Abstract
BackgroundThe Mormon Metalmark (Apodemia mormo) species complex occurs as isolated and phenotypically variable colonies in dryland areas across western North America. Lange’s Metalmark, A. m. langei, one of the 17 subspecies taxonomically recognized in the complex, is federally listed under the U.S. Endangered Species Act of 1973. Metalmark taxa have traditionally been described based on phenotypic and ecological characteristics, and it is unknown how well this nomenclature reflects their genetic and evolutionary distinctiveness. Genetic variation in six microsatellite loci and mitochondrial cytochrome oxidase subunit I sequence was used to assess the population structure of the A. mormo species complex across 69 localities, and to evaluate A. m. langei’s qualifications as an Evolutionarily Significant Unit.ResultsWe discovered substantial genetic divergence within the species complex, especially across the Continental Divide, with population genetic structure corresponding more closely with geographic proximity and local isolation than with taxonomic divisions originally based on wing color and pattern characters. Lange’s Metalmark was as genetically divergent as several other locally isolated populations in California, and even the unique phenotype that warranted subspecific and conservation status is reminiscent of the morphological variation found in some other populations.ConclusionsThis study is the first genetic treatment of the A. mormo complex across western North America and potentially provides a foundation for reassessing the taxonomy of the group. Furthermore, these results illustrate the utility of molecular markers to aid in demarcation of biological units below the species level. From a conservation point of view, Apodemia mormo langei’s diagnostic taxonomic characteristics may, by themselves, not support its evolutionary significance, which has implications for its formal listing as an Endangered Species.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0354-9) contains supplementary material, which is available to authorized users.
Highlights
The Mormon Metalmark (Apodemia mormo) species complex occurs as isolated and phenotypically variable colonies in dryland areas across western North America
This study is the first genetic treatment of the A. mormo complex across western North America and potentially provides a foundation for reassessing the taxonomy of the group. These results illustrate the utility of molecular markers to aid in demarcation of biological units below the species level
Integrative origins [1,16] that were criticized for their subjectivity [22], various redefinitions of the ESU have focused on more objective methods for discriminating populations that have evolutionary potential, such as: 1) the use of consistently congruent gene phylogenies [19], 2) reciprocal monophyly of mitochondrial DNA or allele frequency divergence at nuclear loci [2], and 3) diagnostic characters that exclusively cluster individuals or populations using the phylogenetic species concept [4]
Summary
The Mormon Metalmark (Apodemia mormo) species complex occurs as isolated and phenotypically variable colonies in dryland areas across western North America. Global loss of biodiversity, fueled by unprecedented anthropogenic influences, has elevated the importance of conservation biology in mainstream public consciousness. (or Evolutionary) Significant Units (ESUs) were originally developed to facilitate objective prioritization of conservation units (CUs) below the species level [16]. Integrative origins [1,16] that were criticized for their subjectivity [22], various redefinitions of the ESU have focused on more objective methods for discriminating populations that have evolutionary potential, such as: 1) the use of consistently congruent gene phylogenies [19], 2) reciprocal monophyly of mitochondrial DNA (mtDNA) or allele frequency divergence at nuclear loci [2], and 3) diagnostic characters (including ecological, behavioral, etc.) that exclusively cluster individuals or populations using the phylogenetic species concept [4]. These redefinitions met criticism focused on inconsistent phylogenetic reconstruction [23], the stringency of reciprocal monophyly and diagnostic characters [6,7], and the utility of the phylogenetic species concept [3]
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