Evidence for Interpopulation Differences in Life History Parameters of Adult and F1 Generation Lumbricus Rubellus

We report here on interpopulation differences in life history parameters in L. rubellus collected from acidic, calcareous, and Sr-rich but Ca-poor soils. Size-at-maturity, fecundity and cocoon Ca status were determined for field-collected adult earthworms, maintained in their native soils under laboratory conditions for 18 weeks. After this time the wet weight of adults and cocoon production were significantly greater in earthworms indigenous to the calcareous soil. There were no interpopulation differences in cocoon Ca concentration despite a 28-fold range in soil Ca concentration. However, adults indigenous to the acidic soil produced larger cocoons with a significantly higher Ca content than both other populations. We suggest that adult populations native to low Ca soils may be stressed and allocate disproportionately more assimilated energy to counteract the effects of stress, thus leaving less for reproduction.

Secondly, F1 offspring from the three populations were reciprocally transferred to each soil type so that differentiation between genetic adaptation and individual acclimation to the hypoavailability of environmental Ca could be determined. Von Bertalanffy growth curves were fitted to time series weight values over 48 weeks. There were no significant interpopulation differences in final weight despite the contrasting soil cation status. However, earthworms held in the calcareous soil reached this weight significantly faster than the corresponding populations held in Sr-rich soil, which also took twice as long to develop into subadults. We suggest that populations from Ca-poor soils were phenotypically plastic and able to tolerate a Ca-poor environment by means of efficient Ca-uptake mechanisms. However, when presented with Ca-rich soil, earthworms native to Ca-poor soil may simply have downregulated their efficient Ca acquisition mechanism and performed as well as the population indigenous to Ca-rich soil. Conversely, earthworms from a Ca-rich soil may be genetically limited in their ability to physiologically adjust in a Ca-poor environment and, therefore, performed worse than when in their own soil.