires when occurring in areas inhabited predominantly by collared flycatchers. I investigated selection pressures acting on hybrids. In migratory species, hybrid fitness might be reduced as a consequence of intermediate suboptimal migration routes (extrinsic post zygotic isolation). Comparison of stable isotope signatures of revealed that parental species have separate wintering grounds, but hybrids appear to winter at the same location as pied flycatchers. A possible dominance effect in the inheritance of migration direction may hence reduce this potential cost. This interpretation is supported by the absence of a reduction in juvenile to adult survival of hybrids. By further comparing male hybrid fitness to that of the parental species, using lifehistory data, I demonstrate that hybrid males experience a moderate reduction in fitness (mainly through a sexually selected disadvantage). Sexual selection acting on male hybrids can play a major role in the speciation process because when the same characters affect assortative mating as well as hybrid fitness, reinforcement of reproductive barriers becomes more likely. Even when reproductive isolation is completed- the fate of newly formed species may be uncertain since they may strongly compete for ecological space. Long-term persistence of ecologically similar, species requires that there are spatial or temporal variation in their relative fitness. The growth of nestling pied flycatchers is less affected by harsh environmental conditions. We suggest that a regional co-existence of the two flycatcher species is due to a lifehistory trade-off between interference competitive ability and robustness to a harsh conditions. Overall, the studies in this thesis reveal the complexity of the interactions between mate choice and competition in shaping sexual signals. Furthermore, it suggests that natural selection is moderate on hybrid males and that sexual selection may have strong implications for the maintenance of species integrity.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 32 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 248
Keyword
Biology, postzygotic isolation, prezygotic isolation, asymmetrical isolation, sexual signals, hybrid fitness, co-existence, Biologi
Identifiers
urn:nbn:se:uu:diva-7372 (URN)91-554-6744-X (ISBN)
Public defence
2006-12-16, Zootissalen, Zoologen, Villavägen 9, 75236, Uppsala, 13:00 (English)
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Available from: 2006-11-24 Created: 2006-11-24 Last updated: 2011-02-16Bibliographically approved

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Gustafsson, LarsQvarnström, Anna

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