Contribution of gular pumping to lung ventilation in monitor lizards. (1/73)

A controversial hypothesis has proposed that lizards are subject to a speed-dependent axial constraint that prevents effective lung ventilation during moderate- and high-speed locomotion. This hypothesis has been challenged by results demonstrating that monitor lizards (genus Varanus) experience no axial constraint. Evidence presented here shows that, during locomotion, varanids use a positive pressure gular pump to assist lung ventilation. Disabling the gular pump reveals that the axial constraint is present in varanids but it is masked by gular pumping under normal conditions. These findings support the prediction that the axial constraint may be found in other tetrapods that breathe by costal aspiration and locomote with a lateral undulatory gait.  (+info)

Activity before exercise influences recovery metabolism in the lizard Dipsosaurus dorsalis. (2/73)

During recovery from even a brief period of exercise, metabolic rate remains elevated above resting levels for extended periods. The intensity and duration of exercise as well as body temperature and hormone levels can influence this excess post-exercise oxygen consumption (EPOC). We examined the influence of activity before exercise (ABE), commonly termed warm-up in endotherms, on EPOC in the desert iguana Dipsosaurus dorsalis. The rate of oxygen consumption and blood lactate levels were measured in 11 female D. dorsalis (mass 41.1 +/- 3.0 g; mean +/- s.e.m.) during rest, after two types of ABE and after 5 min of exhaustive exercise followed by 60 min of recovery. ABE was either single (15 s of maximal activity followed by a 27 min pause) or intermittent (twelve 15 s periods of exercise separated by 2 min pauses). Our results indicate that both single and intermittent ABE reduced recovery metabolic rate. EPOC volumes decreased from 0.261 to 0.156 ml of oxygen consumed during 60 min of recovery when lizards were subjected to intermittent ABE. The average cost of activity (net V(O2) during exercise and 60 min of recovery per distance traveled) was almost 40 % greater in lizards that exercised without any prior activity than in lizards that underwent ABE. Blood lactate levels and removal rates were greatest in animals that underwent ABE. These findings may be of particular importance for terrestrial ectotherms that typically use burst locomotion and have a small aerobic scope and a long recovery period.  (+info)

Size matters: ontogenetic variation in the three-dimensional kinematics of steady-speed locomotion in the lizard Dipsosaurus dorsalis. (3/73)

Although many studies have investigated how locomotor capacities change with size, few studies have examined whether different-sized individuals within a species have similar kinematics during locomotion. We quantified the skeletal limb morphology and the three-dimensional kinematics of the hindlimb of four sizes (4-66 g) of the lizard Dipsosaurus dorsalis moving steadily at both the walk-run transition (50 % duty factor) and at a moderately fast speed of 250 cm s(-)(1). We used analyses of variance to test whether limb movements changed with size and to determine whether size and speed had interactive effects on kinematics. The disproportionately long hindlimbs of smaller lizards partly contributed to their relatively greater (i.e. adjusted by snout-vent length) values of linear kinematic variables. Both relative linear and angular kinematics changed significantly with both size and speed, both of which had widespread interactive effects. By having more extension of the knee and ankle joints, and thus a relatively higher hip height during stance, the slow-speed movements of small lizards displayed some of the characteristics of the fast-speed movements in larger lizards. Further, approximately one-fifth and two-fifths of the strides of the two smallest size classes were digitigrade at the lower and higher speeds, respectively, whereas the two largest size classes always had a plantigrade foot posture. Some of the most striking effects of size on kinematics were most evident at the lower of the two speeds. Unlike interspecific studies, which show that the limbs often become more crouched with decreased size, the more extended limbs of smaller lizards in this study suggest that variation in size alone cannot be the causal reason for differences in limb posture.  (+info)

Circulatory impairment induced by exercise in the lizard Iguana iguana. (4/73)

Mechanical integration of the cardiac, muscular and ventilatory pumps enables mammals to vary cardiac output over a wide range to match metabolic demands. We have found this integration lacking in a lizard (Iguana iguana) that differs from mammals because blood flow from the caudal body and ventilation are maximal after, rather than during, exercise. Because Iguana iguana are constrained from ventilation during intense locomotion, they appear to be unable to recruit the abdomen and thorax as a pump for venous return. This constraint on simultaneous running and costal breathing arises from their musculoskeletal design, which is similar to that of basal tetrapods, and so a constraint on venous return during exercise may be ancestral for tetrapods. We suggest that mechanical coupling of the pulmonary and cardiac pumps may have been important for the evolution of high-speed locomotor stamina in terrestrial vertebrates.  (+info)

Comparative study of tongue protrusion in three iguanian lizards, Sceloporus undulatus, Pseudotrapelus sinaitus and Chamaeleo jacksonii. (5/73)

The goal of this study was to investigate the function of the hyolingual muscles used during tongue protraction in iguanian lizards. High-speed videography and nerve-transection techniques were used to study prey capture in the iguanid Sceloporus undulatus, the agamid Pseudoptrapelus sinaitus and the chameleonid Chamaeleo jacksonii. Denervation of the mandibulohyoideus muscle slips had an effect only on P. sinaitus and C. jacksonii, in which tongue protrusion or projection distance was reduced. In C. jacksonii, denervation of the M. mandibulohyoideus completely prevented little hyoid protraction. Denervation of the M. verticalis had no effect on S. undulatus, but reduced tongue protrusion distance in P. sinaitus. Denervation of the accelerator muscle in C. jacksonii inhibited tongue projection completely. The function of the M. mandibulohyoideus and M. verticalis has become increasingly specialized in P. sinaitus and especially in C. jacksonii to allow greater tongue protrusion. The combined results of these treatments suggest that these three groups represent transitional forms, both morphologically and functionally, in the development of a projectile tongue.  (+info)

Mechanics of limb bone loading during terrestrial locomotion in the green iguana (Iguana iguana) and American alligator (Alligator mississippiensis). (6/73)

In vivo measurements of strain in the femur and tibia of Iguana iguana (Linnaeus) and Alligator mississippiensis (Daudin) have indicated three ways in which limb bone loading in these species differs from patterns observed in most birds and mammals: (i) the limb bones of I. iguana and A. mississippiensis experience substantial torsion, (ii) the limb bones of I. iguana and A. mississippiensis have higher safety factors than those of birds or mammals, and (iii) load magnitudes in the limb bones of A. mississippiensis do not decrease uniformly with the use of a more upright posture. To verify these patterns, and to evaluate the ground and muscle forces that produce them, we collected three-dimensional kinematic and ground reaction force data from subadult I. iguana and A. mississippiensis using a force platform and high-speed video. The results of these force/kinematic studies generally confirm the loading regimes inferred from in vivo strain measurements. The ground reaction force applies a torsional moment to the femur and tibia in both species; for the femur, this moment augments the moment applied by the caudofemoralis muscle, suggesting large torsional stresses. In most cases, safety factors in bending calculated from force/video data are lower than those determined from strain data, but are as high or higher than the safety factors of bird and mammal limb bones in bending. Finally, correlations between limb posture and calculated stress magnitudes in the femur of I. iguana confirm patterns observed during direct bone strain recordings from A. mississippiensis: in more upright steps, tensile stresses on the anterior cortex decrease, but peak compressive stresses on the dorsal cortex increase. Equilibrium analyses indicate that bone stress increases as posture becomes more upright in saurians because the ankle and knee extensor muscles exert greater forces during upright locomotion. If this pattern of increased bone stress with the use of a more upright posture is typical of taxa using non-parasagittal kinematics, then similar increases in load magnitudes were probably experienced by lineages that underwent evolutionary shifts to a non-sprawling posture. High limb bone safety factors and small body size in these lineages could have helped to accommodate such increases in limb bone stress.  (+info)

Aural-pharyngeal polyps associated with Cryptosporidium infection in three iguanas (Iguana iguana). (7/73)

Cryptosporidium spp. infection was associated with aural-pharyngeal polyps in three iguanas (Iguana iguana). All iguanas were presented for masses protruding from the ear canal, and the disease was characterized by a chronic clinical course. The masses consisted of nests of cystic glands surrounded by abundant fibrous connective tissue and lined by hyperplastic cuboidal to pseudostratified columnar epithelium that was moderately to heavily colonized by cryptosporidial organisms. Electron microscopy revealed that the majority of organisms were trophozoites.  (+info)

The mitochondrial genomes of the iguana (Iguana iguana) and the caiman (Caiman crocodylus): implications for amniote phylogeny. (8/73)

The complete mitochondrial genomes of two reptiles, the common iguana (Iguana iguana) and the caiman (Caiman crocodylus), were sequenced in order to investigate phylogenetic questions of tetrapod evolution. The addition of the two species allows analysis of reptilian relationships using data sets other than those including only fast-evolving species. The crocodilian mitochondrial genomes seem to have evolved generally at a higher rate than those of other vertebrates. Phylogenetic analyses of 2889 amino-acid sites from 35 mitochondrial genomes supported the bird-crocodile relationship, lending no support to the Haematotherma hypothesis (with birds and mammals representing sister groups). The analyses corroborated the view that turtles are at the base of the bird-crocodile branch. This position of the turtles makes Diapsida paraphyletic. The origin of the squamates was estimated at 294 million years (Myr) ago and that of the turtles at 278 Myr ago. Phylogenetic analysis of mammalian relationships using the additional outgroups corroborated the Marsupionta hypothesis, which joins the monotremes and the marsupials to the exclusion of the eutherians.  (+info)

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