Systematics/Phytogeography / Taxonomie/ Section
Kephart, Susan , Fishbein, Mark , Gross, Briana , Halpin, Kate .
Ecological and evolutionary divergence in Camassia (Agavaceae): linking field and molecular studies to patterns of speciation.
Speciation often occurs in response to ecological factors but is not always accompanied by discernable morphological differentiation. Camassia Lindl. (Agavaceae) provides an exemplary taxon in which to compare ecogeographically and morphologically distinct assemblages that appear to be in various stages of evolutionary divergence from incipient speciation to complete isolation and secondary hybridization. Taxonomic delimitation has been hampered by reliance on inconstant traits and insufficient study of ecological, genetic, and morphological differences among populations. We analyze population-level ecological, morphological, and molecular variation of the North American species and subspecies of Camassia, whose greatest diversity lies in the Pacific Northwest. Previous study revealed significant differences in habitat, flowering time, allozyme patterns, and morphology between the two most common western species and between the two eastern North American species. We extend this analysis to western populations occurring from east of the Cascade mountains to Montana and Utah, north to British Columbia, and south to the Sierra Nevada. In addition to investigating character variation in glasshouse-grown species, we sampled 15-25 individuals, measuring 21 traits in over 30 natural populations, for which we obtained DNA sequence and allozyme data. Congruent morphological, molecular, and ecological data strongly support genetic differentiation of C. quamash and C. leichtlinii and give modest support thus far for delineation of three to four western species. The first molecular phylogeny of the genus, based on cpDNA variation in the trnD-trnT region, reveals strong bootstrap support for three clades: 1) C. howellii, a rare southwest Oregon endemic, 2) northern and southern populations of western great camas, C. leichtlinii and 3) a large, partially unresolved clade consisting of the remaining western species (C. quamash, C. cusickii) and their two disjunct relatives, C. scilloides and C. angusta. Molecular analysis of this polyphyletic clade further suggests phylogeographic differentiation between populations east and west of the Cascades.
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1 - Willamette University, Department of Biology, 900 State Street, Salem, Oregon, 97301, USA
2 - Portland State University, Biology Department, Po Box 751, Portland, Oregon, 97207-0751, USA
3 - Washington University, Dept of Biology, 1 Brookings Drive, Campus Box 1137, St. Louis, MO, 63130, USA
4 - Portland State University, Biology, Po Box 751, Portland, Oregon, 97207, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, July 29th, 2008
Time: 9:15 AM