Riverbeds demarcate distinct conservation units of the radiated tortoise (Geochelone radiata) in southern Madagascar

The radiated tortoise (Geochelone radiata) is an endangered species endemic to Madagascar. It inhabits the semiarid spiny forest of the southern part of the island, an ecosystem heavily affected by habitat destruction. Furthermore, illegal harvesting greatly threatens this species. The main objectiv...

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Bibliographic Details
Published in:Conservation genetics 2007-08, Vol.8 (4), p.797-807
Main Authors: Paquette, Sébastien Rioux, Behncke, Sandra M, O'Brien, Susan H, Brenneman, Rick A, Louis, Edward E. Jr, Lapointe, François-Joseph
Format: Article
Language:English
Subjects:
Endangered species
Endemic species
Environmental degradation
Genetic diversity
Genetic structure
Geochelone radiata
Habitat loss
Management units
Markov chains
microsatellite repeats
Monte Carlo simulation
Radiated tortoise
Reintroduction
Rivers
Tortoises
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Summary:The radiated tortoise (Geochelone radiata) is an endangered species endemic to Madagascar. It inhabits the semiarid spiny forest of the southern part of the island, an ecosystem heavily affected by habitat destruction. Furthermore, illegal harvesting greatly threatens this species. The main objective of our study was to acquire better knowledge of its genetic structure, in order to take appropriate management decisions concerning, for instance, the reintroduction of confiscated individuals. Our hypothesis was that rivers represent effective barriers to tortoise dispersal despite the fact that they are dry most of the year. We used 13 polymorphic microsatellite markers to compare samples from six populations across the range of the species. All analyses (Fisher's exact tests, F ST values, AMOVA) indicated that the radiated tortoise exhibits moderate levels of genetic structure throughout its range. In addition, we used a multiple regression approach that revealed the importance of rivers to explain the observed structure. This analysis supported the role of the Menarandra and Manambovo Rivers as major barriers to the dispersal of most radiated tortoises, but Markov chain Monte Carlo simulations revealed that low levels of recurrent gene flow may explain why F ST values were not higher. We identified three distinct conservation units with relatively high assignments rates (87%), which should be valuable for the management of the species. This is the first study to report the genetic structure of a species sampled throughout the Malagasy spiny forest.
ISSN:1566-0621
1572-9737
DOI:10.1007/s10592-006-9227-5