E5 DLA Project; The genomic aftermath of colliding expansion waves – a case study in Scottish Speckled Wood butterflies

Ecologists are documenting range changes including very rapid expansions in response to climate change for an increasing number of taxa. Focusing on deeper timescales, there is a long history of genetic studies of hybrid zones that have formed via secondary contacts. Hybrid zones are the outcome of natural population collision experiments and the spatial distribution of genetic variation around a hybrid zone contains a wealth of information about the interaction of selection, migration and recombination in natural populations. The recent range expansion of the Speckled Wood butterfly (Pararge aegeria) in the UK offers a unique opportunity to study the embryonic stages of secondary contacts in real time. Populations of P. aegeria that were previously separated in Scotland and England, and known to be genetically distinct started expanding their ranges (south and northwards respectively) in the 70s. Given that the range expansion of P. aegeria is well documented through citizen science records we know that the two expansion waves have recently (2020 -2022) met in Angus on the East coast of Scotland. However, the phenotypic and genomic outcomes of this new contact are unclear and depend on the extent to which genetic variation between the two populations differs and the nature of this variation: e.g. genetic incompatibilities would be exposed in early hybrids and may eventually result in stable clines. In contrast, we would expect globally beneficial but variation that is limited to one populations before the contact to spread rapidly into the other.

Key research questions

This project will address the following questions: 

   • What are the genomic targets of selection during the expansion and to what extent are they shared between the two expansion waves?

   • Does the contact expose pairwise incompatibilities or is most of the deleterious load hybrids suffer due to additive variation?

   • Is there evidence for globally beneficial haplotypes that are introgressing into the new population adaptively?

   • Do the hybrid populations show evidence for transgressive segregation, in the form of extreme wing phenotypes?

Methodology

The project makes use of the extensive spatial records and image data for P. aegeria as well as the new reference genome and whole genome sequence (WGS) data from before the contact. The student will generate and analyse both phenotypic and WGS data from butterfly samples collected from the contact area. While this project involves some collection of butterfly samples in the field and molecular work, it is mainly computational.

Training & requirements

The student will receive comprehensive training in state of the art bioinformatics and statistical genomics. The project can be tailored to the interest of the student, e.g. it may be possible to include machine learning approaches to analyse image data and/or the study of incompatibilities using hybrids phenotyped in lab crosses. Applicants should have at least an upper 2.1 degree in a relevant subject (evolutionary or computational biology or a related quantitative field) and an enthusiasm for population genetics and butterfly ecology. Previous experience in population genetics, butterfly ecology and/or bioinformatic/computational skills would be an advantage.

Further details and how to apply can be found here

APPLICATION DEADLINE - 6 January 2025 at 12:00 noon, GMT