Genetic diversity and paternal origin of domestic donkeys

Origin, Evolution, and Research Development of Donkeys

Lack of archaeological and whole-genome diversity data has restricted current knowledge of the evolutionary history of donkeys. With the advancement of science and technology, the discovery of archaeological evidence, the development of molecular genetics, and the improvement of whole-genome sequencing technology, the in-depth understanding of the origin and domestication of donkeys has been enhanced, however. Given the lack of systematic research, the present study carefully screened and collected multiple academic papers and books, journals, and literature on donkeys over the past 15 years. The origin and domestication of donkeys are reviewed in this paper from the aspects of basic information, cultural origin, bioarcheology, mitochondrial and chromosomal microsatellite sequences, and whole-genome sequence comparison. It also highlights and reviews genome assembly technology, by assembling the genome of an individual organism and comparing it with related sample genomes, which can be used to produce more accurate results through big data statistics, analysis, and computational correlation models. Background: The donkey industry in the world and especially in China is developing rapidly, and donkey farming is transforming gradually from the family farming model to large-scale, intensive, and integrated industrial operations, which could ensure the stability of product quality and quantity. However, theoretical research on donkey breeding and its technical development lags far behind that of other livestock, thereby limiting its industrial development. This review provides holistic information for the donkey industry and researchers, that could promote theoretical research, genomic selection (GS), and reproductive management of the donkey population.

Genomics and the Evolutionary History of Equids

The equid family contains only one single extant genus, Equus, including seven living species grouped into horses on the one hand and zebras and asses on the other. In contrast, the equine fossil record shows that an extraordinarily richer diversity existed in the past and provides multiple examples of a highly dynamic evolution punctuated by several waves of explosive radiations and extinctions, cross-continental migrations, and local adaptations. In recent years, genomic technologies have provided new analytical solutions that have enhanced our understanding of equine evolution, including the species radiation within Equus; the extinction dynamics of several lineages; and the domestication history of two individual species, the horse and the donkey. Here, we provide an overview of these recent developments and suggest areas for further research.

Assessment of genetic diversity and differentiation among four indigenous Turkish sheep breeds using microsatellites

Conservation and breeding programmes of livestock species depend on determination of genetic diversity. Today in livestock species, microsatellite markers are commonly used to reveal population structure and genetic diversity in both breeds and varieties. In this study, population structure, genetic diversity, and differentiation among four native Turkish sheep breeds including Güney Karaman, Kangal, Norduz, and Karakas were assessed by using 21 microsatellite loci. By genotyping 120 individuals belonging to four sheep breeds, a total of 275 different alleles, 37 of which were private alleles, were observed across all loci. The mean number of alleles per breed ranged from 7.28 (Güney Karaman) to 8.09 (Karakas), while allelic richness ranged from 7.22 (Güney Karaman) to 7.87 (Karakas). Mean observed heterozygosity varied from 0.60 (Kangal) to 0.66 (Norduz and Karakas). The lowest pairwiseF ST value (0.084) was between Kangal and Karakas populations, while the highest pairwiseF ST value (0.142) was between Norduz and Karakas populations. Polymorphic information content (PIC) values, ranging from 0.71 (ETH10) to 0.91 (OarFCB304), were highly polymorphic (PIC  >  0.5) and informative in studied populations. In the present study, the results of phylogenetic analysis were of importance, since all studied populations have been accepted as Akkaraman varieties till today. However, factorial correspondence and structure analysis, pairwiseF ST values, and an unweighted pair group method with arithmetic mean analysis (UPGMA) dendrogram revealed that Güney Karaman and Norduz populations have became genetically different from the Akkaraman breed due being raised in different parts of Turkey under different climatic conditions together with their breeding practices. Therefore, we recommend that more comprehensive molecular studies should be conducted to clarify genetic differentiation of Akkaraman sheep varieties.

Morphometric Characteristics of the Extreme Eastern Algerian Domestic Donkey (Equus asinus)

The aim of this study was to define the morphometric variability of the extreme Eastern Algerian donkeys. The study was carried out from June to December 2018 in El-Tarf, Souk-Ahras, and Tebessa provinces. The study population involved 65 individuals (32 jacks and 33 jennies) between the ages of 3 and 16 years old. In total, 13 body measurements were used, and 5 zootechnical indexes were calculated. The quantitative and qualitative characteristics were studied in order to establish an ethnic and functional classification of this particular subspecies. The qualitative data demonstrated that the coat colour was variable. Bay and greyish colours were dominant with a respective rate of 61.5 % and 38.5 %, respectively. The head, the nose, as well as the eyes contour colours were mainly grey with 52.3 %, 58.5 % and 50.8 % respectively. The partial absence of the coat particularities was observed. The population presented a significate relationship between the quantitative characters (P < 0.05). The donkeys were longilinear, of a rectilinear profile, compact with massive trends. They had a hyper-metric format. The animals are good for meat production. The General Linear Model (GLM) showed that the body measurements were variable by sex and body mass. The principal component analysis (PCA), the multiple correspondence analyses (MCA) and the ascending hierarchical classification (AHC) revealed that the population was composed of 2 clusters representing 4 animal classes. This study was the first report on the phenotypic characterization of donkeys in the extreme Eastern Algerian area, based on corporal measurements. The results indicated the existence of heterogeneity and suggested the possibilities of genetic improvement within the species.

Genetic diversity and relationships of Chinese donkeys using microsatellite markers

Donkeys are one important livestock in China because of their nourishment and medical values. To investigate the genetic diversity and phylogenetic relationships of Chinese donkey breeds, a panel of 25 fluorescently labeled microsatellite markers was applied to genotype 504 animals from 12 Chinese donkey breeds. A total of 226 alleles were detected, and the expected heterozygosity ranged from 0.6315 (Guanzhong) to 0.6999 (Jiami). The mean value of the polymorphism information content, observed number of alleles, and expected number of alleles for all the tested Chinese donkeys were 0.6600, 6.890, and 3.700, respectively, suggesting that Chinese indigenous donkeys have relatively abundant genetic diversity. Although there were abundant genetic variations found, the genetic differentiation between the Chinese donkey breeds was relatively low, which displayed only 5.99 % of the total genetic variance among different breeds. The principal coordinates analysis clearly splits 12 donkey breeds into two major groups. The first group included Xiji, Xinjiang, Liangzhou, Kulun, and Guanzhong donkey breeds. In the other group, Gunsha, Dezhou, Biyang, Taihang, Jiami, Qingyang, and Qinghai donkeys were clustered together. This grouping pattern was further supported by structure analysis and neighbor-joining tree analysis. Furthermore, genetic relationships between different donkey breeds identified in this study were corresponded to their geographic distribution and breeding history. Our results provide comprehensive and precise baseline information for further research on preservation and utilization of Chinese domestic donkeys.

Genetic diversity and maternal origin of Northeast African and South American donkey populations

To investigate the mtDNA variation and origin of maternal lineages in South American donkeys and to reassess the domestication of donkeys in northeast Africa, we analyzed sequences (489 bp of the D-loop) from 323 domestic donkeys sampled from Peru, Brazil, Ethiopia and Egypt. Altogether, the 323 sequences displayed 53 different haplotypes (45 in Ethiopia, 14 in Egypt, eight in Peru and six in Brazil). Among the four populations, Egyptian donkeys possessed the highest haplotype diversity (0.910 ± 0.032), followed by Brazilian donkeys (0.879 ± 0.060). The Clade I haplotypes dominated in Peruvian donkeys (65%), whereas Clade II haplotypes dominated in Brazilian donkeys (67%). Estimates of F_ST values showed a high genetic differentiation between Peruvian and Brazilian donkey populations (F_ST  = 0.4066), which could be explained by the complex introduction history of South American donkeys. Phylogeographic analysis indicates that northeast Africa could be the most probable domestication center for Clade I donkeys. Analysis of molecular variance confirmed a weak genetic structure in domestic donkey populations among four continents (Europe, Asia, Africa and South America).

A new molecular screening tool for the detection of chromosomal abnormalities in donkeys

Chromosomal abnormalities are a major cause of infertility and reproductive problems in equids. Nowadays, their detection is rising due to the use of new diagnostic tools based on molecular markers instead of karyotyping. Reports of this kind of genetic aberrations in domestic donkeys (Equus asinus) are extremely scarce, despite their importance in human activities. In the present study, we analysed the implementation of a short-tandem-repeat (STR)-based molecular method initially developed for horses, as a diagnostic tool to detect chromosomal abnormalities in donkeys. The frequency of five X-linked (LEX003, LEX026, TKY38, TKY270 and UCEDQ502) and one Y-linked (ECAYM2) molecular markers and one Y-linked gene (sex-determining region Y, SRY) was characterized in 121 donkeys from two diverse breeds, the Spanish Andalusian and the African Moroccan breeds. The molecular panel showed 100% sensitivity and 99.67% specificity in detecting 10 different chromosomal abnormalities in the species. In conclusion, this methodology is a valid, rapid and low-cost tool for the detection and characterization of chromosomal abnormalities in domestic donkeys.