Effect of quantity and quality of environmental stress on multilocus heterozygosity-growth relationships in Eisenia fetida (Annelida: Oligochaeta)

Abstract

The effects of environmental quantity (moderate soil moisture vs. low soil moisture) and quality (low soil moisture vs. low temperature) on multilocus heterozygosity (MLH)-growth relationships were tested in the earthworm Eisenia fetida. The control treatment was high soil moisture and high temperature. Fresh weight was measured weekly for 4 weeks; MLH was computed for eight polymorphic loci. Moderate moisture limited growth (change in fresh weight) to 50 per cent of control growth; both low moisture and low temperature limited growth to 25 per cent of control growth. MLH was not correlated with growth at any time in the control treatment. MLH was strongly correlated with growth (P<0.01) in three out of four weekly intervals in the moderate moisture treatment; MLH was weakly correlated with growth (P<0.05) in two out of four weekly intervals in the low moisture treatment. MLH was not correlated with growth at any time in the low temperature treatment. Moderate soil moisture produced significantly stronger MLH-growth relationships than high moisture or low temperature. Even though low soil moisture and low temperature depressed growth to the same extent, the former produced MLH-growth relationships whereas the latter did not. Thus both environmental quantity and quality affected the existence and recurrence of MLH-growth relationships.