Data from: Gene flow and the maintenance of species boundaries

Hybrid zones are regions where individuals from genetically differentiated
populations meet and mate, resulting in at least some offspring of mixed
ancestry. Patterns of gene flow (introgression) in hybrid zones vary
across the genome, allowing assessment of the role of individual genes or
genome regions in reproductive isolation. Here, we document patterns of
introgression between two recently diverged species of field crickets. We
sample at a very fine spatial scale and genotype crickets for 110 highly
differentiated SNPs identified through transcriptome scans. Using both
genomic and geographic cline analysis, we document remarkably abrupt
transitions (less than 100 m) in allele frequencies for 50 loci, despite
high levels of gene flow at other loci. These are among the steepest
clines documented for any hybridizing taxa. Furthermore, the cricket
hybrid zone provides one of the clearest examples of the semi-permeability
of species boundaries. Comparisons between data from the fine scale
transect and data (for the same set of markers) from sampling a much
larger area in a different region of the cricket hybrid zone reveal
consistent patterns of introgression for individual loci. The consistency
in patterns of introgression between these two distant and distinct
regions of the hybrid zone suggests that strong selection is acting to
maintain abrupt discontinuities within the hybrid zone, and that genomic
regions with restricted introgression likely include genes that contribute
to non-ecological prezygotic barriers.