Gene Flow of Horses Across The Silk Road

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The networks that involve animal exchange are considered to play a significant part in the determination of the gene flow amid the domesticated animal population. In the human history, the Silk Road is known to be the oldest of the continuous exchange networks. Yet, the nature of effectiveness that it has on the facilitation of animal exchange across the large geographical and topographical distances is still under critical study regarding its role in the facilitation of the gene across the horse population in the Eurasian region (Achilli et al. 2012). Among wild animals, the flow of genes is influenced by the extent to which the topographies within the landscape restrict or facilitate the flow of genes within the population. On the contrary, the flow of genes in the domesticated animals is largely a factor that influenced by the human beings. The genetic structure the populations within the domestic animals is this expected to reflect the patterns used during the exchange of the animals. As a matter of fact, the networks that are used for the exchange of animals have been shown to determine the genetic configuration of the traditional Belgian breeds of sheep as well as the local populations of Vietnamese goats (Singh 2008; Mwacharo et al., 2013). However, some of the previous works have also focused on the exchange networks that were used on a regional scale. These involve the presence of farmers from a similar nationality and several herds that had been disjointed by a few hundred kilometers as the most. This will provide the basis of the study on the exchange networks that operated on a continent scale, which have the capacity to provide the configuration of the populations of domestic animals over kilometers that span several thousand across different topographical features, political boundaries and complex landscapes

The ancient Silk Road is a well-known exchange network that is believed to have expedited the genetic consequences of animals associated with the human movements inside the Silk Road (Mezzavilla et al., 2014). The horse is among the animal species that was extensively traded along the Silk Road. This research study was focused on determining of the degree of gene flows and genetic reconstruction of horses in eastern Eurasia. This study examined the level of gene flows and genetic arrangement of horses in eastern Eurasia.

The role played by Silk Roads in shaping the Equine Genetics of the Horses

Horses are known to be among the animals that were widely transacted via the Silk Roads. Nonetheless, widespread progress of horses relative to the other human undertakings may have prevented the genetic marks of the Silk Roads (Dileo et al, 2013). One of the ways through which the current gene flow of the horses in the Eurasian area can be linked to the Silk Road is by the identification of the molecular variation between the two periods. This can be of help in the identification of the change in the molecular structure of this animal. An experiment can be used for the identification of this aspect. Molecular deviation is mainly measured using a process known as microsatellite analysis. Various factors were deliberated on during the documentation of the genetic account, starting with the segregation of several settlements from the humanoid nomadic systems overtime (Warmuth et al., 2015).

A number of researches have been performed to determine the level of the silk roads on the genes of the horses in the Eurasia. For example, in one of the investigations that were performed by Warmuth, genetic samples were taken from 455 horses (Jombart et al., 2008). The sampling procedure has been done based on the focus on the animals sourced from isolated regions that were largely used by the traders for their routine work. The sampling of the horse was done from each village, which was from the 17 remote areas that span the Mongolia and China in the east (Broadman 2006). This was the case for two horse populations that were taken from the same sampling location. It passes through Ukraine and Lithuania in the West. From each of these locations, a minimum of 15samples were taken to help in the calculation of the genetic diversity in each of the locations. This was also to overcome any form of biases that would result during the sampling process. In most of the cases, the owners offered the information on the history and ancestry of their animals (Harris, Robinson & Juniper, 2002). Whenever this was not the case, the risk was largely minimized by taking the samples of related individuals by making sure that there was one individual from each of the villages included in the analysis (Christian, 2000). The horses from a similar sampling zone are subsequently denoted as populations though it may not be particularly applicable in an exacting biological point of view. The DNA was extracted from the roots of the hairs. They were then genotyped using 26 microsatellite markers (Borraz et al, 2012).

The genetic diversity of the horse was then calculated in all of the 17 populations. This was to test how different or similar the horse population was from the others. A number of other factors were considered to provide an explanation for the genetic structure of the horse populations that had been chosen. Thus, from these investigations, it has been discovered that when the geographical factors are put into consideration during various analyses, the network of the silk roads is found to have a significant role. It has been identified as an important predictor of the flow of genes between the populations of horses (Traore et al, 2015).

There was an overall low level of genetic differentiation between the two horse samples. However, it was consistent with the high levels of gene flow that has been historically exhibited across the region. In addition, there is a spatial genetic structure that is mainly branded by a substantial although weak configuration of segregation owing to the expanse of the continent. It is the reason why there is no distinct genetic cluster. The incorporation of the landscape features in a great way improves the fit of the data though the geographical distance was controlled to get the correlation between the differentiation in genetic features and the significance of the Silk Road. For this reason, the results obtained from the study support the effectiveness of this ancient network of trade in the facilitation of the flow of genes across the vast geographical distances in a landscape with complex topography (Yang 2004).

Furthermore, the historical data on gene flows through the Silk Road regions was deliberated on in combination with the outcomes to provide a guide of the customary arc. The human trade that took part during the ancient times served a fundamental role of facilitating the manner through which the population of horses mixed (Dixon, 2003). These took place over distances that were as long as 8000 Km apart. Most traders travelled along the most arduous routes of the Silk Road. For example, they passed through the Himalayas and the Tibetan Plateau, which was probably more costly since it presents less evidence of the flow of genes. The other elements that depict an equal explanation for the genetic variation of the horse population are the grasslands and the arid desert routes. The routes that are easier to travel are the grassland routes as opposed to the desert routes. It is for this reason that a conclusion is made about horses being in demand and therefore their extensive trade along the desert areas (Djankov & Freund 2002).

  1. Genetic Diversity

Calculation of genetic diversity was done using the anticipated heterozygosity (HE), the experiential heterozygosity (HO) and the richness of the alleles (RS). They help in the provision of the estimates of the allelic richness, which are given to the smallest standards of the sample scope in the data set N=15, where a rarefaction is used in the implementation of the algorithm (Goudet 1995). The genetic differentiation between populations is done using the FST estimator. Statistical significance of the values obtained from these estimations are tested using the permutation tests (Oner, Calvo, &Elmaci, 2013). The linkage disequilibrium is also verified amid all the braces of loci within all the populations. The nonconformities from the Hardy–Weinberg equilibrium (HWE) are also established within the FIS as the test statistics and the whole FIT as the test statistic inhabitants with the use of the permutation tests. The permutation tests were executed using the Bonferroni tests with the various corrections to cater for the multiple tests (Waugh 2007).

  1. Spatial Genetic Structure

Within the data set, the special genetic structure can be determined with the use of the analysis of the spatial genetic structure (Jombart et al. 2008). This is the multivariate technique that is especially explicit and is used to identify the spatial patterns while making use of the data from the allele frequency of the entities that include the individuals and the populations. It can be used in high contrast with the conventional PCA, which makes an effort to identify the autonomous synthetic variables that make the alteration of the units score optimal. It is able to optimize the variance product and the extent of spatial autocorrelation. The alteration is constantly positive. However, the longitudinal autocorrelation can be either constructive or destructive and results to the components in negatives alongside those with the positive Eigen values. The components with the positive Eigen values are described as the global structures (Jombart 2008). These are the structures where the populaces are quite analogous to those of their close neighbors than is anticipated within the random spatial distribution that involve the local structures.

With the use of sPCA, there is a border between the feeble and the sturdy spatial constructions (Engel & Rodgers, 1996). This is designated by the sudden decrease in the scale of the affirmative Eigen values that indicate the global structuring, the negative Eigen values that indicate the local configuring, or both. The occurrence of both the local and the global constructions can be formalized further using the Monte Carlo reproductions (Jombart 2008).

An estimation of the spatial autocorrelation is possible when the sPCA uses the samples from the spatial connectivity, which can be designated using a connectivity graph. Thus, the longitudinal connectivity of the models was demarcated through the Delaunay triangulation. The importance of both the local and the global structures was established with the use of the Monte Carlo approach as N = 10 000. Jombart (2008) indicates that all the sPCA evaluations were conducted using the ADEGENET, version 1.3.6 in the numerical setting (Sazini et al., 2015)

From the research conducted on the varied horse populations, it is apparent that the horses that are found within the regions and countries in the former Soviet Union are not similar in any way to those that are found outside the area. In other words, the results of the study reveal that these horses are most probably the product and result of the activities done during the long-term and ancient trading on the Silk Trade routes. This is more evident than the recent trading practices (McRae, 2006). Therefore, it does not come as a shock owing to the long generation span of horses that were present during that period. In this sense, it implies that the trade route of the former Soviet Union was just as highly effective as many researchers have suggested especially when it comes to horses (Li et al., 2010).

From these results, it is easy to discover and understand how the past human movement patterns have been able to shape the genes of the modern horse in Eurasia. They also provide an insight on the kind of difficulties that were endured by those who conducted their trade along the toughest areas of the routes (Gayden et al., 2007).

There is an indication that a number of factors acted as the possible determining factors of the genetic construction possessed by the Eastern Eurasian horses following the activities that took place during the ancient Silk Road trade activities. In order to determine the extent with which the genetic structure of these horses was influenced, the geographical or the great circle of the distances between the populations was used. First, the pattern of isolation through the distances was established (Gommans, 2007). This was then compared to the models that cost less within the Silk Roads. This should contain the models that possess single geographical features. They should focus on the features, which are likely to have had the most effect on the exchange rate of the domestic animals in the region. In addition, there was also the exploration regarding the segregation of the Soviet trade structure that existed disconnected from Eurasia, the major trade configuration found within the region of study during the last a hundred years. It was to determine the manner with which it has inclined the genetic construction of the available samples (Han et al., 2014).

  1. Great-Circle Distances

In a majority of the organisms, there is a spatially limited dispersal. It leads to the IBD pattern. With the spatial scales that have been investigated, it is possible to have a positive correlation between the distances in the geographical areas that are expressed as the great circle expanses and the genetic detachments that are expressed as distances between the horse populations (Waugh, 2007).

  1. Water Bodies

Koban et al.(2012) indicate that most of the accounts provided in relation to the historic trade indicate that the use of maritime means to transport the horses was considered the most costly when compared to the trade over land. With the high costs of maritime transportation of horses, the enormous water bodies might have served as a barricade to the gene flow in the horses. Therefore, it is expected that the shortest expanses on land are able to provide a better explanation for the genetic diversity that is exhibited within the circles of the great distances.

  1. Altitude

Transportation to altitudes that are higher than 1500 has the potential capability of causing medical problems in humans. It includes a high rate of cerebral edemas and high altitude pulmonary. In Eastern Eurasia, some of the highest mountain ranges such as the Himalayas are available. These have been known to restrict effective human movement (Gayden et al., 2013), while the mountainous terrain is associated with the difference in genetics (Xuebin et al. 2005). It suggests an undesirable outcome on the animal trade by the high altitudes.

8. The Silk Roads

Evidence from the archaeological and historical sources indicates that there was an extensive exchange of material along the Silk routes. The term Silk Road was originally used by Ferdinand von Richthofen to refer to the primary East-West routes that linked China with the main ports of the Mediterranean and Black seas (Waugh 2007). However, most of the sources use the Silk Roads to include the various lands as well as the sea routes that provide a connecting link to the previous Silk Roads. According to Christian (2000), Silk Roads can be defined as the long lands that occurred in the middle distance, which were used for goods, ideas and people through the exchange that took place in the major regions in the Afro-Eurasian region. Thus, the following branches of the Silk Roads were highlighted. The East West routes that linked Chinas to the Mediterranean Sea, a route that passes through the Mongolian strip that is north of the Altay Mountains and through the Pontic steppe that is located North of the Black and Caspian seas. As indicated by Gaubatz 1996), it also encompasses the north–south route that leads from leading from the Silk Roads proper (SRP) to the northern India through the Himalayas (Singh 2008). Finally, it took into consideration the network of trade routes that connect the central and South West China with Tibet and India (Yang 2004). Thus, in case the silk Roads served as the corridors for the gene flow of horses across the vast distances and the landscapes that were topographically diverse, the models that cost leads on the Silk roads are expected to provide a better explanation of the genetic structure of the horses in the eastern Eurasian horses than the models that contain single topographical factors.

9. Conclusion

From the research studies that have been conducted, it is apparent that gene flow among horses that exist in communities along the Silk Road still share an analogous inheritance that bonds them and classifies them as offsprings of past centuries Silk Road travelers. It is pertinent to mention that low levels of differentiation across large geographical distances have been reported from the studies that have been performed using populations of local horses. This is an historical indication of the high gene flow in the region. From the study, it has been shown that the Silk Roads significantly provide an explanation for the genetic structure of the sample population. This has been done in a better way than the previous political boundaries and the distances that minimize the cost of travel.

10. References

Achilli, A., Olivieri, A.,&Soares, P. et al. (2012) Mitochondrial genomes from modern horses reveal the major haplogroupsthat underwent domestication. Proceedings of the National Academy of Sciences, 109, 2449–2454.

Aketarawong, N., Isasawin, S., Thanaphum, S. (2014). Evidence of weak genetic

structure and recent gene flow between Bactroceradorsaliss.s. and B. papaya, across Southern Thailand and West Malaysia, supporting a single target pest for SIT applications. BMC Genet, 14(15) 70.

McRae, B. H. (2006). Isolation by resistance. Evolution, 60, 1551–1561.

Yang, B. (2004). Horses, silver, and cowries: Yunnan in global perspective. Journal of World History, 15, 281–322.

July 19, 2022

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