On the systematic position of the diving-beetle genus Pachydrus (Coleoptera: Dytiscidae: Hydroporinae): evidence from larval chaetotaxy and morphology

MICHAT, M. C.; TORRES, P. L. M.

EUROPEAN JOURNAL OF ENTOMOLOGY (CESKE BUDEJOVICE)

Institute of Entomology

Lugar: Praga, República Checa; Año: 2008 vol. 105

1210-5759

Phylogenetic relationships within the diving-beetle subfamily Hydroporinae are not well understood. Some authors have considered that the genus Pachydrus Sharp, 1882 is included in the tribe Hyphydrini, whereas others have argued in favour of excluding Pachydrus from the Hyphydrini and placing it in its own tribe, Pachydrini. Larval characters have been underutilised in phylogenetic studies, mainly because the larvae of many taxa within the family are unknown. In this study, the phylogenetic relationships of Pachydrus are studied based on a cladistic analysis of 29 taxa and 122 morphological larval characters. For this purpose, larvae of P. obesus Sharp, 1882 are described and illustrated in detail for the first time, with particular emphasis on morphometry and chaetotaxy. First and second instars had been unknown for the genus. The results show high support for a monophyletic origin of the tribe Hyphydrini excluding Pachydrus, based on several unique character states. On the other hand, Pachydrus is resolved as the sister group of Hydrovatini, with a relatively high support. These results suggest the inclusion of Pachydrus in its own tribe, Pachydrini. Given that Hyphydrini minus Pachydrus is a highly distinctive group based on this study, it seems useful to recognise this group as Hyphydrini. Including Pachydrus in Hyphydrini would leave the tribe without larval apomorphies, as the characters present in Hyphydrini and Pachydrus are also present in Hydrovatini. Pachydrus is a highly distinctive genus within Hydroporinae, characterised by several larval apomorphies.