Brain and Skull Morphology in Five Species of Rodents and Their Ecological Relationship

Brain and skull measures and brain weights of five species,Microtus mandarinus,M.fostis,Myospalax cansus,Cricelulus triton,and Apodomus agraius were surveyed.Ratios of measurements and body length,ratios of brain weight and body weight,and cephalization index (k) were calculated.Ratios of cranium measures and body length (RCM),ratios of brain weight and body weight (RBRW) of Microtus mandarinus are larger than other species.RCM and RBRW of Myospalax cansus are minor.The sequence of k from large to small in five species is Microtus mandarinus,Apodomus agraius,M.fostis,Cricelulus triton,and Myospalax cansus.Having no sexual differences in brain measures and having larger brain in mandarin vole may consist with its monogamous mating system.Smaller brain in Myospalax cansus may be related with its polygamous mating system and solitariness.Ratios of zygomatic width and body length (RZW) and ratios of length of upper molar row and body length (RMRL) in Microtus mandarinus and Myospalax cansus are larger than others.This is because the formers feed on leaves,stalks or roots of plant which consist of more cellulose and Apodomus agraius and Cricelulustriton of the others mainly feed on seeds.Microtus mandarinus and Myospalax cansus have smaller cerebellums,more slender optical nerve and larger olfactory bulbs than Apodomus agraius,M.fostis and Cricelulus triton.These maybe relevant to adaptation and evolution of their living underground or on the floor.