Animals

We captured male individuals of 10 species Anolis by hand or noose at different field sites between November 2001 and June 2002. A. carolinensis, A. sagrei, A. distichus, and A. garmani were captured at mainland U.S. sites (A. carolinensis at New Orleans, LA; all the others at Miami, FL); A. grahami, A. lineatopus, and A. valencienni were caught in Jamaica (Discovery Bay), and A. evermanni, A. gundla-chi, and A. pulchellus were caught in Puerto Rico (El Verde). We transported these species back to the laboratory at Tulane University. Upon arrival in the laboratory, we kept the lizards in pairs in 40-L terraria lined with leaf litter. We fed them live crickets dusted with calcium three times a week and sprayed them with water daily.

12.2.2 Morphology

We used digital calipers (Mitutoyo CD-15DC; ± 0.01 mm) to measure snout-vent length (measured from the tip of the snout to the cloaca) on all individuals used in the running trials. Between 1 and 3 individuals of the 10 species included in our analysis were sacrificed for morphological analysis. Specimens were preserved in 10% aqueous formalin and stored in 70% aquous ethanol solution. Before dissection, we weighed the intact specimens to the nearest 0.01 g on an electronic balance (A & D Instruments, FX 3200; ± 0.01 g). We subsequently dissected out all the hind limb muscles of one hind limb. We then weighed all femur retractor muscles and all knee and ankle extensor muscles separately on a Mettler MT 5 electronic balance (± 0.00001 g). We used the mass of these muscles in further analyses because these are the only muscles potentially responsible for generating propulsion. Muscle and body masses were averaged per species.

12.2.3 Running Trials

We induced the lizards to run up a 2-m long dowel (diameter of 8 cm) by clapping our hands and/or by tapping the base of their tails. The plastic dowel, covered with a mesh to provide sufficient traction, was placed against the wall at an angle of 45°. Individual lizards were filmed laterally using a high-speed video camera (Redlake

Motionscope PCI camera) at 250 Hz. We conducted between 5 to 10 trials per individual over several nonconsecutive days. Prior to experimentation and in between trials, we placed the lizards in an incubator set at 32°C for at least 1 h to attain body temperatures similar to their preferred field body temperatures [26].

The running trials for the Puerto Rican species (i.e., A. pulchellus, A. gundlachi, and A. evermanni) were conducted at the field station in Puerto Rico within 24 hr of capture. The experimental setup differed from the laboratory setup in the following ways: lizards were filmed at 240 Hz using a JVC high-speed video camera. Prior to filming and in between trials, the lizards were placed in individual bags in the shade to attain temperatures equal to or near the environmental temperature (30°C).

For analysis, we selected sequences in which the lizard (1) started from a complete standstill, (2) ran over a total distance of at least 25 cm, and (3) ran on top of the dowel (i.e., in a straight line). For these sequences, we digitized the tip of the lizard's snout for every frame using MOTUS software by Peak Performance. A sequence began 20 frames before the first movement and lasted until the lizard ran out of view or stopped. We subsequently smoothed the data using the Quintic Spline Processor implemented in MOTUS. Only data from individuals that performed at least three "good" trials were used in further analyses.

Based on the smoothed displacement data, instantaneous speed and acceleration (i.e., per frame) were calculated in MOTUS. Instantaneous body mass-specific power output for level locomotion can be calculated as the product of instantaneous velocity and instantaneous acceleration, and is derived by using the following formulas:

Power output = rate of doing work = force x distance/time = force x velocity and

Force = mass x acceleration

Then,

Power output = mass x acceleration x velocity and

Body mass-specific power output = acceleration x velocity

Because the animals were running at an angle of 45°, we had to take into account gravitational forces. Specifically, we used the following formula to calculate body mass-specific power output:

Power output (W Kg-1 body mass) = [(instantaneous acceleration) + (acceleration due to gravity x cos 45°)] x instantaneous velocity

The maximal value of body mass-specific power output was selected from each sequence.

To estimate peak muscle mass-specific power output, we took into account which step in each running sequence was associated with peak body mass-specific power output. If peak power output occurred within the first step, then both hind limbs were considered to be generating the propulsion because lizards typically started running from standstill with both hind limbs pushing off the substrate simultaneously. Muscle mass-specific power output was then calculated as body mass-specific power output divided by the ratio of the propulsive muscle mass of both hind limbs to total body mass. However, if peak power output occurred in later steps, then only one hind limb at a time was responsible for generating propulsion, and muscle mass-specific power output was calculated by dividing body mass-specific power output by the ratio of the propulsive muscle mass of only one hind limb to total body mass. The front limbs were not considered as contributing to the propulsion because they do not contribute to acceleration [27].

As an estimate of an individual's maximal muscle mass-specific power output, we selected the single highest peak muscle mass-specific power output from all the sequences for that individual, i.e., one value per individual. We subsequently averaged these values per species. We refer to this variable as "muscle mass-specific power output during running."

12.2.4 Jumping Trials

Jumping trials were performed on the same individuals and under similar laboratory settings as the running trials. As opposed to running, jumping is a single, discrete event making it possible to use a force platform to record the forces and ultimately power output (see further). We recorded forces of individual lizards jumping from a custom-made force platform to a branch positioned just outside the presumed reach of the individual (see Ref. [26] for detailed description). The lizards were induced to jump by clapping our hands or by tapping slightly on the tail. Prior to experimentation, lizards were placed in an incubator set at 28°C for A. gundlachi and 32°C for all the other species for at least 1 h [26,28]. Each animal was subjected to five separate trials, each on a different and nonconsecutive day. In each trial, we induced the lizard to perform as many separate jumps as possible until it was exhausted. In most cases, the animals performed three or more good jumps per trial. Body mass-specific peak (i.e., instantaneous) power output was calculated using an algorithm written in Superscope 11 (see Ref. [26,28] for details of the calculations). Because lizards always used both hind limbs to push off the substrate during jumping, we calculated muscle mass-specific power output by taking into account the propulsive force of two hind limbs as described above. As an estimate of an individual's maximal muscle mass-specific power output, we selected the single highest instantaneous muscle mass-specific power output from all jumping trials for that individual, i.e., one value per individual. We subsequently averaged these values per species. We refer to this variable as "muscle mass-specific power output during jumping."

For two of the species (A. valencienni and A. carolinensis), jumping trials were filmed in lateral view at 250 frames s-1 using the Redlake camera.

(B)

FIGURE 12.1 Lateral view and stick figures of A. valencienni. (A) Footfall prior to peak power (running). (B) Takeoff (jumping). In the right panel, the stick figure (enlarged) is shown with the three two-dimensional angles that were measured. Numbers refer to anatomical landmarks on the body: (1) shoulder, (2) pelvis, (3) knee, (4) ankle, and (5) base of the second toe.

FIGURE 12.1 Lateral view and stick figures of A. valencienni. (A) Footfall prior to peak power (running). (B) Takeoff (jumping). In the right panel, the stick figure (enlarged) is shown with the three two-dimensional angles that were measured. Numbers refer to anatomical landmarks on the body: (1) shoulder, (2) pelvis, (3) knee, (4) ankle, and (5) base of the second toe.

12.2.5 Configuration of Hind Limbs

We quantified three joint angles for the two species (A. valencienni and A. carolin-ensis) for which movies of both running and jumping were available. In both cases, we only used those sequences in which the individual was producing the highest power output. For the running trials, joint angles were quantified on the frame of footfall of the step in which peak power was reached; in those sequences in which peak power was reached in the first step, joint angles were quantified on the frame prior to the start of any movement. For jumping trials, we used the last frame prior to the start of the jump.

The frames were subsequently imported into CorelDraw (version 10; Corel Corporation 2000), and four lines were drawn connecting (1) the hip to the shoulder, (2) the knee to the hip, (3) the ankle to the knee, and (4) the base of the second toe to the ankle. We then calculated the three angles between the different lines, i.e., the hip, knee, and ankle angles (Figure 12.1).

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