Artbildning, det vill säga uppkomst av nya arter, är ett centralt ämne inom evolutionsbiologinoch en process som kan fortskrida på ett flertal olika sätt. Reproduktiva barriärer som är nödvändiga för artbildningsprocessen kan utvecklas mellan populationer och verkar antingen så att individer hindras från att para sig med varandra (prezygotisk isolering) eller så att överlevnad eller reproduktionsframgång hos avkomman är reducerad (postzygotisk isolering).Syftet men där här studien är att först beskriva dessa olika typer av isoleringar och sedan summera den aktuella kunskapen om hur själva artbildningsprocessen kan fortgå. Avslutningvis beskrivs ett exempelsystem med tre geografiskt separerade populationer avarten skogsvitsvinge (Leptidea sinapis). Skillnader i kromosomantal och ekologi mellan vissa av populationerna kan potentiellt vara faktorer som har lett till begränsat genflöde och som i slutänden kan leda till att fullständigt reproduktivt isolerade arter uppkommer.

Recombination is a genetic process of extreme importance in evolutionary biology. It creates novel haplotypes and breaks down existing ones, and can affect the levels of genetic diversity and the efficacy of selection. It also plays an important role in the evolution of sex chromosomes and the divergence process leading to speciation. Considering the particularities of the wood white (Leptidea sinapis) genome, with holocentric chromosomes, female achiasmy and a population-level cline in chromosome number, the study of its recombination landscape represents an opportunity to deepen the understanding of both this particular study system, and the underpinnings and consequences of recombination rate variation in general.  After DNA extraction and sequencing of 96 wood whites sampled across Sweden, population structure analyses were carried out together with a demographic history inference, which was used together with linkage disequilibrium information to establish the recombination rate in short intervals along the different chromosomes.  Population structure analyses showed that the sample set included 12 individuals of a cryptic species (cryptic wood white, L. juvernica) and, consistent with previous studies, a single population of L. sinapis in Sweden. Demographic inference analyses for independent scaffolds showed similar trend, with effective population size (Ne) decreasing considerably over the last 10,000 generations. The obtained recombination maps had a high resolution, and allowed for the identification of 553 putative recombination hotspots with a mean length of 3,770 bp. The genome-wide recombination rate was 9.98 cM/Mb, higher than in any vertebrate and butterfly species previously analysed, but lower than in the honey bee. A negative correlation between recombination rate and chromosome size was found, as well as a lower recombination rate on the Z chromosomes compared to the autosomes. The results are important for understanding the mechanisms underlying regional recombination rate variation in holocentric organisms and the potential for chromosome rearrangements to affect the recombination frequency, and consequently, rates and patterns of molecular evolution.

It is known that chromosomal rearrangements play an important role in speciation by limiting gene flow within and between species. Furthermore, this effect may be enhanced by involvement of sex chromosomes that are known to undergo fast evolution compared to autosomes and play a special role in speciation due to their engagement in postzygotic reproductive isolation. The work presented in this study uses various molecular-genetic and cytogenetic techniques to describe karyotype and sex chromosome evolution of two groups of Lepidoptera, namely selected representatives of the family Tortricidae and Leptidea wood white butterflies of the family Pieridae. The acquired knowledge points to unexpected evolutionary dynamics of lepidopteran karyotypes including the presence of derived neo-sex chromosome systems that originated as a result of chromosomal rearrangements. We discuss the significance of these findings for radiation and subsequent speciation of both lepidopteran groups.

Although transposable elements (TEs) have been subjected to detailed study in various organisms such as humans, maize, and drosophila, this is not the case for all organisms. Despite numerous studies on the effects of TEs in the field of evolution and functional genomics, there has not been many studies yet on how much variation these elements show in populations. To address these questions, we identified TEs in Leptidea sinapis based on a newly produced high-quality genome assembly and identified novel TEs in this project. In the first step of the project, we manually curated consensus sequences of the 150 most abundant TE subfamilies. We could identify 145 of these subfamilies: two of which were non-curatable because of bad consensus sequences, three that were uncertain where they start and end, and one of the subfamilies were divided into two different subfamilies. Hence, we ended up with 146 different TE subfamilies, and the remaining part of the project was carried out using these. In the second step, we examined how the manually curated 146 subfamilies were distributed in 83 different L. sinapis individuals in the Swedish population. Before performing manual curation for our selected TEs, we looked at the TE landscape of the long-read sequenced L. sinapis genome and showed that 58.2% of the L. sinapis genome consists of TEs. In a recent study, it has been shown that 40% of L. sinapis consists of TEs. So, when compared to previous studies, our result showed that the L. sinapis genome contained more TEs than previously reported. When we made the same analysis after manual curation, we showed that this amount increased to 62.4%. The distribution of classified TEs by groups is as follows: LINE 22.6%, DNA 7.43%, SINE 4.76%, LTR 3.10%.  After creating the final TE landscape for our reference genome, we analyzed 83 different individuals collected from different regions of Sweden such as Uppland, Östergötland, Västmanland, Närke, Värmland, Dalarna, Hälsingland, Småland, Medelpad, and Västerbotten for the individual number of non-reference insertions using RelocaTE2. We observed that these 146 subfamilies showed different distributions among individuals based on their sequence coverage. We couldn’t find any correlation between the number of insertions and the latitude of locations where individuals had been collected. When we look at the total number of insertions, we realized type I transposable elements were more abundant compared to type II transposable elements. Also, we checked the percentage of covered bases per individual in our dataset and observed that individuals with greater coverage had more TE insertions. After realizing this, when we analyzed individuals from different locations with very similar coverage, we could not see a significant correlation between the number of TE insertions and the latitude of locations of butterflies from different locations. For this reason, we can say that for the most abundant 146 TE subfamilies in the reference genome, there is not a significant difference between regions of Sweden. This study contributes to a better analysis of TE content in L. sinapis, and the know-how and possible problems with technical bias for individual TE insertion studies in general.