| Neodon was classified as Rodentia Cricetidae Arvicolinae in 2005.Arvicolinae is a widely distributed group with many species.It has been confirmed that Arvicolinae has 49 species in 15 genera worldwide,and 24 species in 7 genera distributed in China,and only distributed in western mountainous areas of China.Niviventer niviventer species complex(NNSC)is one of the most abundant small mammals in Southeast Asia and China.At present,13 species have been described in this group and 11 species have been recorded in China.The latest taxonomic study in 2017 described and identified Niviventer gladiusmaculus as an independent species based on the genetic distance and morphological differences between species within the NNSC.Its type origin was Milin,Tibet,and reported to be found only in Nyingchi Prefecture.During the second national survey of terrestrial wild vertebrate resources,a total of 47 rodent targets were collected in Cuona area of Xizang,and 10 Neodon sp was found.Unknown species specimen,and No.5 Niviventer sp.Unknown Species specimen.Neodon10 specimens had the following morphological characteristics: the average head and body length was less than 100 mm,and the average cranial length was slightly higher than 27 mm.The tail is long,the average tail length is about 42.52% of the head length;There are only 3 angular processes on the lateral side of the first lower molar tooth,and 3 closed triangles in front of the last transverse tooth ring.The second upper molar has posterior angular processes,3 internal angular processes and 3 external angular processes.The third upper molar tooth has 4 inner corners and 3 outer corners;The third lower molar has 5 external and 6 internal angular processes.Based on the results of Cyt b phylogenetic reconstruction and genetic distance analysis,the genetic distance between Neodon species and other Neodon species was 7.9%～11.6%.PCA analysis was used to compare the mean value of morphological data of a total of 8 Neodon species.Neodon sp.Collected from the self-fault area could be clearly distinguished,which could be identified as a new Neodon species and named Neodon tsonaenesis.Species specimens of Niviventer sp.No.5 have the following morphological characteristics:weight 42-57 g,body length 42.7-57.5mm,tail length 142.53-175.76 mm,hind foot length 21.31-27.25 mm,ear length 20.98-21.88 mm.The back hair is dark brown with some black,the tip of the hair is also very short brown or black,the tail is about 10 mm white bristles,the abdomen is basically a large area of soft white hair,there is a black long sword stripe near the neck,extending from the narrow tip to the middle of the abdomen,the sword stripe covers the whole neck area.Consistent with the external morphological characteristics of N.gladiusmaculus.Using MEGA 7.0 multiple sequence alignment,Partition Finder 2.0 selected the evolution model as GTR+I+G.As shown in the results of phylogenetic tree reconstruction using IQ-tree v2.0.4 based on Maximumlikelihood(ML),the likelihood of relatement to specimens from model origin is 100%,and the genetic distance is 0.5%.PCA analysis and comparison of morphological data of 25 N.gladiusmaculus pianmaensi and morphological data of 8 Niviventer pianmaensi of the same group distributed in the same domain can effectively distinguish N.gladiusmaculus but not N.gladiusmaculus.This is the first time that N.gradiusmaculus specimens have been collected outside the type area since the official publication of this species,which enriches and improves the biogeographic data of this species.In this study,a total of 51 rodent species belonging to 21 genera were collected from counties and cities in Tibet based on the literature retrieval and the latest Chinese animal classification and distribution catalog published in 2022.Ward’s method was used to cluster the rodent distribution counties in Tibet,and the geographical distribution pattern of rodents in Tibet was studied.The distribution of rodentia in Tibet can be divided into four provincial zoogeographical regions: C1 Northern Tibet plateau region,C2 Western Himalaya region,C3 Eastern Himalaya region,and C4 Eastern Tibet alpine gorge region.This paper tries to explain the process of N.sonaenesis migration and differentiation from the hypothesis of geographical differentiation.In this study,according to the discovered Neodon population distribution,the common ancestral birthplace of Lasiopodomys and Neodon under the geographical isolation model of biota,migration routes that might match the distribution were simulated,including the phylogenetic routes of clade 1 plateau widespread type,clade 2 Himalaya type,clade 3 Hengduan-mountain type.According to the phylogenetic relationship shown by the geographical flora and phylogenetic tree corresponding to the results of cluster analysis of rodents in Tibet,it was considered that N.juldaschi did not belong to Neodon,which provided data support for the formal revision of Neodon.Niviventer lotipes(8.6%),N.ianmaensi(8.8%)and N.gardiusmaculus in NNSC were more closely related according to Niviventer genetic distance.Previous studies believed that the co-geographical distribution of N.pianmaensi and N.gladiusmaculus was only different in altitude.This study provides a new distribution of N.gladiusmaculus in Tibet except the model habitat,and the new distribution is obviously isolated from the model habitat,so it does not belong to the same zoogeographical flora.The distribution range of N.gladiusmaculus was expanded,and N.pianmaensi and N.gladiusmaculus were distinguished effectively.N.lotipes and N.gladiusmaculus are closely related,but their distribution is completely different,which provides new evidence for the evolution of NNSC caused by geographical movement.The new species and records emphasize how plateau mountain rodents adapt to the new environment of the Tibetan Plateau in different climates and provide important scientific clues for the biological and ecological adaptation of rodents in the cold plateau region. |
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