BACKGROUND: Legless lizards, the slow worms of the genus Anguis, are forming secondary contact zones within their Europe-wide distribution. METHODS: We examined 35 populations of A. fragilis and A. colchica to identify the level of morphological and genetic divergence in Poland. We applied a conventional study approach using metric, meristic, and categorial (coloration) features for a phenotype analysis, and two standard molecular markers, a mitochondrial (NADH-ubiquinone oxidoreductase chain 2; ND2) and a nuclear (V(D)J recombination-activating protein 1; RAG1) one. RESULTS: We found clear differences between A. fragilis and A. colchica in molecular markers and phenotype-in meristic features, e.g., ear opening, number of scales rows around the body, and higher than so far known diversity in ND2 and RAG1 haplotypes. The presence of five hybrids was detected in three populations in the Polish part of the European contact zone. In all hybrids, homozygous alleles of RAG1 were detected, which suggests a back-crossing within the genus. CONCLUSIONS: The ability to produce fertile offspring by A. fragilis x A. colchica hybrids shows inefficient mechanisms of reproductive isolation of the two legless lizards. The hybrids were indistinguishable from parental species in head proportions (principal components and discriminant analyses) but more resembling A. colchica in meristic traits.

• Keywords
• Anguidae, Biogeography, Hybridization, Morphometrics, Speciation, Taxonomy,
• MeSH
• Phenotype MeSH
• Genetic Variation MeSH
• Haplotypes genetics   MeSH
• Homeodomain Proteins MeSH
• Lizards * genetics   anatomy & histology   MeSH
• Reproductive Isolation MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Poland MeSH
• Names of Substances
• Homeodomain Proteins MeSH
• RAG-1 protein MeSH Browser