Carbon and nitrogen stable isotope ratios in body tissue and mucus of feeding and fasting earthworms (Lumbricus festivus)

Abstract

We used natural abundance stable isotope techniques to estimate carbon and nitrogen turnover rates in body tissue and mucus of earthworms. Isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) were monitored simultaneously in body tissue and mucus for up to 101 days in feeding or fasting Lumbricus festivus kept in an artificial substrate. When the diet of the earthworms was switched from clover (C₃ plant, legume) to maize (C₄, non-legume), the new dietary δ¹³C signature manifested itself much more rapidly in the mucus than in the body tissue of the animals, causing a δ¹³C shift of about 4‰ in mucus and 1‰ in tissue after 13.5 days. Turnover of earthworm body tissue carbon, unlike that of mucus carbon, was described adequately by an exponential, single-pool model. Nitrogen turnover could not be assessed because the δ¹⁵N difference between sources was too small. Fasting for 56 days did not result in the expected whole-body ¹⁵N or ¹³C enrichment, but it caused a significant decrease in mucus and tissue C:N ratios and in the ratio (mucus C:N ratio):(tissue C:N ratio). We conclude that the separate analysis of body tissue and mucus has great potential for studying the ecophysiology, feeding ecology and role in elemental cycling of earthworms and other invertebrates.