Dichotrachelus Stierlin, 1853

Christoph Germann, Sofia Wyler & Marco Valerio Bernasconi, 2017, DNA barcoding of selected alpine beetles with focus on Curculionoidea (Coleoptera), Revue suisse de Zoologie 124 (1), pp. 15-38 : 21

Genus Dichotrachelus Stierlin, 1853

The monophyly of the genus Dichotrachelus is strongly supported in both our analyses ( Fig. 1 , Supp. 1). Within this genus, there is definitely more hidden diversity in these relatively immobile typically alpine living species distributed from the Rif Mountains of Morocco to the Carpathians in the east, with a speciation centre in the arc of the Alps. The species are ecologically bound either to mosses (“old” lineages) or Saxifragaceae (“derived” lineages) ( Meregalli et al., 2015). Based on COI sequences, we found at least in three species considerable differences among the samples, promoting the hypotheses of existing cryptic species.

Data from D. koziorowiczi Desbrochers des Loges, 1873 from two localities on Corsica (one in the North at Col de Verghio; the other in the South on Monte Calva) show that two taxa (K2 distance: 0.067; Table 2) are likely to occur on this island, instead of one at present described species. Only the examination of the type specimen(s) will help to resolve this issue, as no precise type locality on the island has been given by Desbrochers (1873).

Similarly, with the D. maculosus Fairmaire, 1869 - species group, where specimens of D. maculosus from rather isolated populations in the Vercors, at the western border of the main distribution area, differ from those from the Swiss Prealps (K2 distance: 0.026).

Also in the D. augusti F. Solari, 1946 - species complex, more morphological diversity was discovered (see Germann, 2011b), here corroborated partly by the detected genetic diversity. The rather isolated population from the Saas Valley (sample 89) differs genetically considerably (K2 distance: 0.115!) from those of samples from the Grand St. Bernard and Col de Balme regions at the Swiss-Italian and Swiss-French border, which is indeed surprising, as it is surprisingly not reflected in their morphology, whereas D. sondereggeri Germann, 2011 shows differences, but solely results in a genetic distance of 0.016 compared with the western populations of D. augusti. Furthermore, the different forms of the penis ( Germann, 2011b) detected in the western populations of D. augusti in turn are not supported by relevant differences in the COI (0.002). However, to definitely delimit and show more solid insights into the systematics of the D. augusti -species complex we would still have to include samples from the type locality of D. augusti from around Champoluc in Valle d’Aosta. Additionally, the highly specialised habitat demands of the D. augusti - species complex might explain for the genetic differences between geographically close populations: all species of this complex live in mosses growing in alpine scree slopes, an unusual and certainly underestimated habitat, less in Carabidae (where exciting discoveries have been reported e.g. Molenda, 1996; Molenda & Gude, 2003; Huber & Molenda, 2004), or Staphylinidae ( Molenda, 1999) , but more in weevils where hardly any research has been done, and a promising field for investigations lies idle (Nikolai Yunakov, personal comm.). The alpine scree slopes thereafter can be seen as islands for the populations of the D. augusti -complex, where gene exchange via migrating individuals across alpine grasslands and glaciers might be very limited. This specific case once more shows that samples from populations of a species, at least if we deal with low mobile species, should be chosen very carefully.

The samples of species assigned to the D. rudenispecies group, based on a similar external morphology and male genitalia with a prolonged, laterally flattened tip of penis, also clustered together ( D. rudeni Stierlin, 1853 , D. imhoffi Stierlin, 1857 and D. variegatus Daniel & Daniel, 1898 ) and therefore support the outcomes from previous morphological investigations ( Table 2). The samples of D. rudeni cluster all together with high bootstrap support (ML 99%, respectively NJ 98%), although there is some herogeneity in it with sample 109 from the eastern border of the distribution near Disentis (sample 109) differing most from the others (0.010 to 0.016).

Figures

Fig. 1. Best Maximum Likelihood tree as selected by MEGA) based on COI sequences of 142 samples of Curculionoidea (Chrysomelidae obtained by using MEGA 6. Values (over 50 %) of bootstrap support from 100 nodes.