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Low fertility of wild hybrid male flycatchers despite recent divergence
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology. (Qvarnström)ORCID iD: 0000-0003-2861-9721
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Evolutionary Biology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.ORCID iD: 0000-0002-1178-4053
2013 (English)In: Biology Letters, ISSN 1744-9561, E-ISSN 1744-957X, Vol. 9, no 3, 20130169Article in journal (Refereed) Published
Abstract [en]

Postzygotic isolation may be important for maintaining species boundaries, particularly when premating barriers are incomplete. Little is known about the course of events leading from minor environmental mismatches affecting hybrid fitness to severe genetic incompatibilities causing sterility or inviability. We investigated whether reduced reproductive success of hybrid males was caused by suboptimal sperm traits or by more severe genetic incompatibilities in a hybrid zone of pied (Ficedula hypoleuca) and collared flycatchers (F. albicollis) on the island of Oland, Sweden. About 4 per cent hybridization is observed in this population and all female hybrids are sterile. We found no sperm in the ejaculates of most sampled hybrid males, and sperm with abnormal morphology in two hybrids. Furthermore, none of the hybrids sired any offspring because of high levels of hatching failure and extra-pair paternity in their nests. These results from a natural hybrid zone suggest that the spermatogenesis of hybrid males may become disrupted despite little genetic divergence between the parental species.

Place, publisher, year, edition, pages
2013. Vol. 9, no 3, 20130169
Keyword [en]
hybrid, sterility-infertility, flycatcher, sperm, postzygotic incompatibility
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:uu:diva-202341DOI: 10.1098/rsbl.2013.0169ISI: 000318762300035OAI: oai:DiVA.org:uu-202341DiVA: diva2:632034
Available from: 2013-06-24 Created: 2013-06-24 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Sex, Sperm and Speciation: On sexual selection and fertility in hybridizing flycatchers
Open this publication in new window or tab >>Sex, Sperm and Speciation: On sexual selection and fertility in hybridizing flycatchers
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Sexual reproduction entails complex co-evolution between the sexes, necessary for successful fertilization, ensuring individual and population-level fitness. Interfertility is the main criterion for species definition and understanding speciation requires detailed studies of reproductive barriers. However, many studies on reproductive barriers are constrained to infer evolutionary processes from patterns. In this thesis, I focus on a hybrid zone between collared and pied flycatchers (Ficedula albicollis and hypoleuca) on the island of Öland, and a trait that is essential for fertilization: sperm. Long-term monitoring of these species, combined with recent advances in molecular tools, allow me to study how complex on-going intersexual and interspecific interactions influence reproductive isolation in this young hybrid zone. I start by exploring the links between pre- and postmating sexual selection within collared flycatchers (paper I and II). I show that secondary sexual characters and indirect mate-choice benefits are tightly linked to physiology (paper I), and that a male’s attractiveness and dominance status dictate which sperm traits are optimal, as a male’s fertilization success depends on an interaction between sperm and display traits (paper II). I then report a source of strong postzygotic isolation between recently diverged collared and pied flycatchers: impaired spermatogenesis resulting in absence of mature sperm cells in hybrid males (paper III). I show however that pied flycatcher females, who are most exposed to hybridization, can mitigate these costs through mechanisms of cryptic female choice impairing heterospecific sperm performance, allowing them to bias paternity towards pure-species offspring (paper IV). Finally, by exploring the testes transcriptomes and sperm proteomes of both species, I highlight the importance of gene and protein regulation mechanisms in facilitating phenotypic divergence between these species (paper V). Thus, my thesis reveals complex interactions between primary and secondary sexual characters in a wild bird and suggests that mechanisms of sexual selection are tightly linked to essential physiological functions. I also show that genetic incompatibilities can evolve rapidly despite low genome-wide levels of divergence but that divergence in regulatory regions and proteins potentially allows fast evolution of molecular mechanisms impairing or preventing costly heterospecific fertilization. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 67 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1533
Keyword
sperm biology, sexual selection, speciation, hybridization, cryptic female choice, fertility, Ficedula flycatchers
National Category
Evolutionary Biology
Research subject
Biology with specialization in Animal Ecology
Identifiers
urn:nbn:se:uu:diva-326807 (URN)978-91-513-0014-6 (ISBN)
Public defence
2017-09-15, Zootissalen, Villavägen 9, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2017-08-23 Created: 2017-07-30 Last updated: 2017-09-08

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Ålund, MurielleImmler, SimoneQvarnström, Anna

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