Diversity and systematics of aquatic oligochaetes

Next to the different projects on the implementation and development of oligochaete indices, we realize various works on the diversity and systematics of aquatic oligochaetes. For example, we published in 2020 an article on the distribution and ecology of the foreign species Quistadrilus multisetosus Smith, 1900 in Lake Geneva. Some oligochaete species cannot be distinguished on the basis of their morphology, but only on the basis of genetics: these are referred to as cryptic species. We are currently involved in two projects on the cryptic diversity within the morphospecies Haplotaxis gordioides (Hartmann in Oken, 1819) and within the genus Chaetogaster Baer, 1827 in Switzerland.

Haplotaxis gordioides inhabits groundwater, so is rarely collected as part of the biomonitoring surveys and specimens of this taxon are most often found in an immature form. A cryptic diversity within this morphospecies have been suspected by many authors. We sequenced the molecular COI (cytochrome c oxidase) barcode of 46 specimens belonging to Haplotaxis gordioides collected in surface sediments of streams, in a cave and as part of a countrywide sampling campaign to study groundwater macroinvertebrates. The obtained results suggest that these specimens belong to at least six different species. The prospects are to perform a morphological study as well as to sequence additional markers (nuclear in particular) to confirm that Haplotaxis gordioides is a complex of cryptic species. In addition, collecting new Haplotaxis gordioides specimens could allow to reveal the presence in Switzerland of additional species belonging to this morphospecies.

The genus Chaetogaster belongs to the subfamily of Naidinae (Naididae), includes mostly species of small size and is diverse and abundant in coarse surface sediments in streams. In Switzerland, six species of Chaetogaster have been found so far on morphological grounds: C. diaphanus (Gruithuisen, 1828), C. diastrophus (Gruithuisen, 1828), C. langi Bretscher, 1896, C. parvus Pointner, 1914, Chaetogaster limnaei (von Baer, 1827) and C. setosus Svetlov, 1925. Recently, Mack et al. (2023) suggested that three commonly referenced species in North America and Europe, C. diaphanus, C. diastrophus and C. limnaei, are a complex of at least 24 cryptic species. In other words, the overall species diversity of Chaetogaster has been largely underestimated on a morphological basis. For this reason, we initiated an inventory of species of Chaetogaster in Switzerland based on a DNA barcoding approach. The aim of this study is to reveal the hidden diversity within Chaetogaster in Switzerland and to newly attribute DNA barcode sequences to the species C. langi and C. setosus. We selected 33 specimens of C. diaphanus, 67 of C. diastrophus, 30 of C. langi and 5 of C. setosus collected at six sites of four streams in four cantons. We sequenced COI from all specimens and the nuclear markers ITS2 and 28S from all or several specimens of each lineage delimited using COI data. We preserved the anterior part of almost all sequenced specimens. We could delimitate in total ten lineages of Chaetogaster. We intend to describe, on a DNA sequence basis, each of them as a new species for science.

Publications

Mack, J.M., Klinth M., Martinsson, S., Lu, R., Stormer, H., Hanington, P., Proctor, H.C., Erséus, C., Bely, A.E. (2023) Cryptic carnivores: Intercontinental sampling reveals extensive novel diversity in a genus of freshwater annelids. Molecular Phylogenetics and Evolution, 182:107748.

Martin, P., Knüsel, M., Alther, R., Altermatt, F., Ferrari, B., & Vivien, R. (2023). Haplotaxis gordioides (Hartmann in Oken, 1819) (Annelida, Clitellata) as a sub-cosmopolitan species: a commonly held view challenged by DNA barcoding. Zoosymposia, 23, 78-93.

Vivien, R., Lafont, M., Lods-Crozet, B., Holzmann, M., Apothéloz-Perret-Gentil, L., Guigoz, Y., & Ferrari, B. J. D. (2020). The foreign oligochaete species Quistadrilus multisetosus (Smith, 1900) in Lake Geneva: morphological and molecular characterization and environmental influences on its distribution. Biology, 9, 436.

Vivien R., Lafont M., Issartel C., Ferrari B.J.D., Martin P. The genus Chaetogaster Baer, 1827 (Annelida, Clitellata) in Switzerland: a first step towards cataloguing its molecular diversity and description of new species on a DNA sequence basis. In prep.