Abstract Detail



Biogeography

Lampley, Jayne [1].

Role of river watersheds on diversification and endemism in native plant species: A phylogeographic study of Trillium lancifolium (Melanthiaceae).

Pleistocene glaciation and river course changes have contributed to speciation in many groups of organisms by the fragmentation and isolation of formerly widespread species.  Historical drainage connections correlate with genetic structure and species diversity in stream-dwelling organisms such as salamanders and fishes.  However, little is known about the effects on plant species.  Several narrowly endemic Trillium species of the southeastern US are restricted to specific river watersheds.  The rivers themselves have been suggested as a possible driver of local endemism by acting as a barrier to gene flow.  The Thin Rhizome group within Trillium provides an excellent opportunity to investigate this observation.  This group of four species is united by morphology (reflexed sepals, incurved anther connectives, thin and brittle rhizomes), molecular evidence, and habitat preference (intermittent floodplains near creeks or rivers).  Trillium lancifolium is scattered discontinuously across multiple watersheds in TN, AL, FL, GA, and SC, whereas Trillium oostingii, of SC, and T. tennesseense, of TN are each narrow endemics of single watersheds.  The remaining species of the group, T. recurvatum, however, is much more widespread, inhabiting the watersheds of the Mississippi, Tennessee, and Ohio rivers.  Though Trillium is primarily dispersed by insects, could incidental hydrochory (propagule dispersal by rivers and streams) during periodic flooding events explain the species distributions in this group?  We tested the hypothesis that rivers and watersheds are both a barrier to gene flow and a means of downstream dispersal for these taxa.  Multiple populations from each of the 12 major watersheds of the southeastern US within the species distribution of Trillium lancifolium (Coosa, Ocmulgee, Alabama, Tombigbee, Savannah, Tennessee, Apalachicola, Chattahoochee, Tallapoosa, Cahaba, Black Warrior, and Conecuh) were sampled.  Additionally, representatives of the other three Trillium species were sampled.  Fixation indices (Φst) were calculated based on chloroplast DNA sequences to determine degree of genetic variation between populations.  A haplotype network was constructed to determine phylogeographic history at the intraspecific level to investigate patterns in the evolutionary relationships among populations of T. lancifolium along the separate river watersheds. The results of phylogenetic inference based on molecular evidence from chloroplast DNA of the Thin Rhizome group will also be presented.  Based on our evidence, we suggest that T. lancifolium may be a paraphyletic complex of multiple cryptic species in need of further taxonomic study.


1 - University Of Tennessee, EEB, 569 Dabney Hall, Knoxville, TN, 37996, United States

Keywords:
Trillium
Watershed
Phylogeography
Endemism
Speciation.

Presentation Type: Oral Paper
Number:
Abstract ID:197
Candidate for Awards:George R. Cooley Award


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