Polydrusus Germar, 1817

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 : 27-28

Genus Polydrusus Germar, 1817

We included five samples of this genus belonging to 3 species out of 2 subgenera ( Piezocnemus Chevrolat, 1869 and Chlorodrosus K. Daniel & J. Daniel, 1898 ). The species were not retrieved in a monophyletic clade ( Fig. 1 , Supp. 1), suggesting that the species concept of Polydrusus is also polyphyletic, which is not really a surprise, regarding the span of morphological variability.

In the case of the sibling alpine species Polydrusus paradoxus Stierlin, 1859 / chaerodrysius Gredler, 1866 the differences in the COI support the very subtle morphological characters; both species can be distinguished mainly by the form of the scales on their femora ( Germann, 2012). Thus it can be stated that small morphological differences are mirrored by a considerable genetic distance (K2 distance: 0.048). Furthermore, although from apparently very isolated populations, the samples of P. chaerodrysius collected in Valchava GR (sample 103) and Schwarenbach BE (208 km from each other; sample 143 / sample 063) differ in solely 0.2 % ( Table 6). More localities were not discovered at present, despite of several specific excursions inbetween.An explanation could be their parthenogenetical reproduction, where no gene-exchange as in sexual reproduction occurs.

species-pair Phyllobius pyri / vespertinus

The species status of Phyllobius vespertinus (Fabricius, 1792) was (and still is) highly debated (e.g. Dieckmann, 1979; Germann, 2011a; Alonso-Zarazaga, 2013) and recently regarded as synonym to P. pyri (Linné, 1758) (e.g. Colonnelli, 2003; Yunakov, 2013). While Phyllobius pyri lives mostly on arboreous Rosaceae and shows a more elongate body and a regularly coloured vestiture, P. vespertinus is more xerothermophilous, lives on various herbaceous plants, its body is more stout, the elytra often with a striped vestiture. We here included further specimens from the southern side of the Alps, where the characters of P. vespertinus are well pronounced [and from there (Monte Rosa, Val d’Entremont, St. Bernhard) once described as separate taxon artemisiae Desbrochers, 1873, junior synonym of P. vespertinus]. However, we provide further support that the taxa are not separable based on analyses of COI sequences ( Fig. 1 , Supp. 1), as already shown by Schütte et al. (2013). Similar to the Hypera nigrirostris -group, COI might be not sensitive enough to show differences, due to recent (ecological) separation of the taxa (i. e. incomplete lineage sorting), and/or genetical interchange (hybridisation) might still occur.

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.