Digestive carbohydrases in two epigeic earthworm species of the Kerguelen Islands (Subantarctic)

Summary In the Kerguelen islands, two epigeic earthworms, one native Microscolex kerguelensis (Lankester 1879) and one introduced Dendrodrilus rubidus tenuis (Eisen 1874) are assumed to occupy the same ecological niche, i.e. to use the same food substrates. To test this hypothesis, the digestive capacities of the two species were compared using natural and synthetic glycosidic substrates. Both species hydrolysed starch, maltose, laminarin and N-acetylglucosamine, suggesting the ability to digest roots, yeasts, brown algae and fungi in soil. The main degradation of carbohydrates took place in the foregut, except in D. rubidus tenuis where some polysaccharides (laminarin, lichenin, xylan, cellulose and CMC) were mostly hydrolysed in the anterior tract. The degradation of carbohydrates mainly took place in the foregut and/or in the midgut, but in D. rubidus tenuis the hydrolysis of some polysaccharides (laminarin, cellulose and CMC) occurred in both the anterior tract and the foregut. The earthworms did not degrade lactose, sucrose and cellobiose; this result could be related to the weakness of the cellulasic and xylanasic activities. Hence, the full enzyme set generally found for the degradation of cellulose was not present in these epigeic earthworms.