| 1. |
- Alavioon, Ghazal, 1986-
(author)
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Haploid selection in animals : Exploring the fitness consequences and underlying mechanisms
- 2018
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Doctoral thesis (other academic/artistic)abstract
- 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.
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| 2. |
- Alavioon, Ghazal, et al.
(author)
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Haploid selection within a single ejaculate increases offspring fitness
- 2017
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In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; :30, s. 8053-8058
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Journal article (peer-reviewed)abstract
- An inescapable consequence of sex in eukaryotes is the evolution of a biphasic life cycle with alternating diploid and haploid phases. The occurrence of selection during the haploid phase can have far-reaching consequences for fundamental evolutionary processes including the rate of adaptation, the extent of inbreeding depression, and the load of deleterious mutations, as well as for applied research into fertilization technology. Although haploid selection is well established in plants, current dogma assumes that in animals, intact fertile sperm within a single ejaculate are equivalent at siring viable offspring. Using the zebrafish Danio rerio, we show that selection on phenotypic variation among intact fertile sperm within an ejaculate affects offspring fitness. Longer-lived sperm sired embryos with increased survival and a reduced number of apoptotic cells, and adult male offspring exhibited higher fitness. The effect on embryo viability was carried over into the second generation without further selection and was equally strong in both sexes. Sperm pools selected by motile phenotypes differed genetically at numerous sites throughout the genome. Our findings clearly link within-ejaculate variation in sperm phenotype to offspring fitness and sperm genotype in a vertebrate and have major implications for adaptive evolution.
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| 3. |
- Alavioon, Ghazal, et al.
(author)
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Selection for longer lived sperm within ejaculate reduces reproductive ageing in offspring
- 2019
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In: Evolution Letters. - : Oxford University Press (OUP). - 2056-3744. ; 3:2, s. 198-206
-
Journal article (peer-reviewed)abstract
- Males produce numerous sperm in a single ejaculate that greatly outnumber their potential egg targets. Recent studies found that phenotypic and genotypic variation among sperm in a single ejaculate of a male affects the fitness and performance of the resulting offspring. Specifically, within-ejaculate sperm selection 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 within-ejaculate sperm selection increases early-life fitness at the cost of accelerated senescence. Alternatively, within-ejaculate sperm selection could improve offspring quality throughout the life cycle, including reduced age-specific deterioration. We tested the two alternative hypotheses in an experimental setup using zebrafish Danio rerio. We found that within-ejaculate sperm selection for sperm longevity reduced age-specific deterioration of fecundity and offspring survival but had no effect on fertilization success in males. Remarkably, we found an opposing effect of within-ejaculate sperm selection on female fecundity, where selection for sperm longevity resulted in increased early-life performance followed by a slow decline, while females sired by unselected sperm started low but increased their fecundity with age. Intriguingly, within-ejaculate sperm selection 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 may have important implications for assisted fertilization programs in livestock and humans.
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| 4. |
- Alavioon, Ghazal, 1986-, et al.
(author)
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Sperm performance traits exhibit low additive genetic component and strong parental effects in external fertilizer
-
Other publication (other academic/artistic)abstract
- Despite their key role in determining reproductive success and with that Darwinian fitness, the heritability and underlying additive genetic variance of reproductive traits is still not fully understood. While some traits show relatively high genetic variance, others show very low genetic variance, which is particularly true for complex non-morphological traits. In line with these general patterns, morphological sperm traits show surprisingly high heritability, whereas heritability reported for sperm quality and performance traits generally is lower. A possible explanation for this is the general notion that more fitness related traits show lower levels of additive genetic variance and heritability. We investigated the additive genetic variance and heritability of sperm swimming velocity, the percentage of motile sperm, sperm concentration in the ejaculate and sperm longevity in the externally fertilizing zebrafish Danio rerio. All sperm traits showed low but significant additive genetic variance and high parental components. While the additive genetic variance was significant it was lower than reported in many other studies. A possible explanation for this is that in externally fertilizing species, sperm traits are the prime determinant of fertilization success and high plasticity is crucial for swift adaptations to changes in the environmental conditions such as competition but also water temperature and currents. Given that this is the first study looking into the heritability of sperm traits in an external fertilizer it will be interesting to understand, whether this is true for other externally fertilizing species and taxa.
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| 5. |
- Alavioon, Ghazal, 1986-, et al.
(author)
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The fitness consequences of selection among sperm within an ejaculate across generations
-
Other publication (other academic/artistic)abstract
- The evolution of a biphasic life cycle with alternating diploid and haploid phases is a necessary consequence of sexual reproduction in eukaryotes. Selection in each of the phases may have far reaching consequences for many evolutionary processes. While our focus in evolutionary biology lies mainly on selection during the diploid phase, we know relatively little about the role and consequences of selection occurring during the haploid gametic stage. This is particularly true in predominantly diploid animals where the haploid gametic phase is very short. To test the importance of haploid selection in animals, we performed a large-scale selection experiment with selection acting on haploid sperm. We selected on sperm longevity within an ejaculate and tested the effects of such selection over three generation. We performed fitness assays for every generation and found that offspring sired by longer-lived sperm generally exhibit higher fitness from early development into adulthood compared to offspring sired by their shorter-lived sibling sperm in all three generations. These fitness effects were carried over into the second generation without further selection in all three generations. Moreover, using RNA sequencing, we assessed differences in tissue specific gene expression between the offspring sired by the two sperm phenotypes in generation F1 and F3. The transcriptomes in both tissues differed significantly between the two treatments. Many very basic housekeeping genes involved in metabolism and development showed small differences in expression in both tissues. Our study provides solid evidence for the far-reaching consequences of selection on different sperm within a single ejaculate in three consecutive generations, and offers exciting new insights into the possible underlying mechanisms. Our results further highlight the importance of selection at the haploid gametic stages for fundamental evolutionary processes and assisted fertilization technologies.
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| 6. |
- Alavioon, Ghazal, 1986-, et al.
(author)
-
Within-ejaculate selection for sperm longevity reduces male reproductive ageing
-
Other publication (other academic/artistic)abstract
- 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.
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| 7. |
- Baur, Julian
(author)
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Condition dependent germline maintenance in seed beetles
- 2022
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Doctoral thesis (other academic/artistic)abstract
- The aim of the work presented in this thesis is to investigate how costly adaptations promoted by sexual selection affect fertility and offspring quality through changes in germline maintenance. Germline maintenance, comprising mechanisms maintaining DNA-integrity and homeostasis within germ cells, is known to be costly and, therefore, may trade-off with other costly reproductive traits that are under sexual selection. However, sexual selection may also act on condition dependent traits that reflect the overall genetic quality of its bearer, in which case sexual selection for high quality mates may lead to improved germline maintenance. Using experimental evolution lines of the seed beetle Callosobruchus maculatus, evolving under three different mating regimes that manipulated the opportunity for sexual and natural selection, I show evidence indicating that sexual selection can lead to improved germline maintenance through selection on condition dependent traits. However, I also found evidence for the alternative hypothesis, suggesting that when sexual selection is much stronger than natural selection it may lead to excessive investment into mating traits that trade-off with and reduce germline maintenance. We present an RNA expression analysis suggesting 18 candidate genes responding to DNA-damage and sociosexual interactions that may be involved in trade-offs between sexual selection and germline maintenance. I also found that the fertility of males and females that evolved under intense sexual selection was more sensitive to heat stress, and male sensitivity of fertility to heat stress was genetically correlated to sperm competitive ability. This suggests a trade-off between male postcopulatory reproductive success and the thermal sensitivity of fertility. The increased sensitivity to heat was also reflected in the fertility of females, suggesting that female heat tolerance may have evolved via genetic correlations with sexually selected male reproductive traits. The work presented in this thesis shows that sexual selection indeed affects germline maintenance. Sexual selection can increase germline maintenance through selection on condition dependent traits. But at the same time, traits under sexual selection can trade off with aspects of germline maintenance. If traits evolved under sexual selection and only weak constraints by natural selection, evolved allocation shifts in response to sexual selection can lead to deleterious repercussions when stressful environmental conditions increase demands on germline maintenance. The results presented in this thesis highlight important aspects of how sexual selection affects condition dependent germline maintenance with significant implications for the maintenance of genetic variation, adaptive processes, and mate choice processes in species under sexual selection.
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| 8. |
- Bergero, Roberta, et al.
(author)
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Meiosis and beyond - understanding the mechanistic and evolutionary processes shaping the germline genome
- 2021
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In: Biological Reviews. - : John Wiley & Sons. - 1464-7931 .- 1469-185X. ; 96:3, s. 822-841
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Research review (peer-reviewed)abstract
- The separation of germ cell populations from the soma is part of the evolutionary transition to multicellularity. Only genetic information present in the germ cells will be inherited by future generations, and any molecular processes affecting the germline genome are therefore likely to be passed on. Despite its prevalence across taxonomic kingdoms, we are only starting to understand details of the underlying micro-evolutionary processes occurring at the germline genome level. These include segregation, recombination, mutation and selection and can occur at any stage during germline differentiation and mitotic germline proliferation to meiosis and post-meiotic gamete maturation. Selection acting on germ cells at any stage from the diploid germ cell to the haploid gametes may cause significant deviations from Mendelian inheritance and may be more widespread than previously assumed. The mechanisms that affect and potentially alter the genomic sequence and allele frequencies in the germline are pivotal to our understanding of heritability. With the rise of new sequencing technologies, we are now able to address some of these unanswered questions. In this review, we comment on the most recent developments in this field and identify current gaps in our knowledge.
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| 9. |
- Chen, Hwei-yen, 1983-, et al.
(author)
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Germline mutation rate is elevated in young and old parents in Caenorhabditis remanei
- 2023
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In: Evolution Letters. - : Oxford University Press. - 2056-3744. ; 7:6, s. 478-489
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Journal article (peer-reviewed)abstract
- The effect of parental age on germline mutation rate across generations is not fully understood. While some studies report a positive linear relationship of mutation rate with increasing age, others suggest that mutation rate varies with age but not in a linear fashion. We investigated the effect of parental age on germline mutations by generating replicated mutation accumulation lines in Caenorhabditis remanei at three parental ages ("Young T1" [Day 1], "Peak T2" [Day 2], and "Old T5" [Day 5] parents). We conducted whole-genome resequencing and variant calling to compare differences in mutation rates after three generations of mutation accumulation. We found that Peak T2 lines had an overall reduced mutation rate compared to Young T1 and Old T5 lines, but this pattern of the effect varied depending on the variant impact. Specifically, we found no high-impact variants in Peak T2 lines, and modifiers and up- and downstream gene variants were less frequent in these lines. These results suggest that animals at the peak of reproduction have better DNA maintenance and repair compared to young and old animals. We propose that C. remanei start to reproduce before they optimize their DNA maintenance and repair, trading the benefits of earlier onset of reproduction against offspring mutation load. The increase in offspring mutation load with age likely represents germline senescence. Germline mutations play a key role in evolution through the generation of novel genotypes. Estimating the mutation rate in species, populations, and individuals is one way to understand the relative timeframe of evolutionary processes, for the timing of historical events and for estimating heritability of traits and diseases. Individual age at reproduction is known to affect the number of mutations being transferred into the next generation and generally mutation rate is thought to increase with increasing parental age. However, preventing mutations in germ cells is potentially costly and it may pay off to optimize germline genome repair and maintenance during peak reproductive periods, and relax it during nonpeak periods. This idea has been put forward to explain for example the reduction of gonad size in seasonally reproducing animals during nonreproductive periods and supported by the finding that the mutation rate seems to be higher in teenage men compared to men during their peak reproductive ages. We further tested this idea of a nonlinear relationship between age and mutation rate by performing a mutation accumulation experiment in a short-lived nematode. We kept experimental lines and allowed adults to reproduce at different ages in different lines, with some lines reproducing before, some during, and some after their reproductive peak. We found that mutation rates are higher in nematode lines reproducing before or after the reproductive peak compared to those reproducing during the peak. Our results therefore support the idea that germline genome maintenance and repair is potentially costly and that the mutation rate does not just increase with age but is optimized during the peak reproductive age of an organism.
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| 10. |
- Chen, Hwei-yen, 1983-, et al.
(author)
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Trade-off between somatic and germline repair in a vertebrate supports the expensive germ line hypothesis
- 2020
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In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences (PNAS). - 0027-8424 .- 1091-6490. ; 117:16, s. 8973-8979
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Journal article (peer-reviewed)abstract
- The disposable soma theory is a central tenet of the biology of aging where germline immortality comes at the cost of an aging soma [T. B. L. Kirkwood, Nature 270, 301–304 (1977); T. B. L. Kirkwood, Proc. R. Soc. Lond. B Biol. Sci. 205, 531–546 (1979); T. B. L. Kirkwood, S. N. Austad, Nature 408, 233–238 (2000)]. Limited resources and a possible trade-off between the repair and maintenance of the germ cells and growth and maintenance of the soma may explain the deterioration of the soma over time. Here we show that germline removal allows accelerated somatic healing under stress. We tested “the expensive germ line” hypothesis by generating germline-free zebrafish Danio rerio and testing the effect of the presence and absence of the germ line on somatic repair under benign and stressful conditions. We exposed male fish to sublethal low-dose ionizing radiation, a genotoxic stress affecting the soma and the germ line, and tested how fast the soma recovered following partial fin ablation. We found that somatic recovery from ablation occurred substantially faster in irradiated germline-free fish than in the control germline-carrying fish where somatic recovery was stunned. The germ line did show signs of postirradiation recovery in germline-carrying fish in several traits related to offspring number and fitness. These results support the theoretical conjecture that germline maintenance is costly and directly trades off with somatic maintenance.
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| 11. |
- Hermans Née Hotzy, Cosima
(author)
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Selection in sperm and its consequences : Exploring haploid selection, ageing and epigenetic effects in sperm
- 2017
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Doctoral thesis (other academic/artistic)abstract
- 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.
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| 12. |
- Hotzy, Cosima, et al.
(author)
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Evolutionary history of sexual selection affects microRNA profiles in Drosophila sperm
- 2022
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In: Evolution. - : John Wiley & Sons. - 0014-3820 .- 1558-5646. ; 76:2, s. 310-319
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Journal article (peer-reviewed)abstract
- The presence of small RNAs in sperm is a relatively recent discovery and little is currently known about their importance and functions. Environmental changes including social conditions and dietary manipulations are known to affect the composition and expression of some small RNAs in sperm and may elicit a physiological stress response resulting in an associated change in gamete miRNA profiles. Here, we tested how microRNA profiles in sperm are affected by variation in both sexual selection and dietary regimes in Drosophila melanogaster selection lines. The selection lines were exposed to standard versus low yeast diet treatments and three different population sex ratios (male-biased, female-biased, or equal sex) in a full-factorial design. After 38 generations of selection, all males were maintained on their selected diet and in a common garden male-only environment prior to sperm sampling. We performed transcriptome analyses on miRNAs in purified sperm samples. We found 11 differentially expressed miRNAs with the majority showing differences between male- and female-biased lines. Dietary treatment only had a significant effect on miRNA expression levels in interaction with sex ratio. Our findings suggest that long-term adaptation may affect miRNA profiles in sperm and that these may show varied interactions with short-term environmental changes.
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| 13. |
- Hotzy, Cosima, et al.
(author)
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Intrinsic post‐ejaculation sperm ageing does not affect offspring fitness in Atlantic salmon
- 2020
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In: Journal of Evolutionary Biology. - 1010-061X .- 1420-9101. ; 33:5, s. 576-583
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Journal article (peer-reviewed)abstract
- Post-meiotic sperm ageing, both before ejaculation and after ejaculation, has been shown to negatively affect offspring fitness by lowering the rate of embryonic development, reducing embryonic viability and decreasing offspring condition. These negative effects are thought to be caused by intrinsic factors such as oxidative stress and ATP depletion or extrinsic factors such as temperature and osmosis. Effects of post-ejaculation sperm ageing on offspring fitness have so far almost exclusively been tested in internal fertilizers. Here, we tested whether intrinsic post-ejaculation sperm ageing affects offspring performance in an external fertilizer, the Atlantic salmon Salmo salar. We performed in vitro fertilizations with a split-clutch design where sperm were subjected to four post-ejaculation ageing treatments. We varied the duration between sperm activation and fertilization while minimizing extrinsic stress factors and tested how this affected offspring fitness. We found no evidence for an effect of our treatments on embryo survival, hatching time, larval standard length, early larval survival or larval growth rate, indicating that intrinsic post-ejaculation sperm ageing may not occur in Atlantic salmon. One reason may be the short life span of salmon sperm after ejaculation. Whether our findings are true in other external fertilizers with extended sperm activity remains to be tested.
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| 14. |
- Hough, Josh, et al.
(author)
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Evolutionarily Stable Sex Ratios And Mutation Load
- 2013
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In: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 67:7, s. 1915-1925
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Journal article (peer-reviewed)abstract
- Frequency-dependent selection should drive dioecious populations toward a 1:1 sex ratio, but biased sex ratios are widespread, especially among plants with sex chromosomes. Here, we develop population genetic models to investigate the relationships between evolutionarily stable sex ratios, haploid selection, and deleterious mutation load. We confirm that when haploid selection acts only on the relative fitness of X- and Y-bearing pollen and the sex ratio is controlled by the maternal genotype, seed sex ratios evolve toward 1:1. When we also consider haploid selection acting on deleterious mutations, however, we find that biased sex ratios can be stably maintained, reflecting a balance between the advantages of purging deleterious mutations via haploid selection, and the disadvantages of haploid selection on the sex ratio. Our results provide a plausible evolutionary explanation for biased sex ratios in dioecious plants, given the extensive gene expression that occurs across plant genomes at the haploid stage.
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| 15. |
- Immler, Simone, et al.
(author)
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Distinct evolutionary patterns of morphometric sperm traits in passerine birds
- 2012
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In: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 279:1745, s. 4174-4182
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Journal article (peer-reviewed)abstract
- The striking diversity of sperm shape across the animal kingdom is still poorly understood. Postcopulatory sexual selection is an important factor driving the evolution of sperm size and shape. Interestingly, morphometric sperm traits, such as the length of the head, midpiece and flagellum, exhibit a strong positive phenotypic correlation across species. Here we used recently developed comparative methods to investigate how such phenotypic correlations between morphometric sperm traits may evolve. We compare allometric relationships and evolutionary trajectories of three morphometric sperm traits (length of head, midpiece and flagellum) in passerine birds. We show that these traits exhibit strong phenotypic correlations but that allometry varies across families. In addition, the evolutionary trajectories of the midpiece and flagellum are similar while the trajectory for head length differs. We discuss our findings in the light of three scenarios accounting for correlated trait evolution: (i) genetic correlation; (ii) concerted response to selection acting simultaneously on different traits; and (iii) phenotypic correlation between traits driven by mechanistic constraints owing to selection on sperm performance. Our results suggest that concerted response to selection is the most likely explanation for the phenotypic correlation between morphometric sperm traits.
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| 16. |
- Immler, Simone, et al.
(author)
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Driven Apart : The Evolution of Ploidy Differences between the Sexes under Antagonistic Selection
- 2014
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In: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 183:1, s. 96-107
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Journal article (peer-reviewed)abstract
- Sexual reproduction in eukaryotes implies a biphasic life cycle with alternating haploid and diploid phases. The nature of the biphasic life cycle varies markedly across taxa, and often either the diploid or the haploid phase is predominant. Why some taxa spend a major part of their life cycle as diploids and others as haploids remains a conundrum. Furthermore, ploidy levels may not only vary across life cycle phases but may also differ between males and females. The existence of two life cycle phases and two sexes bears a high potential for antagonistic selection, which in turn may influence the evolution of ploidy levels. We explored the evolution of ploidy levels when selection depends on both ploidy and sex. Our analyses show that antagonistic selection may drive the ploidy levels between males and females apart. In a subsequent step, we explicitly explored the evolution of arrhenotoky (i.e., haploid males and diploid females) in the context of antagonistic selection. Our model shows that selection on arrhenotoky depends on male fitness but evolves regardless of the fitness consequences to females. Overall we provide a plausible explanation for the evolution of sex differences in ploidy levels, a principle that can be extended to any system with asymmetric inheritance.
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| 17. |
- Immler, Simone, et al.
(author)
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Intra-specific variance in sperm morphometry : A comparison between wild and domesticated Zebra Finches Taeniopygia guttata
- 2012
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In: Ibis. - 0019-1019 .- 1474-919X. ; 154:3, s. 480-487
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Journal article (peer-reviewed)abstract
- The Zebra Finch Taeniopygia guttata is a model bird species for the experimental study of behavioural and evolutionary concepts in captivity and especially sexual selection. The validity of sexual selection studies of domesticated birds is of long-standing concern as little is known about the influence of domestication on sexually selected traits. Most domesticated Zebra Finch populations are maintained under a strict breeding regime to avoid potential inbreeding. However these breeding regimes may interfere with the processes of sexual selection and influence the evolution of sexually selected traits because they may limit or prohibit active mate choice. Here we investigated the potential impact of a monogamous breeding scheme in a domesticated population in which active mate choice is largely inhibited, on the evolution of sperm morphometry as a sexually selected trait. We compared sperm morphometric traits (total sperm length and length of sperm head, midpiece and flagellum), and the variance thereof, between a domesticated and two wild Zebra Finch populations. Although we found significant differences between the three populations for certain sperm traits (head length, midpiece length), which may be of importance in postcopulatory sexual selection, overall, variance in sperm morphometry did not differ between the domesticated and the wild Zebra Finch populations. Our results validate the use of domesticated Zebra Finches for further studies of postcopulatory sexual selection and sperm competition.
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| 18. |
- Immler, Simone, et al.
(author)
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Ploidally antagonistic selection maintains stable genetic polymorphism
- 2012
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In: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 66:1, s. 55-65
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Journal article (peer-reviewed)abstract
- Understanding the maintenance of genetic variation in the face of selection remains a key issue in evolutionary biology. One potential mechanism for the maintenance of genetic variation is opposing selection during the diploid and haploid stages of biphasic life cycles universal among eukaryotic sexual organisms. If haploid and diploid gene expression both occur, selection can act in each phase, potentially in opposing directions. In addition, sex-specific selection during haploid phases is likely simply because male and female gametophytes/gametes tend to have contrasting life histories. We explored the potential for the maintenance of a stable polymorphism under ploidally antagonistic as well as sex-specific selection. Furthermore, we examined the role of the chromosomal location of alleles (autosomal or sex-linked). Our analyses show that the most permissible conditions for the maintenance of polymorphism occur under negative ploidy-by-sex interactions, where stronger selection for an allele in female than male diploids is coupled with weaker selection against the allele in female than male haploids. Such ploidy-by-sex interactions also promote allele frequency differences between the sexes. With constant fitness, ploidally antagonistic selection can maintain stable polymorphisms for autosomal and X-linked genes but not for Y-linked genes. We discuss the implications of our results and outline a number of biological settings where the scenarios modeled may apply.
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| 19. |
- Immler, Simone, et al.
(author)
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Post-mating reproductive barriers in two unidirectionally hybridizing sunfish (Centrarchidae: Lepomis) : Lepomis)
- 2011
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In: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 24:1, s. 111-120
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Journal article (peer-reviewed)abstract
- The evolutionary sequence of events in the evolution of reproductive barriers between species is at the core of speciation biology. Where premating barriers fail, post-mating barriers, such as conspecific sperm precedence (CSP), gamete incompatibility (GI) and hybrid inviability (HI) may evolve to prevent the production of (often) costly hybrid offspring with reduced fitness. We tested the role of post-mating mechanisms for the reproductive isolation between two sunfish species [bluegill (BG) Lepomis macrochirus and pumpkinseed (PS) Lepomis gibbosus] and their first-generation hybrids. Performing in vitro sperm competition experiments, we observed asymmetric CSP as main post-mating isolation mechanism when BG and PS sperm were competing for PS eggs, whereas when sperm from both species were competing for BG eggs it was HI. Furthermore, hybrid sperm - although fertile in the absence of competition - were outcompeted by sperm of either parental species. This result may at least partly explain previous observations that natural hybridization in the study system is unidirectional.
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| 20. |
- Immler, Simone, et al.
(author)
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Resolving variation in the reproductive tradeoff between sperm size and number
- 2011
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In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 108:13, s. 5325-5330
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Journal article (peer-reviewed)abstract
- Spermatozoa are amongst the most variable cells, and three factors are thought to account for this variation in design: fertilization mode, phylogeny, and postcopulatory sexual selection. In addition, it has long been assumed that a tradeoff exists between sperm size and number, and although postcopulatory sexual selection affects both traits, empirical evidence for a tradeoff has so far been elusive. Our recent theoretical model predicts that the nature of a direct tradeoff between sperm size and number varies with sperm competition mechanism and sperm competition risk. We test these predictions using a comparative approach in two very different taxa with different sperm competition mechanisms: passerine birds (mechanism: simple raffle) and Drosophila fruit flies (sperm displacement). We show that in both groups, males increase their total ejaculate investment with increasing sperm competition risk, but whereas passerine birds allocate disproportionately to sperm number, drosophilids allocate disproportionately to sperm size. This striking difference between the two groups can be at least partly explained by sperm competition mechanisms depending on sperm size relative to the size of the female reproductive tract: in large animals (passerines), sperm numbers are advantageous in sperm competition owing to dilution inside the female tract, whereas in small animals (drosophilids), large spermare advantageous for physical competition (sperm displacement). Our study provides two important results. First, we provide convincing evidence for the existence of a sperm size-number tradeoff. Second, we show that by considering both sperm competition mechanism and dilution, can we account for variation in sperm size between different taxa.
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| 21. |
- Immler, Simone, et al.
(author)
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Sequential polyandry affords post-mating sexual selection in the mouths of cichlid females
- 2009
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In: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 0340-5443 .- 1432-0762. ; 63:8, s. 1219-1230
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Research review (peer-reviewed)abstract
- Females mating with multiple males may obtain direct benefits such as nuptial gifts or paternal care or indirect (i.e. genetic) benefits resulting in higher-quality offspring. While direct benefits are easily identified, it is difficult to determine indirect benefits, and it is hence largely unclear how they are obtained. This is particularly true in species with external fertilisation, where females seem to have little control over fertilisation. In cichlids, most maternal mouthbrooders show sequential multiple mating, where females visit several males for egg deposition. Genetic data revealed that multiple paternity of eggs and young in the mouth of females is common, but behavioural data of female spawning decisions are missing. Here, we test four hypotheses to explain female multiple mating in the maternally mouthbrooding cichlid, Ophthalmotilapia ventralis: (1) fertilisation insurance, (2) genetic bet-hedging, (3) female choice and (4) 'sperm shopping' (i.e. induction of sperm competition resulting in sexually selected sperm). Detailed observations of spawning behaviour in the field combined with histological analyses of the male reproductive organs suggest that fertilisation insurance, genetic bet-hedging and pre-mating female choice are unlikely to explain the sequential female multiple mating in O. ventralis. Instead, cryptic female choice by sperm shopping, i.e. post-mating sexual selection, is most compatible with our data and might be the major ultimate cause of multiple mating in females of this species and of mouthbrooding cichlids with maternal care in general. Our study provides new insight into ultimate causes of sequential polyandry in species with external fertilisation, as hitherto post-mating sexual selection by cryptic female choice has been assumed to be incompatible with external fertilisation mechanisms except by components of the ovarian fluid.
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| 22. |
- Immler, Simone, et al.
(author)
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Sperm variation within a single ejaculate affects offspring development in Atlantic salmon
- 2014
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In: Biology Letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 10:2, s. 20131040-
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Journal article (peer-reviewed)abstract
- 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.
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| 23. |
- Immler, Simone, et al.
(author)
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The evolution of sex chromosomes in organisms with separate haploid sexes
- 2015
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In: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 69:3, s. 694-708
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Journal article (peer-reviewed)abstract
- The evolution of dimorphic sex chromosomes is driven largely by the evolution of reduced recombination and the subsequent accumulation of deleterious mutations. Although these processes are increasingly well understood in diploid organisms, the evolution of dimorphic sex chromosomes in haploid organisms (U/V) has been virtually unstudied theoretically. We analyze a model to investigate the evolution of linkage between fitness loci and the sex-determining region in U/V species. In a second step, we test how prone nonrecombining regions are to degeneration due to accumulation of deleterious mutations. Our modeling predicts that the decay of recombination on the sex chromosomes and the addition of strata via fusions will be just as much a part of the evolution of haploid sex chromosomes as in diploid sex chromosome systems. Reduced recombination is broadly favored, as long as there is some fitness difference between haploid males and females. The degeneration of the sex-determining region due to the accumulation of deleterious mutations is expected to be slower in haploid organisms because of the absence of masking. Nevertheless, balancing selection often drives greater differentiation between the U/V sex chromosomes than in X/Y and Z/W systems. We summarize empirical evidence for haploid sex chromosome evolution and discuss our predictions in light of these findings.
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| 24. |
- Jimenez-Gonzalez, Ada, et al.
(author)
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Paternal starvation affects metabolic gene expression during zebrafish offspring development and lifelong fitness
- 2024
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In: Molecular Ecology. - : John Wiley & Sons. - 0962-1083 .- 1365-294X. ; 33:6
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Journal article (peer-reviewed)abstract
- Dietary restriction in the form of fasting is a putative key to a healthier and longer life, but these benefits may come at a trade-off with reproductive fitness and may affect the following generation(s). The potential inter- and transgenerational effects of long-term fasting and starvation are particularly poorly understood in vertebrates when they originate from the paternal line. We utilised the externally fertilising zebrafish amenable to a split-egg clutch design to explore the male-specific effects of fasting/starvation on fertility and fitness of offspring independently of maternal contribution. Eighteen days of fasting resulted in reduced fertility in exposed males. While average offspring survival was not affected, we detected increased larval growth rate in F1 offspring from starved males and more malformed embryos at 24 h post-fertilisation in F2 offspring produced by F1 offspring from starved males. Comparing the transcriptomes of F1 embryos sired by starved and fed fathers revealed robust and reproducible increased expression of muscle composition genes but lower expression of lipid metabolism and lysosome genes in embryos from starved fathers. A large proportion of these genes showed enrichment in the yolk syncytial layer suggesting gene regulatory responses associated with metabolism of nutrients through paternal effects on extra-embryonic tissues which are loaded with maternal factors. We compared the embryo transcriptomes to published adult transcriptome datasets and found comparable repressive effects of starvation on metabolism-associated genes. These similarities suggest a physiologically relevant, directed and potentially adaptive response transmitted by the father, independently from the offspring's nutritional state, which was defined by the mother.
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| 25. |
- Jiménez-Ortega, Dante, et al.
(author)
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Long life evolves in large-brained bird lineages
- 2020
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In: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 74:12, s. 2617-2628
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Journal article (peer-reviewed)abstract
- The brain is an energetically costly organ that consumes a disproportionate amount of resources. Species with larger brains relative to their body size have slower life histories, with reduced output per reproductive event and delayed development times that can be offset by increasing behavioral flexibility. The cognitive buffer hypothesis maintains that large brain size decreases extrinsic mortality due to greater behavioral flexibility, leading to a longer lifespan. Alternatively, slow life histories, and long lifespan can be a pre-adaptation for the evolution of larger brains. Here, we use phylogenetic path analysis to contrast different evolutionary scenarios and disentangle direct and indirect relationships between brain size, body size, life history, and longevity across 339 altricial and precocial bird species. Our results support both a direct causal link between brain size and lifespan, and an indirect effect via other life history traits. These results indicate that large brain size engenders longer life, as proposed by the cognitive buffer hypothesis.
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