Effects of incline on speed, acceleration, body posture and hindlimb kinematics in two species of lizard Callisaurus draconoides and Uma scoparia.

We examined the effects of incline on locomotor performance and kinematics in two closely related species of iguanian lizards that co-occur in sandy desert habitats. Callisaurus draconoides differs from Uma scoparia of equal snout-vent length by being less massive and having greater limb and tail lengths. We analyzed high-speed video tapes of lizards sprinting from a standstill on a sand-covered racetrack which was level or inclined 30 degrees uphill. C. draconoides sprinted significantly faster than U. scoparia on both level and uphill sand surfaces, although U. scoparia is considered to be more specialized for sandy habitats. Initial accelerations (over the first 50 ms) did not differ significantly either between species or between inclines within species. Overall, the effects of incline were more pronounced for C. draconoides than for U. scoparia. For example, the incline caused a significant decrease in the maximum stride length of C. draconoides but not in that of U. scoparia. For C. draconoides, uphill stride durations were significantly shorter than on the level surface, and this partially compensated for the effects of shorter uphill stride lengths on velocity. C. draconoides ran bipedally more often than did U. scoparia on both the level and uphill surfaces.