Biology subjects

Nolen, Z. J.

Publications and source records attributed to Nolen, Z. J..

3 recordsLinked to original sources

bioRxiv2024

On the origin of an insular hybrid butterfly lineage

A new species can form through hybridization between species. Hybrid speciation in animals has been intensely debated, partly because hard evidence for the process has been difficult to obtain. Recent access to whole-genome sequencing data have made it more feasible to detect hybrid lineages. Here we report the discovery of a European hybrid butterfly lineage, a finding that can be considered surprising given the intense and long-term study of European butterflies. The lineage we describe is mainly inhabiting an island in the Baltic Sea and was previously designated as a subspecies (horkei) of one of the parental species (Aricia artaxerxes). By analysing whole-genome resequencing data, we determine that horkei originated by hybridization between the non-sister species A. artaxerxes and A. agestis. This hybridization event occurred approximately 54,000 years ago, predating the last glaciation of the current distribution range. Horkei must therefore have persisted long enough to be able to colonize its current range, despite that this area lies between the current distributions of the parental species. The hybrid origin, the maintenance of genomic integrity across times of dramatic climate change and the expression of a combination of parental traits suggest that horkei could be in the process of hybrid speciation.

evolutionary biology↗

bioRxiv2024

Species-specific loss of genetic diversity and accumulation of genetic load following agricultural intensification

Land-use change from agricultural intensification is a major driver of global insect declines. We investigated the genetic consequences of grassland decline in Sweden by sequencing museum and modern specimens of three focal and five additional Polyommatinae butterfly species. From 59 historical and 90 contemporary genomes, we find a 6% decline in genetic diversity and increased isolation and inbreeding in the grassland specialist Cyaniris semiargus over the past 70 years. In contrast, generalist Polyommatus icarus and heathland specialist Plebejus argus maintained genetic diversity and connectivity. Although currently genomic erosion is mild, we infer it lags considerably larger declines in effective population sizes. Using simulations, we demonstrate that only a small portion of genetic diversity is lost in early stages of decline, creating a genetic extinction debt. Two of five additional species show similar reductions, underscoring that restoration of grassland habitat is necessary to restore gene flow and halt further genomic erosion in grassland insects.

genomics↗

bioRxiv2023

The genomic landscape of adaptation to a new host plant

Adaptation to novel ecological niches is known to be rapid. However, how the loci underlying ecological divergence are coupled to traits reproductively isolating populations, ultimately enabling the formation of persistent species, remains a consequential question in speciation research. Here, we investigated the genomic differences underpinning colonization of a new niche and formation of two partly sympatric host races of Tephritis conura peacock flies. We took advantage of two independent sympatric zones west and east of the Baltic Sea, where host plant specialists using the thistle species Cirsium heterophyllum and C. oleraceum co-occur, and address what regions of the genome maintain the host races in parallel. Using genome-wide association, differentiation and divergence statistics, we identified a large, highly divergent region associated with host use among western and eastern populations. Within this region, we identified unique haplotypes associated with each host race, indicative of a large inversion, adding to the growing body of evidence that structural changes to the genome are important for adaptations to persist in the face of gene flow. We further showed strong signatures of selection in this region, especially in populations of the derived C. oleraceum specialist host race. The region also had reduced introgression, especially in western populations, while the rest of the genome showed signs of extensive gene flow. Genes within highly differentiated windows within the putative inversion were not only enriched for functions involved in host adaptation, including phenology and metabolic responses to different metabolites in the two host plants, but also enriched for gametogenesis, fertilization and embryological development, all of which suggest sequence divergence could have large consequences on reproductive isolation between the host races. In conclusion, this study suggests that structural changes in the genome may facilitate the formation of persistent host races, and ultimately speciation, in face of gene flow.

evolutionary biology↗