The Lansing effect in Lemna turionifera (Lemnoideae) and potential contributing factors

Background/Question/Methods

The Lansing effect is the phenomenon of senescence whereby older parents have shorter-lived offspring than younger parents. The Lansing effect has been observed in a variety of taxa, including plants. Here, I investigated the Lansing effect in the subfamily Lemnoideae (duckweeds) - tiny, aquatic plants found on the surfaces of still and slow-moving bodies of freshwater. My goal was to analyze the relationship between parental age and offspring lifespan in the duckweed Lemna turionifera Landolt. My specific objectives were: Test for the existence of the Lansing effect. Determine whether accelerating senescence or increased frailty at all ages is the basis of the Lansing effect. I observed 396 individuals, half of which were their parent’s first clonal offspring (i.e., offspring of younger parents), and half were fifth clonal offspring (i.e., offspring of older parents). I tracked the fronds daily from birth until death, recording the number of offspring they produced and their lifespan. I then compared these values using Wilcoxon rank-sum tests. I used a model-selection approach to choose among standard demographic models fit to survival curves (exponential, Gompertz, Weibull, logistic), and to determine which of the best-fitting models’ parameters were responsible for differences in these curves.

Results/Conclusions

The Lansing effect is present in Lemna turionifera: On average, offspring of older parents had shorter lifespans and fewer offspring themselves, compared to offspring of younger parents. The logistic model fits survival data best for both first and fifth offspring, with the ‘initial mortality’ parameter being responsible for the differences in the curves. Thus, the Lansing effect in L. turionifera is mainly due to offspring of older parents exhibiting increased frailty at all ages, rather than an accelerated schedule of senescence.