Genetic diversity and classification of Tibetan yak populations based on the mtDNA COIII gene

Possible Consequences of Climate Change on Survival, Productivity and Reproductive Performance, and Welfare of Himalayan Yak (Bos grunniens)

Simple Summary

Climate change is a global issue, with a wide range of ecosystems being affected by changing climatic conditions including the Himalaya. Yak are exquisitely adapted to the high-altitude conditions of the Himalaya and are thus highly likely to be affected by climate change. This paper reviews the evidence of how the reported impacts of climate change on the environment and ecosystem of the Himalaya are affecting the survival, productivity and welfare of Himalayan Yak. This review identified that we do not know how big the impact of climate change is on yak as very few papers have measured that impact and, in many cases, potentially climate-change-related effects (such as changes in feed supply) are principally driven by human factors.

Abstract

Yak are adapted to the extreme cold, low oxygen, and high solar radiation of the Himalaya. Traditionally, they are kept at high altitude pastures during summer, moving lower in the winter. This system is highly susceptible to climate change, which has increased ambient temperatures, altered rainfall patterns and increased the occurrence of natural disasters. Changes in temperature and precipitation reduced the yield and productivity of alpine pastures, principally because the native plant species are being replaced by less useful shrubs and weeds. The impact of climate change on yak is likely to be mediated through heat stress, increased contact with other species, especially domestic cattle, and alterations in feed availability. Yak have a very low temperature humidity index (52 vs. 72 for cattle) and a narrow thermoneutral range (5–13 °C), so climate change has potentially exposed yak to heat stress in summer and winter. Heat stress is likely to affect both reproductive performance and milk production, but we lack the data to quantify such effects. Increased contact with other species, especially domestic cattle, is likely to increase disease risk. This is likely to be exacerbated by other climate-change-associated factors, such as increases in vector-borne disease, because of increases in vector ranges, and overcrowding associated with reduced pasture availability. However, lack of baseline yak disease data means it is difficult to quantify these changes in disease risk and the few papers claiming to have identified such increases do not provide robust evidence of increased diseases. The reduction in feed availability in traditional pastures may be thought to be the most obvious impact of climate change on yak; however, it is clear that such a reduction is not solely due to climate change, with socio-economic factors likely being more important. This review has highlighted the large potential negative impact of climate change on yak, and the lack of data quantifying that impact. More research on the impact of climate change in yak is needed. Attention also needs to be paid to developing mitigating strategies, which may include changes in the traditional system such as providing shelter and supplementary feed and, in marginal areas, increased use of yak–cattle hybrids.

Mitogenomic diversity and phylogeny analysis of yak (Bos grunniens)

Background and aim

Mitochondrial genome has aseries of characteristics such as simple structure, no recombination, maternalinheritance, stable structure, fast evolution rate, and high copy number. Moreover, it is easy to be sequenced,contains high-resolution phylogenetic information, and exists in a wide rangeof taxa. Therefore, it is widely used in the study of biological phylogeny. Atpresent, phylogenetic studies focus mainly on D-loop region, cytochrome b gene,and protein-coding sequence. Phylogenetic studies using the mitochondrialcomplete sequence are rarely reported in yak. Therefore, the present studyaimed to construct phylogenetic tree using yak mitochondrial complete sequenceand compare the subsequent results with previous findings obtained usingpartial sequences.

Results

Complete mitochondrial sequences of five yakpopulations from Qinghai and Xinjiang were obtained. The mitotype diversity ofthe five populations was Xueduo yak (0.992 ± 0.015), Pamir yak (0.990 ± 0.014),Yushu yak (0.963 ± 0.033), Qilian yak (0.948 ± 0.036), and Huanhu yak (0.905 ±0.048), which showed a higher mitotype diversity compared with other breeds fromthe previous reports, including Jiulong yak, Maiwa yak, Zhongdian yak, andTianzhu yak. A total of 78 mitotypes were obtained from 111 individuals. Amongthese, Yushu yak, Huanhu yak, Xueduo yak, and Qilian yak all shared mitotypes,but the Pamir yak did not share mitotypes with these four populations.Phylogenetic analysis showed that yak populations were separable into threedistinct branches. The analysis identified a new phylogenetic branch containingboth wild and domestic yaks. The 155 mitotypes found in 206 individuals weredivided into 3 haplogroups by mitotype clustering. Thehaplogroup was not associated with the geographical distribution of yaks. Theyaks in the same population or the same ecological environment were distributedin different haplogroups. Among the threehaplogroups, haplogroup A and haplogroup B showed a star-shaped distribution ofmitotypes. The central mitotypes were widely distributed and had a highfrequency.

Conclusions

Thegenetic diversity of yaks in Qinghai was high. Both domestic and wild yaks clusteredinto three branches.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07650-x.

Changes in the expression levels of elastic fibres in yak lungs at different growth stages

BACKGROUND

Yaks have a strong adaptability to the plateau environment, which can be attributed to the effective oxygen utilization rate of their lung tissue. Elastic fibre confers an important adaptive structure to the alveolar tissues in yaks. However, little research has been focused on the structural development of lung tissues and the expression levels of elastic fibres in yaks after birth. Therefore, this study aimed to investigate the morphological changes of elastic fibers and expression profiles of fibre-formation genes in yak lungs at different growth stages and the relationship between these changes and plateau adaptation.

RESULTS

Histological staining was employed to observe the morphological changes in the lung tissue structure of yaks at four different ages: 1 day old, 30 days old, 180 days old and adult. There was no significant difference in the area of a single alveolus between the 1-day-old and 30-day-old groups (P-value > 0.05). However, the single alveolar area was gradually increased with an increase in age (P-value < 0.05). Elastic fibre staining revealed that the amount of elastic fibres in alveolar tissue was increased significantly from the ages of 30 days to 180 days (P-value < 0.05) and stabilized during the adult stage. Transcriptome analysis indicated that the highest levels of differentially expressed genes were found between 30 days of age and 180 days of age. KEGG analysis showed that PI3K-Akt signalling pathway and MAPK pathway, which are involved in fibre formation, accounted for the largest proportion of differentially expressed genes between 30 days of age and 180 days of age. The expression levels of 36 genes related to elastic fibre formation and collagen fibre formation were also analysed, and most of these genes were highly expressed in 30-day-old and 180-day-old yaks.

CONCLUSIONS

The content of elastic fibres in the alveolar tissue of yaks increases significantly after birth, but this change occurs only from 30 days of age to 180 days of age. Our study indicates that elastic fibres can improve the efficiency of oxygen utilization in yaks under harsh environmental conditions.

Genetic Diversity, Molecular Phylogeny, and Selection Evidence of Jinchuan Yak Revealed by Whole-Genome Resequencing

Jinchuan yak, a newly discovered yak breed, not only possesses a large proportion of multi-ribs but also exhibits many good characteristics, such as high meat production, milk yield, and reproductive performance. However, there is limited information about its overall genetic structure, relationship with yaks in other areas, and possible origins and evolutionary processes. In this study, 7,693,689 high-quality single-nucleotide polymorphisms were identified by resequencing the genome of Jinchuan yak. Principal component and population genetic structure analyses showed that Jinchuan yak could be distinguished as an independent population among the domestic yak population. Linkage disequilibrium analysis showed that the decay rate of Jinchuan yak was the lowest of the domestic yak breeds, indicating that the degree of domestication and selection intensity of Jinchuan yak were higher than those of other yak breeds. Combined with archaeological data, we speculated that the origin of domestication of Jinchuan yak was ∼6000 yr ago (4000–10,000 yr ago). The quantitative dynamics of population growth history in Jinchuan yak was similar to that of other breeds of domestic and wild yaks, but was closer to that of the wild yak. No significant gene exchange between Jinchuan and other domestic yaks occurred. Compared with other domestic yaks, Jinchuan yak possessed 339 significantly and positively selected genes, several of which relate to physiological rhythm, histones, and the breed’s excellent production characteristics. Our results provide a basis for the discovery of the evolution, molecular origin, and unique traits of Jinchuan yak.