| 1. |
- Alavioon, Ghazal, 1986-
(författare)
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Haploid selection in animals : Exploring the fitness consequences and underlying mechanisms
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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, 1986-, et al.
(författare)
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Sperm performance traits exhibit low additive genetic component and strong parental effects in external fertilizer
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Annan publikation (övrigt vetenskapligt/konstnärligt)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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| 3. |
- Alavioon, Ghazal, 1986-, et al.
(författare)
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The fitness consequences of selection among sperm within an ejaculate across generations
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Annan publikation (övrigt vetenskapligt/konstnärligt)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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| 4. |
- Alavioon, Ghazal, 1986-, et al.
(författare)
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Within-ejaculate selection for sperm longevity reduces male reproductive ageing
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Annan publikation (övrigt vetenskapligt/konstnärligt)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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| 5. |
- Baur, Julian
(författare)
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Condition dependent germline maintenance in seed beetles
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 6. |
- Hermans Née Hotzy, Cosima
(författare)
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Selection in sperm and its consequences : Exploring haploid selection, ageing and epigenetic effects in sperm
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 7. |
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| 8. |
- Silva, Willian T. A. F., 1987-
(författare)
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Non-genetic processes in development and heredity
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is a swiftly increasing amount of empirical evidence that non-genetic factors, such as DNA methylation and small RNAs, play an important role not only in development but also in heredity and, therefore, evolutionary dynamics. One of the most interesting aspects of non-genetic processes is their responsiveness to environmental conditions, which has been shown to affect not only the phenotype and fitness of the individuals directly exposed to the stimulus, but also their offspring even when the stimulus is no longer present, indicating that the transmission of non-genetic factors across generations might work analogously to immunization against recurring conditions. In this thesis, I explored the effects and consequences of non-genetic processes in development and heredity, from both theoretical and experimental perspectives. In Article I, I created a mathematical model of DNA methylation dynamics during the maternal-to-zygotic transition, leading to the zygotic genome activation. I found that there is a developmental constraint on the transition between different cell lineages, with an increasing flexibility of active methylation and decreasing flexibility of maintenance (de-)methylation. In Article II, we explored the dynamics of small RNA production throughout development, including their amplification, transgenerational transmission and responsiveness to environmental conditions. Responsiveness of small RNA production resulted in greater benefits when soma and germline are both responsive, especially in highly correlated environmental conditions. In Article III, I carried out experiments on zebrafish to explore the effects of the male social environment on sperm production in terms of sperm morphology and DNA quality. Males exposed to different social treatments produced sperm with different morphologies and DNA integrity levels. In Article IV, we used the same experimental design to look at the effects of the male social environment on offspring development in terms of differential gene expression patterns. Males exposed to different social treatments sired offspring that showed different expression patterns of genes involved in post-transcriptional processes of gene expression regulation. Our findings shed light on the importance of non-genetic processes in development and heredity and contributes to the current knowledge about which and how non-genetic mechanisms can potentially affect evolutionary dynamics.
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| 9. |
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| 10. |
- Tusso Gomez, Sergio Ivan
(författare)
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Adaptive divergence in fission yeast : From experimental evolution to evolutionary genomics
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- How adaptation and population differentiation occur is fundamental to understand the origin of biodiversity. Work in speciation alongside the increased ease of generating genomic data have allowed the exploration of genomic changes relevant to adaptation. However, it remains challenging to infer the underlying mechanisms from genomic patterns of divergence governed by both genomic properties and external selective pressures. The chronological order of genomic changes, evolutionary history and selective forces can rarely be inferred from natural populations.Currently, I see two promising ways to tackle the problem of the genomic underpinnings of divergence: (1) evolution experiments simulating adaptation and population divergence and measuring genomic changes as they occur through time; (2) empirical studies of closely related populations in which the extent of divergence varies, allowing us to infer the chronology of the genomic changes. In my Ph.D. research I applied these two approaches, using the fungus Schizosaccharomyces pombe. First, I experimentally tested the potential for ecological divergence with gene flow, and investigated genomic and phenotypic changes associated with this process. Next, I studied genomic data obtained from natural populations sampled worldwide. In both cases, the genetic inference relied on different sequencing technologies including the Illumina, Pacific Biosciences and Oxford Nanopore platforms.The experiment explored the effect of gene flow on phenotype and fitness, and uncovered potential molecular mechanisms underlying adaptive divergence. In paper I we demonstrate the emergence of specialisation under low gene flow, but generalist strategies when gene flow was high. Evolved phenotypes were largely influenced by standing genetic variation subject to opposite antagonistic pleiotropy complemented by new mutations enriched in a subset of genes. In paper II, we show that the experimental selective regime also had an effect on mating strategies, result of temporal ecological heterogeneity and selection for mating efficiency. We found that the evolution of mating strategies was explained by a trade-off between mating efficiency and asexual growth rate dependent on environmental stability. Papers III and IV consider the role of gene flow in natural populations. In paper III, we provide evidence that gene flow also played a predominant role in adaptive divergence in nature. All strains resulted from recent hybridization between two ancestral groups manifested in large phenotypic variation and reproductive isolation.This demographic history of hybridization was confirmed in paper IV focusing on patterns of mitochondrial diversity, adding evidence for the geographic distribution of the ancestral populations and potential for horizontal gene transfer from a distant yeast clade.
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