Signals of Pig Ancestry in Wild Boar, Sus scrofa, from Eastern Austria: Current Hybridisation or Incomplete Gene Pool Differentiation and Historical Introgressions?

Abstract

In wild boar, Sus scrofa, from Europe, domestic pig-typical ancestry is traced at varying levels. We hypothesised wild boar with pig-typical gene pool characteristics, i.e., “introgression”, congregate more in peri-urban habitats, because of less shyness and better adaptation to anthropogenic stress. We used 16 microsatellites to study introgression levels of 375 wild boar from peri-urban Vienna, Austria, and rural regions in comparison to commercial slaughter pigs, Mangaliza, and Turopolje pigs. We also expected more introgression in locations of warmer climates and lower precipitation. Despite discrimination of wild boar and pigs with 99.73% and 97.87% probability, respectively, all wild boars exhibited pig-typical gene pool characteristics, mostly at a very low level. Recent hybridisation was suspected in only 0.53% of wild boar, corresponding to the current largely indoor pig breeding/rearing in the region, with no chance of natural gene exchange between pigs and wild boar. Rather, pig ancestry in wild boar stems from incomplete gene pool differentiation during domestication and/or historical introgressions, when free-ranging pig farming was common. Individual introgression levels were lower in wild boar from peri-urban habitats, possibly reflecting the largely historical absence of pig farms there. Moreover, a marginal precipitation effect, but no temperature effect on introgression was observed. The latter, however, needs to be explored further by a more comprehensive data set.

Pig-Typical Gene Pool Characteristics in Wild Boars from Vojvodina, Serbia: A Study of Genetic Diversity, Differentiation, Assignment, and Admixture

“…While collection date and location were available for most of the samples, no specific information was provided on the phenotypic appearance of individual wild boars, such as suspicious fur coloration, that could have given an indication of introgression by pigs. In addition, we used tissue samples from twenty Mangulica, i.e., Serbian Mangaliza, collected in 2014 at Ravno Selo (Bačka, Vojvodina), and of four Hungarian Mangaliza pigs, purchased from a butcher in eastern Austria (at Pamhagen, Province of Burgenland), as well as 48 commercial slaughter pigs (CSP), purchased as pork packages in 2017 and 2018 from supermarkets in Austria, Germany, the Czech Republic, Hungary, Slovenia, and Bulgaria, all of which have already been used in a study for comparison with Austrian wild boars (Böheim et al, 2023).…”

“…We used the same sixteen microsatellite markers, i.e., S0002, S0097, S0101, S0155, S0215, SW24, SW72, SW122, SW240, SW461, SW857, SW936, SW1492, SW2021, SW2496, SW2532, as in Böheim et al (2023) to determine allelic variation and individual overall genotypes for population genetic statistics and as a basis for estimating individual introgression of wild boars by pigs. For DNA extraction, purification, and PCR specifications we followed the procedures detailed in Vetter et al (2014;2016) and applied also by Böheim et al (2023). Marker individuals of the latter study were used to synonymize the currently identified alleles and genotypes with those of the latter study, which enabled a direct comparison of the population genetic results.…”

“…In Europe, natural populations of wild boar, Sus scrofa, may harbor pig-typical gene pool characteristics at varying levels, resulting from recent or historic introgressive hybridization or/and incomplete gene pool separation in the domestication history of pigs (e.g., Scandura et al, 2011;Nikolov et al, 2017;Iacolina et al, 2018). A recent microsatellite-based study (Böheim et al, 2023) revealed, principally in good accordance with the SNPsbased study of Iacolina et al (2018), pig-typical gene pool characteristics in all wild boars studied in eastern Austria, but generally at a very low level. Those microsatellite-based signals of introgression were interpreted as largely indicating shared allelic polymorphism due to a shallow gene pool divergence between wild boars and pigs during domestication (see e.g., Frantz et al, 2015) on the one hand and as possible remaining signals of historic introgressive hybridizations on the other, rather than of ongoing introgression.…”

“…However, so far a Europe-wide SNP-based study has confirmed only regional introgression in Balkan populations, with a low to slightly increased level of introgression in some Serbian wild boars (de Jong et al, 2023). Even though SNPs provide a clearly better resolution of genetic variability, we used the same set of microsatellite markers as in the study on eastern Austrian wild boars (Böheim et al, 2023) to analyze introgression in wild boars from Vojvodina by specifically considering Mangulica (Serbian Mangaliza) in addition to commercial slaughter pigs (CSPs) for a representative sample of whole Vojvodina. Until relatively recentlyin evolutionary termsfree-ranging or semifree ranging farming practices were not uncommon for Mangulica (cf.…”

“…e.g., Nikolić et al, 2017) and perhaps also for other pig breeds of small farm holdings and this might have provided gene flow between free-ranging wild boars and pigs. According to Böheim et al (2023), we expected relative genetic uniformity of CSPs in comparison to the wild boars from Vojvodina. We checked for significant spatial variation of genetic variability as well as possible introgression signals in the wild boars.…”