Elsevier

Mammalian Biology

Volume 75, Issue 4, July 2010, Pages 341-347
Mammalian Biology

Original Investigation
Y-chromosome microsatellite variation in Italian wolves: A contribution to the study of wolf-dog hybridization patterns

https://doi.org/10.1016/j.mambio.2010.02.004Get rights and content

Abstract

One major concern in wolf (Canis lupus) conservation is the risk of genetic contamination due to crossbreeding with domestic dogs. Although genetic monitoring of wolf populations has become widely used, the behavioural mechanisms involved in wolf-dog hybridization and the detrimental effects of genetic introgression are poorly known. In this study we analysed Y-chromosome microsatellite variation in the recovering Italian wolf population and detected strikingly different allele frequencies between wolves and dogs. Four Y haplotypes were found in 74 analysed male wolves, and all of them were present in a focus wolf population in the Apennines. On the other hand, only 1 haplotype was found in the recolonizing wolf population from the Western Alps. The most common haplotype in a sample of domestic dogs, was also found in 5 wolves, 2 of which revealing a signature of recent hybridization. Moreover, another suspect hybrid carried a private haplotype of possible canine origin. These results give support to the idea that female wolves can breed with male stray dogs in the wild. The Y-chromosome variation in Italian wolves contrasts with the previously observed lack of mitochondrial variation. Further investigations are needed to clarify at what extent historical or recent wolf-dog hybridization events may have contributed to the observed haplotype diversity. In conclusion, the two molecular markers employed in this study represent effective means to trace directional genetic introgression into the wolves male lineage and have the noteworthy advantage of being suitable for analyses on low-quality DNA samples.

Introduction

Males and females do not play symmetrical roles in structuring populations in that, for instance, strong asymmetries between sexes were reported that may affect dispersal and breeding strategies (Greenwood, 1980). Y-chromosome markers have been widely used in humans and other primates (Tosi et al., 2000; Hammer et al., 2003; Eriksson et al., 2006; Douadi et al., 2007; Kawamoto et al., 2008). The use of paternally inherited markers in mammals has increased in the past ten years and is most frequent in studies on recolonization, sex-biased dispersal rates and phylogeography. All of this studies are either based on single nucleotide polymorphisms (Meadows et al., 2006) or simple sequence repeats (Van Hooft et al., 2002; Yannic et al., 2008).

Y-chromosome markers were used to investigate the recolonization patterns that led to the wolf (Canis lupus) population recovery in Scandinavia, to distinguish the contribution of each sex to the recolonization, and to determine the gene flow among adjacent countries (Sundqvist et al., 2001). In addition, Vilà et al. (2003) documented the occurrence of a wolf-dog hybridization event and investigated its contribution to the genetic diversity of the recovering Scandinavian wolf population. By combining the use of differently inherited markers, Grewal et al. (2004) described population structure and kin relationships within and among packs in the Algonquin population, while Musiani et al. (2007) focused on the relationships between packs displaying different behaviours (migratory vs. non-migratory) and natal habitats (tundra/taiga vs. boreal coniferous forest).

The conservation of natural wolf populations represents a priority in several European countries, where the species either is currently endangered, or was severely threatened in the recent past (Promberger and Schröder, 1993). The Italian wolf population suffered severe persecution until 1971, when wolf hunting was forbidden and poison baits banned. This change in attitude was completed in 1976 when the species was given fully protected status. However, after World War II the number of wolves inhabiting the peninsula supposedly reached the lowest levels ever and their presence was restricted to a few areas in the Apennines (Cagnolaro et al., 1974). Ever since, the wolf population has recovered and recolonized most of its historical range in Italy.

As a consequence of its history, the Italian wolf shows the effects of a severe bottleneck, which, in association with its prolonged isolation, led to genetic erosion (Lucchini et al., 2004). One mitochondrial haplotype only was found in the whole Italian wolf population (Wayne et al., 1992; Vilà et al., 1997; Vilà et al., 1999; Randi et al., 2000). On the contrary, nuclear markers revealed the reduction in genetic variability to be less severe, with a remarkable reduction in heterozygosity being reported only in the recently re-established Alpine wolf subpopulation, while the Apennine population showed only a slightly lower variability compared to other European populations (Scandura et al., 2001; Lucchini et al., 2004; Fabbri et al., 2007). Finally, a main concern in managing wolf populations is represented by the occurrence of crossbreeding with domestic dogs (Vilà and Wayne, 1999). Although, the frequency of wolf-dog hybridization can be estimated by selecting highly discriminating autosomal markers (e.g., Verardi et al., 2006), the investigation of the directionality of matings (i.e., which gender of each species is involved in the production of hybrids) actually requires the application of unilineal markers. Paternally and maternally inherited allelic variants are also important tools for the study of sex bias in dispersal patterns, this being a crucial aspect in recolonization processes. Nevertheless, no study has so far explored the genetic variation at paternally inherited markers in Italian wolves.

In this study, we investigated Y-chromosome microsatellite variation in a sample of Italian wolves. This was carried out by comparing individuals from a stronghold area in Northern Apennines with wolves from other historical and newly colonized areas across the peninsula and with a sample of domestic dogs. The Italian wolf population is especially interesting because, during its recent expansion, it has experienced a prolonged contact with a large and widespread population of stray dogs (Genovesi, 2002).

Section snippets

Material and methods

The study was part of a long-term monitoring project on the wolf population inhabiting the province of Arezzo, a 3,200-km2 area situated in the Northern Apennines (Italy). The wolf probably never disappeared in the area (Cagnolaro et al., 1974), though its recovery was fully accomplished only during the 1980s. At the beginning of the 1990s, several packs had already established their territories in the Foreste Casentinesi national park (Apollonio et al., 2004), where they relied on a rich

Results

A total of 74 male wolves and 20 dogs were successfully analysed with MS34A and MS34B. These loci were polymorphic with 3 alleles each (Fig. 2), and yielded 4 different haplotypes (Table 1). Each locus showed one common allele in wolves (176 for MS34A and 174 for MS34B), that occurred in all sampling areas and differed from the allele carried by almost all domestic dogs (Fig. 2). Two rare alleles (170 at MS34A and 178 at MS34B) were jointly carried by the same individual that had been sampled

Discussion

The amount of variation observed at Y microsatellites on a limited geographic scale is significant when compared to the absolute lack of variation observed in the mitochondrial DNA of the whole Italian population (Vilà et al., 1999; Randi et al., 2000). This result has two possible explanations: i) the bottleneck experienced by the Italian wolf population was less dramatic in males than in females; ii) the presence of multiple alleles at Y microsatellites is a consequence of genetic

Acknowledgements

We would like to express our gratitude to M. Geri, A. Mandrici, B. Ragni, A. Viviani and all people who helped us in collecting wolf samples, and to P. Borghetti and M. Fossi for providing with dog samples. We would also like to acknowledge the valuable contribution to laboratory activities provided by P.F. Sechi. We thank A. Binelli for linguistic revision. The wolf monitoring project was funded by the Provincial Administration of Arezzo, the Regional Government of Tuscany, and the Italian

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