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Selection in sperm and its consequences: Exploring haploid selection, ageing and epigenetic effects in sperm
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Evolutionary Biology.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Sexually reproducing eukaryotes are typically going through a biphasic life cycle with a diploid and a haploid phase. Unlike in plants where selection on haploid pollen genotypes is well established, the possibility of selection occurring in animal sperm is currently not known. One of the main reasons for this lack of knowledge is the general assumption that due to the shortness and the apparent absence of gene expression in haploid sperm, selection during that phase is unlikely to occur. The aim of this thesis was to fill this gap and address some of the main fundamental questions. I investigated the interaction between sperm phenotype and offspring phenotype with a focus on the trans-generational effects of (i) selection on the haploid sperm genotype, (ii) sperm ageing and (iii) sperm-mediated epigenetic effects. For one, we performed several experimental studies to investigate how selection on the sperm phenotype affects offspring performance in two externally fertilizing fishes, Atlantic salmon and zebrafish. We found that in Atlantic salmon, sperm of intermediate post-activation longevity sire offspring that hatch earlier. In zebrafish, longer living sperm sire more viable offspring with a higher fitness than their short-lived sibling sperm. We explored the mechanisms of these trans-generational effects and found that neither intrinsic post-ejaculation sperm ageing (Atlantic salmon and zebrafish) nor pre-ejaculation sperm ageing (zebrafish) affect offspring performance. However, we identified genetic differences between sperm pools that were obtained by selecting different phenotypes within ejaculates of zebrafish males. These results suggest a genetic basis for intra-ejaculate sperm phenotype variation and show that there is potential for haploid selection in sperm. In a separate experiment, we explored the role of sexual selection in shaping sperm-mediated epigenetic effects, and found that short-time changes in male-male competition affect offspring hatching time and survival. In conclusion, this thesis provides evidence that sperm phenotype affects offspring phenotype, and that sperm phenotype is affected by both epigenetic changes influenced by the male environment and differences in the haploid genome of sperm.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. , 57 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1518
Keyword [en]
sperm, evolution, selection, haploid selection, epigenetics, sperm-mediated effects, trans-generational effects, sperm ageing, sperm senescence
National Category
Evolutionary Biology
Identifiers
URN: urn:nbn:se:uu:diva-320437ISBN: 978-91-554-9918-1 (print)OAI: oai:DiVA.org:uu-320437DiVA: diva2:1089534
Public defence
2017-06-09, Lindahlsalen, Evolutionary Biology Centre, EBC, Norbyvägen 14, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2017-05-18 Created: 2017-04-20 Last updated: 2017-05-18
List of papers
1. Sperm variation within a single ejaculate affects offspring development in Atlantic salmon
Open this publication in new window or tab >>Sperm variation within a single ejaculate affects offspring development in Atlantic salmon
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2014 (English)In: Biology Letters, ISSN 1744-9561, E-ISSN 1744-957X, Vol. 10, no 2, 20131040- p.Article in journal (Refereed) Published
Abstract [en]

It is generally believed that variation in sperm phenotype within a single ejaculate has no consequences for offspring performance, because sperm phenotypes are thought not to reflect sperm genotypes. We show that variation in individual sperm function within an ejaculate affects the performance of the resulting offspring in the Atlantic salmon Salmo salar. We experimentally manipulated the time between sperm activation and fertilization in order to select for sperm cohorts differing in longevity within single ejaculates of wild caught male salmon. We found that within-ejaculate variation in sperm longevity significantly affected offspring development and hence time until hatching. Whether these effects have a genetic or epigenetic basis needs to be further evaluated. However, our results provide experimental evidence for transgenerational effects of individual sperm function.

Keyword
gamete selection, epigenetics, haploid selection, sperm competition, fish
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-222203 (URN)10.1098/rsbl.2013.1040 (DOI)000332378300009 ()
Available from: 2014-04-09 Created: 2014-04-08 Last updated: 2017-04-20Bibliographically approved
2. Intrinsic Post-Ejaculation Sperm Ageing Does Not Affect Offspring Fitness in Atlantic salmon
Open this publication in new window or tab >>Intrinsic Post-Ejaculation Sperm Ageing Does Not Affect Offspring Fitness in Atlantic salmon
(English)Manuscript (preprint) (Other academic)
National Category
Evolutionary Biology
Identifiers
urn:nbn:se:uu:diva-320330 (URN)
Available from: 2017-04-19 Created: 2017-04-19 Last updated: 2017-04-20
3. Haploid selection within a single ejaculate increases offspring fitness
Open this publication in new window or tab >>Haploid selection within a single ejaculate increases offspring fitness
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(English)Manuscript (preprint) (Other academic)
National Category
Evolutionary Biology
Identifiers
urn:nbn:se:uu:diva-320335 (URN)
Available from: 2017-04-19 Created: 2017-04-19 Last updated: 2017-04-20
4. Short-term variation in sperm competition causes sperm-mediated epigenetic effects on early offspring performance in the zebrafish
Open this publication in new window or tab >>Short-term variation in sperm competition causes sperm-mediated epigenetic effects on early offspring performance in the zebrafish
2014 (English)In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 281, no 1785, 20140422- p.Article in journal (Refereed) Published
Abstract [en]

The inheritance of non-genetic factors is increasingly seen to play a major role in ecology and evolution. While the causes and consequences of epigenetic effects transmitted from the mother to the offspring have received ample attention, much less is known about how variation in the condition of the father affects the offspring. Here, we manipulated the intensity of sperm competition experienced by male zebrafish Danio rerio to investigate the potential for sperm-mediated epigenetic effects over a relatively short period of time. We found that the rapid responses of males to varying intensity of sperm competition not only affected sperm traits as shown previously, but also the performance of the resulting offspring. We observed that males exposed to high intensity of sperm competition produced faster swimming and more motile sperm, and sired offspring that hatched over a narrower time frame but exhibited a lower survival rate than males exposed to low intensity of sperm competition. Our results provide striking evidence for short-term paternal effects and the possible fitness consequences of such sperm-mediated non-genetic factors not only for the resulting offspring but also for the female.

Keyword
paternal effects, epigenetic inheritance, social environment, offspring survival, larval hatching, Danio rerio
National Category
Evolutionary Biology
Identifiers
urn:nbn:se:uu:diva-227694 (URN)10.1098/rspb.2014.0422 (DOI)000335812100023 ()
Available from: 2014-07-01 Created: 2014-06-30 Last updated: 2017-04-20Bibliographically approved

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