Data from: Heterogeneity and concordance in locus-specific differentiation and introgression between species of towhees

The maintenance or breakdown of reproductive isolation are observable
outcomes of secondary contact between species. In cases where hybrids
beyond the F1 are formed, the representation of each species’ ancestry can
vary dramatically among genomic regions. This genomic heterogeneity in
ancestry and introgression can offer insight into evolutionary processes,
particularly if introgression is compared in multiple hybrid zones.
Similarly, considerable heterogeneity exists across the genome in the
extent to which populations and species have diverged, reflecting the
combined effects of different evolutionary processes on genetic variation.
We studied hybridization across two hybrid zones of two phenotypically
well-differentiated bird species in Mexico (Pipilo maculatus and P. ocai),
to investigate genomic heterogeneity in differentiation and introgression.
Using genotyping by sequencing (GBS) and hierarchical Bayesian models, we
genotyped 460 birds at over 41,000 single nucleotide polymorphism (SNP)
loci. We identified loci exhibiting extreme introgression relative to the
genome-wide expectation using a Bayesian genomic cline model. We also
estimated locus-specific FST and identified loci with exceptionally high
genetic divergence between the parental species. We found some concordance
of locus-specific introgression in the two independent hybrid zones (6-20%
of extreme loci shared across zones), reflecting areas of the genome that
experience similar gene flow when the species interact. Additionally,
heterogeneity in introgression and divergence across the genome revealed
another subset of loci under the influence of locally specific factors.
These results are consistent with a history in which reproductive
isolation has been influenced by a common set of loci in both hybrid
zones, but where local environmental and stochastic factors also lead to
genomic differentiation.