Towards the phylogeny of chafers (Sericini): analysis of alignment-variable sequences and the evolution of segment numbers in the antennal club.

Scarabaeoid beetles display a distinctive lamellate antenna carrying olfactory sensillae which show various trends of surface enlargement, including the increased number of the terminal lamellate antennomeres. The presence of >3 lamellae ('plurilamellate' antennae) in some groups has been used in the classification of chafers (Melolonthinae) and in particular in the tribe Sericini. However, this character may not be phylogenetically conservative. Here we present a phylogenetic analysis based on partial 28S rRNA, cytochrome oxidase I (cox1) and 16S rRNA (rrnL) for 183 species of Scarabaeidae, representing all traditionally recognized subfamilies, with particular focus on Sericini. Alignments of length-variable sequences were obtained applying various alignment algorithms and parameter settings. Tree topologies from the combined analysis were very similar when rrnL alignment was based on the progressive alignment algorithm MAFFT, MUSCLE, and less so Clustal, but differed greatly when using the probabilistic PRANK and the 'local' alignment procedure BlastAlign, while alignment conditions for the smaller 28S rRNA had little impact on the combined analysis. Preferred conditions were chosen based on an extensive analysis of character congruence between markers and recovery of well established taxonomic groups. Combined analyses on the best alignments using parsimony, maximum likelihood and Bayesian inference generally supported the traditional classification, including the monophyly of Scarabaeidae, with Glaphyridae as its sister, the monophyly of Cetoniinae, and the monophyly of most tribes included. Various levels of support were also obtained in favor of a proposed sister relationship of Sericini with Ablaberini, their close relationships to a melolonthine clade consisting of several tribes with exclusively Southern Hemisphere distribution, and the monophyly of Old World Sericini. In contrast, the generic level relationships were not consistent with the existing taxonomy. The large genera Neoserica, Microserica, and Maladera each split in several distantly related branches. The segment number of the antennal club when optimized onto the preferred tree revealed that plurilamellate antennae originated repeatedly (9-10 times in Sericini, plus multiple origins in other Melolonthinae). This invalidates the use of this trait in the generic classification. The number of lamellae is likely to be relevant to mate recognition, as it affects the spatial organization and number of olfactory sensillae. The high level of homoplasy in antennal characters may indicate a causal link between the morphological diversity of the antennae and the great species richness of Sericini and related melolonthines.