Experimental hybridization between two sub-species of snails (Helix aspersa aspersa and Helix aspersa maxima): consequences for fertility, survival and growth

摘要

The experimental laboratory pairing of hermaphroditic snails of different sub-species, Helix aspersa aspersa (H.a.a) and H. aspersa maxima (H.a.m.), made it possible to obtain both reciprocal hybrids for the first time and to describe their growth.The relatively small number of matings observed (20-25 percent) was partly responsible for the small number of clutches obtained (10-13 percent). The cross H.a.a.M X H.a.m.F is more fertile than the reciprocal. The observed tendency to reproductive isolation (behavioural and anatomical) suggests that H.a.a. and H.a.m. should be considered as two sub-species. Hybridization is not accompanied by a beneficial heterosis effect since significant juvenile mortality and an increased variation in growth were observed. The small size of H.a.a, is a dominant characteristic, whereas the colour of the mantle edge in the F1 individuals is intermediate between the black of H.a.m. and the white of H.a.a. The F1 generation is fertile and gives F2 snails with an adultsize close to that of H.a.a. but slower growing. This approach allows investigations into the mechanisms underlying the reproductive isolation of parental sub-species.