We plan to elucidate the history of chromosomal inversion polymorphisms in the marine snail, Littorina saxatilis, using whole-genome re-sequencing data. We have in hand sequence data from about 450 individuals, covering the entire range of the species, all major ecotypes and the two closest relative, Littorina arcana and L. compressa. From most study sites we also have both males and females. In this project, the sequence reads will be cleaned and mapped to a newly created reference genome of high quality. Variants will then be called and filtered. Once we have this variant information, it will be used to reconstruct the history of the inversion polymorphisms in relation to the demographic history of the species and their phylogenetic relationships. We will then seek to infer the roles of the inversions in local adaptation and speciation.