Correspondence Island crickets (Mogoplistinae: Orne- geological (and evolutionary) time-scales, pre-human clade age, and one additional bius). PLoS ONE, 11, e0148971. and eddies and counter-currents may event is considered unconfirmed. Wilme, L., Waeber, P.O. & Ganzhorn, J.U. facilitate transport against the main cur- We find that 42 of the 48 WIO long-dis- (2016a) Human translocation as an rent direction. We review the cases of the tance dispersal events (87.5%) followed the alternative hypothesis to explain the extant and extinct WIO giant tortoises prevailing marine current, whereas the direc- presence of giant tortoises on remote and suggest that the current distribution tion of only three (6.3%) is contrary to the islands in the south-western Indian of all lineages can be convincingly current. Three events with unknown region Ocean. Journal of Biogeography. explained by overseas dispersal. of origin are omitted. Furthermore, our list Wilme, L., Waeber, P.O. & Ganzhorn, J.U. shows 42 confirmed short-distance dispersal (2016b) Marine turtles used to assist Keywords Aldabrachelys, biogeography, events within archipelagos. We thus count a Austronesian sailors reaching new Cylindraspis, giant tortoise, Madagascar, minimum number of 90 successful dispersal islands. Comptes rendus biologies, 339, marine currents, Mascarenes, overseas dis- events across long and short distances that is 78–82. persal, Seychelles, Western Indian Ocean reflected in the known extant and extinct diversity of WIO terrestrial reptiles. SUPPORTING INFORMATION MULTIPLE OVERSEAS A CLOSER LOOK AT MARINE Additional Supporting Information may be DISPERSAL EVENTS OF CURRENTS found in the online version of this article: TERRESTRIAL REPTILES With few exceptions, terrestrial organisms Appendix S1 Additional methodological Phylogenetic studies of the last decades totally depend on surface currents and information for Fig. 1 and Video S1. have revealed that overseas dispersal is winds for passive transport while drifting Video S1 Surface current dynamics in the much more common than expected earlier, at sea, and many biogeographical studies Indian Ocean 2007–2008. and that it has occurred in a wide range of discuss overseas dispersal along marine Video S2 Aldabra giant tortoise, Aldabra- geological periods (de Queiroz, 2005). The currents versus ‘counter-current’ dispersal chelys gigantea, swimming across a pond islands of the Western Indian Ocean as a factor of similar or higher importance on Aldabra Atoll, Seychelles. (WIO) region are a global hotspot of over- than distance (de Queiroz, 2005; Nathan seas dispersal, and a rich literature on the et al., 2008; Townsend et al., 2011). We topic has been produced. Crottini et al. created a map of oceanic surface currents Editor: Sonya Clegg (2012) reviewed the complex dispersal his- (Fig. 1) which shows that the westward tory of biota from Africa to Madagascar, South Equatorial Current supports drifting doi:10.1111/jbi.12893 and Vences et al. (2003) analysed and from north Madagascar to the submerged reviewed the overseas dispersal of amphib- islands between Madagascar and the ians, which is relatively common in the Comoros (the Geyser and Leven Banks), region. We restrict our review to studies Aldabra, Glorioso Island and the Comoros. relevant to terrestrial reptiles of the WIO Further north along the African coast the region except Madagascar, listed in current turns back eastward near the equa- Table 1. Native terrestrial reptiles inhabit tor. Overseas dispersal from Madagascar to How marine currents the Mascarenes (Mauritius, Rodrigues and the Mascarenes would be ‘counter-current’ influenced the widespread Reunion Island), the Seychelles including and therefore be seen as unlikely, if not natural overseas dispersal of Aldabra, the Comoros and several smaller impossible. reptiles in the Western Indian islands (Fig. 1). Existing literature identi- However, the marine circulation of the Ocean region fies continental Africa, Madagascar and the WIO is more complex than indicated by Eastern Indian Ocean region as major the main currents alone. The region of the source areas for the colonization of the Mascarene Basin between Madagascar and ABSTRACT WIO. This yields a range of minimal the Mascarenes is dominated by eddies and gyres potentially allowing transport in In a recent contribution to this journal, straight-line distances for dispersal in the > > various directions. The South Equatorial Wilme et al. (2016) proposed that the region from 130 to 5000 km, but true Countercurrent varies seasonally, favouring giant tortoises of the islands of the Wes- travelling distances may be much longer. In dispersal from Africa (and Madagascar) to tern Indian Ocean (WIO: Aldabra, the addition to these long-distance dispersal the Seychelles only in the winter. Moreover, Mascarenes, and the Granitic Seychelles) events, overseas dispersal also happened Carton & Giese (2008) and Schott et al. might have originated from translocation within archipelagos across shorter distances. (2009) detected an ‘Eastward Flow’ from by early Austronesian sailors. Prompted Under these criteria we find 35 long-distance the region south-east of Madagascar at by this paper we review recent literature dispersal events that are clearly supported by c. 25 ° south with a northward component. and show that natural overseas dispersal evidence from genetic studies, that is, diver- The occurrence of this flow means that dis- was remarkably widespread in the colo- gent allopatric clades that are clearly old persal from Madagascar to Mascarenes may nization history of terrestrial reptiles in enough to exclude the possibility of human not always be ‘counter-current’. the WIO region. Almost 90% of the suc- translocation. Further 12 events are inferred Furthermore, events such as glaciations, cessful colonization events are supported from currently recognized taxonomy based changes in freshwater influx, tectonic activity by prevailing marine surface currents. on morphological data and dated subfossils, and volcanism may change the oceanic However, these currents may change over suggesting deep genetic divergence and Journal of Biogeography 44, 1426–1440 1435 ª 2016 John Wiley & Sons Ltd Correspondence Table 1 Cases of natural long-distance overseas dispersals of reptiles in the Western Indian Ocean region. Unless otherwise marked, the origin of natural overseas dispersal was inferred from genetic data. The region of origin of the ancestors, the current distribution and the shortest straight-line distance between these regions today are given. The column ‘Along current?’ informs whether the direction of a dispersal event follows the prevailing present-day oceanic currents or not. ‘SDDE’ denotes the minimum number of Short-Distance Dispersal Events (i.e. between islands of an archipelago) following the long-distance dispersal event that are required to explain the observed biogeographical situation. This number is always zero for the granitic Seychelles because these islands were connected during periods of low sea levels. (†) refers to extinct species or populations. * Overseas dispersal inferred from phylogenetic relationships based on morphological data from fossils, subfossils, or museum specimens; no genetic data available. ** No specific age estimates are available for these taxa from the Seychelles (but see Gamble et al., 2012). Some of them may be old enough to pre-date the break-off of the Seychelles micro-continent and may have originated from vicariance rather than dispersal. *** Unconfirmed case. **** Cryptoblepharus spp. have a particularly complex biogeographical history in the WIO. After an initial dispersal from the Eastern Indian Ocean region, almost all islands of the WIO were colonized and are now inhabited by endemic clades. This case therefore comprises several long-distance dispersal events. Some relationships are confirmed by genetic data, while others are inferred through morphological studies. Distance Along Taxon name Origin Distribution [km] current? SDDE Reference Aldabrachelys gigantea Madagascar Aldabra 410 Yes - Austin et al. (2003) Oplurus sp.* Madagascar Aldabra (†) 410 Yes - Arnold (1976) Geckolepis sp.* Madagascar Aldabra (†) 410 Yes - Arnold (1976) Amphiglossus sp.* Madagascar Aldabra (†) 410 Yes - Arnold (1976) Trachylepis sp.* Madagascar or Aldabra (†) > 360 Yes - Arnold (1976) Comoros Paroedura sp.* Madagascar or Aldabra (†) > 360 Yes - Arnold (1976) Comoros Phelsuma sp.* Origin unknown Aldabra (†) 410? Yes? - Arnold (1976) (Madagascar?) Aldabrachampsus dilophus* Origin unknown Aldabra (†) 410? Yes? - Brochu (2006) (Madagascar?) Cylindraspis spp. Origin unknown Mascarenes (†) 700? No? 2 Austin & Arnold (2001) (Madagascar?) Gongylomorphus spp. Madagascar? Mascarenes (partly †) 700 No? 1* Austin & Arnold (2006) Bolyeriidae SE-Asia? Mascarenes (partly †) > 4300? Yes? - Reynolds et al. (2014) Phelsuma spp. Madagascar Mascarenes (partly †) 700 No 3 Austin et al. (2004); Rocha et al. (2009) Nactus spp.* Eastern Indian Ocean Mascarenes (partly †) > 5000 Yes 2 Arnold & Bour (2008) Leiolopisma spp. Eastern Indian Ocean Mascarenes (partly †) > 5000 Yes 1 Austin & Arnold (2006) Archaius tigris Africa Seychelles > 1200 Yes - Townsend et al. (2011) Lycognathophis seychellensis** Africa Seychelles > 1200 Yes - Vidal et al. (2008); Pyron et al. (2013) Urocotyledon spp.** Africa Seychelles > 1200 Yes - Rocha et al. (2011), Gamble et al. (2012) Trachylepis spp. Africa Seychelles > 1200 Yes - Lima et al. (2013) Ailuronyx spp.** Madagascar or Africa Seychelles