Ecological niche modeling of genetic lineages of the great gerbil, Rhombomys opimus (Rodentia: Gerbillinae)

Great gerbil (Rhombomys opimus Lichtenstein, 1823) is distributed in Central Asia and some parts of the Middle East. It is widely found in central and northeast parts of Iran with two distinct genetic lineages: R. o. sodalis in the northern slopes of the Elburz Mountains and R. o. sargadensis in the southern slopes. This large rodent acts as the main host of natural focal diseases. No study has surveyed the ecological niche of the lineages and how their distribution might be influenced by different climatic variables. To examine the distribution patterns of this murid rodent, we aimed to determine the habitat preferences and effects of environmental variables on the ecological niche. Using a species distribution approach for modeling of regional niche specialization, suitable habitats predicted for R. o. sodalis were mainly located in Golestan province in northern Iran, along the northern slope of Elburz, while R. o. sargadensis, showed great potential distribution along the southern slope of Elburz and around the Kavir Desert and the Lut Desert. Despite the widest potential distribution of R. o. sargadensis from northeast to northwest and through Central Iran, the geographic range of R. o. sodalis was smaller and mostly confined to Golestan province. The results support the presence of the two genetic lineages of Rhombomys in Iran and confirm that there is no significant niche overlap between the two subspecies. Furthermore, it provided several perspectives for future taxonomic studies and prevention hygiene programs for public health.

Demarcation of the Boundaries of the Central Asian Desert Natural Focus of Plague of Kazakhstan and Monitoring the Areal of the Main Carrier, Rhombomys opimus

The aim of the study was to clarify the boundaries of the Central Asian natural plague focus of Kazakhstan and the modern boundaries of the areal of the great gerbil (Rhombomys opimus) in order to improve epizootiological monitoring and increase the effectiveness of preventive (anti-epidemic) measures.Materials and methods. Data from the epizootiological monitoring of the great gerbil populations in 14 autonomous foci of the Central Asian desert natural plague focus in the Republic of Kazakhstan between 2010 and 2020 were used for the analysis. An epizootiologic survey of an area of 875350 km2 was carried out. When processing the data, epidemiological, epizootiological, statistical research methods, as well as GIS technologies were used.Results and discussion. An increase in the total area of the Central Asian desert natural plague focus of the Republic of Kazakhstan by 79710 km2 (9.98 %) has been established for the period of 1990–2020. It is noted that the change in the area of plague-enzootic territory was a consequence of the ever changing areal of the main carrier of plague pathogen – the great gerbil – under the influence of climatic and anthropogenic factors. The most significant changes were found in the southeastern part of the plague-enzootic territory, including those for the Betpakdala (50 %), Balkhash (34.3 %), Taukum (13.3 %) and Mojynkum (0.32 %) autonomous foci. The area of the Aryskum-Dariyalyktakyr autonomous focus decreased by 2100 km2 (4 %). In 2000–2002, new Alakol’sky and Ili intermountain autonomous foci with a total area of 26759 km2 were discovered. It is shown that due to the regression of the Aral Sea, the areal of the great girbil expanded and the area of the North Aral and Kyzylkum natural plague foci increased by 10500 km2 (29.2 %) and 560 km2 (0.4%), respectively. The areas of the Aral-Karakum and UralEmba desert autonomous foci, on the contrary, decreased by 2000 km2 (2.6 %) and 12300 km2 (17.6 %), respectively. Passportization and landscape-epizootiologic zoning of the territory of the Central Asian desert natural plague focus of the Republic of Kazakhstan has been completed.

Polygenic plague resistance in the great gerbil uncovered by population sequencing

Pathogens may elicit a high selective pressure on hosts and can alter genetic diversity over short evolutionary timescales. Intraspecific variation in immune response can be observed as variable survivability from specific infections. The great gerbil (Rhombomys opimus) is a rodent plague host with a heterogenic but highly resistant phenotype. Here, we investigate if the most plague-resistant phenotypes are linked to genomic differences between survivors and susceptible individuals by exposure of wild-caught great gerbils from Northwest China to plague (Yersinia pestis). Whole genome sequencing of ten survivors and ten moribund individuals revealed a low genome-wide mean divergence, except for a subset of genomic regions that showed elevated differentiation. Gene ontology (GO) analysis of candidate genes within regions of increased differentiation, demonstrated enrichment of pathways involved in transcription and translation and their regulation), as well as genes directly involved in immune functions, cellular metabolism and the regulation of apoptosis. Differential RNA expression analysis revealed that the early activated great gerbil immune response to plague consisted of classical components of the innate immune system. Our approach combining challenge experiments with transcriptomics and population level sequencing, provides new insight into the genetic background of plague-resistance and confirms its complex nature, most likely involving multiple genes and pathways of both the immune system and regulation of basic cellular functions.

POPULATIONS OF THE MAJOR CARRIER RHOMBOMYS OPIMUS, VECTORS OF XENOPSYLLA FLEAS AND THE CAUSATIVE AGENT OF YERSINIA PESTIS IN THE CENTRAL ASIAN DESERT NATURAL FOCUS OF PLAGUE

In the Central Asia desert natural focus of plague, the major carrier of the Yersinia pestis agent is the great gerbil Rhombomys opimus, and its vectors include fleas of the Xenopsylla genus. Phenotypical and genotypical properties of the R. opimus populations, Xenopsylla fleas and Yersinia pestis strains have been studied in the Central Asia desert natural focus of plague. Phenotypic distinctions and population discreteness have been identified in R. opimus on the cytochrome b gene of the mitochondrial genome from three autonomous plague foci: Pre-Balkhash, Betpakdala and Pre-Ustyurt. Phenotypic distinctions have been found in Xenopsylla fleas in the Central Asia desert natural focus of plague, and the genotype of X. gerbilli minax fleas on the Cox2 gene of the mitochondrial DNA; these had been captured in the Betpakdala autonomous focus. The repertoire diversity in phenotypical properties of Y. pestis strains from different natural foci of plague has been demonstrated, and population discreteness of Y. pestis strains has been determined using the next-generation sequencing method for single nucleotide polymorphism genes. Results of the study suggest that geographical and environmental isolation and natural selection have led to heterogeneity in the three populations of the great gerbil, vector fleas and Y. pestis.

ENVIRONMENTAL, BIOLOGICAL AND GENETIC FEATURES OF CERTAIN POPULATIONS OF GREAT GERBIL (Rhombomys opius Licht., 1823) OF KAZAKHSTAN

The main host of a number of especially dangerous zoonotic infections in the arid zones of Kazakhstan, covering an area of about 1.1 million km2, is the great gerbil (Rhombomys opimus). In the process of formation in natural foci of the parasitic triad (pathogen-host-vector, mutual adaptation of all its members to environmental conditions and their coevolution occurs. The article presents the results of a study of the intraspecific, population heterogeneity of ecological-biological and some genomic features of the great gerbil in three foci of zoonotic Infections: Pribalkash, Betpakdala and Predustyurt. The features of climate, soil and vegetation cover, tendencies of their perennial and seasonal changes were studied. Differences in climatic conditions and characteristics of vegetation between the 3 foci were revealed at a rather high degree of synchronization of the trend of changes in air temperature and precipitation. Analysis of the cytB gene fragment from 88 individuals from three autonomous plague foci identified 19 haplotypes that form three haplogroups, one of which is represented by individuals from the populations of two autonomous plague foci Populations of great gerbils from Kazakhstan and China are included in the same cluster and are genetically distant from the populations of Iran. Geographic isolation, significant differences in climatic, landscape, and forage conditions, microevolutionary changes in the genomic status determined the heterogeneity of three described populations of the great gerbil. A growing negative impact on the population of the great gerbil and the epizootic status of natural foci of climate warming and an increasing anthropogenic pressure, primarily in the form of overgrazing, on natural phytocenoses was noted.

The Genome of the Great Gerbil Reveals Species-Specific Duplication of an MHCII Gene

The great gerbil (Rhombomys opimus) is a social rodent living in permanent, complex burrow systems distributed throughout Central Asia, where it serves as the main host of several important vector-borne infectious pathogens including the well-known plague bacterium (Yersinia pestis). Here, we present a continuous annotated genome assembly of the great gerbil, covering over 96% of the estimated 2.47-Gb genome. Taking advantage of the recent genome assemblies of the sand rat (Psammomys obesus) and the Mongolian gerbil (Meriones unguiculatus), comparative immunogenomic analyses reveal shared gene losses within TLR gene families (i.e., TLR8, TLR10, and the entire TLR11-subfamily) for Gerbillinae, accompanied with signs of diversifying selection of TLR7 and TLR9. Most notably, we find a great gerbil-specific duplication of the MHCII DRB locus. In silico analyses suggest that the duplicated gene provides high peptide binding affinity for Yersiniae epitopes as well as Leishmania and Leptospira epitopes, putatively leading to increased capability to withstand infections by these pathogens. Our study demonstrates the power of whole-genome sequencing combined with comparative genomic analyses to gain deeper insight into the immunogenomic landscape of the great gerbil and its close relatives.

Morphological, Physiological and Genetic Characteristics of Populations of the Main Plague Host Rhombomys opimus Licht., 1823 in the Central Asian Desert Natural Focus of Plague

Revealed by morphological characters, physiological status, and genetic diversity of populations of the main plague host Rhombomys opimus Licht., 1823 in Central Asia desert natural focus is described.Differences in the skull parameters of R. opimus from different populations were revealed. It’s shown that gerbils from Moyunkum are separate autonomous populations group. Samples from Moyunkum and Mangyshlak differed from other samples. In Balkhash-Alakol depression found two regional complexes: Pre-Balkhash and Dzungarian.Study results of free amino acids level in R. opimus blood serum obtained by gas-liquid chromatography of blood sera from animals captured in different zones of Central Asian focus gave statistically significant differences. To determine genetic variability in ecological and geographical isolation of R. opimus populations the DNA was genotyped.DNA samples analysis combined the studied gerbil from the desert focus into four clusters with eighteen haplotypes. R. opimus sequence analysis taking into account data from territories of Iran, Kazakhstan and China, clustered into three large clusters. First cluster combined the sequences of Kazakhstan and China samples, while great gerbil captured in Kazakhstan is located in a separate treasure. Second and third clusters include sequences of a great gerbil captured in Iran.