The evolutionary origin of Indian Ocean tortoises (Dipsochelys).
Abstract
Today, the only surviving wild population of giant tortoises in the Indian Ocean occurs
on the island of Aldabra. However, giant tortoises once inhabited islands throughout
the western Indian Ocean. Madagascar, Africa, and India have all been suggested as
possible sources of colonization for these islands. To address the origin of Indian
Ocean tortoises (Dipsochelys, formerly Geochelone gigantea), we sequenced the 12S,
16S, and cyt b genes of the mitochondrial DNA. Our phylogenetic analysis shows Dipsochelys
to be embedded within the Malagasy lineage, providing evidence that Indian Ocean giant
tortoises are derived from a common Malagasy ancestor. This result points to Madagascar
as the source of colonization for western Indian Ocean islands by giant tortoises.
Tortoises are known to survive long oceanic voyages by floating with ocean currents,
and thus, currents flowing northward towards the Aldabra archipelago from the east
coast of Madagascar would have provided means for the colonization of western Indian
Ocean islands. Additionally, we found an accelerated rate of sequence evolution in
the two Malagasy Pyxis species examined. This finding supports previous theories that
shorter generation time and smaller body size are related to an increase in mitochondrial
DNA substitution rate in vertebrates.
Type
Journal articleSubject
AnimalsBayes Theorem
Biological Evolution
Cytochrome b Group
DNA, Mitochondrial
Genetic Variation
Indian Ocean
Madagascar
Phylogeny
RNA, Ribosomal, 16S
Turtles
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