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Within-ejaculate selection for sperm longevity reduces male reproductive ageing
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics. (Simone Immler)
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics. (Simone Immler)
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics. (Simone Immler)
University of East Anglia.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Males produce numerous sperm in the single ejaculate that greatly outnumber their potential egg targets. Recent studies found that phenotypic variation among sperm in the single ejaculate of a male reflects the phenotype and the genotype of the resulting offspring. Specifically, within-ejaculate sperm selection (WESS) for sperm longevity increased the performance of the resulting offspring in several key life-history traits in early-life. Because increased early-life reproductive performance often correlates with rapid ageing, it is possible that WESS increases early-life fitness at the cost of accelerated senescence. Alternatively, WESS can improve offspring quality throughout the life cycle, including reduced age-specific deterioration. We found that WESS for sperm longevity reduced age-specific deterioration of male fertility and embryo survival, while there is no effect on fertilization success. Remarkably, we found opposing effect of WESS on female fecundity, where selection for sperm longevity resulted in increased early-life performance followed by a slow decline, while unselected controls started low but increased their fecundity with age. Intriguingly, WESS also reduced the age-specific decline in fertilization success in females, suggesting that selection for sperm longevity improves at least some aspects of female reproductive ageing. These results demonstrate that within-ejaculate variation in sperm phenotype contributes to individual variation in animal life histories in the two sexes and have important implications for assisted fertilization programs in livestock and humans. 

Keywords [en]
Ageing, Reproductive Success, Sperm Selection, Sperm Competition, Senescence
National Category
Evolutionary Biology
Research subject
Biology with specialization in Evolutionary Genetics
Identifiers
URN: urn:nbn:se:uu:diva-350186OAI: oai:DiVA.org:uu-350186DiVA, id: diva2:1204331
Available from: 2018-05-07 Created: 2018-05-07 Last updated: 2018-05-07
In thesis
1. Haploid selection in animals: Exploring the fitness consequences and underlying mechanisms
Open this publication in new window or tab >>Haploid selection in animals: Exploring the fitness consequences and underlying mechanisms
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A consequence of sexual reproduction in eukaryotes is the evolution of a biphasic life cycle with alternating diploid and haploid gametic phases. While our focus in evolutionary biology is on selection during the diploid phase, we know relatively little about selection occurring during the haploid gametic stage. This is particularly true in predominantly diploid animals, where gene expression and hence selection have long been thought to be absent in haploid cells like gametes and particularly sperm. During my PhD, I tested the idea of selection during the haploid gametic phase using zebrafish Danio rario as a study species. I combined a large-scale selection experiment over three generations with fitness assays and next-generation sequencing to assess the importance of haploid selection. We measured offspring fitness in all three generations.  In addition, we compared gene expression in brain and testes of F1 and F3 adult male from each treatment by RNA sequencing. We found that offspring sired by longer-lived sperm showed higher survival rate and higher early- and late-life reproductive fitness compared to offspring sired by shorter-lived sperm. We also found differentially expressed genes between the two treatments with functions in metabolic and developmental pathways. These findings suggest that the observed fitness differences to be caused by small expression changes in many basic genes. We also tested for a genetic underpinning of the selected sperm phenotypes and identified allelic differences across the entire genome. Finally, we investigated the additive genetic component and parental effect of different sperm phenotypes. We found generally low additive genetic variation and high parental effects on sperm performance traits. In conclusion, this thesis provides evidence that the phenotypic variation among intact fertile sperm within an ejaculate affects offspring fitness throughout life and provides a clear link between sperm phenotype and offspring fitness and between sperm phenotype and sperm genotype.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 41
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1681
Keywords
sperm, evolution, haploid selection, reproductive aging, fitness
National Category
Evolutionary Biology
Identifiers
urn:nbn:se:uu:diva-350192 (URN)978-91-513-0358-1 (ISBN)
Public defence
2018-09-14, Lindahlsalen, Norbyvagen 18d, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2018-08-24 Created: 2018-05-07 Last updated: 2018-09-06

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