Genetic diversity of a clonal earthworm : gene expression variation and impacts on decomposition in metal contaminated soil

Abstract

Biodiversity affects ecosystem functioning positively. Metal-contamination diminishes species diversity and ecosystem function depends on the remaining species, and the genotypes within them. I studied how the clonally reproducing earthworm Dendrobaena octaedra responds to soil metal contamination and how its genetic diversity affects decomposition. Expression of the gene for the metal tolerance protein metallothionein was compared between populations with or without metal exposure history: with exposure history expression was high and stable and without there was a slow response. Adaptation to metal contamination likely explains the differences. Clonality of D. octaedra was verified with microsatellite markers. However, there was considerable gene expression variation both between and within genotypes, highlighting the need to consider such variation in comparative gene expression studies. The main study question focused on if genetic diversity is important for ecosystem functioning in metalcontaminated soil. I manipulated genetic diversity of a key decomposer, D. octaedra in a microcosm experiment. Indications of positive effects of higher genetic diversity on decomposition were found, especially in the contaminated conditions. However, the differences between the treatments often depended on which genotype was in the low diversity treatment, suggesting that traits of the genotypes might be more important than the level of genetic diversity for ecosystem functioning. An alternative technique to the real-time quantitative PCR, droplet digital PCR, was tested for gene expression measurements, and found to be a promising technique.