Originally published as Genetics Published Articles Ahead of Print on June 8, 2009.

Genetics, Vol. 182, 1197-1206, August 2009, Copyright © 2009
doi:10.1534/genetics.108.092080

Species-Wide Genetic Variation and Demographic History of Drosophila sechellia, a Species Lacking Population Structure

Delphine Legrand*, Maud I. Tenaillon{dagger}, Pat Matyot{ddagger}, Justin Gerlach§, Daniel Lachaise*,1 and Marie-Louise Cariou*,2

* Laboratoire Evolution, Génomes et Spéciation-UPR9034, Centre National de la Recherche Scientifique (CNRS), 91198 Gif-sur-Yvette Cedex, and Université Paris-Sud 11, 91405 Orsay Cedex, France, {dagger} CNRS 0320/UMR 8120, F-91190 Gif-sur-Yvette, France {ddagger} Seychelles Island Foundation, Victoria, Mahé, Seychelles and § Nature Protection Trust of Seychelles, Victoria, Mahé, Seychelles

2 Corresponding author: Laboratoire Evolution, Génomes et Spéciation, UPR 9034 CNRS, Avenue de la Terrasse, Bâtiment 13, Boite Postale 1, 91198 Gif-sur-Yvette, France.
E-mail: Marie-Louise.Cariou{at}legs.cnrs-gif.fr

Long-term persistence of species characterized by a reduced effective population size is still a matter of debate that would benefit from the description of new relevant biological models. The island endemic specialist Drosophila sechellia has received considerable attention in evolutionary genetic studies. On the basis of the analysis of a limited number of strains, a handful of studies have reported a strikingly depleted level of genetic variation but little is known about its demographic history. We extended analyses of nucleotide polymorphism in D. sechellia to a species-wide level using 10 nuclear genes sequenced in 10 populations. We confirmed that D. sechellia exhibits little nucleotide-sequence variation. It is characterized by a low effective population size, >10-fold lower than that of D. simulans, which ranks D. sechellia as the least genetically diverse Drosophila species. No obvious population subdivision was detected despite its fragmented geographic distribution on different islands. We used approximate Bayesian computation (ABC) to test for demographic scenarios compatible with the geological history of the Seychelles and the ecology of D. sechellia. We found that while bottlenecks cannot account for the pattern of molecular evolution observed in this species, scenarios close to the null hypothesis of a constant population size are well supported. We discuss these findings with regard to adaptive features specific to D. sechellia and its life-history strategy.