Molecular and Morphological Discrimination Between the Pulmonate Land Snails Zonitoides Nitidus and Z. Excavatus

In this study, we investigated conchological and anatomical differences between two closely-related Zonitoides species: Z. nitidus and Z. excavatus. Although genital differences were not found, we observed clear conchological differences. Compared to Z. excavatus, Z. nitidus is larger, but has a narrower umbilicus. A parallel allozyme study revealed low variation within and between populations, and suggests that the two species most probably reproduce uniparentally. In contrast, random amplified polymorphic DNA (RAPDs) revealed much more variation in Z. excavatus. In this species, at least nine homozygous multilocus genotypes exist and in all populations several of these strains co-occurred. Two animals contained a fresh spermatophore, which suggests that at least sperm transfer may not be completely absent. Moreover, in one Belgian population both species co-occurred and allozyme patterns suggest possible hybridization. Even if we do not know how much of the conchological differences can be attributed to phenotypic plasticity in relation to different environmental conditions, the species status of both taxa seems supported by the strong genetic differentiation suggested by the allozyme and RAPD data.