Douglas, Norman .
A nuclear phylogeny of Boerhavia (Nyctaginaceae) suggests that expansion of North American deserts has facilitated multiple recent range expansions from the Gulf of California region.
The Sonoran and Chihuahuan deserts only assumed their modern range and composition after the end of the last glacial period. The expansion and assembly of the modern desert flora has been documented by studies of fossil packrat middens. However, relatively few phylogenetic studies have centered on plants of this region; fewer have employed dense population-level sampling. Here I report on a phylogenetic analysis of the nuclear gene, nitrate reductase, across the genus Boerhavia. Boerhavia is found across warmer areas of the world, but previous analyses by the author have established that roughly sixteen species of annual taxa in North America form a clade. Within each of two subclades, there is evidence that some taxa are cohesive species; these possess diagnostic morphological features and are sympatric with their closest relatives. The remaining species in each subclade of annuals are taxonomically ill-defined and do not form cohesive groups with molecular data. In one subclade, Boerhavia xanti, which is endemic to coastal Sonora and the Baja California Peninsula, is ancestral to the cohesive Boerhavia wrightii, which is widespread from Baja California to the southern Chihuahuan Desert. In another annual clade, samples of 3-4 poorly defined morphospecies are interspersed in two clades, with no morphospecies forming a monophyletic group. In this case, samples from the Gulf of California region are placed in both subclades, but northern and eastern samples of the widespread species Boerhavia intermedia are only found in one subclade. This group is also paraphyletic with respect to three unique winged species which have restricted distributions. These patterns suggest that, although some species represent older divergences, areas adjoining the Gulf of California are 1) refugial areas for several now-widespread Boerhavia, and 2) a repository of genetic diversity in annual Boerhavia and the source of two recent, complex radiations of species.
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1 - Duke University, Department of Biology, 139 Biological Sciences Building, PO Box 90338, Durham, North Carolina, 27708, USA
nitrate reductase (NIA)
Low-copy Nuclear Markers.
Presentation Type: Oral Paper:Papers for Topics
Location: Lake Michigan/Hilton
Date: Tuesday, July 10th, 2007
Time: 2:30 PM