Bruce C. Jayne

SELECTION ON LOCOMOTOR PERFORMANCE CAPACITY IN A NATURAL POPULATION OF GARTER SNAKES

Selection on locomotor performance was determined for a series of marked and recaptured individuals from a population of garter snakes (Thamnophis sirtalis fitchi) in Northern California. We measured snake length and mass, burst speed, endurance on a treadmill, and the distance crawled around a stationary circular track. Size‐corrected values (residuals) of mass and locomotor performance were generated from the scaling equations of S–V length (SVL). Randomization tests and regressions were used to determine the probability that a trait was a significant predictor of survivorship, and a nonparametric, cubic spline estimate of the fitness function was used to facilitate detection of the patterns of selection. From 275 (“cohort”) snakes measured and tested within 8 days of birth in 1985, 79 were recaptured in the spring–summer of 1986 and subsequent years. Birth SVL was the only significant (randomization P = 0.022) predictor of neonatal survival from 1985 to 1986 with directional selection favoring larger individuals. In addition to the lab‐born cohort, 382 field‐born snakes from all ages in the population were captured, tested, and released during spring–summer 1986. Similar to the 1985 cohort, the survivorship of 37 of 86 neonates from 1986 to 1987 showed no significant relationship with any residual value using any statistical test. Survivorship from 1986 to 1987 for 127 of 250 yearlings (including 32 lab‐born cohort snakes) analyzed with the randomization test showed that greater values of both speed (P = 0.007) and distance residual (P = 0.008) significantly favored survival, whereas intermediate values of mass residual (P = 0.006) were significantly more likely to survive. Univariate regressions predicting the survival of yearlings from 1986 to 1987 gave similar results to the randomization test, but in a multiple regression with yearling burst speed residual, distance capacity residual, and a quadratic term of mass residual, distance capacity residual was the least important predictor variable. For the survivorship of 37 of the 113 older snakes, greater burst speed residual significantly favored survival (randomization P = 0.001).

Red and white muscle activity and kinematics of the escape response of the bluegill sunfish during swimming

SummaryWe quantified midline kinematics with synchronized electromyograms (emgs) from the red and white muscles on both sides of bluegill sunfish (Lepomis macrochirus) during escape behaviors which were elicited from fish both at a standstill and during steady speed swimming. Analyses of variance determined whether or not kinematic and emg variables differed significantly between muscle fiber types, among longitudinal positions, and between swimming versus standstill trials.At a given longitudinal location, both the red and white muscle were usually activated synchronously during both stages of the escape behavior. Stage 1 emg onsets were synchronous; however, the mean durations of stage 1 emgs showed a significant increase posteriorly from about 11 to 15 ms. Stage 2 emgs had significant posterior propagation, but the duration of the stage 2 emgs was constant (17 ms). Posterior emgs from both stages occurred during lengthening of the contractile tissue (as indicated by lateral bending). Steady swimming activity was confined to red muscle bursts which were propagated posteriorly and had significant posterior decrease in duration from about 50% to 37% of a cycle. Fish performed escape responses during all phases of the steady swimming motor pattern. All kinematic events were propagated posteriorly. Furthermore, no distinct kinematic event corresponded to the time intervals of the stage 1 and 2 emgs. The rate of propagation of kinematic events was always slower than that of the muscle activity. The phase relationship between lateral displacement and lateral bending also changed along the length of the fish. Escape responses performed during swimming averaged smaller amplitudes of stage 2 posterior lateral displacement; however, most other kinematic and emg variables did not vary significantly between these two treatments.

How swimming fish use slow and fast muscle fibers: implications for models of vertebrate muscle recruitment

We quantified the intensity and duration of electromyograms (emgs) from the red and white axial muscles in five bluegill sunfish (Lepomis macrochirus) which performed three categories of behavior including steady swimming and burst and glide swimming at moderate and rapid speeds. Steady swimming (at 2 lengths/s) involved exclusively red muscle activity (mean posterior emg duration = 95 ms), whereas unsteady swimming utilized red and white fibers with two features of fiber type recruitment previously undescribed for any ectothermic vertebrate locomotor muscle. First, for moderate speed swimming, the timing of red and white activity differed significantly with the average onset time of white lagging behind that of red by approximately 40 ms. The durations of these white emgs were shorter than those of the red emgs (posterior mean = 82 ms) because offset times were effectively synchronous. Second, compared to steady and moderate speed unsteady swimming, the intensity of red activity during rapid unsteady swimming decreased while the intensity of white muscle activity (mean white emg duration = 33 ms) increased. Decreased red activity associated with increased white activity differs from the general pattern of vertebrate muscle recruitment in which faster fiber types are recruited in addition to, but not to the exclusion of, slower fiber types.

Kinematics of Terrestrial Snake Locomotion

The lateral undulatory, sidewinding and concertina modes of limbless terrestrial locomotion were analyzed from cinematographic films of five species of snakes and one amphisbaenian crawling on a variety of substrates. For single points on each animal, graphs of V, (overall velocity), V, (longitudinal component) and V, (lateral component) vs time were used to characterize locomotor modes and to detect their simultaneous use. Only concertina locomotion was used by the amphisbaenian Rhineura floridana. While performing lateral undulation, the constricting colubrid snake Elaphe obsoleta did not attain a maximum mean V, as great as that of Nerodia fasciata, a nonconstricting colubrid. Concertina locomotion is described for the snakes Acrochordus javanicus and N. fasciata. Sidewinding is described for N.fasciata, Cerberus rynchops and Crotalus cerastes. Cerberus rynchops moving on sand combined sidewinding with lateral undulation. The relation between V, and frequency of movement is described and compared among each of the terrestrial modes and with aquatic lateral undulation.

The Energetic Cost of Limbless Locomotion

The net energetic cost of terrestrial locomotion by the snake Coluber constrictor, moving by lateral undulation, is equivalent to the net energetic cost of running by limbed animals (arthropods, lizards, birds, and mammals) of similar size. In contrast to lateral undulation and limbed locomotion, concertina locomotion by Coluber is more energetically expensive. The findings do not support the widely held notion that the energetic cost of terrestrial locomotion by limbless animals is less than that of limbed animals.

Interspecific scaling of the morphology and posture of the limbs during the locomotion of cats (Felidae)

SUMMARY For phylogenetically diverse mammals, ranging from small rodents to large ungulates, the generalization that limb erectness increases with increased size is supported by some size-dependent scaling relationships of appendicular skeletal anatomy as well as a limited number of direct observations of limb posture during locomotion. If size alone is the causal basis for different limb posture, then the erectness of limbs should increase significantly with increased size within a phylogenetically narrow lineage, but such data are sparse. Thus, to better establish the correlation between size and posture of mammalian limbs, we quantified the scaling relationships between mass and limb dimensions and kinematics during walking of nine species within the felid (cat) clade, which has qualitatively similar limb design. We studied the domestic cat, serval, ocelot, lynx, leopard, cheetah, cougar, lion and tiger, which had masses ranging from <4 kg to nearly 200 kg. Apart from variation associated with overall size, the lengths of the appendicular skeletal structures of most of the felid species were morphologically very similar in multivariate space. The kinematics of the limbs were also relatively uniform, and size had little predictive value for limb posture among felid species. Only three out of a total of 24 angular variables at footfall and midstance changed significantly (0.02<P<0.05) with increased mass. Thus, in contrast to previous broadly comparative studies of mammals, larger species of felids did not have more upright limbs than smaller species.

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

SUMMARY 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° and uphill 45° and 90°. 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.

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

SUMMARY 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° 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.

RESOURCE USE IN ARBOREAL HABITATS: STRUCTURE AFFECTS LOCOMOTION OF FOUR ECOMORPHS OF ANOLIS LIZARDS

Previous laboratory studies have frequently determined the maximal running speeds of lizards. However, neither the extent to which animals use maximal speeds in nature nor the effects of arboreal habitat structure on undisturbed speeds of locomotion have been well documented. Furthermore, quantitative data describing the physical structure of arboreal habitats are lacking. Thus, we quantified available habitat, perch use, and the undisturbed locomotor behavior of four syntopic ecomorphs of Anolis lizards (A. sagrei, A. distichus, A. carolinensis, and A. angusticeps) in the field. Fifty percent of the cumulative perch length available in the habitat had values of diameter, length, and incline <0.8 cm, 54 cm, and 67°, respectively, indicating that narrow, short, and steep perches dominated the study site. The selection of all perch attributes by A. distichus was biased, whereas each of the remaining species randomly used at least one of the three attributes describing perch structure. Narrow breadth of resource use most often reflected the narrow breadth of available resources rather than selective use of resources. Interestingly, the behavioral and morphological specializations of A. angusticeps facilitate the use of the most common type of perch (twig) rather than a rare resource. Based on median values, the undisturbed speeds and distances of locomotion of A. sagrei (8.9 cm/s and 5.3 cm), A. distichus (31.5 cm/s and 2.8 cm), A. carolinensis (1.6 cm/s and 5.0 cm), and A. angusticeps (2.7 cm/s and 3.9 cm) were exceedingly slow and short, suggesting that neither maximal sprinting speeds nor endurance capacities were used frequently by any species in the field. The effects of habitat structure on undisturbed locomotor speeds and movement distances were highly species specific.

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°), 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.