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ARS Home » Pacific West Area » Logan, Utah » Forage and Range Research » Research » Publications at this Location » Publication #218949
Title: Species Delimitation Tests of Endemic Lepidium Papilliferum and Identification of other Possible Evolutionarily Significant Units (ESUs) in the Lepidium Montanum Complex (Brassicaceae) of Western North America

Author
item Larson, Steven
item CULUMBER, C - UTAH STATE UNIVERSITY
item SCHWEIGERT, ROBERT - INTERMOUNTAIN RANGE CON
item CHATTERTON, N - USDA-ARS (RETIRED)

Submitted to: Conservation Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/29/2009
Publication Date: 11/4/2009
Citation: Larson, S.R., Culumber, C.M., Schweigert, R.N., Chatterton, N.J. 2009. Species Delimitation Tests of Endemic Lepidium Papilliferum and Identification of other Possible Evolutionarily Significant Units (ESUs) in the Lepidium Montanum Complex (Brassicaceae) of Western North America. Conservation Genetics. 11:57-76.

Interpretive Summary: Slickspot pepperwort of southwest Idaho has been considered for possible listing as an Endangered Species since 1990. Slickspot pepperwort was originally described as Lepidium montanum var. papilliferum, but later elevated to L. papilliferum based on descriptions of distinctive growth habit, short lifespan, and unusual pubescence but no genetic comparisons were conducted until now. In this study, we used DNA sequences and profiles to test species delimitations and identify other possible evolutionarily significant units (ESU) based on patterns of genetic differentiation, genetic isolation by geographic distance (IBD), and genetic admixture among 32 L. montanum and 21 slickspot pepperwort collections from the western U.S. The slickspot pepperwort DNA profiles were similar and suport genetic group. However, the DNA profiles of L. montanum samples from eight western sites showed relatively close genetic relationship or possible hybridization with slickspot pepperwort, which forms the basis of a regionally significant group (West group) that shows significant differentiation from eastern L. montanum collections (East group). Neither taxa nor regionally significant groups distinct evolutionary lineages of DNA sequence, but the East and West groups showed stronger slightly greater DNA differentiation compared to differences between taxa. The East and West groups fit models of speciation with relatively strong IBD within groups and weak IBD between groups, based on correlations between genetic and geographic distances among collection sites, but comparisons between taxa did not fit this model. Conversely, relatively strong partial correlations between genetic and taxonomic differences, controlling for geography, support taxonomic delimitations. Results suggest that slickspot pepperwort is a distinct subgroup of L. montanum influenced by speciation. However, gene flow or common ancestry between slickspot pepperwort and western forms of L. montanum provide a basis for other possible ESUs.

Technical Abstract: Lepidium papilliferum of southwest Idaho was previously treated as an infraspecific variety of Lepidium montanum. Chloroplast (cpDNA) sequences, nuclear ribosomal internal transcribed spacer (ITS) sequences, and AFLPs were used to test species delimitations and other possible evolutionarily significant units (ESU) based on genetic differentiation, isolated by distance (IBD), and genetic admixture among 32 L. montanum and 21 L. papilliferum collections from the western U.S. The L. papilliferum AFLP genotypes formed a monophyletic clade. However, the AFLP genotypes of L. montanum samples from eight western sites were more similar to L. papilliferum, which together comprise a regionally significant West clade showing significant differentiation from eastern L. montanum collections (East clade). Bayesian analysis of AFLP genotypes detected possible admixture between L. papilliferum and related western L. montanum collections. Neither taxa nor regionally significant AFLP clades displayed reciprocally monophyletic cpDNA or ITS sequences, but the AFLP clades showed stronger cpDNA differentiation and unique ITS alleles. The East and West clades fit models of speciation with relatively strong IBD within groups and weak IBD between groups, based on correlations between the average number of AFLP differences and geographic distances among collection sites, but comparisons between taxa did not fit this model. Conversely, relatively strong partial correlations between AFLP and taxonomic differences, controlling for geography, support taxonomic delimitations. Results suggest that L. papilliferum is a distinct subgroup of L. montanum influenced by speciation. However, gene flow or common ancestry between L. papilliferum and western forms of L. montanum provide a basis for other possible ESUs.