Genetic relationships among American donkey populations: insights into the process of colonization

Radiographic Appearance of the Fore Digit and Carpal Joint in the Mule Foal from Birth to 3 Months of Age

Few studies have established the normal radiographic anatomical development of the donkey foal and, to date, no data are available for mules. Our aim was thus to evaluate the radiographic development of the fore digit and carpal joint in the mule foal from 0 to 3 months of age. Ten forelimbs of five healthy full-term mule foals were included. Radiographs of the fore digit lateromedial and dorsopalmar and the carpus dorsopalmar were performed weekly for the first month of age, and bi-monthly during the following two months. Fore digit growth plate closure times, morphological, angular, and linear radiographic parameters, and also carpal cuboidal bone mineralization were evaluated. Growth plates were graded as open, closing, and closed. Carpal bone appearance was graded as mature, slightly immature, or immature. Growth plate closure times showed the following: middle phalangeal distal physis (DP) closed at birth, and proximal physis (PP) started to close at around two months; first phalanx DP closed at seven days, and PP started to close at three months; and third metacarpal bone DP started to close at two months. Carpal bones were immature at birth. Distal phalanx (PD) was triangular at birth, palmar processes had developed by one month, and proximal sesamoid bones were trapezoidal by three months. The hoof wall, PD dorsal wall, and palmar angles values changed in parallel, and hoof capsule thickness increased. No PD remodeling evidence within the hoof capsule or variations in the hoof axis with growth were found. We identified a baseline for the interpretation of forelimb radiological features in mule foals. The specific features found were intermediate between those found in horses and 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.

On the origins of American Criollo pigs: A common genetic background with a lasting Iberian signature

American Criollo pigs are thought to descend mainly from those imported from the Iberian Peninsula starting in the late 15th century. Criollo pigs subsequently expanded throughout the Americas, adapting to very diverse environments, and possibly receiving influences from other origins. With the intensification of agriculture in the mid-20th century, cosmopolitan breeds largely replaced Criollo pigs, and the few remaining are mostly maintained by rural communities in marginal areas where they still play an important socio-economic and cultural role. In this study, we used 24 microsatellite markers in samples from 1715 pigs representing 46 breeds with worldwide distribution, including 17 American Criollo breeds, with the major focus of investigating their genetic diversity, structure and breed relationships. We also included representatives of the Iberian, Local British, Hungarian, Chinese and Commercial breeds, as well as Wild Boar, in order to investigate their possible influence in the genetic composition of Criollos. Our results show that, when compared with the other breeds, Criollo pigs present higher levels of genetic diversity, both in terms of allelic diversity and expected heterozygosity. The various analyses indicate that breed differentiation overall explains nearly 21% of the total genetic diversity. Criollo breeds showed their own identity and shared a common genetic background, tending to cluster together in various analyses, even though they differ from each other. A close relationship of Criollos with Iberian breeds was revealed by all the different analyses, and the contribution of Iberian breeds, particularly of the Celtic breeds, is still present in various Criollo breeds. No influence of Chinese breeds was detected on Criollos, but a few were influenced by Commercial breeds or by wild pigs. Our results confirm the uniqueness of American Criollo pigs and the role that Iberian breeds have played in their development.

Donkey Industry in China: Current Aspects, Suggestions and Future Challenges

Donkey domestication has been essential to human culture and development and has played an important role in economic and social life in human history. China is one of the largest donkey breeders worldwide; donkey farming for meat, milk and hide production is becoming an important industry in rural China as it provides income to the rural livelihoods of many people. Currently, the donkey industry in China is small and relatively young, but it is growing fast. The industry is not adequately exploited economically, which means that it requires the diminution of its role in the traditional activities of rural households and a reorientation towards a more profitable industry. Given the growing importance of the donkey industry in rural China, this paper aims to outline the current situations of the donkey industry in China in terms of animal stock, breeds and distribution, donkey products, suggestions and future challenges to the development of the donkey industry.

Genetic Characterization of Native Donkey (Equus asinus) Populations of Turkey Using Microsatellite Markers

Simple Summary

This study was conducted to evaluate the genetic variability of Turkish native donkey (Equus asinus) populations, using polymorphism of 17 microsatellite markers. The results revealed a highly mixed genotype of all the examined donkeys, suggesting that two different group of breeds can be distinguished from each other on the basis of microsatellite markers.

Abstract

This study presents the first insights to the genetic diversity and structure of the Turkish donkey populations. The primary objectives were to detect the main structural features of Turkish donkeys by microsatellite markers. A panel of 17 microsatellite markers was applied for genotyping 314 donkeys from 16 locations of Turkey. One hundred and forty-two alleles were identified and the number of alleles per locus ranged from 4 to 12. The highest number of alleles was observed in AHT05 (12) and the lowest in ASB02 and HTG06 (4), while ASB17 was monomorphic. The mean H_O in the Turkish donkey was estimated to be 0.677, while mean H_E was 0.675. The polymorphic information content (PIC) was calculated for each locus and ranged from 0.36 (locus ASB02) to 0.98 (locus AHT05), which has the highest number of alleles per locus in the present study. The average PIC in our populations was 0.696. The average coefficient of gene differentiation (G_ST) over the 17 loci was 0.020 ± 0.037 (p < 0.01). The G_ST values for single loci ranged from −0.004 for LEX54 to 0.162 for COR082. Nei’s gene diversity index (H_t) for loci ranged from 0.445 (ASB02) to 0.890 (AHT05), with an average of 0.696. A Bayesian clustering method, the Structure software, was used for clustering algorithms of multi-locus genotypes to identify the population structure and the pattern of admixture within the populations. When the number of ancestral populations varied from K = 1 to 20, the largest change in the log of the likelihood function (ΔK) was when K = 2. The results for K = 2 indicate a clear separation between Clade I (KIR, CAT, KAR, MAR, SAN) and Clade II (MAL, MER, TOK, KAS, KUT, KON, ISP, ANT, MUG, AYD and KAH) populations.

Banat donkey, a neglected donkey breed from the central Balkans (Serbia)

The dominant donkey breed in the Balkans is the mid-sized Balkan donkey with a grey to chocolate coat color. Local breeders from Serbia, however, still maintain a few larger individuals of a lighter coat color, named Banat donkey, and speculate that they are descendants of a Spanish donkey heard that had been transferred to the Banat region by the Hapsburg Queen Maria Theresa in the XVIII century for a specific purpose, to work in local vineyards. We have previously found a unique nuclear gene-pool and a prevalence of mitochondrial Clade 2 haplotypes in several such animals. In this study, we: (i) perform a comparative analysis of 18 morphological traits of the Banat donkey (seven individuals), Balkan donkey (53 individuals from two sub-populations of this breed) and the potential hybrids (eight individuals), and demonstrate the morphological distinctiveness of the Banat donkey, highlighting the diagnostic traits for distinguishing the breed: hip height, croup width, body length and chest depth; (ii) re-analyse published nuclear microsatellite data for these groups, and reveal that, although severely depopulated, the genetically distinct Banat donkey is not severely affected by the loss of genetic diversity and inbreeding; (iii) demonstrate that previously published Banat donkey mitochondrial haplotypes, analyzed genealogically together with those reported in ancient and modern individuals from Spain, Italy, Turkey, Cyprus and Africa, are shared with three Spanish breeds and individuals belonging to Amiata and some other Italian breeds. A unique morphological feature present in Banat and Somali wild donkeys, but also in Amiata donkeys, black stripes on legs, suggests that the origin of Clade 2 donkeys may be much more complex than previously thought. Actions to preserve the Banat donkey, a valuable but critically endangered genetic resource (<100 individuals), are urgent.

Potential dual expansion of domesticated donkeys revealed by worldwide analysis on mitochondrial sequences

Molecular studies on donkey mitochondrial sequences have clearly defined two distinct maternal lineages involved in domestication. However, domestication histories of these two lineages remain enigmatic. We therefore compared several population characteristics between these two lineages based on global sampling, which included 171 sequences obtained in this study (including Middle Asian, East Asian, and African samples) plus 536 published sequences (including European, Asian, and African samples). The two lineages were clearly separated from each other based on whole mitochondrial genomes and partial non-coding displacement loop (D-loop) sequences, respectively. The Clade I lineage experienced an increase in population size more than 8 000 years ago and shows a complex haplotype network. In contrast, the population size of the Clade II lineage has remained relatively constant, with a simpler haplotype network. Although the distribution of the two lineages was almost equal across the Eurasian mainland, they still presented discernible but complex geographic bias in most parts of Africa, which are known as their domestication sites. Donkeys from sub-Saharan Africa tended to descend from the Clade I lineage, whereas the Clade II lineage was dominant along the East and North coasts of Africa. Furthermore, the migration routes inferred from diversity decay suggested different expansion across China between the two lineages. Altogether, these differences indicated non-simultaneous domestication of the two lineages, which was possibly influenced by the response of pastoralists to the desertification of the Sahara and by the social expansion and trade of ancient humans in Northeast Africa, respectively.

Organization and Management of Conservation Programs and Research in Domestic Animal Genetic Resources

Creating national committees for domestic animal genetic resources within genetic resource national commissions is recommended to organize in situ and ex situ conservation initiatives. In situ conservation is a high priority because it retains traditional zootechnical contexts and locations to ensure the long-term survival of breeds. In situ actions can be based on subsidies, technical support, structure creation, or trademark definition. Provisional or permanent relocation of breeds may prevent immediate extinction when catastrophes, epizootics, or social conflicts compromise in situ conservation. Ex situ in vivo (animal preservation in rescue or quarantine centers) and in vitro methods (germplasm, tissues/cells, DNA/genes storage) are also potential options. Alert systems must detect emergencies and summon the national committee to implement appropriate procedures. Ex situ coordinated centers must be prepared to permanently or provisionally receive extremely endangered collections. National germplasm banks must maintain sufficient samples of national breeds (duplicated) in their collections to restore extinct populations at levels that guarantee the survival of biodiversity. A conservation management survey, describing national and international governmental and non-governmental structures, was developed. Conservation research initiatives for international domestic animal genetic resources from consortia centralize the efforts of studies on molecular, genomic or geo-evolutionary breed characterization, breed distinction, and functional gene identification. Several consortia also consider ex situ conservation relying on socioeconomic or cultural aspects. The CONBIAND network (Conservation for the Biodiversity of Local Domestic Animals for Sustainable Rural Development) exemplifies conservation efficiency maximization in a low-funding setting, integrating several Latin American consortia with international cooperation where limited human, material, and economic resources are available.

Genetics, Evolution, and Physiology of Donkeys and Mules

The genus Equus is made up of donkeys, horses, and zebras. Despite significant variation in chromosome number across these species, interspecies breeding results in healthy, although infertile, hybrid offspring. Most notable among these are the horse-donkey hybrids, the mule and hinny. Donkeys presently are used for everything from companion animals to beasts of burden. Although closely related from an evolutionary standpoint, differences in anatomy and physiology preclude the assumption that they can be treated identically to the domestic horse. Veterinarians should be aware of these differences and adjust their practice accordingly.

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).

New insights into the origin and the genetic status of the Balkan donkey from Serbia

The Balkan donkey (Equus asinus L.) is commonly regarded as a large-sized, unselected, unstructured and traditionally managed donkey breed. We assessed the current genetic status of the three largest E. asinus populations in the central Balkans (Serbia) by analysing the variability of nuclear microsatellites and the mitochondrial (mtDNA) control region of 77 and 49 individuals respectively. We further analysed our mtDNA dataset along with 209 published mtDNA sequences of ancient and modern individuals from 19 European and African populations to provide new insights into the origin and the history of the Balkan donkey. Serbian donkey populations are highly genetically diverse at both the nuclear and mtDNA levels despite severe population decline. Traditional Balkan donkeys in Serbia are rather heterogeneous; we found two groups of individuals with similar phenotypic features, somewhat distinct nuclear backgrounds and different proportions of mtDNA haplotypes belonging to matrilineal Clades 1 and 2. Another group, characterized by larger body size, different coat colour, distinct nuclear gene pool and predominantly Clade 2 haplotypes, was delineated as the Banat donkey breed. The maternal landscape of the large Balkan donkey population is highly heterogeneous and more complex than previously thought. Given the two independent domestication events in donkeys, multiple waves of introductions into the Balkans from Greece are hypothesized. Clade 2 donkeys probably appeared in Greece prior to those belonging to Clade 1, whereas expansion and diversification of Clade 1 donkeys within the Balkans predated that of Clade 2 donkeys.