Abstract Detail


Thixton, Hana [1], Santee , Mathilda Viola [1], Freudenstein, John [2], Barrett, Craig [1].

Phylogeography and fungal host specificity in the Corallorhiza maculata species complex.

Mycoheterotrophic plants utilize fungi for most or all their nutritional needs and represent a compelling model system for analyzing the ecological and evolutionary consequences of plant-fungal host associations. The Corallorhiza maculata complex is one of the most widespread, fully mycoheterotrophic orchids in North America and parasitizes a single basidiomycete family, Russulaceae. This complex contains C. mertensiana, C. maculata var. maculata, C. maculata var. occidentalis, C. bulbosa, C. maculata var. mexicana, and C. macrantha. The species vary in flowering time, floral morphology, geographic distribution, and fungal associations.  Previous studies have identified patterns of host specificity based on limited sampling and ITS-RFLP profiling, with at least 22 putative species of fungal hosts identified. Complete plastid genome sequences provide robust branch support for relationships within the complex and reveal a single loss of photosynthesis shared by C. mertensiana, C. maculata vars. maculata and occidentalis. However, phylogeographic patterns of variation and the full extent of fungal host diversity across the broad geographic range of this complex are poorly understood. To address these gaps in knowledge, we have sequenced the plant and fungal nuclear Internal Transcribed Spacer (ITS) regions and three plastid loci (ndhA, ndhC-tRNA-V, psbK-I) from 101 samples across the complex, spanning most of North America. We further tested eight microsatellite primers to characterize population structure and quantify gene flow within the complex. Preliminary results of plant nuclear ITS and plastid DNA reveal three principal clades: 1. Mexican taxa (C. macrantha, C. bulbosa, and C. maculata v. mexicana), 2. C. mertensiana, and 3. C maculata vars. maculata and occidentalis within which three subclades primarily grouped by geography. Microsatellite amplifications were successful in all the taxa for five of the eight loci. Fungal ITS sequencing identified 20 putative species using BLAST, with a similar pattern as the plant phylogenetic tree, however fungal associates of C. maculata vars. maculata and occidentalis grouped in several clades but are largely clustered by taxon and geography and Thelephoraceae (Basidiomycota) being the fungal associate for four individuals from the Mexican taxa.  This study expands what is currently known of plant nuclear and plastid loci, revealing uncertainty in relationships among the currently described taxa and fungal ITS results reveal complex patterns of host specificity. In order to address patterns of genomic variation across the geographic range, the next step will be to identify population structure, gene flow, and adaptive polymorphisms to evaluate the evolutionary basis of host specificity in the complex.

1 - West Virginia University, Biology, 53 Campus Drive, Morgantown, WV, 26506, United States
2 - Ohio State University, Evolution, Ecology, and Organismal Biology, 1315 Kinnear Road, Columbus, OH, 43212, United States


Presentation Type: Poster
Session: P, Systematics Posters
Location: Virtual/Virtual
Date: Thursday, July 30th, 2020
Time: 5:00 PM Time and date to be determined
Number: PSY017
Abstract ID:607
Candidate for Awards:None

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