Study On Phylogeny Of Cricetinae And Evolution Of Cricetulus Kamensis(Rodentia,Cricetidae)

Cricetinae belong to the Cricetidae(Rodentia),and are widely distributed in the Palaearctic region.The discovery of a large number of Cricetodon fossils has laid the foundation for the Asian origin of hamsters,but these fossil data have not been completely in line with the extant hamsters.The hamster fossil data that have been discovered are formed in the Middle-Late Pleistocene,but are younger than the interspecific divergence time of extant hamsters,and these fossil data seem to support the theory that extant hamsters are of Asian origin.China is a country with abundant hamsters.There were no reports on hamster resources,spatial distribution patterns and the constraint factors of habitats in China thus far.There were few studies on the molecular evolution of hamsters,in addition,which needed to be improved.As a member of the hamsters,Tibetian hamster Cricetulus kamensis belong to the genus Cricetulus and is endemic to the Qinghai-Tibet Plateau(QTP).The taxonomic issue has been challenged at the genus level,and the subspecies classification was also chaotic.There were few publications on Tibetian hamster except for ecological studies,and massive investigated directions were available.As an endemic species of the QTP,intraspecific phylogeographical study can provide evidence for the history of the QTP.Studying on adaptive evolution can provide basic data for mammals to adapt to the plateau.Studying on ecological genetics and suitable habitats assessment can provide theoretical references for the conservation of Tibetian hamster.The phylogenetic relationships of Cricetinae were constructed using Bayesian Inferenc and Maximum Likelihood methods based on mitochondrial and nuclear genes in this study,and the origin and diversification of hamsters were explored with biogeographical analysis,speciation rate analysis and geographic history.This study comparatively analyized the evolutionary characteristics of hamster mitochondrial genomes(mitogenomes).The spatial distribution pattern of hamsters in China and its constrained factors were discussed using the species distribution model.In addition,Tibetian hamster was used to discuss the phylogeographic pattern,population genetic structure,population dynamic history,morphological and molecular adaptation,and habitat assessment and conservation inferred from the mitochondrial and nuclear genes,digestive track morphology,and geographical distribution data.Moreover,this study has enriched and improved the basic data of Tibetian hamster.The results of this study were as follows:1.The phylogenetic relationships of Cricetinae were constructed using mitochondrial and nuclear genes,and the results indicated that Tibetan hamster was closely related to the Phodopus group but phylogenetically distant from all Cricetulus species.The divergence time of the most recent common ancestor can be dated back to the Late Miocene for Cricetinae.Biogeographical analysis indicated that the extant hamsters originated in the QTP.Climate and environmental changes triggered by the uplift of the QTP enabled speciation and diversification that led to extant hamsters.Diversification analysis indicated that the uplift of the QTP led to a non-adaptive radiation process,and the hamster ancestor did not have the ecological opportunity to adaptively radiate.2.The species richness pattern of hamster in China generally showed a decrease trend of spatial distribution pattern from west to east.The influence of geographical factors on the pattern of hamster richness was that the species richness increased significantly with the increase of longtitude and latitude,and the species richness decreased significantly with the increase of altitude.The influence of atmospheric factors was that the species richness decreased significantly with the increase of temperature difference,and the species richness increased significantly with the increase of seasonal precipitation and land surface temperature.3.Comparative analysis of 10 hamster mitogenomes indicated that they shared similar characteristics with those of other hamsters in terms of genes arrangement,nucleotide composition,codon usage,tRNA structure,nucleotide skew and the origin of replication of light strand without any gene insertion,deletion and rearrangement.Phylogenetic relationship of the subfamily Cricetinae was reconstructed based on mitogenomes data.Phylogenetic analysis indicated that Tibetian hamster was at basal position and phylogenetically distant from all other Cricetulus species but had a close relationship with the group of Phodopus,and the genetic distance between hamsters supported that the genus Urocricetus deserved as a separate genus rank.The phylogenetic status of Tscherskia triton represented a separate clade and the genus-level was rational.The genus Tscherskia was closely related to the diversified hamster lineage,including Cricetulus,Allocricetulus and Cricetus.4.The phylogenetic relationship between C.kamensis populations was inferred from one nuclear and four mitochondrial genes.The results indicated that all total of 13 geographical populations of C.kamensis fell into two major lineages.Molecular clock analysis can be dated to the Early Pleistocene that were influenced by the Qing-Zang tectonic movement from the Middle Pliocene to the Early Pleistocene.Moreover,genetic distance between two major clades did not meet the interspecific level.Demographic history analysis showed that the derivated C.kamensis populations were affected by the Quaternary glacial period.Species distribution model analysis indicated that the suitable habitats of C.kamensis was affected by the Last Glacial Maximum(LGM),and supported that almost the entire QTP was covered by a huge ice sheet during the LGM.In addition,the genetic distance showed that C.alticola was a subspecies of C.kamensis.5.C.kamensis populations showed a higher haplotype diversity and lower genetic diversity.The populations in the Southern QTP showed high genetic diversity by comparison to other geographical populations and the genetic diversity of Tingri population was the highest.Redundancy analysis showed that altitude,average annual vapor pressure(AAVP)and annual sunshine percentage(ASP)had the greatest impact on the genetic diversity of C.kamensis populations.Multiple linear regression analysis indicated that AAVP significantly affected the genetic diversity of C.kamensis populations.There was a significant positive correlation between the pairwise genetic distance and the pairwise geographical distance based on the spatial autocorrelation analysis,showing a positive spatial genetic structure.6.There was no significant sexual difference in the relative fatness of C.kamensis,and there was no significant difference between populations.Multiple linear regression analysis indicated that the relative fatness of C.kamensis was not affected by geographical and atmospheric factors.There was also no significant sexual difference in digestive track morphology of C.kamensis.The digestive track length of C.kamensis varied significantly among different geographical populations.Geographical factors have no significant effect on the digestive track,while AAVP and ASP have a significant effect on it.There was significant difference in the digestive dry weight between C.kamensis populations,but it was not affected by geographical and atmospheric factors.Multiple linear regression of relative fatness and digestive track morphology showed that only the large intestine dry weight had a significant effect on the relative fatness of C.kamensis,while other digestive track morphological factors had no significant effect on it.The site model and branch-site model detected positive signal in interspecies and intraspecies,but did not detect positive selection site,and indicated that C.kamensis have been selected by environmental pressure in adapting to high altitude environments.7.It was found that although C.kamensis had diverse habitat types based on a six years investigation,they have a narrow distribution in the wild and low population density,and was not a dominant species in rodent communities.The species distribution model showed that the QTP has been affected by global climate change.The suitable habitats of C.kamensis will be reduced in the future.The conservation of rodent diversity should be of concern.In summary,this article investigated the origin and diversification of hamsters,spatial distribution pattern,and the evolution and conservation of C.kamensis.It aimed to provide basic data for the hamster research,ecological protection,and biogeographical research in China,and to inherit and develop rodents study.