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Podocnemis lewyana is an endangered endemic river turtle of Colombia. Using ten unlinked polymorphic microsatellite loci and a 691-bp-long DNA fragment corresponding to the more variable portion of the mitochondrial control region, we investigated genetic diversity and population structure throughout its range. Both neutral markers showed extremely low diversity and weak population differentiation. Our data indicate that the genetic history of P. lewyana has been impacted by multiple bottlenecks and population expansion since the Pleistocene. The observed differentiation pattern is most likely the result of historically low genetic variation resulting from restricted geographic range and aggravated by recent anthropogenically induced bottlenecks. Based on slight differences in allele frequencies among populations, we suggest that three regions should be treated as demographically independent Management Units in order to preserve maximal genetic diversity: (1) the Upper Magdalena River Basin, (2) the Lower Magdalena ? Lower Cauca ? San Jorge River Basins, and (3) the Sinú River Basin. Among the Management Units, only low to moderate levels of gene flow were detected; these are largely unidirectional from Management Units 1 and 3 into Management Unit 2.Resumen Podocnemis lewyana es una tortuga endémica y amenazada de Colombia. Usando diez loci polimórficos de microsatélites y un fragmento de 691 pares de bases correspondiente a la porción más variable de la región control mitocondrial, investigamos la diversidad genética y estructura poblacional a través de su rango de distribución. Ambos marcadores neutrales revelaron una diversidad extremadamente baja y débil diferenciación poblacional. Nuestros datos indican que la historia genética de P. lewyana ha sido impactada por múltiples cuellos de botella y expansión poblacional desde el Pleistoceno. El patrón de diferenciación observado es más probable el resultado de la variación genética historica baja derivada del rango de distribución restringido, agravada por cuellos de botella recientes resultado de intervención antrópica. Basados en diferencias tenues de frecuencias alélicas entre poblaciones, sugerimos que tres regiones deben ser tratadas como Unidades de Manejo (UM) demográficamente independientes con el fin de preservar al máximo la diversidad genética. (1) Cuenca del alto río Magdalena, (2) Cuencas del bajo río Magdalena ? Bajo río Cauca ? río San Jorge, y (3) Cuenca del río Sinú. Entre las UM se detectaron niveles bajos a moderados de flujo genético que es principalmente unidireccional de las UM 1 y 3 a la UM 2.

The Magdalena River Turtle (Podocnemis lewyana) is a Colombian endemic species, endangered due to human exploitation and habitat destruction. To date, this species is poorly known ecologically and data on its genetic diversity are lacking. Here we report on the first genetic survey of the species across its distribution range. We obtained mitochondrial DNA sequences (488 bp) of the cytochrome b gene from 109 individuals. Samples belong to populations located at several different localities, grouped in five regions, along the four main river basins: Magdalena, Cauca, San Jorge, and Sinú drainages. We found two haplotypes, which differ in only one nucleotide substitution and which are represented with different frequencies in the five geographic regions. These results suggest that P. lewyana harbors little genetic variation and is a genetically uniform species, but more variable markers (i.e., microsatellites) should be used to unravel fine-scale phylogeographic structures in this species.

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