Several wild boar populations of uncertain origin and genetic status were introduced into Mediterranean islands in recent times, threatening the island biotas. Indeed, invasive wild boar populations frequently lead to ecological disequilibria and taxa extinctions. Additionally, they may also represent a genetic threat, especially if islands are close to the mainland: in fact, if wild boars with ... [Show full abstract] an alien or admixed genetic origin disperse from islands, they may jeopardize the endemic genetic diversity of mainland conspecifics through introgressive hybridization.
Three emblematic and worrying cases are represented by the wild boar populations in Caprera, Asinara and Sant'Antioco, three islands near to the coasts of Sardinia (Italy).In fact, despite the past limited hybridization with local domestic pigs and introduced continental wild boar, the close wild boar population of Sardinia has maintained a clear genetic distinctiveness, and is currently classified as a distinct subspecies (Sus scrofa meridionalis).
We investigated the genetic composition of the wild boar populations in the three islands by using a panel of 16 autosomal microsatellites and a reference dataset including domestic pig and wild boar populations from Sardinia, mainland Italy and other European regions, in order to reconstruct the possible origin and status of the invaders. Our main aim was to evaluate the genetic risk for the Sardinian wild boar due to a possible contact with those gene pools.
The genetic make-up of the three island populations was found to diverge from that of Sardinia to such an extent that they could not be classified as Sardinian wild boar. In fact, their genome bore traces of multiple introductions from different source populations, as well as introgression from the domestic pig, followed by genetic drift. Therefore, besides impacting on island biodiversity, these admixed populations represent a threat to the endemic subspecies inhabiting Sardinia. Accordingly, we argue for their prompt eradication.