Human-mediated dispersals do not explain tortoise distribution on the Indian Ocean's islands

Abstract

Origins of giant tortoises on the Indian Ocean's islands have been debated, and most recently attributed to human translocation (see Wilme, Patrick, & Ganzhorn, 2017). To resolve the issue, we analyse all available molecular sequences from extinct and extant Indian Ocean's giant tortoises, along with major clades of the family Testudinidae using phylogenetic methods, Bayesian inference and maximum likelihood, and a relaxed time calibration approach. Our results most strongly support giant tortoises of the genus Cylindraspis evolving in situ in the Mascarene Islands since the early mid-Miocence, and Aldabra tortoises diverging from a Madagascan lineage in the early Oligocene. The geologic time-scale of these speciation events and the resulting island endemism for each lineage do not support human translocation, but rather demonstrate the impressive ability of giant tortoises to disperse long distances across oceans.