Detecting rare introgression of domestic dog genes into wild wolf (Canis lupus) populations by Bayesian admixture analyses of microsatellite variation

摘要

Hybridization with free-ranging dogs is thought to threat the genetic integrity of wolves in Europe, although available mtDNA data evidenced only sporadic cases of crossbreeding. Here we report results of population assignment and genetic admixture analyses in 107 wild-living Italian wolves, 95 dogs including 30 different breeds and feral dogs, and captive-reared wolves of unknown or hybrid origins, which were genotyped at 18 microsatellites. Two Italian wolves showed unusually dark coats ("black wolves"), and one showed a spur in both hindlegs ("fifth finger wolf"), suggesting hybridization. Italian wolves showed significant deficit of heterozygotes, positive F_(IS) values and deviations from Hardy-Weinberg equilibrium. Genetic variability was significantly partitioned between groups, suggesting that wolves and dogs represent distinct gene pools. Multivariate ordination of individual genotypes and clustering of inter-individual genetic distances split wolves and dogs into two different clusters congruent with the prior phenotypic classification, but hybrids and wolves of unknown origin were not identified from genetic information alone. By contrast, a Bayesian admixture analysis assigned all the Italian wolves and dogs to two different clusters, independent of any prior phenotypic information, and simultaneously detected the admixed gene composition of the hybrids, which were assigned to more than one cluster. Captive-reared wolves of unknown origin were prevalently assigned to the Italian wolf population. Admixture analyses showed that one "black wolf" had mixed ancestry in the dog gene pool and could be a hybrid, while the other two wolves with unusual phenotypes were assigned to the Italian wolf population.