Enchytraeus crypticus fitness: effect of density on a two-generation study.

Organisms' density can influence physiological processes related with fitness. In the present study we assessed the influence of organisms' density on the life-history parameters in two consecutive generations in Enchytraeus crypticus (Oligochaeta), a standard model in soil ecotoxicology. The densities tested were 1 (N1) and 20 (N20) organisms per replicate and 10 vs. 20 g of soil (for the 2nd generation test only). Results showed that reproductive output was affected by density, with organisms in N1 producing three times more juveniles per adult than when at N20. Organisms' length was affected by both density and space, i.e., organisms were smaller when less space available. Further, the density of parental generation (F0) had no influence on the endpoints reproduction and length assessed in F1, hence there was no transference of effects. These findings have potential implications in the standard Enchytraeid Reproduction Test, i.e. early mortality of the adults during toxicant exposure can affect the number and size of the offspring and the final results will also reflect the density related changes in reproduction.