GENOMIC DIFFERENTIATION AMONG NATURAL-POPULATIONS OF ORANGUTAN (PONGO-PYGMAEUS)

Background: Orang-utans exist today in small isolated populations on t he islands of Borneo (subspecies Pongo pygmaeus pygmaeus) and Sumatra (subspecies P. p. abelii). Although, on the basis of their morphologic al, behavioral and cytogenetical characteristics, the Bornean and Suma tran orang-utan populations are generally considered as two separate s ubspecies, there is no universal agreement as to whether their genetic differentiation is sufficient to consider and manage them as species, subspecies or population level taxonomic units. A more precise phylog enetic description would affect many conservation management decisions about captive and free-ranging orang-utans. Results: We analyzed the amount and patterns of molecular genetic variation in orang-utan popul ations using cellular DNA from orang-utans from two locations in Sumat ra and nine locations - representing four isolated populations - in Bo rneo, Genetic and phylogenetic analyses of mitochondrial DNA restricti on fragment length polymorphisms, nuclear minisatellite (or variable n umber tandem repeat) loci and mitochondrial 16S ribosomal RNA sequence s led to three major findings. First, the genetic distance and phyloge netic differentiation between Sumatran and Bornean orang-utans is larg e, greater than that between the common chimpanzee, Pan troglodytes, a nd the pygmy chimpanzee or bonobo, Pan paniscus. The genetic distance suggests that the two island subspecies diverged similar to 1.5-1.7 mi llion years ago, well before the two islands separated and long enough for species-level differentiation. Second, there is considerable ende mic genetic diversity within the Bornean and Sumatran orang-utan popul ations, suggesting that they have not experienced recent bottlenecks o r founder effects. And third, there is little genetic differentiation among four geographically isolated populations of Bornean orang-utans, consistent with gene flow having occurred between them until recently . Conclusions: Our results are consistent with the view that the genet ic differentiation between Sumatran and Bornean orang-utans has reache d the level of distinct species, Furthermore, our findings indicate th at there is not a genetic imperative for the separate management of ge ographically isolated Bornean populations. (C) Current Biology Ltd ISS N 0960-9822