A matter of genes? Possible consequences of genetic introgression from domestic forms in two problematic species

Invasive or problematic species are in some cases exposed to introgressive hybridization with domestic conspecifics. Under such circumstances, the gene pool of natural populations risks to be altered by the acquisition of new alleles that were artificially selected during domestication and breed amelioration. Stochastic factors and selection may lead to the spread of these alleles in a wild population, with often unpredictable effects on its biology.
Instances of such situation in Italy are represented by the wild boar (Sus scrofa) and the wolf (Canis lupus), two species which are currently worrying wildlife managers and public administrations.
Here, we present an updated review on the extent and the possible effects of hybridization in the two species. Specifically, we will focus on i) the methods to track introgression and their main limitations, ii) the life-history traits possibly affected by the introgression, iii) the conditions for introgressive hybridization to occur and iv) the management implications.
After its historical minimum in the early XX century, the wild boar came back to be a common presence in the Italian countryside, becoming a pest. Crossbreeding between wild boar and domestic pigs has been historically important and is likely to have shaped the present-day genetic make-up of both forms. Although intensive farming has reduced the chance of hybridization in nature, gene flow between wild and domestic S. scrofa still takes place either spontaneously in areas where open-air pig husbandry is present or intentionally in captivity, involving animals that could then be released for restocking.There is a concrete possibility that genetic variants selected in commercial pig breeds, once transferred to the wild boar, increase its invasiveness, by affecting body size, fertility and behaviour.
In half a century the Italian wolf has fully recovered in the Apennines and is currently spreading across lowlands and hilly areas of Central and Southern Italy. For years hybridization with domestic dogs has been neglected as a threat to its genetic integrity of the Italian wolf population. In the last decade, however, growing evidences of a diffuse hybridization have been collected in some areas (e.g. in Tuscany), raising a great worry for the conservation of the Italian wolfendemic diversity.Whether the introgression of canine genes had a role in the rapid expansion of the local wolf population is not known, but first insights on the ecology and sociality of hybrid packs suggest full interchangeability with pure wolves.
Although many studies in the last decade have disclosed the spread of this phenomenon in the two species and constantly improved the tools to document hybridization, we still have a very limited knowledge on the possible ecological changes induced by the introgression of domestic genes. Here we stress the necessity to increase the effort on this research field, in order to understand the role of this gene flow on the spread and invasiveness of two problematic species.Meanwhile, preventive management measures to limit hybridization have to be taken into serious consideration.