9400471 Keeler Rare extreme events are part of every ecosystem, but since they are by definition unpredictable, testing what traits might be adaptive for surviving them is difficult. Theoretically, extreme conditions exert brief, strong natural selection for traits that were not previously adaptive. However, surviving species have weathered such events successfully and repeatedly. The 1993 flood in the US Midwest provides such a truly unique opportunity to investigate the following: (1) whether genome level genetic structure is adaptive: specifically, whether polyploidy (or multiple genomic copies within a single individual) is, among other things, an adaptation for maintaining the genes to survive rare events (2) weather the strong selection of a rare event makes permanent (or very long term) changes in the genetic structure of populations. Big bluestem (Andropogon gerardii Vitman) was the dominant grass of the tall grass prairie region, (Ohio to Nebraska, Minnesota to Texas). While dominating the landscape, its distribution ends above recurrently flooded areas, suggesting only limited tolerance to flooding. Weaver and Albertson (e.g. 1936, 1943, 1944) documented the response of A . gerardii and other prairie grasses to the Great Drought of the 1930's. The 1993 flood allows us to compare the impact of excessive water. This project will capitalize on a unique event to the test the dif ficult problem of whether there is selection for higher polypoids in natural population and whether extreme events produce natural selection with permanent impact on the populations. Known populations of dominant grass are available and the more detailed analysis of those populations to be established here will allow future monitoring to detect changes in other years. If this is indeed a unique event, Dr Keeler will learn about the importance of such events and be able to watch results in return of the ongoing selection pressures of ordinary years. If future years are wet, multiple established populations will allow observation of directional selection on natural populations on an ecosystem dominant, an important component of understanding organismal response to climate change.
