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)

Mario Cupello,Fernando Z Vaz-De-Mello,Cibele S Ribeiro-Costa

doi:10.5852/ejt.2020.603

Mario Cupello, Fernando Z Vaz-De-Mello + Show 1 more

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https://doi.org/10.5852/ejt.2020.603

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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.

Highlights

There is probably nowhere else in the world where the dung beetle fauna has been as intensively studied over the past decades as in the New World, in the Neotropics
We present new data on the morphology and distribution of Streblopus based on the examination of these recently collected series of specimens and put forward new hypotheses on the evolution and biogeography of the genus forged in the light of the aforementioned new discoveries about the high-level phylogeny of the Scarabaeinae
Two main groups of questions have been raised about the evolutionary history of Streblopus: first, how many species are there in the genus, and, if more than one, how can we differentiate them? Second, what is the phylogenetic placement of Streblopus in the dung beetle tree of life, and what was the geographical origin of the genus? we address these two issues based both on our new observations about the morphology and distribution of the genus and on a synthesis of these new observations with the information present in the literature

Summary

Introduction

There is probably nowhere else in the world where the dung beetle fauna has been as intensively studied over the past decades as in the New World, in the Neotropics. Different authors have attempted to investigate the systematics of some of these isolated genera, and a general picture has emerged suggesting that many of them are more closely related to groups distributed outside the American continent and, represent cases of either very ancient vicariant events, long-distance dispersals or relict distributions of once widely distributed taxa. The ancestors of the six New World species of Oniticellini, for instance, seem to have reached the continent from the Old World at different moments during the Cenozoic either via land-bridge range expansion through Beringia (for the continental species in the United States and Mexico, and with subsequent extinction of populations in several parts of Asia and North America) or possibly via transoceanic dispersal between Africa and the Caribbean (Zunino 1982; Philips & Bell 2008; Philips 2016)

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