Systematics Section / ASPT
Brunet, Johanne , Di Stilio, Veronica , Liston, Aaron .
Evolution of breeding system and genome size in the genus Thalictrum (meadow rue) (Ranunculaceae).
THALICTRUM species vary in their breeding system, pollination mechanism, and ploidy level. Species can be hermaphroditic (all flowers have both male and female organs), dioecious (male and female individuals), or andromonoecious (male and hermaphroditic flowers on an individual) and are pollinated by wind, insect, or both. The base chromosome number is x=7, and most species are diploid, tetraploid or hexaploid. However, counts as high as 2n=210 have been reported, and some species have multiple chromosome numbers. We obtained ploidy data (from the literature and root tip squashes) for 22 species and measured genome size by flow cytometry in 33 species. Overall we observed smaller genome size in hermaphroditic relative to andromonoecious and dioecious taxa. While wind-pollination is common in dioecious and andromonoecious species, and insect-pollination in hermaphroditic species, both insect- and wind-pollination occur in some dioecious and some hermaphroditic species. We reconstructed the phylogeny of 54 Thalictrum species and four outgroups using two molecular loci, the nrDNA ITS region (internal transcribed spacers of nuclear ribosomal DNA) and the chloroplast DNA rpl16 intron. The species represent 10 of 14 sections in this genus of 190 species. We examined the evolution of breeding system, pollination mechanism, and genome size using character optimization on the phylogeny. We observed two separate origins of dioecy in North America, and one origin of andromonoecy in central/south America with no reversal back to hermaphroditism. Of the known ecological correlates of dioecy (woodiness, fleshy fruits, islands, tropical habitats, and wind-pollination), only wind-pollination is correlated with dioecy in this genus. We test whether wind-pollination and/ or polyploidy (genome size) preceded the evolution of dioecy and andromonoecy in this genus.
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The Thalictrum Database
1 - USDA-ARS, University of Wisconsin, Department of Horticulture, 1575 Linden Drive, Madison, Wisconsin, 53706, USA
2 - University of Washington, Department of Biology, Po Box 35-1800, Seattle, Washington, 98195-1800, USA
3 - Oregon State University, Department of Botany & Plant Pathology, 2082 Cordley Hall, Corvallis, Oregon, 97331-2902, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 31st, 2006
Time: 8:30 AM