Abstract
The North American red‐shouldered hawk, Buteo lineatus, is comprised of two widely allopatric eastern and western populations with an additional well‐marked subspecies in the Florida peninsula. The two eastern populations meet in northern Florida, the location of a well‐known suture zone in many nonavian organisms. We sequenced the complete mitochondrial ND2 gene and two nuclear introns to investigate its genetic population structure and species status. No mitochondrial haplotypes were shared between the eastern and western populations, and genetic variance among 14 populations was 0.42; almost all of this (0.40) was distributed among the three regions. A clade of haplotypes very common in the Florida peninsula decreased in frequency elsewhere and, when modeled as a hybrid zone, had an estimated width of 1,158 km with a center near Ocala, FL. Ecological niche modeling suggests the western, eastern, and Florida peninsula populations were geographically isolated during the last glacial maximum. We consider these to represent three phylogenetic species. A coalescent analysis incorporating incomplete lineage sorting and gene tree uncertainty also suggested the divergence between the western and eastern populations is consistent with species‐level divergence. With the addition of this hawk, four avian species are now known to hybridize along the Gulf Coast of the United States in or near the Northern Florida Suture Zone. The widths of these avian zones vary substantially (176–1,158 km) and appear to reflect magnitude of gene flow, rather than extent of genetic differentiation. None of these birds was suggested as possible exemplars in the original description of the suture zone. Of the six species that were so identified, three have been surveyed to date, but none of those was found to be genetically differentiated.
Highlights
Generally congruent patterns are evident in the postglacial biogeography of Western Europe (Hewitt, 2000), this is less true of North America, in birds (Zink, 1997)
One general result in eastern North America, though, has been the re‐ peated discovery of genetic differentiation across Gulf Coast river systems and the Appalachian Mountain chain in many disparate taxa, including plants, invertebrates, and both aquatic and terrestrial ver‐ tebrates (Avise, 2000; Soltis, Morris, McLachlan, Manos, & Soltis, 2006). These genetic divisions are proximal to Remington's (1968) Northern Florida Suture Zone, a proposed region of postglacial pop‐ ulation convergence and interaction following dramatic landscape alteration during the Pleistocene (Emslie, 1998)
We attempted to obtain tissue samples of Buteo lineatus from through‐ out its known breeding range (Figure 1); all samples came from speci‐ mens cataloged in natural history museums, but many originally came from raptor rehabilitation centers
Summary
Generally congruent patterns are evident in the postglacial biogeography of Western Europe (Hewitt, 2000), this is less true of North America, in birds (Zink, 1997). One general result in eastern North America, though, has been the re‐ peated discovery of genetic differentiation across Gulf Coast river systems and the Appalachian Mountain chain in many disparate taxa, including plants, invertebrates, and both aquatic and terrestrial ver‐ tebrates (Avise, 2000; Soltis, Morris, McLachlan, Manos, & Soltis, 2006) These genetic divisions are proximal to Remington's (1968) Northern Florida Suture Zone, a proposed region of postglacial pop‐ ulation convergence and interaction following dramatic landscape alteration during the Pleistocene (Emslie, 1998). The red‐shouldered hawk is a generally common, sit‐and‐wait predator, especially associated with swamp and riparian habitats (Crocoll, 1994), with disjunct populations in eastern and western North America (Figure 1) In the east, it ranges from Maine and the Canadian Maritimes south to the Florida Keys and west to Minnesota and south‐ ern Texas; in the western United States.
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