Systematics/Phytogeography / Taxonomie/ Section
Specht, Chelsea , Gomez Navarro, Carolina , Driscoll, Heather , Handley, Vanessa .
Phylogeny and clues to population structure in Mexican species of Dioon (Zamiaceae; Cycadales).
As ‘living fossils,’ cycads represent an ancestral form of seed-bearing plants, yet little is known about how historic diversity is represented in extant populations. Cycad fossils appear in the late Pennsylvanian (Carboniferous) around 300 MYA and are thought to represent the oldest living lineage of seed plants as well as the first example of insect pollination in the fossil record. While Mesozoic forests of the late Cretaceous were dominated by cycads, the order currently contains only 250 species in 10 genera. We present here our latest contribution to understanding the evolution of the cycads, focusing on the phylogeny and population structure within the genus Dioon. Most species of Dioon are found in dry, rocky habitats ranging from sea level to 2100 m. All species with the exception of D. mejiae (Honduras) are restricted to the two major coastal mountain chains of Mexico. Many species are localized in their distributions to either the Sierra Madre Occidental or the Sierra Madre Oriental, with the greatest number of species found at the convergence of the two mountain chains in northern Oaxaca & southern Puebla. Initial studies demonstrated a need for rapidly-evolving markers in order to fully elucidate phylogenetic structure. Lack of variable and informative characters from chloroplast intron and ITS sequence data, particularly among species found in the central Mexican center of diversity, suggest either recent diversification or remarkably slow rates of molecular evolution. Phylogenetic results using new and recently published chloroplast and nuclear molecular markers will be presented. Species-level relationships will be discussed and compared with previous phylogenetic results based on both molecular and morphological data, and ages of diversification using estimated branch lengths and well-documented fossil calibration points will be correlated with climatologic and geographic events to determine the potential role of historic and modern geography in speciation and diversification.
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1 - University of California, Berkeley, Plant and Microbial Biology, 111 Koshland Hall MC 3102, Berkeley, California, 94720-3102, USA
2 - University of California, Berkeley, Plant and Microbial Biology, 111 Koshland Hall MC 3102, Berkeley, CA, 94720-3102, USA
3 - Holy Names University, Biological Sciences, 3500 Mountain Blvd., Oakland, CA, 94619, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Room 6/Woodward
Date: Tuesday, July 29th, 2008
Time: 10:15 AM