Origin of Madagascan Scarabaeini dung beetles (Coleoptera : Scarabaeidae) : dispersal from Africa

Abstract

Madagascar, the world’s fourth largest island, has a long history of isolation (160 MY) and a wide range of climates and ecosystems which have in turn resulted in high levels of endemism across different taxonomic levels. Although Madagascar has a rich dung beetle fauna that belongs to various tribes only three species of the Scarabaeini are found there, namely Scarabaeus viettei, S. radama and S. sevoistra. These three species are superficially quite distinctive and have, consequently, had a relatively tortured taxonomic history since the first was described in1896. The morpholgical differences between these species resulted in them being placed in different genera at different times. However, currently, based on cladistic analysis, they are all classified in the genus Scarabaeus. In this study, two of the species, S. viettei and S. radama, were included in a phylogenetic analysis based on two mitochondrial gene regions - cytochrome oxidase I (COI) and 16S rRNA - and a 247 morphological and behavioural dataset of 23 members of the Scarabaeinae. A Bayesian phylogram supports the monophyly of the genus Scarabaeus, with the two species from Madagascar appearing sister to three species of Scarabaeus from southwest Africa. Estimated times of divergence based on published mutation rates of 0.012 and 0.0075 for COI indicate that a shared African/Madagascan origin occurred around 15.18 or 24.15 MYA, respectively. This study is another example in support of Madagascan fauna having an African origin with colonisation having occurred via dispersal as opposed to ancient vicariant events.