Cladistic analysis and host plant use of the American seed beetle genus Sennius Bridwell (Coleoptera, Chrysomelidae, Bruchinae)

The beetle genus Sennius comprises 58 species, with several undescribed South American species. While new host plants may also appear, the genus has strong association with legumes of the tribe Cassieae (Caesalpinioideae) as host plants. Here we present the first phylogetic hypotesis for Sennius based on morphology to test its monophyly and its species groups, proposed mainly for the North and Central American species. The matrix includes 58 characters and 94 terminals, with 77 species of Sennius and 17 outgroup species. We used implicit weighing with optimal constant K chosen based on the retention index and the SPR-distance. Monophyly of Sennius is recovered following ten new combinations (transference of one species from Sennius to Acanthoscelides, one from Megasennius to Sennius, and eight from Acanthoscelides to Sennius). Sennius is supported by the synapomophy of hinge sclerites in the internal sac of male genitalia. This phylogeny provides an overview of the evolution of the internal sac with its spicules and lobes. The cladogram recovered five major clades, each with five or more species, all supported by a few derived characters. Species groups stablished in literature appears as paraphyletic or polyphyletic, not being corroborated. Additionally, the basal clades are strongly associated with the host-plant genus Chamaecrista, in contrast with apical clades that tend to use the genus Senna as host, and some host shifts to other host-plants in the same subfamily (Caesalpinioideae: Cassia and Tachigali).