Data from: Replicate geographic transects across a hybrid zone reveal parallelism and differences in the genetic architecture of reproductive isolation

Determining the genetic architecture of traits involved in adaptation and
speciation is one of the key components of understanding the evolutionary
mechanisms behind biological diversification. Hybrid zones provide a
unique opportunity to use genetic admixture to identify traits and loci
contributing to partial reproductive barriers between taxa. Many studies
have focused on temporal dynamics of hybrid zones, but geographical
variation in hybrid zones that span distinct ecological contexts has
received less attention. We address this knowledge gap by analyzing
hybridization and introgression between black-capped and Carolina
chickadees in two geographically remote transects across their extensive
hybrid zone, one located in eastern and one in central North America.
Previous studies demonstrated that this hybrid zone is moving northward as
a result of climate change, but is staying consistently narrow due to
selection against hybrids. In addition, the hybrid zone is moving ~5x
slower in central North America compared to more eastern regions,
reflecting continent-wide variation in the rate of climate change. We use
whole genome sequencing of 259 individuals to assess whether variation in
the rate of hybrid zone movement is reflected in patterns of hybridization
and introgression, and which genes and genomic regions show consistently
restricted introgression in distinct ecological contexts. Our results
highlight substantial similarities between geographically remote transects
and reveal large Z-linked chromosomal rearrangements that generate
measurable differences in the degree of gene flow between transects. We
further use simulations and analyses of climatic data to examine potential
factors contributing to continental-scale nuances in selection pressures.
We discuss our findings in the context of speciation mechanisms and the
importance of sex chromosome inversions in chickadees and other species.