Effects of human perturbation on the genetic make-up of an island population: the case of the Sardinian wild boar

Abstract

Game species are often manipulated by human beings, whose activities can deeply affect their genetic make-up and population structure. We focused on a geographically isolated wild boar population (Sardinia, Italy), which is classified, together with the Corsican population, as a separate subspecies (Sus scrofa meridionalis). Two hundred and ten wild boars collected across Sardinia were analysed with a set of 10 microsatellites and compared with 296 reference genotypes from continental wild populations and to a sample of domestic pigs. The Sardinian population showed remarkable diversity and a high proportion of private alleles, and strongly deviated from the equilibrium. A Bayesian cluster analysis of only the Sardinian sample revealed a partition into five subpopulations. However, two different Bayesian approaches to the assignment of individuals, accounting for different possible source populations, produced consistent results and proved the admixed nature of the Sardinian population. Indeed, introgressive hybridization with boars from multiple sources (Italian peninsula, central Europe, domestic stocks) was detected, although poor evidence of crossbreeding with free-ranging domestic pigs was unexpectedly found. After excluding individuals who carried exotic genes, the population re-entered HardyWeinberg proportions and a clear population structure with three subpopulations emerged. Therefore, the inclusion of introgressed animals in the Bayesian analysis implied an overestimation of the number of clusters. Nonetheless, two of them were consistent between analyses and corresponded to highly pure stocks, located, respectively, in northwest and south-west Sardinia. This work shows the critical importance of including adequate reference samples when studying the genetic structure of managed wild populations.

Invasion ecology of wild pigs (Sus scrofa) in Florida, USA: the role of humans in the expansion and colonization of an invasive wild ungulate

“…No official records exist about wild pig translocations into these particular sites, but the genetic uniqueness compared to wild pigs from other surrounding locations suggests that animals at these sites were recently introduced. This introduction would likely be associated with unreported/illegal transport and release to increase local hunting opportunities (Vernesi et al 2003;Spencer and Hampton 2005;Scandura et al 2011;Lopez et al 2014).…”

“…Previous population genetic studies of wild pigs, largely conducted in Europe and Oceania, have identified individual membership to particular populations and levels of population admixture (i.e. interbreeding among isolated populations which produces offspring with a mixture of alleles from different ancestral populations) (Vernesi et al 2003;Hampton et al 2004;Spencer and Hampton 2005;Nikolov et al 2009;Scandura et al 2011;Lopez et al 2014). Although these data will help inform population management and control efforts, little is known about wild pig dispersal and expansion throughout North America.…”

“…Microsatellite markers are a widely used molecular tool to infer population connectivity and dispersal among sampling locations, thus allowing a greater understanding of the location-specific ecology of this species (Vernesi et al 2003;Hampton et al 2004;Nikolov et al 2009;Scandura et al 2011). Previous population genetic studies of wild pigs, largely conducted in Europe and Oceania, have identified individual membership to particular populations and levels of population admixture (i.e.…”

High domestic pig contribution to the local gene pool of free-living European wild boar: a case study in Poland

“…In addition, mtDNA sequencing, microsatellite genotyping, and a single-nucleotide polymorphism (SNP) assay have been used to look for evidence of introgression (Giuffra et al 2000;Scandura et al 2008, 2011b, Frantz et al 2012, 2013, Goedbloed et al 2013bHerreroMedrano et al 2013;Iacolina et al 2016b).…”

Substantial hybridisation between wild boars (Sus scrofa scrofa) and East Balkan pigs (Sus scrofa f. domestica) in natural environment as a result of semi-wild rearing in Bulgaria

“…Scandura et al 2011a;Frantz et al 2012Frantz et al , 2013. Microsatellite loci are very useful to analyze gene flow and admixture even between closely related populations due to their high level of polymorphism and mutation rate (Roy et al 1994) and they have been widely used in combination with Bayesian clustering and admixture analysis (Pritchard et al 2000) in order to analyze hybridisation between wild boars and different pig breeds (e.g.…”