The Molecular Phylogeography Of Meriones Meridianus (Rodentia:Cricetidae) In Northern China

The range of Meriones meridianus (Rodentia:Cricetidae:Meriones) spans several major arid and semi-arid biogeographic regions in northern China (Luo, Chen et al.2000). In northern China, this desert-dwelling rodent species is distributed along the edge of deserts, and it is an important component of the desert systems that it inhabits. It could serve as an indicator of desertification. Northern China is endowed with a complicated terrain of deserts, high mountains, rivers, lakes, and basins which vary widely in elevation from the Qaidam Basin, which is over2700m above sea level to the Turpan Basis, which is103m below sea level. These complex and varied terrains, in conjunction with climate fluctuations, have facilitated the diversification and vicariance of M. meridianus. The species provide good models for reconstructions of how environmental parameters influenced the history of biota. This is because its short generation time, rapid mtDNA substitution rate, relatively limited dispersal ability, and strong associations with particular habitats give rise to informative contemporary patterns of genetic variation. In particular, the midday gerbil M. meridianus may display especially informative phylogeographical patterns due to its strong habitat preferences in arid regions. Here, we used three separate gene regions (Cyt-b, D-loop and IRBP) and the combined dataset to analyse phylogeographical patterns and the historical demography of M. meridianus.In this paper our aims are:(1) to determine the influence of the potential geographical isolation barrier on the phylogeographical structure within the current geographical range of M. meridianus.(2) to investigate the historical demography of this species and to determine the influence of climatic fluctuations and environmental variation on the phylogeographical structure within the current geographical range of M. meridianus.(3) solve the taxonomical issues by using phylogenetic analyses and sequence divergence values.(4) to assess whether, and to what extent, out results, obtained using a mitochondrial marker, are concordant with those achieved by nuclear markers.(5) Herein, through testing the genetic differentiation between the populations inhabiting inside and outside the regions of the Qaidam Basin, we presented a comparative phylogeographic study to determine whether there are similar in the phylogeographic patterns of the three rodents that may have resulted from a parallel response to the same historical events, or the three species display spatially and temporally distinct phylogeographic patterns as a consequence of different ecological niche modeling and altitude distributions. We then reconstructed the demographic history of each species to determine whether qualitative differences in demographic history. The main results are following:(1) The phylogeographical patterns and demographic history of mitochondrial DNA (cytochrome b,n=327and D-loop, n=252) and nuclear DNA (IRBP gene, n=235) haplotypes were studied for M. meridianus in northern China, a desert-dwelling gerbil species. The phylogenetic analyses, which were performed on the separate and combined (mitochondrial+nuclear) datasets, revealed two divergent clades (Clade A and Clade B) corresponding to distinct geographical regions. Clade A contained the haplotypes found mostly in individuals from the Tianshan Mountains area. Clade B contained haplotypes from populations located in other deserts in northern China. The divergence times indicated that the history of M. meridianus was influenced by the uplift of the Tianshan Mountains and climate-induced habitat fluctuations. In the Pleistocene, the expansion of forests and grasslands during interglacial period led to the isolation of M. meridianus, which preferred to inhabit deserts. Hence, long geological isolation and M. meridianus adaptation to local ecological conditions led to its genetic divergence.(2) Clade A had long-lasting demographic stability, most likely because the populations of this clade remained in a stable desert environment for a long time. However, the extension of other deserts and disappearance of palaeolakes during the last glacial period resulted in demographic expansion of Clade B.(3) In our study, the K2P distances (for the Cyt-b, D-loop, and IRBP gene regions) between clades suggested the intraspecific value. Thus, our results indicated that two subspecies may exist within the M. meridianus.(4)The IRBP-gene tree supports a reciprocally monophyletic relationship, whereas AVPR2-gene tree did not. Compared to the IRBP-gene tree, low genetic divergence was observed in the the AVPR2-gene tree, depicting a polyphyletic relationship. The inactivating mutations of the AVPR2gene are lethal to the desert-dwelling rodent under conditions of water restriction, because it causes an inherited NDI which is caraterized by the inability to concentrate the urine and an increased urine volume. Thus, AVPR2gene of this desert-dwelling rodent is likely suffer strong selective constraints to maintain the vital important gene function. When the gene expressed in several tissues some mutations are detrimental to be weeded out by selection. Thus, the AVPR2gene is more likely to be conserved among populations. For M. meridianus which is a nocturnal species, functional and structural abnormalities in IRBP do not play fatal role in the survive and reproduce because of an evolutionary sensory modality tradeoff, and visual impairment can be complemented by other sense, such as olfactory and auditory. The IRBP gene tend to accumulate mutations and lead to high level of genetic diversity.(5) We conducted a comparative phylogeography of three rodent species(Allactaga sibirica, M. meridianus and Dipus sagitta) endemic on the northeast margin of the Tibetan Plateau (i.e. Qaidam Basin) and outside Qaidam Basin based on fragments of the mitochondrial Cyt-b gene in275individuals from34populations. Our analyses indicated that intraspecific genetic structures across the three rodents did not originate by the same historical events and they experienced different geological and climatic histories. A. sibirica with high-altitude distributions was subjected to strong isolation as a result of the fragmented habitats caused by complicated topology of high-altitude regions in Qaidam Basin. No clear signal of population expansion was recorded in A. sibirica, with a potential explanation that successive phases of population expansion obscured the signal during its migration process. M. meridianus and D. sagitta with low-altitude distributions experienced less isolation due to a relatively homogeneous habitat and lack of geographical barriers through Qaidam Basin. The two desert-dwelling rodent species, M. meridianus and D. sagitta, experienced a sudden demographic expansion during LGM with disappearance of the ancient lakes and the maximal extent of desert expansion.