| 1. |
- Boman, Jesper
(author)
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Genetic architecture of speciation
- 2024
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Doctoral thesis (other academic/artistic)abstract
- New species are formed either by the splitting of a lineage in two or through hybridization of divergent lineages. Using genetics to understand the origin and persistence of species is a central theme in evolutionary biology. The genetic architecture of speciation refers to the number, types and effect sizes of different genetic loci underlying the process of speciation. Insightful models and painstaking laboratory and field work have provided the first sketches of the genetic architecture of speciation in a handful of model organisms. In this thesis, I explore different aspects of speciation genetics in several less studied model systems: from birds to butterflies. In Paper I, I investigate the genetic architecture of hybrid inviability between chromosomal races of the wood white butterfly (Leptidea sinapis) and find an association between chromosome fusions and the evolution of hybrid inviability. In Paper II, I study whether the many chromosomal differences separating the L. sinapis races show evidence of non-Mendelian inheritance. We observe the preferential inheritance of the ancestral state at chromosome fusions in line with the meiotic drive model. Thus, meiotic drive acts against karyotype change and thus potentially opposes the evolution of reproductive isolation. Recent work has highlighted that epigenetic mechanisms, such as DNA methylation, could be important for the dysfunction of hybrids. In Paper III, we test this prediction in naturally occurring hybrids between the collared flycatcher (F. albicollis) and the pied flycatcher (F. hypoleuca). I show that DNA methylation differences in promoter regions are often correlated with signatures of differential gene expression between species, but does not predict misexpression in hybrids. Hybridization between species is expected to reduce the genetic differentiation and erode species differences. However, hybridization can also be the trigger of speciation if the combination of alleles and traits allow the hybrid species to persist. In Paper IV, I discover a hybrid Aricia butterfly species on the island of Öland in the Baltic Sea. Using whole-genome resequencing data and species models I infer that the main hybridization event occurred approximately 54,000 years ago, long before Öland arose from the sea after the last ice age. To conclude, this thesis highlights different aspects of speciation genetics: from the genetic underpinnings of viability of hybrids (Paper I and III) to causes of speciation (Paper II and IV). Hopefully this work will provide a few more lines to the blueprint that is our understanding of the genetic architecture of speciation
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| 2. |
- Boman, Jesper, et al.
(author)
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Meiotic drive against chromosome fusions in butterfly hybrids
- 2024
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In: Chromosome Research. - : Springer. - 0967-3849 .- 1573-6849. ; 32:2
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Journal article (peer-reviewed)abstract
- Species frequently differ in the number and structure of chromosomes they harbor, but individuals that are heterozygous for chromosomal rearrangements may suffer from reduced fitness. Chromosomal rearrangements like fissions and fusions can hence serve as a mechanism for speciation between incipient lineages, but their evolution poses a paradox. How can rearrangements get fixed between populations if heterozygotes have reduced fitness? One solution is that this process predominantly occurs in small and isolated populations, where genetic drift can override natural selection. However, fixation is also more likely if a novel rearrangement is favored by a transmission bias, such as meiotic drive. Here, we investigate chromosomal transmission distortion in hybrids between two wood white (Leptidea sinapis) butterfly populations with extensive karyotype differences. Using data from two different crossing experiments, we uncover that there is a transmission bias favoring the ancestral chromosomal state for derived fusions, a result that shows that chromosome fusions actually can fix in populations despite being counteracted by meiotic drive. This means that meiotic drive not only can promote runaway chromosome number evolution and speciation, but also that it can be a conservative force acting against karyotypic change and the evolution of reproductive isolation. Based on our results, we suggest a mechanistic model for why chromosome fusion mutations may be opposed by meiotic drive and discuss factors contributing to karyotype evolution in Lepidoptera.
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| 3. |
- Culicchi, Alessandro, 1989-
(author)
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Ecological and evolutionary effects of anthropogenic change in freshwater fish communities
- 2024
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Doctoral thesis (other academic/artistic)abstract
- Environmental change is ongoing, driven by human activities that have profoundly modified the modern world. Natural ecosystems are directly affected by these anthropogenic activities. This thesis explores the effects of anthropogenic change on natural ecosystems. Being this an extremely broad topic, we narrow down our research to some key areas of investigation, without aiming to be exhaustive. We also explore related themes. In Paper I, we review the effects of anthropogenic change on the process of speciation. We show that human intervention can alter geography or selective regimes. In both cases, this can either lead to an increase or decrease in reproductive isolation between species. In the following papers, we focus on the study case of two sister species with similar morphology and ecological niches, the common bream (Abramis brama) and the white bream (Blicca bjoerkna). In Paper II, we demonstrate that changes in abiotic and biotic conditions in lakes can disrupt the delicate co-occurrence and abundance patterns between the two species. In particular, increases in turbidity, predation and competition pose a threat to the local survival of white bream. In Paper III, we examine the effects of abiotic and biotic conditions on the phenotype of our species of interest. For this purpose, we focus on the average individual size and its relative difference between the species as a phenotypic proxy. We show that the relative difference in size is quite insensitive to external perturbations. However, we find that the presence of pike in the lake increases the similarity in the size between the study species. This can potentially threaten niche specialisation and species cohesion. Throughout Paper II and Paper III, we investigate the temporal trends of environmental and biotic factors over the last few decades, finding an increase in temperature, turbidity and the proportion of perch, along with a decrease in the proportions of pike and roach. In Paper IV, we conduct a genomic study based on whole-genome resequencing, which reveals that the morphological approach is inadequate for the taxonomical identification of our study species. Genomic data also show that hybridisation occurs, but it does not pose an immediate threat to species cohesion in the study area. Intra-specific genetic variation is low, and it suggests a pattern of isolation-by-distance. Overall, this thesis highlights that an analysis of anthropogenic influences on natural systems should be approached from different angles, to provide a comprehensive overview of such a complex phenomenon.
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| 4. |
- Höglund, Jacob, et al.
(author)
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A Chromosome-Level Genome Assembly and Annotation for the Clouded Apollo Butterfly (Parnassius mnemosyne) : A Species of Global Conservation Concern
- 2024
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In: Genome Biology and Evolution. - : Oxford University Press. - 1759-6653. ; 16:2
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Journal article (peer-reviewed)abstract
- The clouded apollo (Parnassius mnemosyne) is a palearctic butterfly distributed over a large part of western Eurasia, but population declines and fragmentation have been observed in many parts of the range. The development of genomic tools can help to shed light on the genetic consequences of the decline and to make informed decisions about direct conservation actions. Here, we present a high-contiguity, chromosome-level genome assembly of a female clouded apollo butterfly and provide detailed annotations of genes and transposable elements. We find that the large genome (1.5 Gb) of the clouded apollo is extraordinarily repeat rich (73%). Despite that, the combination of sequencing techniques allowed us to assemble all chromosomes (nc = 29) to a high degree of completeness. The annotation resulted in a relatively high number of protein-coding genes (22,854) compared with other Lepidoptera, of which a large proportion (21,635) could be assigned functions based on homology with other species. A comparative analysis indicates that overall genome structure has been largely conserved, both within the genus and compared with the ancestral lepidopteran karyotype. The high-quality genome assembly and detailed annotation presented here will constitute an important tool for forthcoming efforts aimed at understanding the genetic consequences of fragmentation and decline, as well as for assessments of genetic diversity, population structure, inbreeding, and genetic load in the clouded apollo butterfly.
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| 5. |
- Höök, Lars, et al.
(author)
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Temporal dynamics of faster neo-Z evolution in butterflies
- 2024
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In: Evolution. - 0014-3820 .- 1558-5646.
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Journal article (peer-reviewed)abstract
- The faster-Z/X hypothesis predicts that sex-linked genes should diverge faster than autosomal genes. However, studies across different lineages have shown mixed support for this effect. So far, most analyses have focused on old and well-differentiated sex chromosomes, but less is known about the divergence of more recently acquired neo-sex chromosomes. In Lepidoptera (moths and butterflies), Z-autosome fusions are frequent, but the evolutionary dynamics of neo-Z chromosomes have not been explored in detail. Here, we analyzed the faster-Z effect in Leptidea sinapis, a butterfly with three Z chromosomes. We show that the neo-Z chromosomes have been acquired stepwise, resulting in strata of differentiation and masculinization. While all Z chromosomes showed evidence of the faster-Z effect, selection for genes on the youngest neo-Z chromosome (Z3) appears to have been hampered by a largely intact, homologous neo-W chromosome. However, the intermediately aged neo-Z chromosome (Z2), which lacks W gametologs, showed fewer evolutionary constraints, resulting in particularly fast evolution. Our results therefore support that neo-sex chromosomes can constitute temporary hot-spots of adaptation and divergence. The underlying dynamics are likely causally linked to shifts in selective constraints, evolution of gene expression, and degeneration of W-linked gametologs which gradually expose Z-linked genes to selection.
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