Genetic diversity of widespread moss-dwelling nematode species in German beech forests

• Pilot study assessing the genetic structure of three moss-dwelling nematode species.
• High level of genetic diversity uncovered for each of the studied plectid species.
• Molecular analyses provided no evidence for cryptic diversity.
• Morphological- and DNA-based species delineation showed mostly a close match.

Molecular studies suggest that the number of microscopic animal species has been severely underestimated because of a high level of cryptic diversity. Using traditional methods of morphological species identification, a large number of species have remained undetected. In fact, many aquatic nematode morphospecies with an assumed widespread distribution instead may comprise cryptic species complexes. In terrestrial moss habitats, the diversity of nematode communities has yet to be evaluated in molecular surveys. Thus, the aim of this study was to assess the potential for cryptic diversity among the three dominant moss-dwelling nematode species (Plectus parietinus, Plectus cirratus, and Chiloplectus andrassyi) detected at five locations within four German beech forests. Analyses of the molecular variation in a mitochondrial (COI) gene and in two ribosomal (LSU and SSU) subunit genes were complemented by morphological identification of specimens. The morphological-based plectid species delineation was supported by the COI gene topology, but less by the analyses of nuclear marker genes. Furthermore, the results revealed a high level of high genetic diversity in terms of number of mitochondrial haplotypes (n = 24) detected overall for the three investigated morphospecies at the five locations, with no evidence of cryptic diversity. However, the large number of haplotypes only to be found at a single sampling location suggested a restricted level of gene flow even over short geographic distances (6 km).