Genetic patterns of a range expansion: The spur-thighed tortoise Testudo graeca graeca in southeastern Spain

Abstract

Abstract In the present work we analyzed the genetic structure of the populations of the terrestrial tortoise Testudo graeca graeca in southeastern Spain, identified as a recent range expansion from North Africa. The study and interpretation of the species' genetic spatial pattern could provide clues to the processes related to the species' arrival and, because of its endangered status, is especially useful in implementing appropriate management measures. We used microsatellite markers to analyze 17 populations located in the coastal region of the species' range in southeastern Spain, and an external group of Algerian tortoises. Three genetic units with a high level of spatial coherence and moderate levels of admixture resulted from a cluster analysis, and an isolation-by-distance pattern covering the entire study area was detected. These results suggest that southeastern Spanish populations show a complex spatial genetic pattern resulting from their isolation from North African populations and their natural dispersal in this region. Finally, our work shows that conservation actions such as captive breeding, introductions or translocations, may have played a relevant role in the modification of the genetic structure of some populations in southeastern Spain. Therefore, these types of conservation measures should be carried out with more caution.