Correlation between Relative Weights of Hindlimb Muscles and Locomotor Patterns in Japanese Anurans

Abstract

The correlation between the relative weights of the hindlimb muscles and the locomotor patterns was examined in four species of Japanese anurans, Bufo bufo japonicus (terrestrial walker), Rana catesbeiana and R. rugosa (amphibious jumpers), and Rhacophorus arboreus (arboreal climber). The relative weight is represented as a percentage of each muscle weight to the total weight of the thigh and shank muscles. In Rana catesbeiana and R. rugosa, the relative weights of the same muscles are nearly equivalent, whereas those of Bufo b. japonicus are fairly different from the two Ranas. For example, distinct differences occur in the ratio of the muscle weight of the thigh to that of the shank and in the relative weights of three muscle groups acting on the hip, the knee, and the ankle joints. Arboreal Rhacophorus arboreus is intermediate between Rana and Bufo in the thigh muscle weights, whereas in the shank muscles, the characteristics of Bufo are amplified, and, therefore, Rh. arboreus is considered to have a hindlimb musculature different from Bufo and Rana. Each locomotor movement is discussed with reference to the mechanism of jumping with sepcific assumptions on the action of the three muscle groups. These assumptions are supported by the weight composition of the hindlimb musculature, and the locomotor patterns seemed to correspond with the characteristics of musculature.