Skeleton play an important role in the life of an organism. It provides mechanical support, protection for the organism, and the adhesive surface for muscle tissue. Researchers propose that amphibian species’ skeletal morphology is directly associated with its habitat.Therefore, the skeletal morphology provides a good springboard for learning about adaptive evolution.
Jiatang LI’s research group of Chengdu Institute of Biology (CIB), Chinese Academy of Sciences (CAS) studied the osteological morphology of the forelimbs and the third metacarpals of arboreal frog (Rhacophoridae and Hylidae) and non- arboreal frog samples (Bombinatoridae, Bufonidae, Megophryidae, Ranidae and Microhylidae), analyzed the adaptive evolution of arboreal frog using phylogenetic comparative methods and niche analysis.
The results revealed that the bony knob on the third metacarpal, which formed by a dilated and elongated lateral articular cartilage (AL) through endochondral ossification, occurred only in species of Rhacophorinae. The results of the phylogenetic comparative methods and correlation analysis strongly supported the conclusion that the bony knob is a phylogenetic independent evolution trait and had a significant correlation with the arboreal habitat. Furthermore, anatomical observation showed that a muscle adhered to the bony knob. Therefore, we speculated that the bony knob might act as an enlarged attachment point for larger or more musculatures to help with grasping. In addition, the study showed a bend with the same direction of the bony knob on the mid-side of the third metacarpal in Hyla, which might act as a unique insertion site or force-bearing point that helped to generate higher grasping forces in the grasping patterns. The relative length of the hand showed a significant difference between arboreal and non-arboreal species. Longer hands might enhance the ability of arboreal frogs to grasp branches of trees or plants.
The research was funded by Young Talent Development Program, Southeast Asian Nations Center for Biodiversity, China Academy of Sciences, National Natural Science Foundation and International Cooperation Fund of Sichuan Science and Technology Agency. And the research result was published on the journal of Acta Zoologica (Click on the links below to see the original articles
Left: arboreal frog; right: Hyla
The morphology of the third metacarpals: a. samples of non-arboreal frog; b. samples of and Rhacophorinae (arboreal frog); c. samples of Hylidae (arboreal frog).
Comparing the value of RL/SVL and HL/SVL between arboreal and non- arboreal species: a: relative radioulna length, b. relative hand length