Systematics of the enigmatic South American Streblopus Van Lansberge, 1874 dung beetles and their transatlantic origin: a case study on the role of dispersal events in the biogeographical history of the Scarabaeinae (Coleoptera: Scarabaeidae)

Abstract

Streblopus Van Lansberge, 1874 has been one of the most mysterious dung beetle groups of the Neotropical fauna, having a rather peculiar morphology, very few known specimens in collections and a difficult placement among the scarabaeine lineages. In this work, based on the examination of a recently collected series of specimens and a synthesis of some scattered, but deeply valuable, information available in the literature, we readdress many of the questions posed by past authors. It is shown that Streblopus is a relict genus composed of two currently living species of widely disjunct distribution, namely S. opatroides Van Lansberge, 1874, from patches of Atlantic Forest in the Brazilian states of Bahia and Espírito Santo, and S. punctatus (Balthasar, 1938), known from a few localities across Sub-Andean humid forests in the Peruvian and Ecuadorian Amazon Forest. We redescribe both and present in detail the evidence pointing to their validity as two independent species; a discussion of their remarkable sexual dimorphism is also given. The biogeography of Streblopus in South America is addressed, and we conclude that the present disjunct distribution of the genus is a consequence of the retreat of the tropical forest corridors that once connected the Atlantic Forest to the Amazon Basin through the South American Dry Diagonal during several periods of the Neogene, particularly until the Middle Miocene. Finally, we propose an African origin for the genus based on its close phylogenetic relationship with a group of Old World taxa ‒ particularly Circellium Latreille, 1825 and Scarabaeini. Having diverged from those groups in the late Upper Cretaceous, we argue that the ancestor of Streblopus arrived in South America crossing the Atlantic Ocean by rafting. We present a synthesis of data from a wide variety of biological groups to support our ideas and contend that long-distance dispersal hypotheses should be taken more seriously by scarab beetle specialists.

Paleogene forest fragmentation and out‐of‐Africa dispersal explain radiation of the Paleotropical dung beetle tribe Epactoidini trib. nov. (Coleoptera: Scarabaeinae)

“…Alternatively, it is logical to propose the existence of multiple corridors that might have been separated in time due to oscillating aridification events.Summing up, our study suggests that that the current distribution of Epactoidini was predominantly shaped by the interplay of two mechanisms. One is the routine transoceanic dispersal events: two such events have mediated the overwater migration of Epactoidini ancestors from Africa to Madagascar and further to Réunion island.Another mechanism is the Gomphotherium forest corridor that mediated the dispersal of Epactoidini to Oriental Region from Africa.Transoceanic and transcontinental dispersals shaped the current distribution of various Scarabaeinae clades(Cupello et al, 2020;Gillett & Toussaint, 2020;Gunter et al, 2019;Sole et al, 2011;Sole & Scholtz, 2010). The exclusively Paleotropical disjunct distribution of the tribe Epactoidini is remarkable within the subfamily Scarabaeinae.The use of the Gomphotherium corridor as dispersal route has never been previously proposed for any other dung beetle clade.Members of the tribeEpactoidini are obligate forest-dwellers, which makes them habitat specialists.…”

Towards a comprehensive taxonomic revision of the Neotropical dung beetle subgenus Deltochilum (Deltohyboma) Lane, 1946 (Coleoptera: Scarabaeidae: Scarabaeinae): Division into species-groups

“…As noted by Cupello et al . [ 66 ] in Deltochilini genera as well as in other so-called “roller” genera, which lack cephalic or pronotal horns, both strong sexual dimorphism as well as allometric variation in some male structures are uncommon. Several species of Deltohyboma present sexually dimorphic allometry, expressed mainly on insertion of the metatibial spur and in tubercles on the posterior edge of the meso- and metafemur.…”

Metagenomics reveals that Dung Beetles (Coleoptera: Scarabaeinae) broadly feed on Reptile dung and could feed on that of Dinosaurs

“…The endemic clades found in New Caledonia and New Zealand dispersed from Australia at 50-55 Mya (Gunter et al, 2016). According to this evidence, it is reasonable to assume that the first colonizers evolved the generalist diet, which included feeding on sauropsid dung, as a way to circumvent food shortages caused by the lack of large mammals on the islands (Cupello et al, 2020). Nevertheless, a conclusion of this nature requires further investigation in the phylogenetic framework in order to reconstruct ancestral diets and refine colonization times.…”