The Phanaeus tridens species group (Coleoptera: Scarabaeoidea): a dung beetle group with genital morphological stasis but a changing ecological niche

Abstract: The Phanaeus tridens species group is revised and found to consist of twelve species: P. tridens Castelnau, 1840, P. moroni Arnaud, 2001 stat. rev., P. balthasari Arnaud, 2001 stat. rev., P. daphnis Harold, 1863, P. coeruleus Bates, 1887 stat. rev., P. herbeus Bates, 1887 stat. rev., P. substriolatus Balthasar, 1939 stat. rev., P. furiosus Bates, 1887, P. pseudofurcosus Balthasar, 1939 stat. rev., P. nimrod Harold, 1863, P. victoriae Moctezuma sp. nov., and P. eximius Bates, 1887. The majority of the name-bearing types of the group were revised. The neotype for P. tridens is suggested herein. The following junior subjective synonymies are recognized: P. frankenbergeri Balthasar, 1939 = P. tridens Castelnau, 1840, P. tricornis Olsoufieff, 1924 = P. herbeus Bates, 1887, and P. babori Balthasar, 1939 = P. nimrod Harold, 1863; while P. furcosus Felsche, 1901 = P. furiosus Bates, 1887 is recognized as a junior objective synonymy. The species within the P. tridens species group are diagnosed by the morphology of the pronotum and elytra, while the genital morphology of males is found to be homogeneous and uninformative for species delimitation. Most species within the group show a wide diversity of colouration (showing green, red, and blue chromatic phases). This probably led to taxonomical confusion by previous authors. Here, we present a new identification key, species distribution models. Habitus photographs and character illustrations for all the species within the group are provided. The climatic niches overlap widely in P. herbeus and P. daphnis, but the other species within the group show a reduced overlap in their climatic niches. Consequently, the P. tridens species group is proposed as a case of morphological stasis that might be explained by a trade-off between the evolution of pronotal structures and genitalia, while differences in the ecological niche might promote speciation.

Key words: Coleoptera, Scarabaeidae, Phanaeini, scarab rainbow dung beetles, iridescence, chromatic variation, ecological niche, distribution model, Mexico, Neotropical Region