The correlated evolution of biomechanics, gait and foraging mode in lizards

SUMMARYAdaptations promoting greater performance in one habitat are thought to reduce performance in others. However, there are many examples of animals in which, despite habitat differences, such predicted differences in performance do not occur. One such example is the relationship between locomotory performance to habitat for varanid lizards. To explain the lack of difference in locomotor performance we examined detailed observations of the kinematics of each lizard's stride. Differences in kinematics were greatest between climbing and non-climbing species. For terrestrial lizards, the kinematics indicated that increased femur adduction, femur rotation and ankle angle all contributed positively to changes in stride length, but they were constrained for climbing species, probably because of biomechanical restrictions on the centre of mass height (to increase stability on vertical surfaces). Despite climbing species having restricted stride length, no differences have been previously reported in sprint speed between climbing and non-climbing varanids. This is best explained by climbing varanids using an alternative speed modulation strategy of varying stride frequency to avoid the potential trade-off of speed versus stability on vertical surfaces. Thus, by measuring the relevant biomechanics for lizard strides, we have shown how kinematic differences among species can mask performance differences typically associated with habitat variation.

Section: Discussionsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Lizard tricks: Overcoming conflicting requirements of speed vs climbing ability by altering biomechanics of the lizard stride

Clemente

Withers

Thompson

et al. 2013

“…This is particularly true in species that do not routinely move at steady speed, which is true of many small sprawling animals (Reilly et al, 2007). For example, studies of ground reaction forces in lizards and other sprawling animals have used changes in speed anywhere from 5% to 50% as a criteria to define 'steady speed' locomotion (Full and Tu, 1991;Farley and Ko, 1997;Ahn et al, 2004;Autumn et al, 2006;Chen et al, 2006;Reilly et al, 2006;McElroy et al, 2008;McElroy and Reilly, 2009). In fact, the study of individual limb forces in the house gecko ) used a speed change of <15%, which was similar to our study.…”

Section: Discussionmentioning

confidence: 99%

“…First, we ensured that speed over any 10 cm interval as measured by digitizing the lizard's snout was <20% different than the average speed down the racetrack; by this definition the lizard moved with only small speed fluctuations down the entire surface of the force platform (see also McElroy et al, 2008;McElroy and Reilly, 2009). To further ensure that trials were at steady speed down the length of the force platform, we compared the magnitude of the braking versus accelerative impulse within each trial for the portion of the trial that included whole body forces (Fig.…”

Section: Research Articlementioning

confidence: 99%

A comparative study of single leg ground reaction forces in running lizards

McElroy

Wilson

Biknevicius

et al. 2013

The role of different limbs in supporting and propelling the body has been studied in many species with animals appearing to have either similarity in limb function or differential limb function. Differential hindlimb versus forelimb function has been proposed as a general feature of running with a sprawling posture and as benefiting sprawled postured animals by enhancing maneuvering and minimizing joint moments. Yet only a few species have been studied and thus the generality of differential limb function in running animals with sprawled postures is unknown. We measured the limb lengths of seven species of lizard and their single-limb three-dimensional ground reaction forces during high-speed running. We found that all species relied on the hindlimb for producing accelerative forces. Braking forces were forelimb dominated in four species and equally distributed between limbs in the other three. Vertical forces were dominated by the hindlimb in three species and equally distributed between the forelimb and hindlimb in the other four. Medial forces were dominated by the hindlimb in four species and equally distributed in the other three, with all Iguanians exhibiting hindlimbbiased medial forces. Relative hindlimb to forelimb length of each species was related to variation in hindlimb versus forelimb medial forces; species with relatively longer hindlimbs compared with forelimbs exhibited medial forces that were more biased towards the hindlimbs. These results suggest that the function of individual limbs in lizards varies across species with only a single general pattern (hindlimb-dominated accelerative force) being present.

“…In addition, we employed multiple regression to test for the relative effects of three independent variables on each kinematic variable: age, relative body (to substrate) size and (because there is ample evidence that speed influences many aspects of locomotor kinematics) Froude number. Because it is conventional to regress limb phase against duty factor, and duty factor has been shown to be correlated with limb phase (Cartmill et al, 2002;Lemelin et al, 2003;Hutchinson et al, 2006;Young et al, 2007;McElroy, 2008;Young, 2008), we also included duty factor as a fourth independent variable in the multiple regression for limb phase. Froude number has no significant effect on limb phase once duty factor is controlled for.…”

Section: Statistical Analysesmentioning

confidence: 99%

Kinematics of quadrupedal locomotion in sugar gliders (Petaurus breviceps): effects of age and substrate size

Shapiro

Young

2012

SUMMARY Arboreal mammals face unique challenges to locomotor stability. This is particularly true with respect to juveniles, who must navigate substrates similar to those traversed by adults, despite a reduced body size and neuromuscular immaturity. Kinematic differences exhibited by juveniles and adults on a given arboreal substrate could therefore be due to differences in body size relative to substrate size, to differences in neuromuscular development, or to both. We tested the effects of relative body size and age on quadrupedal kinematics in a small arboreal marsupial (the sugar glider, Petaurus breviceps; body mass range of our sample 33-97 g). Juvenile and adult P. breviceps were filmed moving across a flat board and three poles 2.5, 1.0 and 0.5 cm in diameter. Sugar gliders (regardless of age or relative speed) responded to relative decreases in substrate diameter with kinematic adjustments that promote stability; they increased duty factor, increased the average number of supporting limbs during a stride, increased relative stride length and decreased relative stride frequency. Limb phase increased when moving from the flat board to the poles, but not among poles. Compared with adults, juveniles (regardless of relative body size or speed) used lower limb phases, more pronounced limb flexion, and enhanced stability with higher duty factors and a higher average number of supporting limbs during a stride. We conclude that although substrate variation in an arboreal environment presents similar challenges to all individuals, regardless of age or absolute body size, neuromuscular immaturity confers unique problems to growing animals, requiring kinematic compensation.