Systematics Section / ASPT
Jakob, Sabine S. , Blattner, Frank R. .
Combining phylogeography with ecological niche modeling reveals speciation mechanisms within Mediterranean Hordeum marinum (Poaceae).
HORDEUM marinum Huds. is an annual grass of Eurasian origin, occurring in saline meadows or marshes along the coast lines or in inland habitats. The species consists of two morphologically clear, distinguishable subspecies, the diploid subsp. marinum and subsp. gussoneanum with a di- and a tetraploid cytotype. These two cytotypes are morphologically undistinguishable but show alternative ecological preferences. Of special interest are the conflicting nuclear and chloroplast phylogenies of this species, indicating a monophyletic (nuclear) or a polyphyletic (chloroplast) status of the two subspecies. Using chloroplast sequences of the trnL-F region, chloroplast microsatellite fragment length variation, and ecological niche models we uncovered reasons for this inconsistency and reconstructed the phylogeography of H. marinum. The combined data displayed that a common ancestor of the subspecies was distributed throughout the Mediterranean and became divided about 2 million years ago. The subspecies originated allopatrically and were subjected to different phylogeographical histories. For subsp. gussoneanum we postulate an ice age refuge in the Eastern Mediterranean, probably in Turkey or Greece. Here originated also the tetraploid cytotype. Repeated range contractions caused a decrease in chloroplast diversity resulting in single chloroplast haplotypes per cytotype. Subspecies marinum originated during the ice ages in the Western Mediterranean. Here we uncovered a clear subdivision between populations from the Iberian Peninsula and the remaining Mediterranean, indicating that a former population was divided and the two subpopulations evolved independently. The extant sympatric occurrence of subsp. marinum and the diploid subsp. gussoneanum in the Mediterranean region is interpreted as a result of secondary contact.[c.e.:srb]
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1 - IPK Gatersleben, Taxonomy & Evol. Biology, Gatersleben, D-06466, Germany
Presentation Type: Poster:Posters for Sections
Location: Auditorium/Bell Memorial Union
Date: Tuesday, August 1st, 2006
Time: 12:30 PM