1. Introduction
In the 1830s the Serbian Sumadia pig breed was crossed with the local Hungarian stock and applying an intensive selection, a rustic curly-haired pig was created called Blonde Mangalica [
1]. The Swallow Belly Mangalica breed was established later by crossbreeding Mangalica pigs and Szerémségi pigs. The latest breed is the Red Mangalica one, which is the result of the crossbreeding of Mangalica pigs with Szalontai type pigs as well as by using Újszalontai type pigs cross-bred with Mangalica pigs at the beginning of the 19th century [
2]. The Mangalica pigs could be characterized by excellent fat production strong motherliness and good adaptability to extensive housing conditions nevertheless, their prolificacy is low [
1]. The Mangalica was the main Hungarian pig breed until the 1950s. After World War II due to the changing dietary habits, Mangalica lost its former popularity [
3]. Although in 1976, a national program was established to preserve its gene pool the Mangalica almost went to extinction by early 1990 [
4]. Fortunately, in 1994 the National Association of Mangalica Breeders was founded to preserve the genetic and phenotypic appearance of the Mangalica pig in an unchanged form [
2]. Due to their efficient activity in 2019, the number of registered sows and boars (combining the three breeds) was 6723 and 354, respectively [
5]. At present, the Mangalica has three different colour variations (Blonde, Red, Swallow Belly), and based on the molecular genetic analysis Zsolnai et al. [
6] it could be stated that these colour variants represent different breeds. Concerning gene conservation, the Mangalica pig breeds are among the most recognized ones in Hungary therefore the maintenance of these breeds has high importance. However, from the aspect of breed loss, to establish an appropriate management assessment and conservation of genetic variability, examining population structure and gene flow is necessary [
7]. Recently all the Mangalica breeds were evaluated employing pedigree analysis where the demography parameters, inbreeding level, and the proportion of the maintained genetic diversity were presented [
8]. However, since all the breeds are kept in multiple herds these herds can be interpreted as subpopulations. Evaluating the population subdivision based on these herds and the contribution of migration intensity to the population subdivision was the objective of the present study.
4. Discussion
Some research about genetic variability between breeds has been done in Mangalica pigs [
6,
14]. An examination of the Hungarian population of Mangalica pigs, genotyped at 10 microsatellite loci, revealed the presence of three clusters, being representative of three different breeds, namely Swallow-Belly, Red, and Blond [
6]. However, analyses utilizing mtDNA markers were unable to distinguish subpopulations within this Mangalica population [
14]. Although studies employing various methods do not consistently delineate the three distinct breeds, in Hungary, breed management and conservation treat the three different fur colour variations of Mangalica as if they were three separate breeds. There is no interbreeding among these distinct variations. Examining the genetic variability within populations and the structure of these breeds could unveil their evolutionary patterns during more than four decades of conservation efforts across numerous herds in Hungary.
Traditionally, conservation priorities have given significant weight to between-breed diversity, as indicated by Barker [
15] that the foremost objective in safeguarding domestic animal diversity is the preservation of specific breeds. However, there is a contention that approaches emphasizing the between-breed component of genetic diversity may not be the most effective, as they neglect the within-breed component of variation [
16,
17,
18]. According to Cervantes et al. [
7] accessing genetic variability within populations, understanding population structures, and analysing gene flow are crucial stages in the execution of selection programs. This assessment plays a pivotal role in formulating efficient management strategies for genetic stock, aiming to enhance the genetic basis for selection purposes. According to Molnár et al. [
14], populations within a breed that are geographically and/or ecologically isolated may acquire distinct physiological characteristics due to specific selection criteria employed in the breeding process. Consequently, these isolated populations can diverge genetically from other populations of the same breed that share similar phenotypes, potentially leading them to be recognized as distinct breeds [
14]. According to Wilkinson et al. [
19] the genetic substructure within a breed, as revealed by individual clustering methods, is likely rare in domestic species, with the presence of limited genetic substructure typically observed in only one or two exceptional breeds. However, the intra-breed stratification has been reported in various farm animals, such as chickens [
19], horses [
20], castles [
21], goats [
22,
23], rabbits [
24,
25], dogs [
26,
27], and pigs [
28,
29].
Estimating the Fixation Index (F
ST) provides insights into the degree of differentiation among a group of populations, as applied in the present study to assess the differentiation among herds belonging to three Mangalica breeds. The F
ST values, ranging from 0 to 1, convey the extent of genetic differentiation. A value of 0 signifies complete sharing of genetic material, allowing for free interbreeding. On the other hand, a value of 1 indicates that all genetic variation is accounted for population structure, indicating no shared genetic diversity, and the populations are considered fixed or distinct [
30]. The interpretation guidelines for the fixation index (F
ST) were presented by Hartl and Clark [
30] as follows: F
ST < 0.05 _little genetic difference; F
ST = 0.05–0.15 _moderate genetic difference; F
ST = 0.15–0.25 _ great genetic difference; F
ST > 0.25 _ very great genetic differentiation. In addition, Frankham et al. [
31] reported that FST values greater than 0.15 indicate significant differentiation, while FST values below 0.05 suggest insignificant differentiation. In the current study, the F
ST among herds ranged from 0.00 to 0.35, being representative of the heatmap colours (
Figures S1a, S4a, S7a). Most of the examined herds, surpassing 58% entire population (
Table 1), exhibited insignificant genetic differentiation by Frankham et al. (2002) guidelines. This group is even more dominant in active herds with more than 65%. Moreover, multidimensional scaling showed that the analysed populations are not sufficient to form clusters for both dimensions 1-2 and dimensions 1-3 (
Figures S2a-d, S5a-d, S8a-d), although there are some visual divergence herds. Among active herds, the Swallow-Belly showed quite a big distance from each other, but the substructures also are not formed in this breed (
Figures S5c, S5d). This could be because of the smallest population size of this breed. In pigs, by using Bayesian Analysis of Population Structure on genotypic data, Wilkinson et al. [
29] detected the substructure within British Meishan but it was not present in other methods. Snegin et al. [
28] found the high variability between individual herds within the four commercial pig breeds, contributing to the significant difference between breeds of studied populations.
The Swallow-Belly and Red breeds exhibited a higher inclination towards intra-breed differentiation, with a larger percentage of herds displaying moderate genetic differences compared to the Blonde breed. Nevertheless, the average FST values between herds remained similar across all three breeds (0.07). This phenomenon may be clarified by the smaller population sizes of the Swallow-Belly and Red breeds.
Significant genetic differentiation was observed in certain herds across the entire studied populations (
Figures S1a, S4a, S7a), but they could not establish a substructure (
Figures S2a, S2b, S5a, S5b, S8a, S8b). The studied herds, present in pedigrees since 1981, include both active and inactive ones so far. Analysing entire populations provides a comprehensive overview, but accurate information on genetic subdivision relies on active herds. Among active herds, these differentiated herds constituted a minute fraction, amounting to less than 0.30% (
Table 1). Examining these herds, such as 1645 and 1630 in the Blonde breed (
Figure S1b) and 1436 and 1646 in the Red breed (
Figure S7b), each herd featured only one selected sire. When calculating the average coancestry of the herd, the predominant self-coancestry contributes to high F
ST values. Consequently, this results in a distinct separation from other groups, as depicted in
Figures S2c, S2d, S5c, S5d, S8c, and S8d. However, despite this observed differentiation, the details of the substructure within the herds remain indistinct in the whole view.
The results showed strong migration intensity among herds across three breeds as approximately 60% of herds have some connections with other herds. In addition, more than 90% of the migration involves one sire and more than 2 sows. The extensive exchange of animals between individual herds could be the reason for genetic similarity among herds in this study. Achmann et al. [
32] in research on Lipizzan horses found out that the interchange of horses among studs plays a crucial role in mitigating the genetic divergence among the subpopulations. Dumasy et al. [
33] determined that an increase in genetic distance is attributed to reduced connectivity among herds. This conclusion was drawn by examining the correlation between Reynolds' genetic distances and the shortest path lengths calculated by the exchange network method. In addition, the Blonde breed exhibits a smaller average F
ST (0.04) compared to the Swallow-Belly and the Red breeds (0.05), corresponding to a higher number of exchanged animals between herds within the Blonde breed. Dumasy et al. [
33] highlighted the importance of considering the number of exchanged animals in explaining genetic differentiation, and the increase in exchanged animals within the Blonde breed aligns with its lower F
ST value. While both male and female individuals play crucial roles in establishing robust connections between herds within breeds, females would have a greater impact on genetic similarity in the current study. This could be attributed to the significantly larger number of exchanged animals involving females in the studied breeds.
According to Snegin et al. [
28] the intrabreed differentiation was attributed to many factors, including gene flow, geographic isolation, breeding preferences, and the distinctive genetic backgrounds found in the genealogical groups (sire/dam lines) of the breed's founders. The geographic isolation contributed to the formation of intrabreed divergence of local goats in Spain and Portugal [
22]. The divergence in dog breeds, as evidenced by Wiener et al. [
27] was driven by the direction of breeding or artificial selection [
27]. This is primarily not happening in the current study because all registered herds adhere to the same breeding strategy mandated by the Hungarian National Association of Mangalica Breeders. Additionally, there are no notable barriers to gene exchange discovered during the investigation.
Author Contributions
Conceptualization, T.A.N, I.C, and I.N; methodology, T.A.N, I.C, and I.N; software, T.A.N, G.K, A.B and I.N; validation, T.A.N, G.K, A.B, I.C, P.T and I.N; formal analysis, T.A.N, G.K, A.B and I.N; resources, G.K, P.T and I.N; data curation, T.A.N, G.K, P.T and I.N; writing—original draft preparation, T.A.N and I.N; writing—review and editing, T.A.N, I.C and I.N ; visualization, T.A.N, G.K, A.B and I.N; supervision, G.K, I.C and I.N. All authors have read and agreed to the published version of the manuscript.