Larval morphology of the diving beetle Celina and the phylogeny of ancestral hydroporines (Coleoptera : Dytiscidae : Hydroporinae)

摘要

Phylogenetic relationships within diving beetles (Dytiscidae) are imperfectly known. In particular, some authors have considered that the tribe Methlini is included in the subfamily Hydroporinae (a large group including about half of the dytiscid species worldwide), whereas others have argued in favour of excluding Methlini from the Hydroporinae and giving it subfamilial rank. Larval characters have been underutilised in phylogenetic studies, mainly because the larvae of many taxa within the family are still unknown. The larval morphology of the dytiscid tribe Methlini, in particular, remains poorly known. In this study, the phylogenetic relationships among ancestral lineages of the Hydroporinae are investigated based on a cladistic analysis of 34 taxa and 127 morphological larval characters. For this purpose, larvae of the Methlini (Celina parallela (Babington, 1841)) and C. imitatrix Young, 1979) are described and illustrated in detail for the first time, with particular emphasis on morphometry and chaetotaxy. The results show high support for a monophyletic origin of the Hydroporinae, including Methlini, based on eight unique character states. Giving Methlini subfamily rank would leave Hydroporinae with a single unique larval apomorphy. This supports the inclusion of Methlini as a tribe of Hydroporinae. Other interesting but less well supported results include: 1, the clade Laccornini + Hydrovatini + Canthyporus Zimmermann, 1919 (Hydroporini) resolved as the sister-group to the other Hydroporinae minus Methlini; and 2, Hydrovatini and Canthyporus resolved as sister-groups. The presence of a galea, albeit in a reduced form, in larvae of Methlini, Laccornini and Hydrovatini is of the utmost interest. The putative hypothesis of an ancestral position for these genera within Hydroporinae suggests that hydroporines lost the galea secondarily.