Data from: Genomic divergence in allopatric Northern Cardinals of the North American warm deserts is linked to behavioral differentiation

Biogeographic barriers are thought to be important in initiating
speciation through geographic isolation, but they rarely indiscriminately
and completely reduce gene flow across the entire community. Understanding
which species’ attributes regulate a barrier could help elucidate how
speciation is initiated and isolation maintained. Here, we investigated
the association of behavioral isolation on population differentiation in
Northern Cardinals (Cardinalis cardinalis) distributed across the Cochise
Filter Barrier, a region of transitional habitat which separates the
Sonoran and Chihuahuan deserts of North America. Using genome-wide
markers, we modeled demographic history by fitting the data to isolation
and isolation-with-migration models. The best-fit model indicated that
desert populations diverged in the Pleistocene with low, historic, and
asymmetric gene flow across the barrier. We then tested behavioral
isolation using reciprocal call-broadcast experiments to compare song
recognition between deserts, controlling for song dialect changes within
deserts. We found that male Northern Cardinals in both deserts were most
aggressive to local songs and failed to recognize across-barrier songs. A
correlation of genomic differentiation despite historic introgression and
strong song discrimination is consistent with a model where speciation is
initiated across a barrier and maintained by behavioral isolation.