Morphological aspects and phylogenetic analyses of pollination systems in the Tylophora–Vincetoxicum complex (Apocynaceae-Asclepiadoideae) in Japan
Pollinators of two Cynanchum, five Tylophora, and 16 Vincetoxicum species were observed in 26 populations in Japan. The following pollination systems were observed in 18 species: moth pollination, generalized insect pollination, wasp pollination, dipteran pollination, both dipteran and moth pollination, and autogamy. Principal component analysis based on 13 floral characters indicated that the size of the pollinator tended to increase with sizes of all characters measured. Furthermore, species that have developed interstaminal parts of the corona and concealed stigmatic chambers tend to be pollinated by long-tongued insects. The phylogenetic distribution of pollinator types showed that species belonging to Clade I are pollinated exclusively by Diptera, whereas those of Clade II are pollinated by four insect orders. The most prominent pollinator transition in the Tylophora–Vincetoxicum complex is dipteran to moth pollination. The most common morphological change of the plants from dipteran pollination to moth pollination, or vice versa, is modification of the corolla. In the Tylophora–Vincetoxicum complex, pollination mode shifts are generally accompanied by modifications of the corona and the structure of gynostegium. One hypothesis for the rapid radiation observed in Clade II is that a widely distributed species may have partitioned its distribution in the relatively near past and adapted to various environments, in which the dominant pollinators were different, and that the local races may then have diverged from each other after they were isolated. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 93, 325–341.
Document Type: Research Article
Department of Life Sciences, Faculty of Integrated Arts and Sciences, The University of Tokushima, 1-1 Minami-josanjima, Tokushima 770-8502, Japan
Graduate school of Human and Natural Environment Sciences The University of Tokushima, 1-1 Minami-josanjima, Tokushima 770-8502, Japan
Department of Biology, Faculty of Science, Yamagata University, 1-4-12 Kojirakawa, Yamagata 990-8560, Japan
Division of Ecology and Evolutionary Biology, Graduate School of Life Sciences, Tohoku University, Aoba, Sendai 980-8578, Japan
Publication date: February 1, 2008