Genetic divergence and migration patterns in a North American passerine bird: implications for evolution and conservation

Abstract

Like many other migratory birds, the black-throated blue warbler (Dendroica caerulescens) shows pronounced differences in migratory behaviour and other traits between populations: birds in the southern part of the breeding range have darker plumage and migrate to the eastern Caribbean during the winter, whereas those in the north have lighter plumage and migrate to the western Caribbean. We examined the phylogeography of this species, using samples collected from northern and southern populations, to determine whether differentiation between these populations dates to the Pleistocene or earlier, or whether differences in plumage and migratory behaviour have arisen more recently. We analysed variation at 369 bp of the mitochondrial control region domain I and also at seven nuclear microsatellites. Analyses revealed considerable genetic variation, but the vast majority of this variation was found within rather than between populations, and there was little differentiation between northern and southern populations. Phylogeographic analyses revealed a very shallow phylogenetic tree, a star-like haplotype network, and a unimodal mismatch distribution, all indicative of a recent range expansion from a single refugium. Coalescent modelling approaches also indicated a recent common ancestor for the entire group of birds analysed, no split between northern and southern populations, and high levels of gene flow. These results show that Pleistocene or earlier events have played little role in creating differences between northern and southern populations, suggesting that migratory and other differences between populations have arisen very recently. The implications of these results for the evolution of migration and defining taxonomic groups for conservation efforts are discussed.

Asymmetric discrimination of geographical variation in song in a migratory passerine

“…Such asymmetries in female preferences may evolve when new populations are founded by a few individuals, such that selection favours 'nondiscriminating' females in the new populations (Kaneshiro & Boake 1987). A Kaneshiro effect for southern populations of the black-throated blue warbler may be unlikely, as phylogeographical analyses indicate that all current populations expanded from a single refugium during the recent Pleistocene (Davis et al 2006;Grus et al 2009). This interpretation also relies on the assumption that females prefer the same signals that elicit strong responses from males, which may (e.g.…”

“…These differences in plumage signals and migratory behaviour apparently arose recently and likely in the face of ongoing gene flow, as all extant populations appear to have derived from a recent population expansion from a single glacial refugium (Davis et al 2006;Grus et al 2009). In this study, we were interested in determining whether any differences in song exist between the north and the south, whether males discriminate against nonlocal songs, whether such discrimination is symmetric or asymmetric, and whether variation in responses is due to variation in assessment strategy or species recognition.…”

Assessing population structure and migratory patterns of White-throated Sparrow (Zonotrichia albicollis) breeding populations in western Canada.

“…Similar results have been obtained in other avian passerine species such as the Black-throated Blue Warbler, in which lack of differentiation was attributed to similar phenomenon (Davis et al 2006). On the other hand, birds which were originated from two or more refugia (e.g., Yellow Warbler) showed clear genetic differentiation along an East/West axis (Boulet and Gibbs 2006).…”

“…In order to find this differentiation, it may be necessary to develop a high number of markers, which can be difficult and time consuming in the case of non-model species. Additionally, finding population structure can be problematic in cases where avian species originate from a recent expansion from a single refugium (e.g., Davis et al 2006).…”

“…Finding population differentiation with genetic markers could be a challenging task, as in many cases, it is necessary to develop high number of markers, which can be difficult and time consuming in the case of non-model species (as the White-throated Sparrow). Additionally, avian species that have originated from a single refugium and have recently separated or high levels of gene flow could present low levels of differentiation between populations {e.g., Davis et al 2006). …”