The Role of Morphology in the Locomotor Performance of Arboreal Snakes

Adaptation is difficult to directly demonstrate. However, the role that a morphological character, or suite of characters plays in the fitness of a species can be elucidated by examining the intermediate link between morphology and fitness â?? performance. Linking morphology to performance, and then performance to fitness can demonstrate the adaptive significance of a morphological character. Arboreal snakes possess a suite of characteristic morphological traits that differentiate these snakes from their terrestrial counterparts, and these characteristic traits have been presumed to be of an adaptive nature. To determine if these characteristic traits are of an adaptive nature I have taken eight closely related snake species pairs â?? one highly arboreal and one highly terrestrial â?? and compared the pairsâ?? locomotor performance. Each pair was evaluated in their arboreal locomotor performance capabilities: climbing endurance, vertical sprint speed, gap bridging, and the traversing of narrow diameter objects. Likewise, each pair was evaluated in their terrestrial locomotor performance capabilities: crawling endurance and horizontal sprint speed. With few exceptions, arboreal snakes outperformed their terrestrial counterparts in arboreal tasks, while terrestrial snakes outperformed their arboreal counterparts in terrestrial tasks. These findings indicate that functional locomotor trade-offs have occurred with the evolution of arboreality in snakes. That is, arboreal snakes have forfeited proficiency in the terrestrial plane for increased performance in the discontinuous arboreal substrate. Furthermore, these same locomotor trade-offs have occurred across each familial line examined. The implications of these findings are great. With the decimation of forested habitats the world over, arboreal snakes would appear ill-suited to the resulting deforested terrestrial habitats. Forced into the terrestrial plane, arboreal snakes would be less able to compete with terrestrial snakes for resources and evade predators. The conservation concerns are self-evident. Now that it has been shown that morphology is linked to performance in snakes, the next stage of inquiry is to determine if performance is linked to fitness, and if so, show that the characteristic morphology of arboreal snakes is in fact an adaptation for life in the trees