A species delimitation approach in the Trochulus sericeus/hispidus complex reveals two cryptic species within a sharp contact zone.
BACKGROUND
Mitochondrial DNA sequencing increasingly results in the recognition of genetically divergent, but morphologically cryptic lineages. Species delimitation approaches that rely on multiple lines of evidence in areas of co-occurrence are particularly powerful to infer their specific status. We investigated the species boundaries of two cryptic lineages of the land snail genus Trochulus in a contact zone, using mitochondrial and nuclear DNA marker as well as shell morphometrics.


RESULTS
Both mitochondrial lineages have a distinct geographical distribution with a small zone of co-occurrence. In the same area, we detected two nuclear genotype clusters, each being highly significantly associated to one mitochondrial lineage. This association however had exceptions: a small number of individuals in the contact zone showed intermediate genotypes (4%) or cytonuclear disequilibrium (12%). Both mitochondrial lineage and nuclear cluster were statistically significant predictors for the shell shape indicating morphological divergence. Nevertheless, the lineage morphospaces largely overlapped (low posterior classification success rate of 69% and 78%, respectively): the two lineages are truly cryptic.


CONCLUSIONS
The integrative approach using multiple lines of evidence supported the hypothesis that the investigated Trochulus lineages are reproductively isolated species. In the small contact area, however, the lineages hybridise to a limited extent. This detection of a hybrid zone adds an instance to the rare reported cases of hybridisation in land snails.
Dépraz
Aline
A
Lab Centre, Biodiversity & Climate Research Centre, Biocampus Siesmayerstrasse, D-60054 Frankfurt am Main, Germany. adepraz@gmail.com
Hausser
Jacques
J
Pfenninger
Markus
M
D000818:Animals; D001499:Bayes Theorem; D002467:Cell Nucleus / Q000235:genetics; D016000:Cluster Analysis; D004272:DNA, Mitochondrial / Q000235:genetics; D019143:Evolution, Molecular; D005819:Genetic Markers; D049810:Genetic Speciation; D005828:Genetics, Population; D006239:Haplotypes; D017422:Sequence Analysis, DNA; D012908:Snails / Q000033:anatomy & histology / Q000235:genetics*; D013045:Species Specificity
D004272:DNA, Mitochondrial; D005819:Genetic Markers