The Quick and the Fast: The Evolution of Acceleration Capacity in Anolis Lizards

Abstract

Abstract. Although of prime ecological relevance, acceleration capacity is a poorly understood locomotor performance trait in terrestrial vertebrates. No empirical data exist on which design characteristics determine acceleration capacity among species and whether these design traits influence other aspects of locomotor performance. In this study we explore how acceleration capacity and sprint speed have evolved in Anolis lizards. We investigate whether the same or different morphological traits (i.e., limb dimensions and muscle mass) correlate with both locomotor traits. Within our sample of Anolis lizards, relative sprint speed and acceleration capacity coevolved. However, whereas the variation in relative acceleration capacity is primarily explained by the variation in relative knee extensor muscle mass, the variation in relative sprint speed is correlated to the variation in relative femur, tibia, and metatarsus length as well as knee extensor muscle mass. The fact that the design features required to excel in either performance trait partly overlap might explain the positive correlation between the variation in relative sprint speed and acceleration capacity. Furthermore, our data show how similar levels of sprint performance can be achieved through different morphological traits (limb segment lengths and muscle mass) suggesting that redundant mapping has potentially played a role in mitigating trade-offs.Key words. Ecomorphology, interspecific, comparison, locomotion, muscle, performance.Received July 12, 2006. Accepted July 20, 2006 Although rarely empirically demonstrated, locomotor performance is believed to be a crucial determinant of organismal fitness (see LeGalliard et al. 2004;Miles 2004;Husak 2006). Not surprisingly, the study of locomotor performance, in all its facets, has undergone explosive growth over the last decades. During this time, a wealth of data has become available on how genetics, morphology, physiology, kinematics, behavior, and ecology affect locomotor performance (reviews in Bennett and Huey 1990;Garland and Losos 1994;Irschick and Garland 2001;Autumn et al. 2002;Biewener 2002). One aspect most of these locomotion studies share is that they focus on steady-state locomotion in which movement is typically linear and uniform (i.e., at a constant speed). In nature, however, animals often show intermittent locomotion, including pauses alternating with fast and unpredictable bursts of movement (see Kramer and McLaughlin 2001;Weinstein 2001). Although non-steady-state locomotion, during which movement is nonuniform and typically unpredictable (i.e., accelerating and decelerating bouts), is thus likely of prime ecological relevance, it has hardly been investigated in detail (Garland and Losos 1994).Surprisingly, an extensive literature search revealed no empirical data on which functional characteristics actually determine acceleration capacity among species, and how. In addition, it is unclear whether the design traits determining acceleration capacity influence other aspects of locomot...

Out on a limb: the differential effect of substrate diameter on acceleration capacity inAnolislizards

“…The error variance depends on the nature of the data and is estimated for each sequence that is analyzed. We chose to use the QSP because in this routine the derivatives are computed directly from the spline coefficients, and instantaneous velocity and acceleration are subsequently calculated (see also Bergmann and Irschick, 2006;Vanhooydonck et al, 2006). The QSP method, however, consistently underestimates maximal acceleration (Walker, 1998).…”

“…Maximal acceleration capacity, in turn, is determined by the morphological and physiological properties of the limb muscles [e.g. muscle mass (Curtin et al, 2005;Vanhooydonck et al, 2006)]. The absence of massive limb muscles in twig anoles as compared to other ecomorphs, thus explains A. valencienni's diminished acceleration capacities (Vanhooydonck et al, 2006).…”

Mechanical sensitivity and the dynamics of evolutionary rate shifts in biomechanical systems

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