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

<b>Abstract</b><br/><p>Studying species interactions at hybrid zones allows biologists to understand the forces that promote speciation. Hybridization among <i>Sphyrapicus nuchalis</i>, <i>S. varius</i>, and <i>S. ruber</i> has long been acknowledged, and hybrid zones between <i>S. nuchalis/S. ruber</i> and <i>S. varius/S. ruber</i> 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 <i>S. nuchalis/S. varius</i> 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.</p>