Low prevalence of wolf-dog hybrids in the Iberian Peninsula

Wolf ( Canis lupus )—dog ( Canis familiaris ) hybrids are a widely recognized example of anthropogenic hybridization of conservation concern. In the Iberian Peninsula, wolves and dogs coexist in highly humanized landscapes, with many opportunities for interbreeding. Previous studies have documented wolf-dog hybridization here; however, their ability to estimate the frequency of this phenomenon was limited because of opportunistic, or geographically restricted sampling. Further, the use of non-standardized genetic markers limited comparability across studies. Here, we conducted a systematic non-invasive survey, collecting over 800 fecal samples across the species range in Iberia. Genetic analyses combined a mitochondrial DNA barcode for species identification, 13 autosomal microsatellites for individual identification, two sex markers, and a panel of 96 ancestry-informative SNP markers specifically developed for wolf-dog hybrid detection across Europe, which enables the assignment of hybrid classes up to second-generation backcrosses. Our results revealed a very low prevalence (< 2%) of wolf-dog hybrids in this population. Among 204 individually identified wolves, we detected three first-generation (F1) and one later-generation (F2/BCw) hybrids. Two of the identified hybrids were related, thus representing only three hybridization events, all located at the edge of the species distribution or in human disturbed areas. Simulations regarding the expected change in the genetic composition of the population with this prevalence of hybrids, and the observed underrepresentation of backcrosses, suggest reduced reproductive success in hybrids. The results imply that the risk of genetic swamping of wild wolves by domestic dogs is currently low in Iberia.