Life-history patterns in reference and metal-exposed earthworm populations

The growth and development of F1 Lumbricus rubellus bred from reference and one metal-exposed (smelter) populations were assessed in soils from both s ites. In the clean soil, faster growth (as reflected by mean weight) and ma turation were found at selected time intervals for the smelter worms. This result is in agreement with predictions from life-cycle models, which indic ate that polluted-site populations will be adapted for faster growth, earli er maturation and increased reproductive effort. Life-history adaptation is not however the only explanation for the differences in maturation rates f ound. During the exposures, mortality of smelter worms was higher than for the reference strain. This resulted in a reduction in the density of the sm elter strain. In earthworms, both growth rate and maturation time are known to be density dependent. Thus it is probable that density-mediated respons es of growth and development, rather than adaptation, are primarily respons ible for the observed life-history. Exposure of the two strains to the smelter site soil was carried out to qua ntify differences in performance indicative of physiological resistance in the smelter worms. In fact, no consistent differences in growth or maturati on were found. Thus it is unlikely that growth and development responses of Lumbricus rubellus are adapted to the metals present in soils at the smelt er site.