Over 2000 basepairs of mitochondrial DNA (mtDNA) sequences were compared to (1) examine evolution in protein coding versus noncoding [control region (CR)] segments, and (2) test the species-level distinctiveness of the California gnatcatcher (Polioptila californica) and clarify its phylogenetic and biogeographic relationships to other arid-adapted gnatcatchers. Unlike some studies, CR region I (left domain) was not as variable as coding genes. As expected, the central domain of the CR varied little, whereas CR II (right domain) showed high levels of variation. CR sequences tended to be "phylogenetically noisy" as evidenced by lower rescaled consistency indices, relative to those for coding genes. The California gnatcatcher differs from its sister-species, the black-tailed gnatcatcher (P. melanura), by approximately 4.0%, which supports species-level recognition. Two other aridland gnatcatchers, the black-capped gnatcatcher (P. nigriceps) and white-lored gnatcatcher (P. albiloris), are closely related to the previous two species, also at a level of about 4 to 4.5% sequence divergence. These species evolved over a relatively short time, but prior to the most recent Pleistocene glaciations.
Bibliographical noteFunding Information:
We thank SEDESOL for collecting permits and USFW and USDA for import permits. A grant (DEB-9317945) from the National Science Foundation is acknowledged. A. Navarro S. assisted with permits and localities and J. L. Atwood assisted with localities, tape recordings, and feather samples of California gnatcatchers. B. Hernandez-Baños assisted in several ways. We thank C. Tarr for some CR PCR primer sequences that were vital in our study. S. M. Russell suggested a collecting locality in Sonora, and we thank Sr. Porchas at ‘‘lo de Campa’’ for permission to collect. D. L. Dittmann prepared some purified mtDNAs. Field assistance was provided by G. F. Barrow-clough, A. J. Fry, O. Rojas S., J. T. Klicka, T. W. Chesser, S. W. Cardiff, and S. J. Weller. J. L. Atwood, A. J. Baker, R. C. Fleischer, S. B. Hedges, C. G. Sibley, M. Springer, and S. M. Lanyon made helpful suggestions during the preparation of the manuscript.