The Lower Mekong: an insurmountable barrier to amphibians in southern Indochina? PETER GEISSLER 1 *†, TIMO HARTMANN 1 *†, FLORA IHLOW 1 , DENNIS RÖDDER 1 , NIKOLAY A. POYARKOV JR 2,3 , TRUONG Q. NGUYEN 4 , THOMAS ZIEGLER 5 and WOLFGANG BÖHME 1 1 Zoologisches Forschungsmuseum Alexander Koenig, Adenauerallee 160, D-53113 Bonn, Germany 2 Department of Vertebrate Zoology, Biological Faculty, Lomonosov Moscow State University, Leninskiye Gory, GSP-1, Moscow 119991, Russia 3 Joint Russian–Vietnamese Tropical Research and Technological Centre of the A.N. Severtsov Institute of Ecology and Evolution, South Branch, 3, Street 3/2, 10 District, Ho Chi Minh City, Vietnam 4 Institute of Ecology and Biological Resources, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Vietnam 5 AG Zoologischer Garten Köln, Riehler Straße 173, D-50735 Köln, Germany Received 13 September 2014; revised 13 October 2014; accepted for publication 13 October 2014 Geographical information system (GIS)-based cluster analyses and comparative ecological approaches were applied to unravel the hitherto controversially discussed role of the Mekong River as a biogeographical barrier to the amphibian fauna in Indochina. Referring to the unique and independent history of the Lower Mekong, south of the Lao–Cambodian border, this approach focused on the amphibians of southern Indochina and adjacent parts of eastern Thailand. To date, 131 amphibian species have been recorded from this region. In concordance with previous studies, our GIS-based analyses revealed that the amphibian fauna of the Cardamom Mountains, west of the Mekong, possessed no closer affinity to the herpetofauna of the Southern Annamites. In addition, a statistical comparison of ecological characters showed an occurrence of ecological differentiation among amphibians across the Lower Mekong. Our results suggest that the Lower Mekong serves as, or at least coincides with, a biogeographical barrier in southern Indochina. Here, we discuss this hypothesis, together with selected species spatial distribution patterns, their species-specific ecological traits and the palaeogeographical background of the region. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114, 905–914. ADDITIONAL KEYWORDS: Anura – biogeography – Cambodia – Gymnophiona – Laos – Thailand – Vietnam. INTRODUCTION The biogeographical research on amphibians in Indochina dates back to 1942, when René Bourret published his major comprehensive treatise on amphibians (Bourret, 1942). In this book, Bourret provided taxonomic accounts and assignations to bio- geographical units for each species. However, the majority of these units were defined according to the administrative boundaries of the ‘Union Indochinoise’: Cochinchine (comprising parts of south- ern Vietnam), Cambodge (Cambodia), Laos, Annam (central Vietnam) and Tonkin (northern Vietnam). Biogeographical research in this area was then inter- rupted for decades by political unrest in the region. In the 1990s, subsequent works repeatedly dis- cussed the biogeographical relationship of Indochina’s *Corresponding authors. E-mail: pgeissler84@yahoo.de; t.hartmann.zfmk@uni-bonn.de †These authors contributed equally to this work. Biological Journal of the Linnean Society, 2015, 114, 905–914. With 4 figures © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114, 905–914 905