Diagnostic and phylogenetic character variation in the genus Canthon Hoffmannsegg and related genera (Coleoptera: Scarabaeidae: Scarabaeinae)

Abstract

Morphological variation was examined in 58 species of Canthon and 18 species of other genera of the subtribe Canthonina (Anisocanthon, Canthonella, Cryptocanthon, Deltochilum, Hansreia, Holocanthon, Malagoniella, Melam canthon, Scybalocanthon, and Sylvicanthon). A total of 667 specimens was used for examination of morphological characters. Variation in head structures such as clypeus, eyes, labium, gula, and epipharynx is described. Thoracic structures examined include the pronotum, prosternum, and posterior and medial tibiae. Other structures examined were the elytra, pygidium, and male genitalia, including the sclerites and bushes of the internal sac of the aedeagus. Secondary sexual features (shape of anterior tibial spur and shape of last abdominal segment) were also examined. The characteristics examined include diagnostic characters for the genus Canthon. This analysis revealed that Canthon is a very heterogeneous and artificial group, the limits of which are based on a combination of characters that is not exclusive to genus. Many characters that have been used in the diagnosis of Canthon are general characters that show wide variation within Canthon as well as in other genera of Canthonina. Only a few derived characters were exclusively shared by species of Canthon. However, several genera of Canthonina shared with Canthon some characters, mainly in structures such as the epipharynx and the internal sac of the aedeagus, (epipharynx with two well-defined lateral combs, internal sac with a complete ring-shaped sclerite, reduction in the postero-dorsal aperture of the eye, and reduction in the setae of the anterior margin of the mentum). Due to the fact that the external morphology shows great variation, it is important to consider the study of the other possible sources of characters to resolve the phylogenetic relationships among groups.