Multilocus ribosomal RNA phylogeny of the leaf beetles (Chrysomelidae)

Basal relationships in the Chrysomelidae (leaf beetles) were investigated using two nuclear (small and partial large subunits) and mitochondrial (partial large subunit) rRNA (approximate to 3000 bp total) for 167 taxa covering most major lineages and relevant outgroups. Separate and combined data analyses were performed under parsimony and model-based tree building algorithms from dynamic (direct optimization) and static (Clustal and BLAST) sequence alignments. The performance of methods differed widely and recovery of well established nodes was erratic, in particular when using single gene partitions, but showed a slight advantage for Bayesian inferences and one of the fast likelihood algorithms (PHYML) over others. Direct optimization greatly gained from simultaneous analysis and provided a valuable hypothesis of chrysomelid relationships. The BLAST-based alignment, which removes poorly aligned sequence segments, in combination with likelihood and Bayesian analyses, resulted in highly defensible trees obtained in much shorter time than direct optimization, and hence is a viable alternative when data sets grow. The main taxonomic findings include the recognition of three major lineages of Chrysomelidae, including a basal "sagrine" clade (Criocerinae, Donaciinae, Bruchinae), which was sister to the "eumolpine" (Spilopyrinae, Eumolpinae, Cryptocephalinae, Cassidinae) plus "chrysomeline" (Chrysomelinae, Galerucinae) clades. The analyses support a broad definition of subfamilies (i.e., merging previously separated subfamilies) in the case of Cassidinae (cassidines + hispines) and Cryptocephalinae (chlamisines + cryptocephalines + clytrines), whereas two subfamilies, Chrysomelinae and Eumolpinae, were paraphyletic. The surprising separation of monocot feeding Cassidinae (associated with the eumolpine clade) from the other major monocot feeding groups in the sagrine clade was well supported. The study highlights the need for thorough taxon sampling, and reveals that morphological data affected by convergence had a great impact when combined with molecular data in previous phylogenetic analyses of Chrysomelidae.(c) The Willi Hennig Society 2007.