The evolution and phylogeography of a glade-restricted species of prairie clover (Dalea cahaba J. Allison) from Bibb County, Alabama: A molecular approach.

摘要

The Cahaba prairie clover (Dalea cahaba) is one of eight species endemic to the dolomitic glades of Bibb County, Alabama. The evolutionary history of this species is currently unknown. This study tests the hypothesis that the species is a result of adaptive radiation from a widespread congener. The phylogenetic histories of several eastern species of Dalea are reconstructed using two genes that have previously been informative in plant molecular systematic studies: the internal transcribed spacer (ITS) and the matK gene. Morphological similarities between D. cahaba and a Texas-endemic species, D. tenuis, have prompted questions of whether similar traits imply common descent or are the result of convergent evolution, as well as questions about which characteristics are ancestral and whether species occurrences of modern traits contain useful phylogenetic signal. Samples of tissue from the Texas endemics were collected and their ITS and matK genes sequenced, and compared with those of the eastern species. Ancestral flower color, calyx vestiture, and habitat preference were estimated across the deep nodes of the phylogeny, and the phylogenetic signal of each trait was calculated to determine whether the phylogeny is useful in explaining the distribution of trait characters across the tips of the tree. Community dynamics of the glades were also investigated, controlling for glade identity, edge effects, season of year, and taxonomic distribution of species. It was found that D. cahaba and D. tenuis share common descent. Flower color and habitat preference were found to be useful in predicting ancestral characters in the deep phylogeny, while calyx vestiture was not. Calyx vestiture and habitat preference exhibited phylogenetic signal, and flower color did not. Community analysis showed that there were significant differences between the overall species assemblages in the core group of glades and the outlying glade (R=0.311, p<0.001) and in their communities of rare, endemic, and disjunct species (R=0.374, p<0.001). In the endemic and rare plant community, the species most responsible for the difference between groups were Amsonia ciliata var. tenuifolia (19.89% contribution to the sampled core glades, 39A, 39B, 41A, and 41B) and Rudbeckia triloba var. pinnatiloba (26.84% contribution to outlier glade 57).