Detection of farm fox and hybrid genotypes among wild arctic foxes in Scandinavia Karin Nore´n 1 , Love Dale´n 1 , Kirsti Kvaløy 2 & Anders Angerbjo¨rn 1, * 1 Department of Zoology, Stockholm University, S-106 91, Stockholm, Sweden; 2 Norwegian Institute for Nature Research, N-7845, Trondheim, Norway (*Corresponding author: Phone: +46-8-164035; Fax: +46- 8-167715; E-mail: Anders.Angerbjorn@zoologi.su.se) Received 30 November 2004; accepted 24 March 2005 Key words: Alopex lagopus, farmed, hybridization, microsatellites, mtDNA Abstract In Scandinavia, farmed arctic foxes frequently escape from farms, raising concern about hybridization with the endangered wild population. This study was performed to find a genetic marker to distinguish escaped farm foxes from wild Scandinavian foxes. Microsatellite and mitochondrial control region variation were analyzed in 41 farm foxes. The results were compared with mitochondrial and microsatellite data from the wild population in Scandinavia. The farm foxes were genetically distinct from the wild foxes (F ST =0.254, P < 0.00001) and all farm foxes had a single control region haplotype different from those observed in the wild population. We developed a method based on Restriction Fragment Length Polymorphism (RFLP) on the mitochondrial control region to differentiate between farmed and wild arctic foxes. This test was subsequently successfully used on 25 samples from free-ranging foxes, of which four had a suspected farm origin. All four of the suspected foxes, and none of the others, carried the farm fox haplotype. Three of these were successfully genotyped for all eleven microsatellite loci. A population assignment test and a Bayesian Markov Chain Monte Carlo analysis indicated that two of these individuals were escaped farm foxes, and that the third possibly was a hybrid between a farmed and a wild arctic fox. Introduction Hybridization has led to extinction of many pop- ulations and species (Rhymer and Simberloff 1996; Allendorf et al. 2001). According to theoretical simulations, hybridization is one of the most significant threats to endangered species (Wolf et al. 2001). It has also been suggested that low population size greatly affects the extinction risk due to hybridization (Wolf et al. 2001). Evidence of hybridization between divergent species or populations in the wild has been described in a variety of carnivore species (e.g., Fergus 1991; Lehman et al. 1991; Rozhnov 1993; Reich et al. 1999). Introgression of alien alleles can cause out- breeding depression and reduce fitness by two different mechanisms (Templeton 1986; Lynch 1991; Edmands and Timmerman 2003). Firstly, hybridization between genetically distinct popula- tions, who are highly adapted to their local environment, can disrupt interactions between genes and the environment and thereby result in offspring with reduced fitness in both parental environments. Secondly, outbreeding depression can be caused by disruption of coadapted gene complexes. Outbreeding depression has been reported in a variety of species (e.g. Coyne and Orr 1989; Brown 1991; Garnier-Ge´re´ et al. 2002; McGinnity et al. 2003; Gilk et al. 2004), Conservation Genetics (2005) 6:885–894 Ó Springer 2006 DOI 10.1007/s10592-005-9075-8