Efficiency of uphill locomotion in nocturnal and diurnal lizards

Extreme tolerance for nocturnal emergence at low body temperatures in a high-latitude lizard: implications for future climate warming

High-latitude lizards live in environments where ambient air temperature at night is frequently below retreat temperatures, which likely has implications for nocturnal emergence and activity. However, patterns of lizard activity at night under current temperate climates are poorly understood, a situation that limits our understanding of potential effects of climate change. We investigated patterns of nocturnal emergence and activity in the cold-adapted, viviparous gecko (Woodworthia 'Otago/Southland'). We measured operative environmental temperature (T _e) available to geckos that emerged at night and simultaneously assessed nighttime emergence activity using time-lapse trail cameras. Also, we assessed field body temperature (T _b) of emerged geckos of various life history groups at night using thermography to understand how current weather conditions affect field T _b of emerged geckos. Our results show that T_e , nocturnal emergence activity and field-active T _b increased with nighttime air temperature. Nocturnal emergence was highest in spring and summer but also occurred in autumn and (unexpectedly) in winter. Geckos were active over a broad range of T _b down to 1.4°C (a new record low for lizards) and on rock surfaces typically warmer than air temperature or T _b. We conclude that this nocturnal, high-latitude lizard from the temperate zone is capable of activity at low winter temperatures, but that current climate limits emergence and activity at least in autumn and winter. Activity levels for cool-temperate reptiles will probably increase initially as climates warm, but the consequences of increased nocturnal activity under climate change will probably depend on how climate change affects predator populations as well as the focal species' biology.

Interactive effects of leg autotomy and incline on locomotor performance and kinematics of the cellar spider, Pholcus manueli

Leg autotomy can be a very effective strategy for escaping a predation attempt in many animals. In spiders, autotomy can be very common (5–40% of individuals can be missing legs) and has been shown to reduce locomotor speeds, which, in turn, can reduce the ability to find food, mates, and suitable habitat. Previous work on spiders has focused mostly on the influence of limb loss on horizontal movements. However, limb loss can have differential effects on locomotion on the nonhorizontal substrates often utilized by many species of spiders. We examined the effects of leg autotomy on maximal speed and kinematics while moving on horizontal, 45° inclines, and vertical (90°) inclines in the cellar spider Pholcus manueli, a widespread species that is a denizen of both natural and anthropogenic, three‐dimensional microhabitats, which frequently exhibits autotomy in nature. Maximal speeds and kinematic variables were measured in all spiders, which were run on all three experimental inclines twice. First, all spiders were run at all inclines prior to autotomization. Second, half of the spiders had one of the front legs removed, while the other half was left intact before all individuals were run a second time on all inclines. Speeds decreased with increasing incline and following autotomy at all inclines. Autotomized spiders exhibited a larger decrease in speed when moving horizontally compared to on inclines. Stride length decreased at 90° but not after autotomy. Stride cycle time and duty factor increased after autotomy, but not when moving uphill. Results show that both incline and leg autotomy reduce speed with differential effects on kinematics with increasing incline reducing stride length, but not stride cycle time or duty factor, and vice versa for leg autotomy. The lack of a significant influence on a kinematic variable could be evidence for partial compensation to mitigate speed reduction.

The metabolic cost of walking on an incline in the Peacock (Pavo cristatus)

Altering speed and moving on a gradient can affect an animal's posture and gait, which in turn can change the energetic requirements of terrestrial locomotion. Here, the energetic and kinematic effects of locomoting on an incline were investigated in the Indian peacock, Pavo cristatus. The mass-specific metabolic rate of the Indian peacock was elevated on an incline, but this change was not dependent on the angle ascended and the cost of lifting remained similar between the two inclines (+5 and +7°). Interestingly, the Indian peacock had the highest efficiency when compared to any other previously studied avian biped, despite the presence of a large train. Duty factors were higher for birds moving on an incline, but there was no difference between +5 and +7°. Our results highlight the importance of investigating kinematic responses during energetic studies, as these may enable explanation of what is driving the underlying metabolic differences when moving on inclines. Further investigations are required to elucidate the underlying mechanical processes occurring during incline movement.

The metabolic cost of walking on gradients with a waddling gait

Using open-flow respirometry and video footage (25 frames s–1), the energy expenditure and hindlimb kinematics of barnacle geese, Branta leucopsis, were measured whilst they were exercising on a treadmill at gradients of +7 and –7 deg, and on a level surface. In agreement with previous studies, ascending a gradient incurred metabolic costs higher than those experienced on level ground at comparable speeds. The geese, however, are the first species to show an increased duty factor when ascending a gradient. This increased duty factor was accompanied by a longer stance time, which was probably to enable the additional force required for ascending to be generated. Contrary to previous findings, the geese did not experience decreased metabolic costs when descending a gradient. For a given speed, the geese took relatively shorter and quicker strides when walking downhill. This ‘choppy’ stride and perhaps a lack of postural plasticity (an inability to adopt a more crouched posture) may negate any energy savings gained from gravity's assistance in moving the centre of mass downhill. Also contrary to previous studies, the incremental increase in metabolic cost with increasing speed was similar for each gradient, indicating that the efficiency of locomotion (mechanical work done/chemical energy consumed) is not constant across all walking speeds. The data here suggest that there are species-specific metabolic responses to locomotion on slopes, as well as the established kinematics differences. It is likely that a suite of factors, such as ecology, posture, gait, leggedness and foot morphology, will subtly affect an organism's ability to negotiate gradients.

How forelimb and hindlimb function changes with incline and perch diameter in the green anole, Anolis carolinensis

The range of inclines and perch diameters in arboreal habitats poses a number of functional challenges for locomotion. To effectively overcome these challenges, arboreal lizards execute complex locomotor behaviors involving both the forelimbs and the hindlimbs. However, few studies have examined the role of forelimbs in lizard locomotion. To characterize how the forelimbs and hindlimbs differentially respond to changes in substrate diameter and incline, we obtained three-dimensional high-speed video of green anoles (Anolis carolinensis) running on flat (9 cm wide) and narrow (1.3 cm) perches inclined at 0, 45 and 90 deg. Changes in perch diameter had a greater effect on kinematics than changes in incline, and proximal limb variables were primarily responsible for these kinematic changes. In addition, a number of joint angles exhibited greater excursions on the 45 deg incline compared with the other inclines. Anolis carolinensis adopted strategies to maintain stability similar to those of other arboreal vertebrates, increasing limb flexion, stride frequency and duty factor. However, the humerus and femur exhibited several opposite kinematic trends with changes in perch diameter. Further, the humerus exhibited a greater range of motion than the femur. A combination of anatomy and behavior resulted in differential kinematics between the forelimb and the hindlimb, and also a potential shift in the propulsive mechanism with changes in external demand. This suggests that a better understanding of single limb function comes from an assessment of both forelimbs and hindlimbs. Characterizing forelimb and hindlimb movements may reveal interesting functional differences between Anolis ecomorphs. Investigations into the physiological mechanisms underlying the functional differences between the forelimb and the hindlimb are needed to fully understand how arboreal animals move in complex habitats.

Perch diameter and branching patterns have interactive effects on the locomotion and path choice of anole lizards

Natural branches vary conspicuously in their diameter, density and orientation, but how these latter two factors affect animal locomotion is poorly understood. Thus, for three species of arboreal anole lizards found on different size branches and with different limb lengths, we tested sprinting performance on cylinders with five diameters (5–100 mm) and five patterns of pegs, which simulated different branch orientations and spacing. We also tested whether the lizards preferred surfaces that enhanced their performance. The overall responses to different surfaces were similar among the three species, although the magnitude of the effects differed. All species were faster on cylinders with larger diameter and no pegs along the top. The short-limbed species was the slowest on all surfaces. Much of the variation in performance resulted from variable amounts of pausing among different surfaces and species. Lizards preferred to run along the top of cylinders, but pegs along the top of the narrow cylinders interfered with this. Pegs on top of the 100-mm diameter cylinder, however, had little effect on speed as the lizards ran quite a straight path alongside pegs without bumping into them. All three species usually chose surfaces with greater diameters and fewer pegs, but very large diameters with pegs were preferred to much smaller diameter cylinders without pegs. Our results suggest that preferring larger diameters in natural vegetation has a direct benefit for speed and an added benefit of allowing detouring around branches with little adverse effect on speed.

The metabolic cost of incline locomotion in the Svalbard rock ptarmigan (Lagopus muta hyperborea): the effects of incline grade and seasonal fluctuations in body mass

In a terrestrial environment animals must locomote over different terrain; despite this, the majority of studies focus on level locomotion. The influence moving up an inclined surface has on the metabolic cost of locomotion and the efficiency with which animals perform positive work against gravity is still not well understood. Generally speaking, existing data sets lack consistency in the use of grades, further compounded by differences between species in terms of morphology and locomotor gait. Here we investigated the metabolic cost of locomotion using respirometry in the Svalbard ptarmigan (Lagopus muta hyperborea). The Svalbard ptarmigan provides a unique opportunity to investigate the cost of incline locomotion as it undergoes a seasonal fluctuation in body mass, which doubles in winter, meaning the requirement for positive mechanical work also fluctuates with season. We demonstrate that at the same degree of incline, the cost of lifting 1 kg by 1 vertical metre remains relatively constant between seasons despite the large differences in body mass from summer to winter. These findings are consistent with the notion that positive mechanical work alone dictates the cost of lifting above a certain body mass. However, our data indicate that this cost may vary according to the degree of incline and gait.

Oxygen consumption (V̇O2) during trotting on a 10% decline

REASONS FOR PERFORMING STUDY

Although there have been reports of oxygen consumption measurements of horses running on the level and incline, there are no measurements during decline locomotion. This may be due, in part, to the potential for muscle damage produced by eccentric contractions. In man, running on a 10% decline, VO2 decreased by 35% and stride frequency (SF) decreased by 3% when compared to level locomotion.

HYPOTHESIS

The rate of O2 consumption and SF would be decreased in horses on a 10% decline when compared to the level.

METHODS

Six horses (average 467 +/- 68 kg) were acclimated to trotting on the level and decline prior to data collection. VO2 under moderate conditions was measured (using open flow respirometry) during trotting between 2.25 and 4.0 m/sec (at 0.25 m/sec increments) on a treadmill on the level and declined 10%. Stride frequencies were counted manually.

RESULTS

VO2 decreased (P<0.009) on the decline by an average of 45% (range 42-47%), and SF was 2.7% slower. The speed at which the minimum Cost of Transport occurs on the decline was faster than on the level. SF was reduced on the decline. No evidence of muscle soreness was noted in response to the downhill running.

CONCLUSIONS AND POTENTIAL RELEVANCE

Downhill trotting, eccentric exercise, can be done safely in the horse and requires almost half the energetic costs as trotting on the level. It is not known whether this is the optimum downhill gradient or if the horse adjusts its preferred speed to accommodate downhill trotting.

The respiratory basis of locomotion in Drosophila

The respiratory system of insects has evolved to satisfy the oxygen supply during rest and energetically demanding processes such as locomotion. Flapping flight in particular is considered a key trait in insect evolution and requires an increase in metabolic activity of 10-15-fold the resting metabolism. Two major trade-offs are associated with the extensive development of the tracheal system and the function of spiracles in insects: the risk of desiccation because body water may leave the tracheal system when spiracles open for gas exchange and the risk of toxic tracheal oxygen levels at low metabolic activity. In resting animals there is an ongoing debate on the function and evolution of spiracle opening behavior, focusing mainly on discontinuous gas exchange patterns. During locomotion, large insects typically satisfy the increased respiratory requirements by various forms of ventilation, whereas in small insects such as Drosophila diffusive processes are thought to be sufficient. Recent data, however, have shown that during flight even small insects employ ventilatory mechanisms, potentially helping to balance respiratory currents inside the tracheal system. This review broadly summarizes our current knowledge on breathing strategies and spiracle function in the genus Drosophila, highlighting the gas exchange strategies in resting, running and flying animals.

Jettisoning ballast or fuel? Caudal autotomy and locomotory energetics of the Cape dwarf gecko Lygodactylus capensis (Gekkonidae)

Many lizard species will shed their tail as a defensive response (e.g., to escape a putative predator or aggressive conspecific). This caudal autotomy incurs a number of costs as a result of loss of the tail itself, loss of resources (i.e., stored in the tail or due to the cost of regeneration), and altered behavior. Few studies have examined the metabolic costs of caudal autotomy. A previous study demonstrated that geckos can move faster after tail loss as a result of reduced weight or friction with the substrate; however, there are no data for the effects of caudal autotomy on locomotory energetics. We examined the effect of tail loss on locomotory costs in the Cape dwarf gecko Lygodactylus capensis ( approximately 0.9 g) using a novel method for collecting data on small lizards, a method previously used for arthropods. We measured CO(2) production during 5-10 min of exhaustive exercise (in response to stimulus) and during a 45-min recovery period. During exercise, we measured speed (for each meter moved) as well as total distance traveled. Contrary to our expectations, tailless geckos overall expended less effort in escape running, moving both slower and for a shorter distance, compared with when they were intact. Tailless geckos also exhibited lower excess CO(2) production (CO(2) production in excess of normal resting metabolic rate) during exercising. This may be due to reduced metabolically active tissue (tails represent 8.7% of their initial body mass). An alternative suggestion is that a change in energy substrate use may take place after tail loss. This is an intriguing finding that warrants future biochemical investigation before we can predict the relative costs of tail loss that lizards might experience under natural conditions.

Low metabolic cost of locomotion in ornate box turtles, Terrapene ornata

Evolution has produced a wide range of body plans, but for a given body mass, the energetic cost of transport (COT) of terrestrial animals falls in a relatively narrow range. Previous research indicates that the COT depends on the proficiency of minimizing mechanical work performed, efficiency of performing that work, and cost of generating force to support weight. Turtles are unique in that their protective shell and shoulder-girdle articulation may eliminate the need for the ;muscular sling'. In addition, turtles have slower, more efficient muscles than other vertebrates. However, slow locomotion may raise the COT by confounding mechanical-energy conservation via the inverted-pendulum mechanism. Our goal was to determine the metabolic COT and efficiency of a terrestrial turtle species during locomotion. We studied 18 ornate box turtles, Terrapene ornata. Walking speed was extremely slow (0.07+/-0.005 m s(-1)). The average minimum COT was 8.0+/-0.70 J kg(-1) m(-1) attained at approximately 0.1 m s(-1). Ornate box turtles consume only half the energy predicted by the allometric relationship for all terrestrial animals (15.9+/-0.35 J kg(-1) m(-1)), and, thus, appear to be very economical walkers. When walking up a 24 deg. incline turtles moved significantly slower (0.04+/-0.004 m s(-1)), but performed the extra work required to walk uphill with very high efficiencies (>49%). It appears that the co-evolution of a protective shell, the associated shoulder morphology, and very slow, efficient muscles produce both economical level walking and efficient uphill walking.

Low Cost of Locomotion in Lizards That Are Active at Low Temperatures

The nocturnality hypothesis of K. Autumn and coworkers states that nocturnal geckos have evolved a low energetic cost of locomotion (C(min)). A low C(min) increases maximum aerobic speed and partially offsets the decrease in maximum oxygen consumption caused by activity at low nocturnal temperatures. We tested whether a low C(min) is unique to nocturnal geckos or represents a more general pattern of convergent evolution among lizards that enables nocturnality and/or cold-temperature activity. We measured C(min) in four carefully selected lizard species from New Zealand (two nocturnal and two diurnal; n=5-9 individuals per species), including a nocturnal and diurnal gecko (a low C(min) is a gecko trait and is not related to nocturnality), a nocturnal skink (a low C(min) is related to being nocturnal), and a diurnal skink active at low temperatures (a low C(min) is related to being active at low body temperatures). The C(min) values of the four species measured in this study (range=0.21-2.00 mL O(2) g(-1) km(-1)) are lower than those of diurnal lizards from elsewhere, and the values are within or below the 95% confidence limits previously published for nocturnal geckos. A low C(min) increases the range of locomotor speeds possible at low temperatures and provides an advantage for lizards active at these temperatures. We accepted the hypothesis that nocturnal lizards in general have a low C(min) and provide evidence for a low C(min) in lizards from cool-temperate environments. The low C(min) in lizards living at high latitudes may enable extension of their latitudinal range into otherwise thermally suboptimal habitats.

Differential leg function in a sprawled-posture quadrupedal trotter

Legs of sprawled-posture, quadrupedal trotting geckos (Hemidactylus garnotii) each functioned differently during constant average-speed locomotion. The center of mass decelerated in the first half of a step and accelerated in the second half, as if geckos were bouncing in fore–aft and side-to-side directions. Forelegs decelerated the center of mass only in the fore–aft direction. Hindlegs provided all the acceleration in the latter half of the step. Lateral ground reaction forces were always directed toward the midline and exceeded the magnitude of fore–aft forces. The differential leg function of sprawled-posture geckos resembled sprawled-posture hexapods more than upright-posture quadrupeds. The pattern of leg ground reaction forces observed may provide passive, dynamic stability while minimizing joint moments, yet allow high maneuverability. Integrating limb dynamics with whole body dynamics is required to resolve the trade-offs,if any, that result from stable sprawled-posture running with differential leg function.

Total lactate dehydrogenase activity of tail muscle is not cold-adapted in nocturnal lizards from cool-temperate habitats

The dependence of metabolic processes on temperature constrains the behavior, physiology and ecology of many ectothermic animals. The evolution of nocturnality in lizards, especially in temperate regions, requires adaptations for activity at low temperatures when optimal body temperatures are unlikely to be obtained. We examined whether nocturnal lizards have cold-adapted lactate dehydrogenase (LDH). LDH was chosen as a representative metabolic enzyme. We measured LDH activity of tail muscle in six lizard species (n=123: three nocturnal, two diurnal and one crepuscular) between 5 and 35 degrees C and found no differences in LDH-specific activity or thermal sensitivity among the species. Similarly, the specific activity and thermal sensitivity of LDH were similar between skinks and geckos. Similar enzyme activities among nocturnal and diurnal lizards indicate that there is no selection of temperature specific LDH enzyme activity at any temperature. As many nocturnal lizards actively thermoregulate during the day, LDH may be adapted for a broad range of temperatures rather than adapted specifically for the low temperatures encountered when the animals are active. The total activity of LDH in tropical and temperate lizards is not cold-adapted. More data are required on biochemical adaptations and whole animal thermal preferences before trends can be established.

In vivo muscle activity in the hindlimb of the arboreal lizard, Chamaeleo calyptratus: general patterns and the effects of incline

Arboreal animals often move on surfaces with variable and steep inclines, but the changes in hindlimb muscle activity in response to incline are poorly understood. Thus, we studied the hindlimb muscle activity in the arboreal specialist, Chamaeleo calyptratus, moving up and down 45 degrees inclines and on a horizontal surface. We quantified electromyograms (EMGs) from nine hindlimb muscles, and correlated EMGs with three-dimensional hindlimb kinematics. Kinematics changed little with incline, but the EMGs changed substantially. Most of the changes in EMGs were for amplitude rather than timing, and the EMGs of the hip and thigh muscles had more conspicuous changes with incline than those of the lower limb muscles. Unlike most other vertebrates, chameleons flexed the knee substantially during the first half of stance while the foot was anchored to the perch, and the amplitude of two large knee flexors increased when moving uphill compared to level and downhill. Thus, knee flexion in early stance probably contributes significantly to propulsion in C. calyptratus. During stance, the caudofemoralis EMGs of C. calyptratus correlated well with femur retraction, knee flexion and posterior femur rotation, and their amplitudes were higher on uphill and level surfaces than on the downhill surface. During the second half of stance, iliotibialis EMGs correlated well with knee extension, and their amplitude was highest on the uphill surface and lowest on the downhill surface. Many of the muscles in the hindlimb of C. calyptratus changed activity with incline in a manner similar to the propulsive limb muscles in mammals. Although muscle strain often increases when animals need more power to move uphill, the minimal changes in the hindlimb kinematics of C. calyptratus with incline imply little change in muscle strain.

Locomotion of lizards on inclines and perches: hindlimb kinematics of an arboreal specialist and a terrestrial generalist

Arboreal animals, especially lizards, often traverse three-dimensional networks of narrow perches with variable and steep inclines, but the effects of both incline and narrow surfaces on the locomotor movement and function of limbs are poorly understood. Thus, we quantified the three-dimensional hindlimb kinematics of a specialized arboreal lizard, Chamaeleo calyptratus, moving horizontally, and up and down a 30 degrees incline on a narrow (2.4 cm) perch and a flat surface. We compared the flat-surface data of C. calyptratus with those of an anatomically generalized terrestrial lizard, Dipsosaurus dorsalis. Inclines had significant main effects for relatively few kinematic variables of C. calyptratus (11%) compared to D. dorsalis (73%). For C. calyptratus, the main effects of locomotor surface were nearly three times more widespread than those of incline. The foot of C. calyptratus was markedly anterior to the hip at footfall, primarily as a result of an unusually extended knee for a lizard. A large amount of knee flexion during early stance may be used by C. calyptratus to actively pull the body forward in a manner not found in D. dorsalis. Unexpectedly, the pelvic rotation of C. calyptratus greatly exceeded that of D. dorsalis and, unlike D. dorsalis, was not affected by incline. The more medial location of the foot of C. calyptratus on the narrow perch during stance was primarily a result of knee flexion rather than femur depression. Unlike previous qualitative descriptions of chameleons, our data for the hindlimb posture of C. calyptratus during stance indicate that the limb was not particularly erect.

The effects of surface diameter and incline on the hindlimb kinematics of an arboreal lizard (Anolis sagrei)

Arboreal animals often move in habitats with dense vegetation, narrow perches and variable inclines, but effects of arboreal habitat structure on locomotor function are poorly understood for most animals. Several species of Anolis lizards, which have served as a model group for relating locomotor performance to morphology, have decreased maximal sprinting speeds when perch diameter decreases. However, the effects of perch diameter on the limb movements of Anolis have not been previously studied. Hence, we quantified the hindlimb movements of Anolis sagrei, which naturally occurs on a wide variety of perch diameters and inclines. We analyzed similar speeds of steady locomotion for combinations of flat surfaces and round perches with diameters of 1, 3, 6 and 10 cm and inclines of 0 degrees and uphill 45 degrees and 90 degrees. Diameter significantly affected more kinematic variables than incline, but many kinematic variables changed little with increases in diameter beyond 6 cm. As surface diameter increased, the limb posture of A. sagrei became progressively more sprawled. Significantly greater knee flexion during stance was important for locating the foot more medially during movement on narrow perches. Stride length increased and femur depression, femur retraction and long-axis femur rotation decreased significantly as the surface diameter increased. The low hip heights on the vertical incline and the narrowest perches suggest that bringing the center of mass closer to the locomotor surface is important in these circumstances for reducing the tendency to topple backwards or sideways. Most of the kinematic changes of A. sagrei with decreased perch diameter were opposite those correlated with increased speeds of locomotion for terrestrial lizards. The foot was most lateral to the hip during the swing phase and maximal lateral displacements decreased with decreased perch diameter. Consequently, the width required to accommodate limb movement also decreased as perch diameter decreased.

Kinematics of the transition between aquatic and terrestrial locomotion in the newtTaricha torosa

California newts (Taricha torosa) are capable of locomotion in both aquatic and terrestrial environments. The transition between swimming and terrestrial walking was examined by videotaping individual Tarichawalking both up and down a ramp, inclined at 15° to the horizontal, that had its lower end immersed in water and its upper end out of the water. When ascending the ramp, California newts first approached it by swimming, then used their limbs to walk while still in water, and finally left the water using a normal terrestrial walking gait. The reverse of this sequence was observed when individuals descended the ramp. In both directions, Taricha used a lateral sequence walk with a duty factor of approximately 76% when out of the water. Timing of footfalls was more variable in water and featured shorter duty factors, leading to periods of suspension. Comparison of angular and timing variables revealed effects due to direction and degree of immersion. Few timing variables showed differences according to stride within sequence (indicating whether the animal was in or out of the water), suggesting that the basic walking pattern is equally good in both environments.

Effects of surface grade on proximal hindlimb muscle strain and activation during rat locomotion

Sonomicrometry and electromyography were used to determine how surface grade influences strain and activation patterns in the biceps femoris and vastus lateralis of the rat. Muscle activity is generally present during much of stance and is most intense on an incline, intermediate on the level, and lowest on a decline, where the biceps remains inactive except at high speeds. Biceps fascicles shorten during stance, with strains ranging from 0.07-0.30 depending on individual, gait, and grade. Shortening strains vary significantly among grades (P = 0.05) and average 0.21, 0.16, and 0.14 for incline, level, and decline walking, respectively; similar trends are present during trotting and galloping. Vastus fascicles are stretched while active over the first half of stance on all grades, and then typically shorten over the second half of stance. Late-stance shortening is highest during galloping, averaging 0.14, 0.10, and 0.02 in the leading limb on incline, level, and decline surfaces, respectively. Our results suggest that modulation of strain and activation in these proximal limb muscles is important for accommodating different surface grades.

Spatio-temporal gait characteristics of level and vertical locomotion in a ground-dwelling and a climbing gecko

The effects of incline (vertical versus horizontal) on spatio-temporal gait characteristics (stride and step length, frequency, duty factor, degree of sprawling) were measured over a range of speeds in a ground-dwelling (Eublepharis macularius) and a climbing (Gekko gecko) species of gecko. Surprisingly, the climbing species also performs very well when moving on the horizontal substratum. In the present experiments, climbing speeds ranged from 0.6 to 1.2 m s(−)(1), whereas speeds for level locomotion were between 0.6 and 1.8 m s(−)(1). In contrast, the vertical climbing capacities of the ground-dweller are limited (speeds below 0.1 m s(−)(1)versus level speeds between 0.2 and 1.1 m s(−)(1)). In general, we demonstrate that very little adjustment in gait characteristics is made by either species when they are forced to move on their non-habitual substratum. Moreover, gait characteristics differ little between the species despite the clear differences in ecological niche. Higher level or climbing speeds are realized mainly (or exclusively in the case of level locomotion in G. gecko) by increasing stride frequency. Stride lengths and duty factors vary with speed in the ground-dweller, but not in the climbing species. Step length and the degree of sprawling are speed-independent (except for hind-limb sprawling in G. gecko on the level). It is argued that this common strategy suits climbing (fixed spatial variables, no floating phases) rather than level locomotion.

Comparative and behavioral analyses of preferred speed: Anolis lizards as a model system

I quantified the movement patterns of eight morphologically and ecologically diverse Caribbean Anolis lizard species in the field to address the following questions: (1) Do these eight species move at preferred speeds, and if so, what are these speeds? (2) What proportion of their maximum sprinting capacities do the anole species use when moving undisturbed? (3) What percentage of the time do lizards spend moving, and how far do they typically travel on a daily basis? (4) Have the preferred speeds of anoles coevolved with structural habitat use? Most of the distributions of speeds were highly skewed, with a preponderance of slow-speed locomotion (<20% of maximum capacity). Median speeds varied almost eightfold among species, from a low of 4.9 cm/s (3.0% of maximum) to a high of 38.0 cm/s (22.4% of maximum). For all eight species, at least 75% of their locomotor movements took place between 0% and 40% of maximum capacity. The eight species varied almost 15-fold in the percentage of time they spent moving, indicating that not all anole species are equally sedentary. Through usage of modern comparative methods, I showed that Anolis species that move slowly through their environments also tend to use narrow perch diameters and have large habitat breadths. These findings show how evolutionary approaches can be profitably integrated with physiological data to understand how species use their habitats.

Secondarily diurnal geckos return to cost of locomotion typical of diurnal lizards

Previous studies showed that nocturnal geckos evolved a low energetic cost of locomotion (Cmin), which increases maximum aerobic speed and partially offsets the decrease in maximal oxygen consumption caused by activity at low nocturnal temperatures. Because the advantage of a low Cmin should apply at high diurnal temperatures as well as at low nocturnal temperatures, I hypothesized that Cmin remained low in geckos that have secondarily evolved diurnality. I measured Cmin in two secondarily diurnal gecko species, Rhoptropus bradfieldi (4.7 g+/-0.71 SE) and Phelsuma madagascariensis (23.9 g+/-3.7 SE), during steady exercise on a treadmill and rejected the hypothesis that secondarily diurnal geckos retain the low Cmin of their nocturnal ancestors. The Cmin in R. bradfieldi (2.468 mL O2 g-1 km-1+/-0.489 SE) and P. madagascariensis (1.389 mL O2 g-1 km-1+/-0.119 SE) returned to values typical of ancestrally diurnal lizards. This suggests that there is a trade-off that outweighs the performance advantage of low Cmin in a diurnal environment and that may cause an evolutionary association between Cmin and activity time (diurnality/nocturnality).

Effects of incline and speed on the three-dimensional hindlimb kinematics of a generalized iguanian lizard (Dipsosaurus dorsalis)

Lizards commonly move on steep inclines in nature, but no previous studies have investigated whether the kinematics of the limbs of lizards differ on inclined surfaces compared with level surfaces. Therefore, we examined how the kinematics of the hindlimb were affected by both incline (downhill 30 degrees, level and uphill 30 degrees) and different speeds of steady locomotion (50–250 cm s-1) in the morphologically generalized iguanian lizard Dipsosaurus dorsalis. On the uphill surface, the strides of lizards were shorter and quicker than those at a similar speed on the level and downhill surfaces. A multivariate analysis revealed that the kinematics of locomotion on all three inclines were distinct, but several kinematic features of locomotion on the downhill surface were especially unique. For example, downhill locomotion had the lowest angular excursions of femur rotation, and the knee and ankle were flexed more at footfall which contributed to a very low hip height. For D. dorsalis, changes in knee and ankle angles on the uphill surface were similar to those described previously for mammals moving up inclines, despite fundamental differences in limb posture between most mammals and lizards. Several features of the kinematics of D. dorsalis suggest that a sprawling limb enhances the ability to move on inclines.

A field study of the effects of incline on the escape locomotion of a bipedal lizard, Callisaurus draconoides

We analyzed footprints on the surface of a sand dune to estimate maximal running speeds and the incidence of bipedality in nature, as well as to investigate the effects of incline on the escape locomotion of the lizard Callisaurus draconoides. Previous laboratory tests predicted that inclines would negatively affect sprinting performance in C. draconoides. Although physiologists commonly assume that escape locomotion will be near maximal capacity, we found that only 11% of all strides were greater than 90% of maximal speed of C. draconoides. Escape paths averaged 10 m in length and were generally straight. Approximately 30% of the strides taken by C. draconoides were bipedal, and this value was three times greater than previously found for the closely related species Uma scoparia. The modal value of bipedal stride lengths was greater than that for quadrupedal strides. Inclines negatively affected velocity of only the first meter of C. draconoides escape paths. The location of nearest cover had better predictive value for the initial orientation of C. draconoides escapes than incline. On steep slopes (>15 degrees), C. draconoides avoided running directly downhill and uphill and primarily ran horizontally, whereas on shallow slopes, lizards exhibited approximately equal amounts of horizontal, direct uphill, and direct downhill running.