Biology subjects

Nilsson, K. J.

Publications and source records attributed to Nilsson, K. J..

3 recordsLinked to original sources

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↗

bioRxiv2023

Colonization of a novel host plant reduces phenotypic variation

Understanding the evolutionary potential of populations -evolvability- is key to predicting their ability to cope with novel environments. Despite growing evidence that evolvability determines the tempo and mode of adaptation, it remains unclear how adaptations to novel environments influence evolvability in turn. Here we address the interplay between adaptation and evolvability in the peacock fly Tephritis conura, which recently underwent an adaptive change in the length of female ovipositor following a host shift. By comparing evolvability in various morphological traits including female ovipositor length between ancestral and derived host races, we found that evolvability is decreased in females of the derived host race compared to the ancestral host race. We found a correlation between evolvability and divergence between populations in both sexes, indicating that the overall pattern of evolvability has not been disrupted by the host shift despite the reduction in females of the derived host race. Exploration of the pattern of phenotypic integration further revealed that the ovipositor length constitutes a module that is separated from other measured traits. These results suggest that adaptation to novel environments can affect evolvability, and that modularity helps minimizing detrimental effects that adaptations may cause to other correlated traits.

evolutionary biology↗

bioRxiv2021

Non-parallel morphological divergence following colonization of a new host plant

Divergent ecological selection may diversify conspecific populations evolving into different niches, and may lead to speciation if gene flow is ceased, e.g, due to reinforcement leading to character displacement. Adaptation to the same niche is expected to be parallel. Whether selection against maladaptive hybridization in secondary sympatry also results in parallel divergence in traits that are not directly related to the ecological niches remains an empirical challenge, although such character displacement can be decisive for if ecotypes develop into new species. Here, we use a host shift in the phytophagous peacock fly Tephritis conura, with both host races represented in two geographically separate areas East and West of the Baltic Sea to investigate convergence in morphological adaptations. We asked i) if there are consistent morphological adaptations to a host plant shift and ii) if the response to secondary sympatry with the alternate host race is parallel across contact zones. We found surprisingly low and variable, albeit significant, divergence between host races. Only one trait, the length of the female ovipositor, which serves an important function in the interaction with the hosts, was consistently different. Instead, co-existence with the other host race significantly affected the degree of morphological divergence, but the divergence was largely driven by different traits in different contact zones. Thus, local stochastic fixation or reinforcement could generate trait divergence, and additional evidence is needed to conclude whether divergence is locally adaptive.

evolutionary biology↗