Systematics Section / ASPT
Ghebretinsae, Amanuel , Barber, Janet C. .
Phylogenetic Relationships among species of Cucumis and Cucumella (Cucurbitaceae): Evidence from ITS, rpl16 and trnS-G sequences.
CUCUMIS is a well-known member of the Cucurbitaceae and comprises ca. 32 species including several of major economic importance (e.g. cucumbers, melons, the West Indian Gherkin, the Kiwano). Two subgenera are recognized, differing in geographical distribution and chromosome number. Subgenus Melo (30 spp., n = 12) is native to Africa whereas subgenus Cucumis (4 spp., n = 7) is indigenous to Asia. However, the recent discovery of an Asian species (C. hystrix) with basic chromosome number n = 12 has challenged the classification, suggesting a possible bridge between the subgenera. Furthermore, origin of the subgenera is under debate. The taxonomic relationship of species of Cucumis and the closely related genus Cucumella is also poorly understood. Cucumella comprises 11 species with a distribution that mirrors that of Cucumis. Morphologically, Cucumella is separated from Cucumis by a single morphological character: anther shape. Numerous molecular studies at various taxonomic levels have included species of Cucumis, but none have addressed generic-wide phylogenetic relationships and none have included any species of Cucumella. In the current study, sequences of nuclear ribosomal DNA from the internal transcribed spacer (ITS) region, as well as plastid rpl16 and trnS-G sequences were used to explore relationships within and between the two genera. The results reported here support the separation of Cucumis and Cucumella as distinct genera. Within the genus Cucumis, the Asian species form a clade that is embedded within the African clade, contradicting with the existing morphological infrageneric classification. Within subgenus Melo, two sections and two series were found to be monophyletic. Our findings also suggest the probable ancestral region for Cucumis to be Africa. Future work will include employing gene regions that evolve more rapidly than were used in the present study, to improve resolution among species of Cucumis, and a more in-depth look at relationships within Cucumella.
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1 - Saint Louis University, Department of Biology, 3507 Laclede Avenue, St Louis, Missouri, 63103-2010, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 134/Performing Arts Center
Date: Tuesday, August 1st, 2006
Time: 9:30 AM