High molecular diversity in Carabus (Hygrocarabus) variolosus and C. nodulosus

Abstract

The Carabus subgenus Hygrocarabus contains two taxa: C. variolosus and C. nodulosus, the species or subspecies status of which is handled far from uniform in the literature. Both taxa show a similar morphology, the shape of the tip of the aedeagus provides a reliable morphological marker for identification. We analysed two mitochondrial gene parts (COI-5’ and COI-3’) and a nuclear one (ITS2). High diversity was found showing specific geographical patterns. Introgressive hybridisation was detected but interpreted not as an argument for subspecies status because high genetic distances indicated that it must have taken place in former times. In a laboratory hybridisation experiment, the male did not accept the female of the other taxon, supporting the conclusion that these are separate species. A series of refuges was expected for the period of ice ages. Although only the taxon C. variolosus is listed in Annex II and IV of the EU Habitats Directive, C. nodulosus also falls under this listing, as at the time of including the species into the Annexes in 2004, the two taxa were considered subspecies and hence the listing would include both, independent of later taxonomic revisions.

Museomics ofCarabusgiant ground beetles shows an Oligocene origin andin situAlpine diversification

“…Within Carabus ( Hygrocarabus ), we recover C. variolosus nested within C. nodulosus . This result contrasts with the ones of Mossakowski et al . (2020) where the two species were suggested to be well differentiated genetically.…”

“…Except for a minority of analyses, our results strongly suggest that C. ( Hygrocarabus Within C. (Hygrocarabus), we recover C. variolosus nested within C. nodulosus. This result contrasts with the ones of Mossakowski et al (2020) where the two species were suggested to be well differentiated genetically. In their study, these authors argued based on the analysis of two gene fragments that both taxa form distinct clades although several specimens caused each species to be paraphyletic.…”

“…Other studies based on reduced genomic sampling, often a single gene fragment, either failed to recover Arcifera as monophyletic (Imura et al 2000;Osawa et al 2004), or had too limited a taxon sampling to properly test the placement and otherwise monophyly of each subgenus (Su et al 2003;Sota & Ishikawa 2004;Deuve et al 2012). Except for a minority of analyses, our results strongly suggest This result contrasts with the ones of Mossakowski et al (2020) where the two species were suggested to be well differentiated genetically. In their study, these authors argued based on the analysis of two gene fragments that both taxa form distinct clades although several specimens caused each species to be paraphyletic.…”

“…We argue that in the current state of our knowledge it is not yet possible to definitively test species boundaries, past introgression and signature of hybridization between Carabus nodulosus and C. variolosus . A desired approach would be to combine a large geographical sampling as in Mossakowski et al . (2020) with a genomic scale dataset as developed in the present study to revisit the systematic conundrum within this subgenus at the population level.…”

“…It currently includes four subgenera: Carabus (Hygrocarabus) Thomson, 1875, Carabus (Platycarabus) Morawitz, 1886, Carabus (Chaetocarabus) Thomson, 1875 and Carabus (Heterocarabus) Morawitz, 1886 (Deuve 2019(Deuve , 2021. Within Arcifera, the subgenus Carabus (Hygrocarabus) contains two species found from France to Ukraine, the status of which has been extensively debated over the past decades due to reduced morphological differences and inconsistent genetic admixture patterns (Müller-Kroehling et al 2006;Müller-Kroehling et al 2014); Matern et al 2009Matern et al , 2010Mossakowski et al 2020). These hygrophilous nocturnal species live in river banks and hunt close or in the water of cold forest streams.…”