Barrett, Craig F. , Freudenstein, John .
Species delimitation, phylogeography, and identification of evolutionarily significant units in a rare but widespread North American mycoheterotrophic orchid, Corallorhiza striata (Orchidaceae: Epidendroideae).
Rangewide phylogeographic studies are important for informing taxonomic decisions and crafting conservation strategies, but are generally lacking for mycoheterotrophic plants. We employed floral morphometrics, nuclear DNA, and plastid DNA in a phylogeographic analysis of Corallorhiza striata, a North American mycoheterotroph distributed from Mexico to Canada. In a previous study, we detected four morpho-geographically associated plastid DNA clades based on rbcL psuedogene and rpl32-trnL spacer. However, the question remains whether nuclear and plastid loci display similar patterns of variation. Here we have doubled the number of individuals sampled (n = 155) and included nuclear intron sequences from F3H and RPB2 along with ITS to investigate patterns of variation in the C. striata complex across its geographic range. Plastid+nuclear DNA and morphology differentiated C. bentleyi+C. striata involuta from the remaining C. striata ( = C. striata sensu stricto). Corallorhiza striata involuta and C. bentleyi, disjunct by thousands of kilometers (Mexico-Appalachia), were genetically identical but morphologically distinct based on labellum characters. Also, three entities corresponding to the major plastid clades in C. striata s.s. were significantly differentiated. In light of these findings, the C. striata complex likely represents three species: C. bentleyi, C. involuta, and a widespread, variable C. striata s.s. Bayesian assignment tests within C. striata s.s. based on plastid+nuclear DNA indicated three clusters, corresponding to C. striata striata, C. striata vreelandii, and Californian accessions; a few individuals displayed admixed multilocus genotypes. Analysis of molecular variance indicated that the majority of variation in both nuclear and plastid DNA was explained among these clusters. Coalescent analysis indicated very low levels of nuclear gene flow among the three clusters. Therefore each of these clusters comprises an evolutionarily significant unit, based on both morphology and DNA sequences from two genomes. Results of coalescent divergence time estimates and Approximate Bayesian Computation, testing various plausible population-historical scenarios for C. striata s.s., are discussed in light of the population histories of codistributed species (e.g. Pseudotsuga).
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1 - Ohio State University, Department of Evolution, Ecology, and Organismal Biology, OSU Herbarium (OS), Museum of Biological Diversity, 1315 Kinnear Rd., Columbus, Ohio, 43212, USA
2 - Ohio State University, Department of Evolution, Ecology and Organismal Biology, Museum of Biological Diversity, 1315 Kinnear Rd., Columbus, Ohio, 43212, USA
Presentation Type: Oral Paper:Papers for Topics
Location: 552B/Convention Center
Date: Tuesday, August 3rd, 2010
Time: 9:00 AM