Project 7: Determinants of Extreme Longevity in a Plant Species Senescence is defined demographically as an increase in mortality after reproductive maturity. Our current understanding of mortality patterns may be limited by the fact that most studies have been made with short-lived model organisms under laboratory conditions. This project uses a new model system, with a relatively long lifespan and unique trajectories of growth and reproduction with age. At the foundation of this project is a population of 30,000 individuals of Plantago lanceolata, a perennial plant species. Results from an earlier study suggest that continued growth after maturity might allow this species to minimize, or even escape, the aging process. This preliminary project showed that there are many determinants of mortality in this species including extrinsic environmental factors, spatial location, genetics, reproduction, cohort history, and most importantly size of an individual. This new project will expand this analysis to another population and to later years. It will test whether the importance of size, and the minimal importance of age, will continue to the latest ages. Data will be collected to test some of the assumptions in our covariate regression model that we have written to explore age-specific mortality in this species. We also have an established population of P. lanceolata that has been growing for over five years under the controlled conditions of the greenhouse. Few individuals, in the natural environment, live to this late age but under these protected conditions, the majority of the population has survived and is beginning to show an increase in mortality. This protected population offers a unique opportunity to study the mortality dynamics of a species at extremely late ages and it will test the hypothesis that patterns of senescence are only apparent at ages that are much later than individuals would survive in their natural environment.
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