Life On a Limb: The Evolution of Locomotion in Arboreal Specialists

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An important goal in ecological and evolutionary physiology is to reveal the underlying mechanisms behind differences in habitat use. Studies of locomotor capacity have played a key role in this goal because many species have evolved locomotor abilities in concert with the use of different habitats. Most studies of locomotion are modeled after relatively simple terrestrial habitats (i.e., broad surfaces), and therefore are not ecologically realistic for arboreal species. However, understanding how variables commonly encountered in arboreal habitats (steep inclines, narrow perch diameters) affect locomotion could provide general insights into specialization to different habitats. The tremendous morphological and phylogenetic diversity of lizards exploiting arboreal habitats makes them ideally suited for studying arboreal locomotion. We propose to build on prior work with a group of eight species of Anolis lizards because their phylogeny is well resolved and these species have been characterized as belonging to distinct ecomorphs that occur in different arboreal habitats. The sprinting performance of these Anolis species has been correlated with limb length and the diameters of surfaces in laboratory studies, but virtually nothing is known regarding how the limbs are used on different surfaces and inclines. Thus, in laboratory studies we will conduct three experiments: (1) Examine the effects of incline and surface diameter on the kinematics of steady-speed locomotion in three species of Anolis lizards. (2) Focus on the effects of surface diameter on the kinematics of steady-speed locomotion in 8 species of Anolis lizards. This second experiment will provide a comparative basis for understanding how surface diameter affects locomotion. (3) Study how acceleration and performance is affected by surface diameter for a group of diverse Anolis species. Together, these experiments will reveal the underlying mechanistic and behavioral bases for why some anole species are affected by incline while others are not. Further, they will provide a valuable link between habitat use and quantitative functional morphology. More generally, we will also test whether function, morphology, and habitat use have co-evolved among species, and whether locomotion in arboreal environments differs from locomotion in terrestrial environments. The second goal will be achieved by comparing data from the proposed experiments to those recently performed on terrestrial lizard locomotion.