More twists and turns in this story:
Interpreting negative results with taxonomic and conservation implications: Another look at the distinctness of coastal California Gnatcatchers
John E. McCormack* and James M. Maley
abstract
A recent study by Zink et al. (2013) raises questions about how to interpret negative results in studies when the distinctness of a species of conservation concern is in question. Zink et al. found no evidence for genetic or ecological distinctness of the coastal California Gnatcatcher (Polioptila californica californica). We discuss why the genetic markers they chose were not well suited to the question of distinctness and how they overinterpreted negative results in their genetic and ecological analyses. We reanalyze their genetic data and find evidence that several genetic loci show significant differentiation in the coastal California Gnatcatchers. We provide recommendations for best practices in determining distinctness in phenotype, genetics, and ecology for California Gnatcatchers and other populations of conservation concern.
link (need access?)
http://www.aoucospubs.org/doi/full/10.1642/AUK-14-184.1
Zink et al 2013:
Zink, R. M., J. G. Groth, H. Vázquez-Miranda, and G. F. Barrowclough (2013). Phylogeography of the California Gnatcatcher (Polioptila californica) using multilocus DNA sequences and ecological niche modeling: Implications for conservation. The Auk 130:449–458.
pdf (need access? )
http://www.aoucospubs.org/doi/pdf/10.1525/auk.2013.12241
abstract:
An important step in conservation is to identify whether threatened populations are evolutionarily discrete and significant to the species. A prior mitochondrial DNA (mtDNA) phylogeographic study of the California Gnatcatcher (Polioptila californica) revealed no geographic structure and, thus, did not support the subspecies validity of the threatened coastal California Gnatcatcher (P. c. californica). The U.S. Fish and Wildlife Service concluded that mtDNA data alone were insufficient to test subspecies taxonomy. We sequenced eight nuclear loci to search for historically discrete groupings that might have been missed by the mtDNA study (which we confirmed with new ND2 sequences). Phylogenetic analyses of the nuclear loci revealed no historically significant groupings and a low level of divergence (G ST = 0.013). Sequence data suggested an older population increase in southern populations, consistent with niche modeling that suggested a northward range expansion following the Last Glacial Maximum (LGM). The signal of population increase was most evident in the mtDNA data, revealing the importance of including loci with short coalescence times. The threatened subspecies inhabits the distinctive Coastal Sage Scrub ecosystem, which might indicate ecological differentiation, but a test of niche divergence was insignificant. The best available genetic, morphological, and ecological data indicate a southward population displacement during the LGM followed by northward range expansion, without the occurrence of significant isolating barriers having led to the existence of evolutionarily discrete subspecies or distinct population segments that would qualify as listable units under the Endangered Species Act.
Interpreting negative results with taxonomic and conservation implications: Another look at the distinctness of coastal California Gnatcatchers
John E. McCormack* and James M. Maley
abstract
A recent study by Zink et al. (2013) raises questions about how to interpret negative results in studies when the distinctness of a species of conservation concern is in question. Zink et al. found no evidence for genetic or ecological distinctness of the coastal California Gnatcatcher (Polioptila californica californica). We discuss why the genetic markers they chose were not well suited to the question of distinctness and how they overinterpreted negative results in their genetic and ecological analyses. We reanalyze their genetic data and find evidence that several genetic loci show significant differentiation in the coastal California Gnatcatchers. We provide recommendations for best practices in determining distinctness in phenotype, genetics, and ecology for California Gnatcatchers and other populations of conservation concern.
link (need access?)
http://www.aoucospubs.org/doi/full/10.1642/AUK-14-184.1
Zink et al 2013:
Zink, R. M., J. G. Groth, H. Vázquez-Miranda, and G. F. Barrowclough (2013). Phylogeography of the California Gnatcatcher (Polioptila californica) using multilocus DNA sequences and ecological niche modeling: Implications for conservation. The Auk 130:449–458.
pdf (need access? )
http://www.aoucospubs.org/doi/pdf/10.1525/auk.2013.12241
abstract:
An important step in conservation is to identify whether threatened populations are evolutionarily discrete and significant to the species. A prior mitochondrial DNA (mtDNA) phylogeographic study of the California Gnatcatcher (Polioptila californica) revealed no geographic structure and, thus, did not support the subspecies validity of the threatened coastal California Gnatcatcher (P. c. californica). The U.S. Fish and Wildlife Service concluded that mtDNA data alone were insufficient to test subspecies taxonomy. We sequenced eight nuclear loci to search for historically discrete groupings that might have been missed by the mtDNA study (which we confirmed with new ND2 sequences). Phylogenetic analyses of the nuclear loci revealed no historically significant groupings and a low level of divergence (G ST = 0.013). Sequence data suggested an older population increase in southern populations, consistent with niche modeling that suggested a northward range expansion following the Last Glacial Maximum (LGM). The signal of population increase was most evident in the mtDNA data, revealing the importance of including loci with short coalescence times. The threatened subspecies inhabits the distinctive Coastal Sage Scrub ecosystem, which might indicate ecological differentiation, but a test of niche divergence was insignificant. The best available genetic, morphological, and ecological data indicate a southward population displacement during the LGM followed by northward range expansion, without the occurrence of significant isolating barriers having led to the existence of evolutionarily discrete subspecies or distinct population segments that would qualify as listable units under the Endangered Species Act.
