Systematics/Phytogeography / Taxonomie/ Section
Gruenstaeudl, Michael , Park, Seon-Joo , Santos-Guerra, Arnoldo , Jansen, Robert K. .
Phylogenetic relationships in Tolpis (Asteraceae) and the utility of ETS sequence variation despite incomplete rDNA homogenization.
The small genus Tolpis (Asteraceae) has proven phylogenetically challenging. Native to all the major Macaronesian archipelagos (Azores, Canary Islands, Cap Verde and Madeira), its 15 insular species inhabit distinct ecological zones. Allopatry, high degrees of morphological plasticity and variability in life history suggest clearly demarcated species. Yet, neither DNA restriction site nor nucleotide sequence data have generated well-resolved phylogenetic trees. We utilized the external transcribed spacer region (ETS) of the nuclear ribosomal DNA cistron to elucidate interspecific relationships within Tolpis. ETS has been shown to provide phylogenetically informative sequence variation at a level similar to, or higher than, ITS. Incomplete rDNA homogenization necessitated extensive cloning of repeat subtypes. Combined phylogenetic analyses of cloned and direct rDNA sequences did not change inferred relationships based on direct sequencing alone, and sequence diversity between paralogous rDNA was minimal. Phylogenetic analyses indicate four strongly supported clades, each correlating with a unique geographic distribution. Species from the Azores represent the basal-most clade, and a species disjunct between Madeira and the Azores is found to be polyphyletic. Species of the Madeiran archipelago form a monophyletic group that is sister to a clade comprising all continental and Canary Island taxa. The latter constitute a clade of seven endemic and several undescribed species. Cloned ETS sequences of the only known polyploid on this archipelago are recovered in three independent positions. Inferred dispersal routes indicate a single colonization of each of the three archipelagos, Azores, Madeira, and Canary Islands. The single Cape Verde endemic, T. farinulosa, is nested within the Canary Island clade, suggesting a separate colonization of this archipelago. Finally, the phylogenetic placement of Tolpis within the Lactuceae is discussed.
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1 - University of Texas at Austin, Section of Integrative Biology, 1 University Station, #A6700, Austin, TX, 78712, USA
2 - Yeungnam University, Department of Biology, Kyeungsan, Kyeungbuk, 712-742, Korea
3 - Jardín de Aclimatación de La Orotava, Puerto de la Cruz, Canary Islands, Tenerife, Spain
Presentation Type: Oral Paper:Papers for Sections
Date: Wednesday, July 30th, 2008
Time: 3:30 PM