DOI: 10.5061/dryad.j407q
title: Data from: Hybridization between Townsend’s Dendroica townsendi and black-throated green warblers D. virens in an avian suture zone

description: Hybrid zones between species provide natural systems for the study of
 processes involved in divergence, reproductive isolation and speciation.
 Townsend’s Dendroica townsendi and black-throated green D. virens warblers
 are phenotypically and genetically divergent groups that occur in western
 and eastern North America respectively, with potential for range contact
 in the Rocky Mountains of British Columbia, where other west-east avian
 pairs come into contact. Although one potential hybrid (a phenotypic
 Townsend’s warbler with the black-throated green mitochondrial DNA) has
 been previously reported, there have been no studies of interactions
 between the taxa in potential areas of sympatry. To determine whether
 interbreeding between these species is a regular occurrence we examined
 variation in individuals across the area of putative range overlap.
 Analysis of plumage, morphology, and mitochondrial (COI) and nuclear
 molecular markers (CHD1Z and numt-Dco1) shows surprisingly extensive
 hybridization between these species, with at least 38% of individuals in
 the hybrid zone being either hybrids or backcrosses. Each of the traits
 displays a sigmoidal cline centred along the eastern slope of the Rocky
 Mountains (molecular cline centres averaging 50 km east of the crest of
 the Rockies, ranging from 41 to 56 km). The clines are narrow (average
 molecular cline width is 60 km, ranging from 40 to 87 km) relative to the
 dispersal distance of related warbler species, suggesting that selection
 is maintaining the hybrid zone; we discuss possible sources of selection.
 Given the narrowness of the zone we recommend the two forms should
 continue to be treated as separate taxonomic species. Townsend’s warblers
 also form an extensively studied hybrid zone with their more closely
 related southern relative, the hermit warbler D. occidentalis. The
 combined system of three discrete forms separated by narrow hybrid zones
 provides an excellent system for the study of hybridization, reproductive
 isolation and speciation.
description: BREAST ANALYSIS - PHOTOS
 FOR PLUMAGE - Toews et al 2011Compressed package
 containing photographs used for plumage analysis for Toews et al. 2011.
 Each folder (breast, crown, face) corresponds to the plumage scores for
 each of the plumage traits. Each photograph is identified by a unique
 record number (see supplementary material).CROWN ANALYSIS - PHOTOS
 FOR PLUMAGE - Toews et al 2011Compressed package
 containing photographs used for plumage analysis for Toews et al. 2011.
 Each folder (breast, crown, face) corresponds to the plumage scores for
 each of the plumage traits. Each photograph is identified by a unique
 record number (see supplementary material).FACE ANALYSIS - PHOTOS
 FOR PLUMAGE - Toews et al 2011Compressed package
 containing photographs used for plumage analysis for Toews et al. 2011.
 Each folder (breast, crown, face) corresponds to the plumage scores for
 each of the plumage traits. Each photograph is identified by a unique
 record number (see supplementary material).