COS 177-3 - Offspring of older parents have reduced capacity for population growth in the aquatic plant Lemna minor

Abstract: Parental-age effects occur when the offspring of older parents have different traits than the offspring of younger parents. Typically, increased parental age has a deleterious effect on offspring, and therefore parental-age effects constitute a third component of parental senescence, along with decreased survival and reproduction. Most research on parental-age effects has considered relatively tangential proxies for offspring fitness, such as their size, lifespan, or total reproduction. Recent work on duckweeds – tiny, clonal, floating aquatic plants in the family Lemnaceae – has demonstrated parental age effects in terms of a more direct proxy for offspring fitness, the intrinsic rate of natural increase measured at the individual level. Here, we report the results of a growth chamber experiment on the duckweed Lemna minor, designed to investigate whether the predicted parental-age effect on offspring fitness is realized in terms of population growth. We established 229 populations founded from the offspring of 20 parent plants of known age. The populations grew in sealed jars of growth medium under light-, photoperiod-, and temperature-conditions conducive for clonal population growth. The populations founded from the offspring of half of the parents (randomly assigned; n = 112) were harvested after two weeks; the populations founded from the offspring of the other half of the parents (n = 117) were harvested after four weeks. Using mixed models to account for parent plant identity, we show that Lemna population size, surface area, and dry mass all decreased with parental age in both the two- and four-week-old populations. Our results demonstrate that parental-age effects on individuals can scale-up to produce strong negative effects on population dynamics.