Complex hybridization dynamics between golden‐winged and blue‐winged warblers (Vermivora chrysoptera and Vermivora pinus) revealed by AFLP, microsatellite, intron and mtDNA markers

Abstract

Blue-winged (Vermivora pinus) and golden-winged warblers (Vermivora chrysoptera) have an extensive mosaic hybrid zone in eastern North America. Over the past century, the general trajectory has been a rapid replacement of chrysoptera by pinus in a broad, northwardly moving area of contact. Previous mtDNA-based studies on these species' hybridization dynamics have yielded variable results: asymmetric and rapid introgression from pinus into chrysoptera in some areas and bidirectional maternal gene flow in others. To further explore the hybridization genetics of this otherwise well-studied complex, we surveyed variation in three nuclear DNA marker types--microsatellites, introns, and a panel of amplified fragment length polymorphisms (AFLPs)--with the goal of generating a multilocus assay of hybrid introgression. All markers were first tested on birds from phenotypically and mitochondrially pure parental-type populations from outside the hybrid zone. Searches for private alleles and assignment test approaches found no combination of microsatellite or intron markers that could separate the parental populations, but seven AFLP characters exhibited significant frequency differences among them. We then used the AFLP markers to examine the extent and pattern of introgression in a population where pinus-phenotype individuals have recently invaded a region that previously supported only a chrysoptera-phenotype population. Despite the low frequency of phenotypic hybrids at this location, the AFLP data suggest that almost a third of the phenotypically pure chrysoptera have introgressed genotypes, indicating the presence of substantial cryptic hybridization in the history of this species. The evidence for extensive cryptic introgression, combined with the lack of differentiation at other nuclear loci, cautions against hybrid assessments based on single markers or on phenotypic traits that are likely to be determined by a small number of loci. Considered in concert, these results from four classes of molecular markers indicate that pinus and chrysoptera are surprisingly weakly differentiated and that far fewer genetically 'pure' populations of chrysoptera may exist than previously assumed, two findings with broad implications for the conservation of this rapidly declining taxon.

Genetic Introgression: An Integral but neglected component of speciation in birds

“…At the same time, studies on birds have played an important role in revealing large variation in the extent of introgression not only among distinct genomic compartments but also among autosomal loci themselves (e.g., Borge et al 2005a, Kvist and Rytkönen 2006, Secondi et al 2006, Martínez-Cruz and Godoy 2007, Peters et al 2007, Vallender et al 2007, Carling and Brumfield 2008, Gay et al 2008, Carling et al 2010. For instance, among 13 autosomal loci sampled across a Passerina hybrid zone, Carling et al (2010) detected differences of more than an order of magnitude in levels of haplotype and nucleotide diversity, attributing these to locus-specific differences in introgression.…”

The use of microsatellite loci for accurate hybrid detection in a recent contact zone between an endangered and a recently-arrived hummingbird

“…Chatfield et al 2010;Väli et al 2010), amplified fragment length polymorphisms (e.g. Vallender et al 2007;Sternkopf et al 2010) and restriction fragment length polymorphisms (e.g. Gill 1997;Koutsogiannouli et al 2010).…”

Modeling and Mapping Golden-winged Warbler Abundance to Improve Regional Conservation Strategies

“…is particularly favored by this warbler but this habitat is decreasing in area; for instance, in central Wisconsin, aspen exhibited a 36% decrease in area between the 1983 and 1996 Forest Inventories (Schmidt 1997) as forest disturbance, i.e., logging and fire, essential for this species was reduced (Cleland et al 2001). Although the exact nature of the relationship between the Golden-winged Warbler and their conspecific the Blue-winged Warbler (Vermivora cyanoptera) is unknown, it appears that Golden-winged Warblers are being replaced by Blue-winged Warblers in large areas of sympatry, including the southern portions of Minnesota, Wisconsin, and Michigan (Vallender et al 2007(Vallender et al , 2009). To conserve this species will require focusing critical resources in areas of their greatest impact (Possingham and Wilson 2005, Buehler et al 2007, Thogmartin et al 2009).…”