On Functional Morphology In Skulls Of Mandarin Vole And Brandt’s Vole

As sibling species, Mandarin vole (Lasiopodomys mandarinus) and Brandt’svole (L. brandtii) are both belong to genus Lasiopodomys of Microtinae, Cricetidae,Rodentia in Mammalia. Their morphological structures are similar, but their lifehistories differet significanly. Mandarin vole is subterranean rodent species, mainlyperching in farmland, woodland and orchard. Brandt’s vole is ground-living specie,mainly occurred in grassland. The skull morphological structure of Mandarin voleand Brandt’s vole was studied to investigate the influence of different livingenvironments for the skull morphological development of the two different mouses,the relationship between the skull morphological development and mining methods,feeding habits, social behaviors. In the same time, different evolutionary mechanismof subterranean rodents and ground rodents, the relationship between environmentalstress and biological evolution can be illuminated by this research.In this study,123and106skull specimens of Mandarin vole and Brandt’s volewere prepared respectively. Based on profile length and zygomatic breadth, the skullswere age identified, and those adults were chosen for testing. Totally69variablessuch as profile length were measured among the skull. First, profile length ascovariate was chose to covariance analysis on other skull variables to compare thedifferences between the two different mouse species. Then One-Way ANOVA wasused to compare the sexual differences between the two vole species. Finally profile length was used as independent variable and allometric analysis was carried by usingthe formula Y=aXb. The results of this study were listed as follows:1) Compared with Brandt’s vole, Mandarin vole skull had developed zygomatic,mandible was wider and higher. The traits of zygomatic and mandible provide morechewing muscle attachment points on Mandarin vole. Mandible of Mandarin vole wassolid. Its lower incisors was well-developed and the outermost edge of the toothsurface was spade, so there is a high excavating efficiency of lower incisors. Thisseries features were adapted with the excavation activities of Mandarin vole.Allometric analysis shows that zygomatic and mandible of Mandarin vole werepositive allometric. It was also an adaptation in excavation activities of Mandarinvole.2) Compared with Brandt’s vole, Mandarin vole has larger chewing surfaces andpowerful incisors. It was fitted with feeding on the root and stem of green plants orother fiber foods. Allometric analysis shows that mandible and zygomatic ofMandarin vole and Brandt’s vole were positive allometric. It was related to that theyare herbivorous animal. In addition, their molars variables were negative allometric.When the skull grew continuely, chewing surfaces of molars had basically reachedthe intrinsic state. It would be more conducive to their feeding behavior.3) Compared with Brandt’s vole, Mandarin vole skull had developed nasal. Thistrait may provide a structural basis for the evolution of olfactory. Tympanic bulla ofMandarin vole was small but dense. It may be related to the vibration ofcommunications. Tympanic bulla of Brandt’s vole was bigger. This feature wasadapted with the complicated living environment on the ground. Allometric analysisshows that the nasals variables of Mandarin vole were positive allometric. It reflectsthe evolution of olfactory communication. Orbits variables of Mandarin vole werenegative allometric. It may represent visual degradation.4) The differences on sexual dimorphism of Mandarin vole skull were notobvious. This was related to the monogamous rodent. There was obvious sexualdimorphism in Brandt’s vole skull. The male skulls were stronger than females. Thiswas related to its polyandry mate system, and eusured males face greater pressure onfinding food, spouses and field.