Data from: Contact zones reveal restricted introgression despite frequent hybridization across a recent lizard radiation

Introgression — the exchange of genetic material through hybridization —
is now recognized as common among animal species. The extent of
introgression, however, can vary considerably even when it occurs: for
example, introgression can be geographically restricted or so pervasive
that populations merge. Such variation highlights the importance of
understanding the factors mediating introgression. Here we used
genome-wide SNP data to assess hybridization and introgression at 32
contact zones, comprising 21 phylogenetic independent contrasts across a
recent lizard radiation (Heteronotia). We then tested the relationship
between the extent of introgression (average admixture at contact zones)
and genomic divergence across independent contrasts. Early-generation
hybrids were detected at contact zones spanning the range of genomic
divergence included here. Despite this, we found that introgression is
remarkably rare and, when observed, geographically restricted. Only the
two most genomically similar population pairs showed introgression beyond
5 km of the contact zone. Introgression dropped precipitously at only
modest levels of genomic divergence, beyond which it was absent or
extremely low. Our results contrast with the growing number of studies
indicating that introgression is prevalent among animals, suggesting that
animal groups will vary considerably in their propensity for
introgression.