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Revisiting the definition of “sperm quality”: selection on sperm length depends on a male’s attractiveness and dominance in wild collared flycatchers
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics. (Qvarnström)ORCID iD: 0000-0003-2861-9721
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.ORCID iD: 0000-0002-0706-458X
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.ORCID iD: 0000-0002-1178-4053
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Dominance over rivals, sexual attractiveness and highly efficient ejaculates are all known to be essential for male fertilization success but the theories of how primary and secondary sexual characters may co-evolve largely remain to be tested. Here, we measure sperm morphology in 131 wild-caught collared flycatchers over a four-year period and investigate the links between male display traits, sperm characteristics and siring success among 425 offspring sired by 71 of these males. We show that the optimal sperm length to attain high relative fertilization success depends on the size of a male’s secondary sexual character. Males with small ornaments sire more offspring in their own nest when they produce long sperm and vice-versa. These results are not compatible with theories based on simple relationships between secondary sexual traits and sperm “quality” but imply that the optimal fertilization strategy (and hence optimal sperm traits) differ between males even in a predominantly socially monogamous population with moderate extra-pair copulation rates. Thus, a better knowledge of the complex chain of behavioural interactions between the sexes and their gametes is needed for a complete understanding of how sexual selection operates in nature.

Keywords [en]
sperm morphology, secondary sexual character, mating strategy, fertilization success, Ficedula flycatcher, extra-pair copulation
National Category
Evolutionary Biology
Identifiers
URN: urn:nbn:se:uu:diva-326808OAI: oai:DiVA.org:uu-326808DiVA, id: diva2:1128854
Available from: 2017-07-30 Created: 2017-07-30 Last updated: 2017-07-30
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. p. 67
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1533
Keywords
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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