9509071 Whitten The Stanhopeinae orchids of the American tropics are a group of ca. 250 species of epiphytic orchids with flowers of strange and contorted shapes and usually with strong fragrances. Many are now known to be pollinated by male fragrance-collecting bees, which are suspected to use these floral fragrances in the manufacture of their own pheromones. The diversity of floral shape and size in these orchids appears linked to the pollination behaviors of native tropical bees. Yet the taxonomic and phylogenetic relationships of the orchid species are typically based on these same morphological characters of the flowers. This raises the problem of circular argument in arguing the co-evolution of plants and insects, and emphasizes the need for an independent set of characters on which to construct a phylogeny of the orchids. Researchers Mark Whitten and William Stern at the University of Florida, in collaboration with Mark Chase at Kew in England, are analyzing chloroplast and nuclear DNA sequences in Stanhopeinae orchids, in order to assemble a large dataset of independent molecular characters, as well as new features of vegetative and reproductive anatomy. Preliminary molecular data of mutational differences between DNAs of different species show promise for resolving close species-level relationships in this group of orchids. By comparing and combining the molecular data with new and traditional morphological characters, the researchers will be able to construct an improved classification that reflects phylogenetic relationships. Using this framework, they can then superimpose various ecologically related traits onto the phylogenetic tree, to generate hypotheses about the rate and direction of change in floral features. In turn, such hypotheses will guide the study of how pollinating inects have interacted or coevolved with their plant associates.
