A demographic assessment of the Lansing Effect in duckweed (Lemna turionifera Landolt)

The Lansing Effect is the propensity for offspring of older parents to have shorter lifespans than offspring of younger parents. A recent review identified two demographic patterns that can produce the Lansing Effect: (i) a greater offspring mortality rate at all offspring ages in offspring of older versus younger parents (greater initial mortality parameter); and (ii) an offspring mortality rate that increases more rapidly with offspring age in offspring of older versus younger parents (greater mortality rate parameter). Here, we report on a longitudinal study designed to investigate these patterns, using the duckweed Lemna turionifera. We tracked asexually produced offspring that detached from parents that were comparatively young versus old (first versus fifth offspring, respectively). Offspring of older parents lived 15% shorter, on average, than offspring of younger parents, providing evidence of the Lansing Effect. A model-selection approach revealed that the difference between survival curves of first versus fifth offspring was mainly attributable to greater initial mortality in fifth compared to first offspring, though alternative models also received some support. Our study provides a demographic explanation for the Lansing Effect in L. turionifera in particular and provides a method for assessing the survival patterns underpinning the Lansing Effect in general.