Speciation and Geographic Variation in Black-Tailed Gnatcatchers

Abstract

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Molecular Systematics and Biogeography of Aridland Gnatcatchers (GenusPolioptila) and Evidence Supporting Species Status of the California Gnatcatcher (Polioptila californica)

“…The aridland gnatcatchers are each morphologically (Hubbard, 1973), vocally (Atwood, 1988), and genetically distinct, with sequence divergence values of 4.0 to 4.8%; these are typical values for avian congeneric comparisons (Baker and Marshall, 1997;Hackett, 1996). However, morphological differentiation is not extensive, and species limits were clear only after careful analysis of vocalizations (Atwood, 1988). No explicit phylogenetic analysis has used morphological or vocal characters to infer species relationships.…”

“…Morphological evidence favors a sister-species relationship for black-tailed gnatcatcher and California gnatcatcher, two species previously considered conspecific and which likely hybridize in Baja California (Atwood, 1988). White-lored gnatcatcher and blackcapped gnatcatcher were considered conspecific in some previous taxonomies and they share a 12-base insert in the CR, which we counted as a single synapomorphy.…”

“…The genetic distinctness of the California gnatcatcher is important for conservation (Atwood, 1993). Prior to Atwood's (1988) study, the California gnatcatcher was considered a subspecies of the black-tailed gnatcatcher (P. melanura). Our data confirm that the California gnatcatcher should be evaluated as a threatened species in the coastal sage scrub community in California and northwestern Baja California, where habitat loss is a major concern (Atwood, 1993).…”

“…1) suggested to Hubbard (1973) a series of speciation events coincident with late Pleistocene glacial cycles (e.g., Wisconsinian). Atwood (1988) studied morphological and vocal characters and concluded that the California gnatcatcher merited species status (it was once considered a subspecies of P. melanura) and that it was the sister-species of the black-tailed gnatcatcher. We used mtDNA sequence information to test the species-level distinctiveness of the California gnatcatcher, to determine its sister species, and to test the biogeographic hypothesis suggested by Hubbard (1973).…”

“…We used mtDNA sequence information to test the species-level distinctiveness of the California gnatcatcher, to determine its sister species, and to test the biogeographic hypothesis suggested by Hubbard (1973). Because of the apparent recency of the origin of these species (Hubbard, 1973;Atwood, 1988), we sequenced segments of protein coding (ND2, ND6, and Cyt b) and noncoding mtDNA (tGlu, CR). Thus, our study tests for rapid evolution of mtDNA CR sequences and evaluates previous taxonomic and biogeographic hypotheses.…”