Drummond , Chloe , Bruenn, Riva , Joffe, Jonah , Mostow, Rebecca , Stalberg, Gabriel , Brockington, Samuel , Douglas, Norman , Ochoterena Booth, Helga , Flores Olvera, Hilda , Moore, Michael .
The age and origins of arid adaptations and gypsum endemism in Nyctaginaceae inferred using relaxed molecular dating.
Islands of exposed gypsum are scattered throughout the Chihuahuan Desert region of northern Mexico and the southwestern US. Although gypsum forms a hard crust and is generally low in nutrients, many plant species have adapted to grow on this substrate, with some fully restricted to it. Morphological, phylogenetic, and biogeographic evidence suggest that clades of gypsum endemics exist, and that some of these groups may have originated as early as the late Miocene. If true, these endemics must have persisted throughout the Pleistocene full-glacial periods, when the Chihuahuan Desert was largely replaced by grassland and savanna. The flowering plant family Nyctaginaceae is unusually rich in gypsum endemics, with 10 species in four genera in the family restricted to gypsum in the Chihuahuan Desert. In two of these genera, Anulocaulis and Acleisanthes, morphologically distinct and geographically widespread clades of multiple gypsum endemic species have evolved. In contrast, gypsum endemic taxa in the genera Abronia and Mirabilis are narrowly distributed and morphologically similar to taxa that grow off of gypsum. To determine whether gypsum endemism evolved within Nyctaginaceae before the Pleistocene, and to determine if gypsum endemism originated simultaneously in all lineages, we undertook molecular dating analyses of Caryophyllales. Because nyctages lack a reliable fossil record, broad taxon sampling of Caryophyllales is necessary for incorporating reasonable fossil calibration points. Consequently, we sequenced portions of the three most rapidly evolving plastid genes (matK, ndhF, and ycf1) for over 150 species of Caryophyllales, including nearly all families, with densest taxon sampling in the core Caryophyllales, particularly Phytolaccaceae and Nyctaginaceae. Phylogenetic analyses suggest that gypsum endemism within Nyctaginaceae evolved at least 4 times. BEAST UCLN and r8s penalized likelihood analyses suggest that the localized endemic taxa within Mirabilis and Abronia appeared in the Pleistocene, and that the gypsum endemic clades in Anulocaulis and Acleisanthes originated and began diversifying in either the Pliocene (BEAST) or Pleistocene (r8s). Diversification of the arid-adapted lineages of Nyctaginaceae began in the Oligocene or Miocene, which was concurrent with the onset of a drier climate in southwestern North America in the Oligocene/Miocene. A sharp increase in diversification within these lineages was found beginning in the late Miocene.
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Phylogenetics and phylogeography of Chihuahuan Desert gypsum endemics
1 - Oberlin College, Department of Biology, 119 Woodland St., Oberlin, OH, 44074, United States
2 - Pennsylvania State University, Department of Biology, 403 Life Sciences, University Park, PA, 16802, United States
3 - Department Of Plant Science, Downing Site, Cambridge, N/A, CB23AE, United Kingdom
4 - Oberlin College, Department of Biology, 119 Woodland St., Oberlin, OH, 44074, USA
5 - Universidad Nacional Autónoma de México, Instituto de Biología, Apartado Postal 70-233, México, DF, 04510, Mexico
Presentation Type: Poster:Posters for Sections
Location: Battelle South/Convention Center
Date: Monday, July 9th, 2012
Time: 5:30 PM