Evolution of senescence in plants

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Senescence, known colloquially as `aging', is the progressive deterioration of individuals leading to decreased rates of survival and reproduction in old age. Senescence is extremely common in diverse organisms including humans, other animals, plants, and even fungi and bacteria. Theory predicts that in addition to age-related declines in survival and reproduction, we should also expect declines in offspring quality. Yet most work on senescence ignores these parental age effects, implicitly assuming that all offspring are of equal quality. This suggests that current approaches underestimate evolutionarily favoured rates of senescence, providing opportunities for innovative research. The long-term goal of my research program is to develop and test evolutionary theories of senescence with a focus on parental age effects. My team combines theory, field, and lab work, and uses floating aquatic plants in the genus Lemna as a model system. Four major objectives support my long-term goal: 1. Test whether offspring of old parents are less stress tolerant than those of young parents. Experiments will focus on three important stressors: salinity, high temperatures, and pH. We will determine whether advanced parental age exacerbates negative effects of stress on offspring. 2. Test whether parental age effects occur in wild plants. Plants will be grown in ponds using floating platforms to determine whether parental age effects observed in the lab also occur in nature, or if they are simply a result of benign lab conditions. 3. Test whether parental age effects alter population growth. We will develop extensions of classic population growth models to incorporate parental age effects. We will then test whether including parental age effects in population growth models improves their predictive power. 4. Test whether parental age effects occur at the whole-clone level. As Lemna is clonally reproducing, prior studies have focused on senescence at the level of physiological individuals. We will manipulate the `effective age' of whole clones (using temperature treatments to vary the number of clonal generations) to test whether older clones produce lower-fitness offspring than younger ones. Senescence is a central topic in ecology and evolution. My ongoing research demonstrates the necessity of considering parental age effects to understand the evolution of senescence. The proposed work builds on this foundation by linking parental age effects to diverse topics such as stress biology, modes of reproduction, and population growth. The discoveries delivered by my research program will be valuable to demographers, evolutionary biologists, and ecologists. Due to my unified conceptual focus, my research will be relevant to understanding senescence in general, not just in plants. Additionally, 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.