Maneuvering in an arboreal habitat: the effects of turning angle on the locomotion of three sympatric ecomorphs of Anolis lizards.

Although the maximal speeds of straight-ahead running are well-documented for many species of Anolis and other lizards, no previous study has experimentally determined the effects of turning on the locomotor performance of a lizard. Anolis lizards are a diverse group of arboreal species, and the discrete paths created by networks of perches in arboreal environments often force animals to turn in their natural habitats. For three species of Anolis with similar overall body size but different shape, we quantified the escape locomotor performance for arboreal locomotion on 4.8 cm diameter perches that were straight (0 degrees ) or had turning angles of 30 degrees and 90 degrees. The turning angle had widespread significant effects that were often species-dependent. This was shown by measuring the average gross velocity (including the times while the lizards paused) of the three species covering the middle 30 cm of a racetrack with either 30 degrees or 90 degrees turns. The results were expressed as a percentage of the gross velocity over the same distance on a straight racetrack. The values obtained for A. grahami (99 % for 30 degrees turns and 79 % for 90 degrees turns) showed a smaller effect of turning angle than for A. lineatopus (79 % for 30 degrees turns and 50 % for 90 degrees turns) and A. valencienni (74 % for 30 degrees turns and 48 % for 90 degrees turns). Consequently, the rank order of species based on speed depended on the angle of the turn. Some of the magnitudes of decreased locomotor speed associated with turning exceeded those reported previously for the effects of decreasing perch diameter for these species. For all species, more pausing occurred with increased turning angle, with the twig ecomorph (A. valencienni) pausing the most. Approximately half the individuals of each species jumped to traverse the 90 degrees turn, but some of the potential benefits of jumping for increasing speed were offset by pauses associated with preparing to jump or recovering balance immediately after a jump. The tail of Anolis lizards may facilitate the substantial rotation (>60 degrees ) of the body that often occurred in the airborne phase of the jumps.