Phylogenetic analysis of Hydrophiloidea (Coleoptera: Polyphaga) based on molecular data and morphological characters of adults and immature stages

An extensive combined data set comprising 160 morphological characters of adults and immature stages of Hydrophiloidea and sequences of six different genes were analysed using parsimony and a Bayesian approach. Analyses were carried out with equal weight for individual morphological and molecular characters, and alternatively with approximately equivalent weight for the entire partitions, i.e., 147 informative morphological characters x 9.5 approximate to 1383 informative molecular characters. With the former approach some conventional groups such as the histeroid lineage (Histeridae and Sphaeritidae), Helophorinae and Sphaeridiinae were recovered. However, the branching pattern as a whole is strongly in contrast to the results of previous studies. The results obtained with the modified weighting scheme (9.5:1) conform more to morphology based analyses. The monophyly of Hydrophiloidea, Histeridae + Sphaeritidae, Epimetopinae + Georissinae, Helophorinae, Sphaeridiinae and of the hydrophiline-sphaeridiine lineage is supported in the parsimony analysis. Spercheinae is placed as sister group of all the remaining hydrophiloid groups and a clade is formed by the subfamilies Epimetopinae, Georissinae, Hydrochinae and Helophorinae. In the Bayesian analysis the monophyly of Hydrophilidae is supported. Georissinae form a clade with Hydrochinae, and Epimetopinae are placed as sister group of a clade comprising Spercheinae + the hydrophiline-sphaeridiine lineage. Berosus is placed as the sister group of the remaining groups of Hydrophilinae-Sphaeridiinae in both analyses, and Sphaeridiinae are always nested within a paraphyletic Hydrophilinae. The divergent results of the different analyses show that important questions in the phylogeny of Hydrophiloidea such as for instance the placement of Spercheinae are still open.