Population structure and genetic characterization of two native Danish sheep breeds

ABSTRACT

Genetic diversity in livestock animals has become recognized as important genetic resource for future sustainable livestock production. Especially native breeds, adapted to their local environment, are of considerable interest. Here, we report a genome-wide characterization of two native Danish sheep breeds, the Danish Landrace sheep and the Danish White-Headed Marsh sheep. We investigated the genetic diversity both at national and European breed level using a European-derived reference panel. The native Danish breeds are genetically distinct from other Nordic breeds. Their closest relatives are Border Leicester, Galway, and Texel. Apart from gene flow between native Danish breeds, Texel admixture was most dominant. For Danish Landrace sheep, a population split into two genetically distinct sub-populations was detected. Compared to other livestock species, genomic inbreeding was moderate. However, among European-derived sheep the native Danish breeds were among the 10 most inbred investigated, illustrating the need for sustainable management strategies to preserve genetic diversity.     

Analysis of genetic diversity and the determination of relationships among western Mediterranean horse breeds using microsatellite markers

The distribution of genetic diversity and the genetic relationships among western Mediterranean horse breeds were investigated using microsatellite markers. The examined sample included seven Spanish and three Italian local horse breeds and populations, plus a Spanish Thoroughbred outgroup. The total number of animals examined was 682 (on average 62 animals per breed; range 20–122). The microsatellite marker set analysed provided 128 alleles (10.7 alleles per locus). Within‐breed genetic diversity was always high (>0.70), with breeds contributing about 8% of the total genetic variability. The mean molecular coancestry of the entire population examined was 0.205, Losino being the breed that contributed most. In addition to Nei's standard and Reynolds’ genetic distances, pair‐wise kinship distance and molecular coancestry were estimated. Remarkably similar breed rankings were obtained with all methods. Clustering analysis provided an accurate representation of the current genetic relationships among the breeds. Determining coancestry is useful for analysing genetic diversity distribution between and within breeds and provides a good framework for jointly analysing molecular markers and pedigree information. An integrated analysis was undertaken to obtain information on the population dynamics in western Mediterranean native horse populations, and to better determine conservation priorities.     

Genetic diversity of Swiss sheep breeds in the focus of conservation research

There is constant pressure to improve evaluation of animal genetic resources in order to prevent their erosion. Maintaining the integrity of livestock species as well as their genetic diversity is of paramount interest for long-term agricultural policies. One major use of DNA techniques in conservation is to reveal genetic diversity within and between populations. Forty-one microsatellites were analysed to assess genetic diversity in nine Swiss sheep breeds and to measure the loss of the overall diversity when one breed would become extinct. The expected heterozygosities varied from 0.65 to 0.74 and 10.8% of the total genetic diversity can be explained by the variation among breeds. Based on the proportion of shared alleles, each of the nine breeds were clearly defined in their own cluster in the neighbour-joining tree describing the relationships among the breeds. Bayesian clustering methods assign individuals to groups based on their genetic similarity and infer the number of populations. In STRUCTURE, this approach pooled the Valais Blacknose and the Valais Red. With BAPS method the two Valais sheep breeds could be separated. Caballero & Toro approach (2002) was used to calculate the loss or gain of genetic diversity when each of the breeds would be removed from the set. The changes in diversity based on between-breed variation ranged from −12.2% (Valais Blacknose) to 0% (Swiss Black Brown Mountain and Mirror Sheep); based on within-breed diversity the removal of a breed could also produce an increase in diversity (−0.6% to + 0.6%). Allelic richness ranged from 4.9 (Valais Red) to 6.7 (Brown Headed Meat sheep and Red Engadine Sheep). Breed conservation decisions cannot be limited to genetic diversity alone. In Switzerland, conservation goals are embedded in the desire to carry the cultural legacy over to future generations.     

Mitochondrial DNA diversity of Anatolian indigenous domestic goats

Anatolia has been an important region for civilizations and agricultural revolution as a major domestication centre for livestock species. Goats (Capra hircus) were among the earliest domesticated animals in this region. In this study, genetic diversity of Anatolian goat breeds was characterized by comparison of mitochondrial DNA hypervariable region 1. A total of 295 individuals, including 99 Anatolian Black goats, 96 Angora goats and 100 Kilis goats, were used. Haplogroup A was found to be the dominant haplogroup in all three breeds. The highest haplogroup diversity, including haplogroups A, B2, C and G, was observed in the Anatolian Black breed. Haplogroup D was only observed in Kilis and Angora goats. Haplogroup G was found in Angora and Anatolian Black breeds. The Anatolian goat breeds had high genetic diversity values and a weak phylogeographical structure. The nucleotide diversity values were found to be higher than those in previously studied goat breeds. The fact that Anatolia is a domestication centre and its geographical position as a junction of trade routes may have caused the higher genetic diversity of Anatolian goat breeds.     

Population genetic analysis of the Brahman cattle (Bos indicus) in Colombia with microsatellite markers

Summary The Brahman is one of the most popular breeds for meat production in the Neotropics. However, genetic studies of the breed in Latin American countries have only recently begun. In total, 178 animals of the Brahman breed from 20 Colombian provinces were genotyped at 11 microsatellite markers with the aim of studying the genetic diversity of this population and its genetic relationships with zebuine and taurine breeds. The outcomes of multivariate analyses, Bayesian inferences and inter‐individual genetic distances suggested that there is no genetic sub‐structure in the population, because of the high rate of animal migration among provinces. The population shows a high degree of heterozygosity and allelic diversity compared with other breeds, reflecting its multibreed origin. The study of the genetic relationships among the breeds reveals that the Brahman breed belongs to the zebuine group. However, it is the population nearest to taurine breeds with high frequencies of taurine alleles. Intensive artificial selection may have favoured the taurine alleles after the breed was formed. There has also been some degree of mixture with local taurine breeds while the Brahman breed has evolved in Colombia.     

Genetic characterization of the Blonde d'Aquitaine cattle breed using microsatellite markers and relationship with three other French cattle populations

This study was conducted to evaluate the genetic diversity of Blonde d'Aquitaine, a well-muscled native French beef breed, and to understand the relationships between Blonde d'Aquitaine, Limousin and Salers. We also compared these three beef breeds to the Holstein dairy breed. For this purpose, a set of 16 microsatellite markers were investigated. The obtained results show that Blonde d'Aquitaine has a high level of genetic diversity. Our study shows also that the French beef breeds have genetic differentiation among them, with approximately 9% of the total variation owing to breed differences. Our results show also that Blonde d'Aquitaine and Salers populations are genetically more similar to each other than to the Limousin.     

The biodiversity and genetic structure of Balearic sheep breeds

The Balearic sheep breeds, Mallorquina, Menorquina, Roja Mallorquina, Ibicenca and one possible new genetic group, Formentera, constitute a unique genetic resource in the Mediterranean farming landscape, displaying high genetic diversity levels and being well differentiated among themselves and with respect to the continental sheep breeds. We used a microsatellite panel of markers to study genetic diversity and relationships with other Spanish breeds. The results reported in this study have important implications for the use, conservation and breeding of Balearic sheep stocks. A mean number of 7.59 alleles was found among the Balearic sheep breeds for the microsatellites scored. The whole mean value of observed heterozygosity amounted to 0.62, whereas the expected heterozygosity value was 0.69, suggesting the presence of a great degree of genetic variability, although a significant deficit of heterozygotes was detected for some markers. Genetic distance estimates showed that Balearic sheep are differentiated from the other Spanish breeds and in particular, from the Merino type. The Ibicenca breed showed the highest distance value from other breeds. The neighbour‐net method of analysis clustered the Roja Mallorquina, Menorquina and Mallorquina breeds. The Structure results clearly demonstrated the genetic differentiation among the four Balearic sheep breeds, with the Ibicenca and Formentera races joined, with slight migration among them. Few external genetic influences from the Spanish mainland breeds were detected.     

Genetic diversity and differentiation of five Cuban cattle breeds using 30 microsatellite loci

Conservation and improvement strategies in farm animals should be based on a combination of genetic and phenotypic characteristics. Genotype data from 30 microsatellites were used to assess the genetic diversity and relationships among five Cuban cattle breeds (Siboney de Cuba, Criollo Cubano, Cebú Cubano, Mambí de Cuba and Taíno de Cuba). All microsatellite markers were highly polymorphic in all the breeds. The expected heterozygosity ranged from 0.67 ± 0.02 in the Taíno de Cuba breed to 0.75 ± 0.02 in the Mambí de Cuba breed, and the observed heterozygosity ranged from 0.66 ± 0.03 in the Cebú Cubano breed to 0.73 ± 0.02 in the Siboney de Cuba breed. The genetic differentiation between the breeds was significant (p < 0.01) based on the infinitesimal model (F_ST). The exact test for Hardy‐Weinberg equilibrium within breeds showed a significant deviation in each breed (p < 0.0003) for one or more loci. The genetic distance and structure analysis showed that a significant amount of genetic variation is maintained in the local cattle population and that all breeds studied could be considered genetically distinct. The Siboney de Cuba and Mambí de Cuba breeds seem to be the most genetically related among the studied five breeds.     

Relationships between Podolic cattle breeds assessed by single nucleotide polymorphisms (SNPs) genotyping

Italian Maremmana, Turkish Grey and Hungarian Grey breeds belong to the same Podolic group of cattle, have a similar conformation and recently experienced a similar demographic reduction. The aim of this study was to assess the relationship among the analysed Podolic breeds and to verify whether their genetic state reflects their history. To do so, approximately 100 single nucleotide polymorphisms (SNPs) were genotyped on individuals belonging to these breeds and compared to genotypes of individuals of two Italian beef breeds, Marchigiana and Piemontese, which underwent different selection and migration histories. Population genetic parameters such as allelic frequencies and heterozygosity values were assessed, genetic distances calculated and assignment test performed to evaluate the possibility of recent admixture between the populations. The data show that the physical similarity among the Podolic breeds examined, and particularly between Hungarian Grey and Maremmana cattle that experienced admixture in the recent past, is mainly morphological. The assignment of individuals from genotype data was achieved using Bayesian inference, confirming that the set of chosen SNPs is able to distinguish among the breeds and that the breeds are genetically distinct. Individuals of Turkish Grey breed were clearly assigned to their breed of origin for all clustering alternatives, showing that this breed can be differentiated from the others on the basis of the allelic frequencies. Remarkably, in the Turkish Grey there were differences observed between the population of Enez district, where in situ conservation studies are practised, and that of Bandirma district of Balikesir, where ex situ conservation studies are practised out of the original raising area. In conclusion, this study demonstrates that molecular data could be used to reveal an unbiased view of past events and provide the basis for a rational exploitation of livestock, suggesting appropriate cross-breeding plans based on genetic distance or breeding strategies that include the population structure.     

Genetic diversity studies in farm animals – a survey

During the past decade a large number of genetic diversity studies in domestic livestock based on microsatellite loci was carried out all over the world. A survey among research groups reveals that in 50% of 87 projects more than eight breeds are investigated. Breeds are chosen mainly because of their long history of isolation, unique phenotypic qualities or an evolution within a unique environment. In half of the projects the average planned sample size per breed is higher than 50. Small ruminants are investigated in the majority of projects. The most preferred type of sample is blood and the most preferred markers are microsatellite loci. To combine results from different diversity studies, the adherence to recommendations, e.g. which loci to genotype or required sample sizes per breed, is necessary. The so called International Society for Animal Genetics (ISAG)/FAO recommendations, which were developed for that purpose, are well known, but the use of recommended microsatellite loci varies between species. The highest acceptance was found in pig, and the lowest in chicken.     

利用微卫星标记分析江苏三个地方鸡品种的遗传多样性

利用30个微卫星DNA标记对3个江苏地方鸡品种进行遗传多样性分析，通过计算等位基因频率、多态信息含量、平均杂合度、有效等位基因数和遗传距离，评估各品种内遗传变异和各品种间遗传相关。结果表明：江苏的3个品种在30个微卫星上共发现196个等位基因，其中96个等位基因为三个品种共有，47个等位基因为各品种所特有；3个地方鸡品种的平均杂合度：狼山鸡为0．655，鹿苑鸡为0．681，溧阳鸡为0．687；狼山鸡与溧阳鸡的遗传距离较小，而两鸡与鹿苑鸡的遗传距离较远。     

山东省地方山羊品种群微卫星基因座的遗传多样性

选用来源于牛和绵羊的27个微卫星DNA标记,对山东省4个地方山羊品种进行遗传多样性分析,通过计算等位基因频率、多态信息含量、不同标记的平均杂和度、总群体杂合度、亚群体杂合度、群体杂合度、基因分化系数、不同群体的F-统计量、基因流动数、不同群体间的基因流动个数和遗传距离并进行聚类分析,评估其种内变异和种间变异的关系,以群体平均杂合度、F-统计量和遗传分化系数为基础,结合四个山羊种群的实际生存状况,提出避免近交和种群间杂交符合山东山羊种群实际状况的保种模式。研究结果可为山东地方种质特性研究提供基础数据,为山东地方山羊种群的合理保护利用提供科学依据。     

Prioritization based on neutral genetic diversity may fail to conserve important characteristics in cattle breeds

Conservation of the intraspecific genetic diversity of livestock species requires protocols that assess between-breed genetic variability and also take into account differences among individuals within breeds. Here, we focus on variation between breeds. Conservation of neutral genetic variation has been seen as promoting, through linkage processes, the retention of useful and potentially useful variation. Using public information on beef cattle breeds, with a total of 165 data sets each relating to a breed comparison of a performance variable, we have tested this paradigm by calculating the correlations between pairwise breed differences in performance and pairwise genetic distances deduced from biochemical and immunological polymorphisms, microsatellites and single-nucleotide polymorphisms. As already observed in floral and faunal biodiversity, significant positive correlations (n=54) were found, but many correlations were non-significant (n=100) or significantly negative (n=11). This implies that maximizing conserved neutral genetic variation with current techniques may conserve breed-level genetic variation in some traits but not in others and supports the view that genetic distance measurements based on neutral genetic variation are not sufficient as a determinant of conservation priority among breeds.     

The impact of using old germplasm on genetic merit and diversity—A cattle breed case study

Artificial selection and high genetic gains in livestock breeds led to a loss of genetic diversity. Current genetic diversity conservation actions focus on long‐term maintenance of breeds under selection. Gene banks play a role in such actions by storing genetic materials for future use and the recent development of genomic information is facilitating characterization of gene bank material for better use. Using the Meuse‐Rhine‐Issel Dutch cattle breed as a case study, we inferred the potential role of germplasm of old individuals for genetic diversity conservation of the current population. First, we described the evolution of genetic merit and diversity over time and then we applied the optimal contribution (OC) strategy to select individuals for maximizing genetic diversity, or maximizing genetic merit while constraining loss of genetic diversity. In the past decades, genetic merit increased while genetic diversity decreased. Genetic merit and diversity were both higher in an OC scenario restricting the rate of inbreeding when old individuals were considered for selection, compared to considering only animals from the current population. Thus, our study shows that gene bank material, in the form of old individuals, has the potential to support long‐term maintenance and selection of breeds.     

Conservation priorities for the different lines of Dutch Red and White Friesian cattle change when relationships with other breeds are taken into account

From a genetic point of view, the selection of breeds and animals within breeds for conservation in a national gene pool can be based on a maximum diversity strategy. This implies that priority is given to conservation of breeds and animals that diverge most and overlap of conserved diversity is minimized. This study investigated the genetic diversity in the Dutch Red and White Friesian (DFR) cattle breed and its contribution to the total genetic diversity in the pool of the Dutch dairy breeds. All Dutch cattle breeds are clearly distinct, except for Dutch Friesian breed (DF) and DFR and have their own specific genetic identity. DFR has a small but unique contribution to the total genetic diversity of Dutch cattle breeds and is closely related to the Dutch Friesian breed. Seven different lines are distinguished within the DFR breed and all contribute to the diversity of the DFR breed. Two lines show the largest contributions to the genetic diversity in DFR. One of these lines comprises unique diversity both within the breed and across all cattle breeds. The other line comprises unique diversity for the DFR but overlaps with the Holstein Friesian breed. There seems to be no necessity to conserve the other five lines separately, because their level of differentiation is very low. This study illustrates that, when taking conservation decisions for a breed, it is worthwhile to take into account the population structure of the breed itself and the relationships with other breeds.     

The legacy of Columbus in American horse populations assessed by microsatellite markers

Criollo horse populations descend from horses brought from the Iberian Peninsula over the period of colonization (15th to 17th century). They are spread throughout the Americas and have potentially undergone genetic hybridization with other breeds in the recent past. In this study, 25 autosomal microsatellites were genotyped in 50 horse breeds representing Criollo populations from 12 American countries (27 breeds), breeds from the Iberian Peninsula (19), one breed each from France and Morocco and two cosmopolitan horse breeds (Thoroughbred and Arabian). The genetic relationships among breeds identified five clusters: Celtic; Iberian; North American with Thoroughbred influence; most Colombian breeds; and nearly all other Criollo breeds. The group of “all other Criollo breeds” had the closest genetic relationship with breeds originating from the Iberian Peninsula, specifically with the Celtic group. For the whole set of Criollo breeds analysed, the estimated genetic contribution from other breeds was approximately 50%, 30% and 20% for the Celtic, Iberian and Arab-Thoroughbred groups, respectively. The spatial distribution of genetic diversity indicates that hotspots of genetic diversity are observed in populations from Colombia, Ecuador, Brazil, Paraguay and western United States, possibly indicating points of arrival and dispersion of Criollo horses in the American continent. These results indicate that Criollo breeds share a common ancestry, but that each breed has its own identity.     

The importance of genetic diversity in livestock populations of the future

Farm animal genetic diversity is required to meet current production needs in various environments, to allow sustained genetic improvement, and to facilitate rapid adaptation to changing breeding objectives. Production efficiency in pastoral species is closely tied to the use of diverse genetic types, but greater genetic uniformity has evolved in intensively raised species. In poultry, breeding decisions are directed by a few multinational companies and involve intense selection, the use of distinct production lines, and very large populations. In dairy cattle, the Holstein breed dominates production. Intensive sire selection is leading to relatively rapid inbreeding rates and raises questions about long-term effects of genetic drift. Key questions in management of farm animal genetic diversity involve the distribution of potentially useful quantitative trait locus alleles among global livestock breeds. Experiments with tomato, maize, and mice suggest that favorable alleles can exist in otherwise lowly productive stocks; this cryptic variation may potentially contribute to future selection response. Genetic improvement under relatively intense unidirectional selection may involve both increases in the frequency of favorable additive alleles as well as the progressive breakdown of homeostatic regulatory mechanisms established under the stabilizing selection that is characteristic of natural populations. Recombination among closely linked regulatory loci and new, potentially favorable mutations are possible sources of long-term genetic variation. A greater understanding of the potential that these alternative mechanisms have for supporting long-term genetic improvement and of genetic relationships among global livestock populations are priorities for managing farm animal genetic diversity.     

Half of 23 Belgian dog breeds has a compromised genetic diversity,as revealed by genealogical and molecular data analysis

The genetic diversity in 23 dog breeds raised in Belgium was investigated using both genealogical analysis and microsatellite markers. Some of these breeds are native breeds, with only small populations maintained. Pedigree and molecular data, obtained from the Belgian kennel club, were used to calculate the inbreeding coefficients, realised effective population size as well as probabilities of gene origin and average observed heterozygosity. Inbreeding coefficients ranged from 0.8 to 44.7% and realised effective population size varied between 3.2 and 829.1, according to the used method and breed. Mean observed heterozygosity ranged from 0.47 to 0.73. Both pedigree and molecular methods reveal low genetic diversity and presence of bottlenecks, especially in native Belgian breeds with small population sizes. Furthermore, principal component analysis on the set of investigated diversity parameters revealed no groups of breeds that could be identified in which similar breeding strategies could be applied to maintain genetic diversity.     

The assessment of genetic diversity within and among the eight subpopulations of Japanese Black cattle using 52 microsatellite markers

Japanese Black cattle are at risk for genetic homogeneity due to intensive use of a few sires. Therefore, assessment of the actual genetic diversity of this breed is important for future breeding plans. In the present study, we investigated the genetic diversity within and among eight subpopulations of Japanese Black cattle using 52 microsatellite markers. The parameters for genetic diversity of Japanese Black cattle were comparable to those of other cattle breeds, suggesting that the relatively high genetic diversity of the breed. However, upon comparison among the eight subpopulations, the Hyogo subpopulation showed markedly low genetic diversity. The results of the pairwise F_ST values, phylogenetic network and structure analysis indicated that the Hyogo population has remarkably high level of genetic differentiation from other populations, while Yamagata, Niigata, Hiroshima and Kagawa populations have low levels of genetic differentiation. Furthermore, multidimensional scaling plots indicated that individuals in some subpopulations were separated from individuals in the other subpopulations. We conclude that while the overall genetic diversity of Japanese Black cattle is still maintained at a relatively high level, that of a particular subpopulation is significantly reduced, and therefore the effective population size of the breed needs to be controlled by correct mating strategies.     

The effects of dog breed development on genetic diversity and the relative influences of performance and conformation breeding

Genetic diversity was compared among eight dog breeds selected primarily for conformation (Standard Poodle, Italian Greyhound and show English Setter), conformation and performance (Brittany), predominantly performance (German Shorthaired and Wirehaired Pointers) or solely performance (field English Setter and Red Setter). Modern village dogs, which better reflect ancestral genetic diversity, were used as the standard. Four to seven maternal and one to two Y haplotypes were found per breed, with one usually dominant. Diversity of maternal haplotypes was greatest in village dogs, intermediate in performance breeds and lowest in conformation breeds. Maternal haplotype sharing occurred across all breeds, while Y haplotypes were more breed specific. Almost all paternal haplotypes were identified among village dogs, with the exception of the dominant Y haplotype in Brittanys, which has not been identified heretofore. The highest heterozygosity based on 24 autosomal microsatellites was found in village dogs and the lowest in conformation (show) breeds. Principal coordinate analysis indicated that conformation‐type breeds were distinct from breeds heavily used for performance, the latter clustering more closely with village dogs. The Brittany, a well‐established dual show and field breed, was also genetically intermediate between the conformation and performance breeds. The number of DLA‐DRB1 alleles varied from 3 to 10 per breed with extensive sharing. SNPs across the wider DLA region were more frequently homozygous in all pure breeds than in village dogs. Compared with their village dog relatives, all modern breed dogs exhibit reduced genetic diversity. Genetic diversity was even more reduced among breeds under selection for show/conformation.