Introgression between Sphyrapicus nuchalis and S. varius sapsuckers in a hybrid zone in west-central Alberta

Studying species interactions at hybrid zones allows biologists to
understand the forces that promote speciation. Hybridization among
Sphyrapicus nuchalis, S. varius, and S. ruber has long been acknowledged,
and hybrid zones between S. nuchalis/S. ruber and S. varius/S. ruber have
been characterized with both genetic and genomic data. Using a combination
of next-generation Restriction Site-Associated DNA sequencing (RAD-Seq)
and traditional genetic methods, we examined patterns of introgression in
the poorly characterized S. nuchalis/S. varius contact zone; the two most
similar species in the complex, though they are not each other’s closest
relatives. We found high introgression rates, with several early and many
advanced generation hybrids along a 275 km stretch of Rocky Mountain
foothill, pointing to a well-established hybrid zone with hybrid
individuals backcrossing with individuals from the parental species and
each other. Plumage colouration in the hybrid zone was a relatively poor
indicator of parental or hybrid status, which could be attributed to the
possible involvement of few large effect genes.