Ito, Yu , Cota-Sanchez, Hugo , Changkyun, Kim , Tanaka, Norio .
A phylogenetic view of habitat transitions in the aquatic genus Sparganium (Typhaceae).
Aquatic plants include ca. 1,000 species worldwide; a third of which are adapted to submerged lifestyle while the rest are known as emergent plants. The habitat preferences are generally unique within each aquatic genus, but Sparganium (Typhaceae), a rare genus distributed in cold and temperate regions, includes both submerged and emergent species. A comprehensive generic taxonomic revision in the late 80s recognized two subgenera with 14 species worldwide, including 11 species in Asia, 10 in North America, seven in Europe, and only two in Oceania. This revision used habitat type or leaf characters in relation to habitat differences as major diagnostic characters. However, some emergent species exhibit high levels of phenotypic plasticity between habitats, e.g., S. emersum, causing taxonomic confusion with morphologically similar submerged taxa. The inflorescence type is the most important taxonomic character in Sparganium, and while it varies in submerged and emergent species, these structures look similar to those of other taxa in different ecological habitats, indicating the occurrence of multiple evolutionary transitions. The evolutionary time in the transitions of this genus is also significant. Submerged species are only known in the northern hemisphere and restricted to relatively high northern latitudes. Possibly submerged species evolved during the ice ages when terrestrial habitats were covered by glacial ice.We conducted molecular analyses to unveil the phylogenetic relationships of Sparganium, using ingroup taxa from Eurasia and North America covering most of the Northern hemisphere distribution. Typha (Typhaceae) and Ananas (Bromeliaceae, sister family to Typhaceae) were selected as outgroup. Combined plastid DNA sequences (rbcL and matK genes) were subjected to maximum parsimony analyses. The consensus tree is different from the two subgenera (Sparganium and Xanosparganium) context proposed by Cook & Nicholls (1986), and instead supports the S. erectum clade and the rest of species in a sister clade. The submerged species are divided into four lineages; one of them, S. angustifolium, is clustered with an emergent species, S. emersum, which share many morphological traits with each other, while the others place alone. The divergent time of these twin species was calculated with mcmctree program under the Bayesian method, using multiple fossil calibration points, dating it back to ca. 3 mya, when the glacial ice started to form. This suggests that early in the evolutionary history of Sparganium the submerged lifestyle was advantageous and played an important role in the evolution of genus when the earth's climate was cold and arid.
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1 - University of Saskatchewan, Department of Biology, 112 Science Pl. Saskatoon, Saskatoon, SK, S7N 5E2, Canada
2 - UNIVERSITY OF SASKATCHEWAN, Department Of Biology, 112 SCIENCE PLACE, SASKATOON, SK, S7N 5E2, Canada
3 - Kunming Institute of Botany, Chinese Academy of Science, China
4 - TSUKUBA BOTANICAL GARDEN, NATL SCI MUSEUM-AMAKUBO 4-1-1, Tsukuba, IBARAKI, 305-0005, Japan
Presentation Type: Oral Paper:Papers for Sections
Location: Franklin B/Hyatt
Date: Monday, July 9th, 2012
Time: 2:15 PM