Evolution of senescence in plants

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Senescence-bodily deterioration leading to an elevated risk of death and a lower rate of reproduction with advancing age-spans the tree of life, from bacteria to complex multi-cellular species. Despite its ubiquity, senescence is puzzling because all else being equal, natural selection should favour individuals that don't senesce over those that do. This apparent paradox makes senescence a topic of perennial interest in biology and inspires the long-term goal of my research program: to develop and test evolutionary theories of senescence, with an emphasis on aging in plants.****Ideally, senescence studies should track populations longitudinally over multiple generations, a difficult goal in long-lived species. Thus, I propose to study senescence in Lemna minor, a short-lived aquatic plant that allows, in weeks, the amassment of data that would take years to acquire even in other short-lived plants (e.g., annuals). My students and I will deploy this model system on several fronts:*** ***1. Trans-generational effects of aging. Advanced age not only reduces survival and reproduction, it can also reduce offspring quality; yet this `third component' of senescence is poorly understood. Our studies of this phenomenon will generate important insights into demography, with broad implications not only for plants, but also for the many species (e.g., humans) thought to experience a progressive erosion of offspring fitness.*** ***2. Environmental variation and rates of aging. Theory predicts that conditions that speed growth lead to faster senescence. For instance, in plants, temperature, light, nutrient and CO2 availability are among environmental attributes whose variation may alter rates of senescence. We will test this by manipulating these variables alone and interactively. In particular, CO2 and temperature are relevant to understanding changes in life-history trajectories in a changing climate. ***3. Evolutionary malleability of senescence. Theory predicts that a population's rate of senescence should, in a sense, match its members' expected lifespan in the environmental conditions under which their ancestors evolved. This suggests that Lemna collected from ponds whose conditions consistently lead to rapid growth should have faster senescence than those whose conditions lead to slow growth, even when transferred to common conditions. We will collect Lemna from across Western Canada, and, using modern comparative methods to account for inter-population relatedness, determine whether rates of senescence in a common-garden experiment are related to relevant environmental data from the source ponds.****Along with anticipated discoveries in the subjects of evolutionary biology, population ecology, and aquatic botany, this research will help advance-and provide training in-the field of biodemography, a discipline of increasing socio-economic importance due to Canada's aging population. ********