Conservation Genetics

, Volume 8, Issue 4, pp 797–807 | Cite as

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

  • Sébastien Rioux Paquette
  • Sandra M. Behncke
  • Susan H. O’Brien
  • Rick A. Brenneman
  • Edward E. LouisJr.
  • François-Joseph Lapointe
Original Paper


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.


Genetic structure Management units Microsatellites Radiated tortoise Madagascar 



This study was in part supported by a NSERC scholarship, a FES scholarship from Université de Montréal and a scholarship from the Agence Universitaire de la Francophonie (AUF) to S.R.P., and NSERC grant no. 0155251 to F.J.L. This research was further supported by the Ahmanson Foundation, which provided the laboratory at the Henry Doorly Zoo with three ABI automated sequencers. This project would not have been possible without the support of the Institute for Conservation of Tropical Environments, Madagascar (ICTE-MICET), the Parc Botanique et Zoologique de Tsimbazaza (PBZT), the Université de Tuléar, the Centre Écologique de Libanona (CEL) at Fort-Dauphin, the Association Nationale pour la Gestion des Aires Protégées (ANGAP) and the Ministère des Eaux et Forêts of Madagascar. Deeply appreciated additional logistical assistance was provided by the staff of WWF at Tulear and Fort-Dauphin, and by the staff of ANGAP at Bezaha-Mahafaly Special Reserve and at Andohahela National Park. Special thanks go to all local guides, cooks and drivers from southern Madagascar, to Ny Andry Ranarivelo (ANGAP), Jules Médard (PBZT), Emahalala Ellis (CEL) and Vicki Beard for their invaluable help in the field, and to Barry Ferguson for making this project possible. We also wish to thank P. Palsboll and two anonymous reviewers for critical comments that considerably improved the manuscript, and members of the Laboratoire d’Écologie Moléculaire et Évolution (LEMEE) for their help in the lab and with the redaction.


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Copyright information

© Springer Science+Business Media, Inc. 2006

Authors and Affiliations

  • Sébastien Rioux Paquette
    • 1
  • Sandra M. Behncke
    • 2
  • Susan H. O’Brien
    • 3
  • Rick A. Brenneman
    • 2
  • Edward E. LouisJr.
    • 2
  • François-Joseph Lapointe
    • 1
  1. 1.Département de Sciences BiologiquesUniversité de MontréalMontréalCanada
  2. 2.Center for Conservation and ResearchHenry Doorly ZooOmahaUSA
  3. 3.Macaulay InstituteAberdeenUK

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