Evolution of dispersal and pollination in ecologically dominant grasses

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The tallgrass prairie of North America is an iconic landscape, central to America history. The grasses from which the prairie takes its name are close relatives of those that make up the vast grasslands of eastern Africa. The grasses provide food for livestock and wild animals, and habitat for birds; they also pull carbon from the atmosphere and bury it deep in the ground where it supports beneficial microbes that make the rich soil on which American agriculture depends. This project is a collaboration between research scientists at the Donald Danforth Plant Science Center in St. Louis, Missouri, undergraduates at Principia College in Elsah, Illinois, and colleagues in eastern Africa, and is aimed at unraveling the ways the grasses spread their pollen, how they provide their seeds with carbon, and how the seeds are dispersed across the landscape. This information will tell us how the grasslands will respond in the face of current disturbance such as fire, urbanization, and conversion to farmland, and future disturbances caused by a changing climate. This project focuses on three major grass genera, Andropogon, Schizachyrium, and Hyparrhenia, plus a few smaller related genera, that together include some 250 species many of which are ecological dominants. Researchers will first use DNA sequences to uncover the phylogenetic history of the group, and then use that history to trace how the seed-bearing portions of the plant have changed over evolutionary time and how they correlate with climate, fire, and moisture. The seeds in these plants do not simply drop off the plant. Instead they are released as part of a complex dispersal structure that includes pieces of floral stalks and leaf-like bracts. The dispersal structure varies between species in size, presence or absence of hairs, presence of male and female flowers, and presence or absence of awns (hygroscopic extensions of bracts). The structure may be an adaptation for seed dispersal, for the control of germination in particular soil types, or for resistance to fire. However, the same structures may also help with pollination. In addition, many parts of the dispersal structure are green during development, and may provide photosynthate for the developing seed. Thus the structure could be selected for functions at three different life history stages: pollination, grain filling, and dispersal. This project will use both a historical phylogenetic approach and an experimental approach to test the current function of the dispersal structure. The dispersal structure studied here is much like that of sorghum, sugarcane and Miscanthus, so the data will apply to those crops as well as to the major grassland species.