Restoration of experimentally depleted coelomocytes in juvenile and adult composting earthworms Eisenia andreiE. fetida and Dendrobaena veneta

Abstract

Earthworms irritated by various noxious stimuli expel coelomic fluid through dorsal pores in the body wall. Coelomic fluid contains coelomocytes (amoebocytes and riboflavin-storing eleocytes) and soluble factors responsible for immune functions, thus efficient restoration of the depleted coelomocyte system has an important adaptive value for soil-dwelling species. The aim of present experiments was to compare restoration of coelomocytes and riboflavin (vitamin B2) after experimental expulsion performed in composting earthworms reared for generations in the same laboratory conditions. Dendrobaena veneta, Eisenia andrei and Eisenia fetida were identified according to morphological criteria, species-specific fluorophores, and DNA sequences of mitochondrial COI genes. Analyses (cell counting, flow cytometry, spectrofluorimetry) were conducted on juveniles and adults at the time of electric shock-induced depletion of coelomocyte-containing coelomic fluid and then three weeks later in worms recovering their immune systems, and in their untreated counterparts. Electric shock induced expulsion of approximately 90% amoebocytes, eleocytes, and riboflavin, followed by their gradual restoration that was still in progress 3 weeks later. Amoebocytes were restored faster than riboflavin and eleocytes. Riboflavin content was higher in restored than senescent eleocytes of adult worms. Process of restoration was faster in juveniles than in adults and in the former was connected with accelerated gain in body mass. Senescent coelomocytes of adult earthworms easily undergo fragmentation, while it was seldom observed in coelomocytes of juveniles and in newly formed coelomocytes replacing expelled cells in both adult and juvenile worms. Molecular basis of these phenomena are worth further elucidation.