Data from: Hybrid zone barriers comparative data set

Many recent studies have addressed the mechanisms operating during the
early stages of speciation, but surprisingly few studies have tested
theoretical predictions on the evolution of strong reproductive isolation
(RI). To help address this gap, we first undertook a quantitative review
of the hybrid zone literature for flowering plants in relation to
reproductive barriers. Then, using Populus as an exemplary model group, we
analysed genome-wide variation for phylogenetic tree topologies in both
early- and late-stage speciation taxa to determine how these patterns may
be related to the genomic architecture of RI. Our plant literature survey
revealed variation in barrier complexity and an association between
barrier number and introgressive gene flow. Focusing on Populus, our
genome-wide analysis of tree topologies in speciating poplar taxa points
to unusually complex genomic architectures of RI, consistent with earlier
genome-wide association studies. These architectures appear to facilitate
the ‘escape’ of introgressed genome segments from polygenic barriers even
with strong RI, thus affecting their relationships with recombination
rates. Placed within the context of the broader literature, our data
illustrate how phylogenomic approaches hold great promise for addressing
the evolution and temporary breakdown of RI during late stages of
speciation. This article is part of the theme issue ‘Towards the
completion of speciation: the evolution of reproductive isolation beyond
the first barriers’.