Journal of Heredity Advance Access published online on October 30, 2008
Journal of Heredity, doi:10.1093/jhered/esn093
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Assessing Natural Introgression in 2 Biomedical Model Species, the Rhesus Macaque (Macaca mulatta) and the Long-Tailed Macaque (Macaca fascicularis)
From the Université Paul Sabatier, Laboratoire Evolution et Diversité Biologique, UMR CNRS 5174, Toulouse cedex 9, France (Bonhomme, Cuartero, and Crouau-roy); and the Laboratoire d'Immunogénétique Moléculaire, Faculté de Médecine de Rangueil, Université Paul Sabatier, Toulouse III, France (Blancher)
Address correspondence to B. Crouau-Roy at the address above, or e-mail: bcrouau{at}cict.fr.
Rhesus macaque (Macaca mulatta) and long-tailed macaque (Macaca fascicularis) are the 2 most commonly used primate model species in biomedical sciences. Although morphological studies have revealed a weak hybridization at the interspecific contact zone, in the north of Indochina, a molecular study has suggested an ancient introgression from rhesus to long-tailed macaque into the Indo-Chinese peninsula. However, the gene flow between these 2 taxa has never been quantified using genetic data and theoretical models. In this study, we have examined genetic variation within and between the parapatric Chinese rhesus macaque and Indo-Chinese long-tailed macaque populations, using 13 autosomal, 5 sex-linked microsatellite loci and mitochondrial DNA sequence data. From these data, we assessed genetic structure and estimated gene flow using a Bayesian clustering approach and the "Isolation with Migration" model. Our results reveal a weak interspecific genetic differentiation at both autosomal and sex-linked loci, suggesting large population sizes and/or gene flow between populations. According to the Bayesian clustering, Chinese rhesus macaque is a highly homogeneous gene pool that contributes strongly to the current Indo-Chinese long-tailed macaque genetic makeup, whether or not current admixture is assumed. Coalescent simulations, which integrated the characteristics of the loci, pointed out 1) a higher effective population size in rhesus macaque, 2) no mitochondrial gene flow, and 3) unilateral and male-mediated nuclear gene flow of 
10 migrants per generation from rhesus to long-tailed macaque. These patterns of genetic structure and gene flow suggest extensive ancient introgression from Chinese rhesus macaque into the Indo-Chinese long-tailed macaque population.
Corresponding Editor: William Murphy
Received April 22, 2008
Revised September 26, 2008
Accepted September 26, 2008