Molecular phylogenetics and evolutionary analysis of body shape in the genus Cyrtonus (Coleoptera, Chrysomelidae)

Abstract

The leaf beetle genus Cyrtonus Latreille, 1829 (Chrysomelidae, Chrysomelinae) is a species-rich genus subendemic to the Iberian Peninsula, with only a few species in the neighbouring France and Morocco. All the species are wingless and preferentially inhabiting mountainous areas. The taxonomic knowledge of this group is extremely poor and its systematics almost inexistent. Here, we analyse and characterize with a morphometric analysis one promising systematic trait, the adult body profile, distinguishing between elongated and rounded shapes. Although the monophyly of the genus is not contentious, we test for it using mitochondrial rrnl sequences and the chrysomeline homologous sequences available in GenBank. In addition, four genetic markers, two mitochondrial and two nuclear are used to produce a phylogenetic hypothesis for half the species within the genus and to analyse the evolution of shape, summarized as two continuous variables, length and width, and their ratio. These traits covary significantly with the phylogeny, showing a strong phylogenetic association: elongated species appear to constitute a clade within a paraphyletic assemblage of rounded species. In addition, the mitochondrial DNA tree is used to test for constant rate of evolution in this marker and is calibrated using both biogeographical evidence and the standard insect mitochondrial average substitution rate. This molecular clock hypothesis is used to date the age of speciation events on the phylogeny, reconstructing the origin of the genus in the Middle Miocene, with a relatively constant speciation rate until the end of the Pliocene and an apparent increase in this rate in the Pleistocene, possibly associated with the effect of dramatic climatic changes in this period. Finally, the high systematic value of shape profile in Cyrtonus is discussed, arguing the absence of evidence relating it to adaptation. © 2007 The Authors.