Canthonini (Scarabaeidae: Scarabaeinae) of Gondwana : comparison of male genitalia evolutionary trends and phylogeny

Abstract

The current study is about the evolution and the morphology of dung beetles, subfamily Scarabaeinae. The study includes the systematics of the tribe Canthonini and an exhaustive analysis of the morphological variation of male genitalia including species from the 11 tribes of the subfamily, mainly Canthonini, Ateuchini, Scarabaeini and Coprini. With the aim to go deep in the phylogenetic relationships of the tribe Canthonini, the largest of the subfamily Scarabaeinae, with 91 genera and 875 species, a total of 109 genera, 327 species and 513 specimens were reviewed. The tribe Canthonini is mainly distributed in Gondwana, with species in America, Africa, Madagascar, Australia, New Zealand and the Oriental region. Species of the different regions were included in the detailed examination of male genitalia as well in the cladistic analysis using morphological characters. Strong evidence of a need for sub-division of Canthonini in natural groups, morphologically and ecologically more solid groups, is one of the main results obtained. Three tribes are proposed, the tribe Byrrhidiini (Byrrhidium, Dicranocara, Namakwanus, and Versicorpus), tribe Circelliini (monotypic genus Circellium), and the tribe Canthonini, firstly with the American genera (Canthon, Malagoniella, Megathopa, Megathoposoma, Eudinopus, Canthonidia, Tetraechma, Anisocanthon, Melanocanthon, Sylvicanthon, and Hansreia), as well as the African genera Gyronotus and Anachalcos. Genera from Madagascar, Australia and the Oriental region should be treated in separate analyses, and probably the pre-established tribes such as Panelini, Epilissini and Mentophilini, could acquire validity in the context of a new classification for these groups currently in Canthonini. The phylogeny of the genus Epirinus and description of six new species is also presented. Epirinus is a monophyletic group, although by morphological differences, is not considered under the tribe Canthonini. Equally the genus Deltochilum is not considered as part of the tribe Canthonini, since in the phylogenetic analysis of American genera, Deltochilum appear polyphyletic, and this genus deserves a more detailed analysis of its systematics and classification. Patterns of variation in the genitalia structures, mainly the sclerites, were useful in species separation and to define genera. However, the patterns were not so suitable in setting the limits of the tribes. To date, taxonomists have been trying to fit the whole range of variation in species and genera into a preestablished and limited Scarabaeinae tribal classification. Based on this study the recommendation for a better understanding of the evolutionary history, and to improve the taxonomic classification of the tribe Canthonini and the Scarabaeinae dung beetles, is to study in detail each group, in morphological, molecular and even ecological and biogeographical aspects. Information from these different approaches, will help to establish the borders for the tribes, and therefore to have more accurate classifications.