Multilocus molecular systematics and evolution in time and space of Calligrapha (Coleoptera: Chrysomelidae, Chrysomelinae)

摘要

Calligrapha (Coleoptera: Chrysomelidae) is a genus with species present in most of the American continent, from the Arctic polar circle to the Pampas in Argentina. In its current concept, the genus comprises some 80 species, but the diagnosis of the genus is problematic, based on a combination of potentially symplesiomorphic character states. In this study, we investigate the largest taxonomic sample of Calligrapha diversity to date (43 species) using a phylogenetic perspective based on more than 6000 molecular characters from eight genes (four mitochondrial and four nuclear) for a systematic evaluation of the genus. The analyses also include thirteen species in the closely related Zygospila (currently a subgenus of Zygogramma) to assist the systematic delimitation of Calligrapha. Partitioned and total evidence phylogenetic trees were additionally used for molecular clock analyses and dating based on standard mtDNA evolutionary rates, and for likelihood-based inference of ancestral areas. Calligrapha and Zygospila are reciprocally paraphyletic, and our interpretation of taxonomic stability merges both taxa into a larger genus Calligrapha which plausibly originated in the dry steppes of southern North America in the Late Miocene. The genus includes a minimum of five strongly supported lineages which initially diversified in the Pliocene, fully congruent with expectations from morphology, but of uncertain mutual relationships. Only two of these lineages dispersed to South America: the group of C. polyspih right at the time of the final closure of the Isthmus of Panama in the Early Pliocene and the group of C. argus only in recent times, well in the Pleistocene. The most species-rich lineage of Calligrapha, associated to trees and shrubs typical of riverine and lacustrine environments (as opposed to herbaceous steppe plants, generally Malvaceae and Asteraceae, for most other groups) diversified and spread in North America in the Late Pliocene. The ecological shift to a stable habitat spreading in the continent due to climate change is hypothesized as one possible explanation for the evolutionary success of this group.