Abstract : Almost all lumbricid earthworms (Oligochaeta Lumbricidae) harbor species-specific Verminephrobacter
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Abstract : Almost all lumbricid earthworms (Oligochaeta Lumbricidae) harbor species-specific Verminephrobacter (Betaproteobacteria) symbionts in their nephridia (excretory organs). The function of the symbiosis and whether the symbionts have a beneficial effect on their earthworm host is unknown however the symbionts have been hypothesized to enhance nitrogen retention in earthworms. The effect of Verminephrobacter on the life history traits of the earthworm Aporrectodea tuberculata (Eisen) was investigated by comparing the growth development and fecundity of worms with and without symbionts given high (cow dung)- and low (straw)-nutrient diets. There were no differences in worm growth or the number of cocoons produced by symbiotic and aposymbiotic worms. Worms with Verminephrobacter symbionts reached sexual maturity earlier and had higher cocoon hatching success than worms cured of their symbionts when grown on the low-nutrient diet. Thus Verminephrobacter nephridial symbionts do have a beneficial effect on their earthworm host. Cocoons with and without symbionts did not significantly differ in total organic carbon total nitrogen or total hydrolyzable amino acid content which strongly questions the hypothesized role of the symbionts in nitrogen recycling for the host.
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