COS 177-4 - Temporal scaling in Lemna minor survival trajectories

Abstract: At the population level, senescence is defined as age-related declines in survival and reproduction. Across a variety of taxa, interventions such as changes in temperature, diet, and oxidative stress exposure, as well as the disruption of select genes, can alter lifespan distributions by the apparent ‘stretching’ or ‘compressing’ of time, whereby the pace of aging (i.e., average lifespan) is altered, but the time-standardized shape of survival curves remains the same. This phenomenon, known as temporal scaling, is well known in animals, but is largely unexplored in plants. In this talk, we report the results of a suite of laboratory experiments in which we demonstrate that Lemna minor L. (common duckweed, a tiny aquatic angiosperm) exhibits reduced lifespan under various environmental scenarios including raised temperature, reduced growth medium nutrient concentration, and greater light availability. More importantly, despite these environmental manipulations leading to different lifespans, when survivorship curves from long- and short-lifespan environments are plotted against relative age (i.e., in mean lifespans) instead of absolute age (i.e., in days) they overlap, and have similar shape (measured as the coefficient of variation of lifespan), providing strong evidence of temporal scaling in this plant species. Temporal scaling implies a related phenomenon, temporal shifting, whereby organisms that are switched at early ages from a long- to a short-lifespan environment (or vice versa) exhibit quantitatively predictable shifts in mean age-at-death. Thus, we will also discuss the results of a current, ongoing laboratory experiment in which we examine 110 individuals switched from a short- to a long-lifespan light environment (bright to dim), and 112 individuals switched from a long- to a short-lifespan light environment (dim to bright), at pre-specified ages. Based on existing theory, we predict the following temporal shift in the mean lifespan of switched individuals: ∆L = x(1 – L2/L1), where L1 and L2 are the mean lifespans in the first (‘switched-from’) and second (‘switched-to’) environments, respectively, and x is the age at switching. Studying stochastic phenomena such as senescence can improve our knowledge of the variables that affect the aging process and determine which variables effectively describe aging and contribute to the processes that determine lifespans.