Genetic identification of wild and domestic cats (Felis silvestris) and their hybrids using Bayesian clustering methods

Crossbreeding with free-ranging domestic cats is supposed to threaten the g enetic integrity of wildcat populations in Europe, although the diagnostic markers to identify "pure" or "admixed" wildcats have never been clearly de fined. Here we use mitochondrial (mt) DNA sequences and allelic variation a t 12 microsatellite loci to genotype 128 wild and domestic cats sampled in Italy which were preclassified into three separate groups: European wildcat s (Felis silvestris silvestris), Sardinian wildcats (Felis silvestris libyc a), and domestic cats (Felis silvestris catus), according to their coat col or patterns, collection localities, and other phenotypical traits, independ ently of any genetic information. For comparison, we included some captive- reared hybrids of European wild and domestic cats. Genetic variability was significantly partitioned among the three groups (mtDNA estimate of F-ST = 0.36; microsatellite estimate of R-ST = 0.30; P < 0.001), suggesting that m orphological diversity reflects the existence of distinct gene pools. Multi variate ordination of individual genotypes and clustering of interindividua l genetic distances also showed evidence of distinct cat groups, partially congruent with the morphological classification. Cluster analysis, however, did not enable hybrid cats to be identified from genetic information alone , nor were all individuals assigned to their populations. In contrast, a Ba yesian admixture analysis simultaneously assigned the European wildcats, th e Sardinian wildcats, and the domestic cats to different clusters, independ ent of any prior information, and pointed out the admixed gene composition of the hybrids, which were assigned to more than one cluster. Only one puta tive Sardinian wildcat was assigned to the domestic cat cluster, and one pr esumed European wildcat showed mixed (hybrid) ancestry in the domestic cat gene pool. Mitochondrial DNA sequences indicated that three additional pres umed European wildcats might have hybrid ancestry. These four cats were sam pled from the same area in the northernmost edge of the European wildcat di stribution in the Italian Apennines. Admixture analyses suggest that wild a nd domestic cats in Italy are distinct, reproductively isolated gene pools and that introgression of domestic alleles into the wild-living population is very limited and geographically localized.