Geographical Differentiation And Interspecies Difference In Geometrical Morphology Of Skull In Plateau Zokor And Its Influencing Factors

Phenotypic evolution plays an important role in the formation of species,and it is influenced by many factors.As an integral part of sensory perception in animals,the skull is closely related to phenotypic evolution and is particularly sensitive to environmental changes,and the structure also is hard and constant.In course of species differentiation,the skull bears the effect of natural selection all the time,and its morphological differences can show the differentiation of species.It is significant to further reveal the formation process of species(morphological characters)and its adaptive evolution by analyzing the morphological differences and the influencing factors between intraspecific and interspecific.In this study,we analyzed the intraspecific morphologic variations of skull morphology in plateau zokor(Eospalax baileyi)across seven populations from Gansu Province,China and the interspecific differences among Eospalax cansus,Eospalax rufescens,Eospalax smithi,Eospalax fontanieri and plateau zokor of Eospalax.Meanwhile,canonical variate analysis was uesd to show the morphologic variations trend and regression analysis was used to illustrate the changes trend in the geometry of the skull under several environmental aspects including altitude,latitude,mean annual temperature and mean annual precipitation by MorphoJ.Moreover,we used two-block partial least square(PLS)to determine the key ecological factors affecting the morphological changes of the skull.The correlations between the geographic distance matrix of plateau zokor and skull morphological change matrix was also analyzed by Matlab.The interrelationship between 5 species of Eospalax was explored based on Procrustes and Mahalanobis distances as well.The main results are as follows:1.The differences in skull shape among 7 populations were significant,these differences on the dorsal of the skull mainly located on the zygomatic arches,mastoid,nasal,foramen infraorbitale and entire posterior position of skull.The morphological variations on ventral of skull mainly recorded on the upper tooth row,tympanic bulla,zygomatic arches,zygomatic bone and foramen magnum.Results of multivariate regression analysis showed that the variations in skull shape were associated withecological factors.Along with the decrease of altitude and latitude and the increase of mean annual temperature and mean annual precipitation,the shape of nasal,zygomatic arches,back of the skull,foramen infraorbitale,mastoid and occipital in the dorsal surface of skull changed;Along with the increase of altitude,mean annual temperature and mean annual precipitation,the shape of tympanic bulla,upper tooth row,zygomatic arches and foramen magnum in the ventral surface of the skull changed as well.Therefore,we found that the ecological factors have significant influence on the morphological difference of the skull in the one species,and the mean annual temperature is the key factor that affects the morphological changes of the skull in both dorsal and ventral surfaces.The morphology of the dorsal and ventral srufaces of the skull changed significantly with the increase of geographical distance between different populations of plateau zokor.2.The differences in skull shape between the Eospalax cansus,Eospalax rufescens,Eospalax smithi,Eospalax fontanieri and plateau zokor were significant,these morphological differences on the dorsal surface of skull mainly were found in the foramen infraorbitale,nasal,zygomatic arches,frontal,occipital and mastoid.The morphological differences on the ventral surface of skull mainly recorded in incisors,palatal foramen,zygomatic bone and upper tooth row.Results of multivariate regression analysis showed that the variations in skull shape were associated with ecological factors.Within 5 species,the species distributed in low altitude,high mean annual temperature and high mean annual precipitation environment showed the following characteristics in the dorsal surface of skull: the positions of two anterior points of foramen infraorbitale and two posterior tips of foramen infraorbitale are located more laterally,the foramen infraorbitale is small,the distance between two anterior tips of zygomatic arches are wide,the width of frontal is narrow,the distance between two mastoids is longer and their position is on lower side,the distance between two occipitals is longer and their position is on upper side;Meanwhile,the ventral surface showed the following criteria: the angle of two incisors is wider,the position of two anterior tips of zygomatic bone are on upper side,the length of zygomatic bone is longer,the length of palatal foramen is shorter,the position of twoposterior tips of zygomatic arches are on upper side and the distance is shorter,the length of zygomatic arches is shorter and the length of upper tooth row is longer.It could be concluded that the ecological factors affect the morphological diversity of skull in different species,especially the mean annual precipitation which comprises the key factor that affects the morphology changes of skull in both dorsal and ventral surfaces.By calculating Mahalanobis distance and Procrustes distance in the dorsal and ventral surfaces of skulls of 5 species,supporting that Eospalax baileyi and Eospalax smithi are independent species.