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Abstract:
Chromosomal inversions are frequently documented for their involvement in adaptation and speciation across various organisms. However, their effect on evolution across the lifetime of the inversion is not well understood; hence, it is important to study their relative effects at various scales of divergence from ecotypes to species. While we have made a start with characterising structural variants (SVs) in the marine snails Littorina in existing short read datasets, including rearrangements involved in habitat adaptation, there is still a lot to be studied about them. We focus on identifying inversions and their origins in the ecotypes of flat periwinkle, L. fabalis, in exposed and sheltered habitats across North Europe, and comparing their patterns of differentiation and divergence to the sister species L. obtusata and the more distant relative L. saxatilis. Here, through haplotagging, a scalable linked-read method for large populations, and Illumina sequencing, we can systematically discover SVs, particularly adaptive/ecotype-specific inversions, as well as characterise inversion breakpoints that have been challenging to identify in existing short read datasets. We hypothesise that inversions can segregate as standing variants, i.e., be used repeatedly, in the L. fabalis ecotypes across their range to adapt to similar habitats, as well as in L. obtusata and L. saxatilis. Whether these inversions pre-date species divergences or are passed between hybridising species will provide insight into how frequently SVs are shared across species and their role in promoting speciation and adaptation.
