Data from: Targeted resequencing reveals geographical patterns of differentiation for loci implicated in parallel evolution

Parallel divergence and speciation provide evidence for the role of
divergent selection in generating biological diversity. Recent studies
indicate that parallel phenotypic divergence may not have the same genetic
basis in different geographical locations - “outlier loci” (loci
potentially affected by divergent selection) are often not shared among
parallel instances of phenotypic divergence. However, limited sharing may
be due, in part, to technical issues if false positive outliers occur.
Here, we test this idea in the marine snail Littorina saxatilis, which has
evolved two partly isolated ecotypes (adapted to crab predation vs. wave
action) in multiple locations independently. We argue that if the low
extent of sharing observed in earlier studies in this system is due to
sampling effects, we expect outliers not to show elevated FST when
sequenced in new samples from the original locations, and also not to
follow predictable geographical patterns of elevated FST. Following a
hierarchical sampling design (within vs. between country), we applied
capture sequencing, targeting outliers from earlier studies and control
loci. We found that outliers again showed elevated levels of FST in their
original location, suggesting they were not generated by sampling effects.
Outliers were also likely to show increased FST in geographically close
locations, which may be explained by higher levels of gene flow or shared
ancestral genetic variation compared to more distant locations. However,
in contrast to earlier findings, we also found some outlier types to show
elevated FST in geographically distant locations. We discuss possible
explanations for this unexpected result.