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An Indo-Malayan stag beetle, Aegus chelifer Macleay 1819, was found for the first time in the Seychelles (Mahé, Praslin, La Digue, Cerf ) during four surveys conducted between 2006 and 2009. The species had not been recorded in previous research on the insect fauna of these islands, even in the most recent and comprehensive studies. A. chelifer now appears to be common and widespread in the granitic islands of the archipelago, especially in Mahé, suggesting that a stable population occurs at least on this island. As all the records were made after the 2004 Indian Ocean tsunami, the occurrence of the species in the Seychelles could be explained by transoceanic dispersal from South East Asia by floating tree trunks, due to the action of ocean currents on logs removed from Asia by the tsunami.
KEY WORDS: Lucanidae, Aegus, Seychelles, biological invasion, tropical islands, fauna, biogeography, dispersal.
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INTRODUCTION
One of the major threats to biodiversity is represented by alien species, i.e. plant and animals that expand their primary range, favoured by human activities. It is now widely accepted that island ecosystems worldwide are severely affected by these invaders, which alter the interspecific relationships within biological communities and lead to the extinction of indigenous taxa (Sax et al. 2005, Lockwood et al. 2006, Whittaker & Fernandez-Palacios 2007, New 2008). For these reasons, evaluating the current distribution of invasive species and their spread is one of the most important targets of insular biogeography applied to biodiversity conservation.
The Republic of the Seychelles comprises 115 islands in the Western Indian Ocean, including both granitic and coralline islands. The granitic islands are larger and are situated in the northern part of the archipelago. They are the remnants of the Seychelles microcontinent that was isolated following the breakup of Gondwanaland, in the Mesozoic Era, 65-100 million years ago (Stoddart 1984, Gerlach 2008). More specifically, the initial rift was from Madagascar in the Middle Cretaceous, then from India at the end of the Cretaceous (Collier et al. 2004). For this reason, these islands harbour a complex mosaic of components in their species assemblages, due to both vicariant and dispersal events involving Africa, Madagascar and India. The vicariance component includes taxa of ancient origin like the sooglossid...