| 1. |
- Nieuwenhuis, Bart P. S., et al.
(författare)
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Repeated evolution of self-compatibility for reproductive assurance
- 2018
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Sexual reproduction in eukaryotes requires the fusion of two compatible gametes of opposite sexes or mating types. To meet the challenge of finding a mating partner with compatible gametes, evolutionary mechanisms such as hermaphroditism and self-fertilization have repeatedly evolved. Here, by combining the insights from comparative genomics, computer simulations and experimental evolution in fission yeast, we shed light on the conditions promoting separate mating types or self-compatibility by mating-type switching. Analogous to multiple independent transitions between switchers and non-switchers in natural populations mediated by structural genomic changes, novel switching genotypes readily evolved under selection in the experimental populations. Detailed fitness measurements accompanied by computer simulations show the benefits and costs of switching during sexual and asexual reproduction, governing the occurrence of both strategies in nature. Our findings illuminate the trade-off between the benefits of reproductive assurance and its fitness costs under benign conditions facilitating the evolution of self-compatibility.
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| 2. |
- 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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| 3. |
- Tusso, Sergio, et al.
(författare)
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Experimental evolution of adaptive divergence under varying degrees of gene flow
- 2021
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Ingår i: Nature Ecology & Evolution. - : Springer Nature. - 2397-334X. ; 5:3
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Tidskriftsartikel (refereegranskat)abstract
- Adaptive divergence is the key evolutionary process generating biodiversity by means of natural selection. Yet, the conditions under which it can arise in the presence of gene flow remain contentious. To address this question, we subjected 132 sexually reproducing fission yeast populations, sourced from two independent genetic backgrounds, to disruptive ecological selection and manipulated the level of migration between environments. Contrary to theoretical expectations, adaptive divergence was most pronounced when migration was either absent (allopatry) or maximal (sympatry), but was much reduced at intermediate rates (parapatry and local mating). This effect was apparent across central life-history components (survival, asexual growth and mating) but differed in magnitude between ancestral genetic backgrounds. The evolution of some fitness components was constrained by pervasive negative correlations (trade-off between asexual growth and mating), while others changed direction under the influence of migration (for example, survival and mating). In allopatry, adaptive divergence was mainly conferred by standing genetic variation and resulted in ecological specialization. In sympatry, divergence was mainly mediated by novel mutations enriched in a subset of genes and was characterized by the repeated emergence of two strategies: an ecological generalist and an asexual growth specialist. Multiple loci showed consistent evidence for antagonistic pleiotropy across migration treatments providing a conceptual link between adaptation and divergence. This evolve-and-resequence experiment shows that rapid ecological differentiation can arise even under high rates of gene flow. It further highlights that adaptive trajectories are governed by complex interactions of gene flow, ancestral variation and genetic correlations. This study uses evolve-and-resequence experiments with fission yeast populations subjected to disruptive ecological selection under different levels of migration to ask how gene flow, ancestral variation and genetic correlations affect the evolution of adaptive divergence.
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