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Abstract Detail

Systematics Section/ASPT

Nicolas, Antoine [1], Heenan, Peter [2], Plunkett, Gregory [3].

Allopolyploidy, Concerted Evolution, and Biogeography: Inferences from Phylogenies of Azorella (Azorelloideae, Apiaceae) and Related Genera.

The Azorella group comprises the largest of three major clades of subfamily Azorelloideae (Apiaceae). The group includes six genera (Azorella, Laretia, Schizeilema, Mulinum, Huanaca, and Stilbocarpa) with Austral-Antarctic affinities and a geographic distribution that extends from Oceania to the páramos of Central and South America. We sampled all recognized species and reconstructed phylogenetic trees based on multiple plastid and nuclear markers. Stilbocarpa, which includes three megaherb species in the Subantarctics, appears to be the only monophyletic genus in the group. In light of knowledge from chromosome counts, incongruence between trees resulting from nuclear and plastid markers revealed evidence of reticulate evolution, mostly due to multiple polyploid events in different clades in the group. Many of these events were most likely caused by hybridization among ancestral species, leading to the origin of multiple allopolyploid taxa, but backcrossing and hybridization still appear to occur among some extant species. In addition, we observed cases where concerted evolution led to the fixation of different copies of the same nuclear regions in the same allopolyploid species, which is an evidence of concerted evolution occurring at a slower rate than speciation. The highest ploidal levels in the group are found in the Oceanian species of Schizeilema, with chromosome numbers from 2n = 32 to 2n = 80 (compared to 2n = 16 in diploid species). An allopolyploid origin in Schizeilema appears to have involved ancestral species that hybridized and dispersed in southern South America, the Subantarctics, and Oceania. This was followed by rapid speciation in New Zealand (c. 13 species) during the Late Pleiocene-Early Pleistocene, involving multiple hybridization events. Such events were facilitated by a glaciation cycles that may have caused contraction of species ranges and subsequent isolation in fragmented refugia, followed by range expansions during warmer interglacial periods, resulting in species with overlapping ranges.

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1 - New York Botanical Garden, Cullman Program For Molecular Systematics, 2900 Sothern Blvd., Bronx, NY, 10458-5126, USA
2 - Landcare Research , Allan Herbarium, Lincoln, New Zealand
3 - New York Botanical Garden, Cullman Program For Molecular Systematics, 2900 Southern Blvd., Bronx, NY, 10458-5126, USA


Presentation Type: Oral Paper:Papers for Sections
Session: 45
Location: Delaware D/Hyatt
Date: Wednesday, July 11th, 2012
Time: 11:30 AM
Number: 45014
Abstract ID:943

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