Oxygen transfer during aerobic exercise in a varanid lizard Varanus mertensi is limited by the circulation

Oxygen transfer during sustained maximal exercise while locomoting on a treadmill at 0.33 m s(-1) was examined in a varanid lizard Varanus mertensi at 35degreesC. The rate of oxygen consumption ((V)over dot (O 2)) increased with locomotion from 3.49+/-0.75 (mean+/-S.D.) to 14.0+/-4.0 ml O-2 kg(-1) min(-1). Ventilation (V-E) increased, aided by increases in both tidal volume and frequency, in direct proportion to (V)over dot(O 2). The air convection requirement ((V)over dot(E)/(V)over dot(O 2)=27) was therefore maintained, together with arterial Pa-CO 2 and Pa-O 2. The alveolar-arterial P-O 2 difference (PA(O 2)-Pa-O 2) also remained unchanged during exercise from its value at rest, which was approximately 20 mmHg. Pulmonary diffusion for carbon monoxide (0.116+/-0.027 ml kg(-1) min(-1) mmHg(-1)) was double the value previously reported in V. exanthematicus and remained unchanged with exercise. Furthermore, exercise was associated with an increase in the arterial-venous O-2 content difference (Ca-O2-Cv(O 2)), which was assisted by a marked Bohr shift in the hemoglobin saturation curve and further unloading of venous O-2. During exercise the increase in cardiac output ((Q)over dot(tot)) did not match the increase in (V)over dot(O2) such that the blood convection requirement ((Q)over dot(tot)/(V)over dot (O 2)) decreased from the pre-exercise value of approximately 35 to 16 during exercise. Together, the results suggest that ventilation and O-2 transfer across the lung are adequate to meet the aerobic needs of V. mertensi during exercise, but the decrease in the blood convection requirement in the presence of a large arterial-venous O-2 content difference suggests that a limit in the transport of O-2 is imposed by the circulation

Effects of seasonal variation in prey abundance on field metabolism, water flux, and activity of a tropical ambush foraging snake

The responses of animals to seasonal food shortages can have important consequences for population dynamics and the structure and function of food webs. We investigated how an ambush foraging snake, the northern death adder Acanthophis praelongus, responds to seasonal fluctuations in prey availability in its tropical environment. In the dry season, field metabolic rates and water flux, as measured by doubly labeled water, were significantly lower than in the wet season. Unlike some other reptiles of the wet-dry tropics, death adders showed no seasonal difference in their resting metabolism. About 94% of the decrease in energy expended in the dry season was due to a decrease in activity and digestion, with lower body temperatures accounting for the remainder. In the dry season, death adders were less active and moved shorter distances between foraging sites than in the wet season. Analysis of energy expenditure suggested that adders fed no more than every 2-3 wk in the dry season but fed more frequently during the wet season. Unlike many lizards that cease feeding during the dry season, death adders remain active and attempt to maximize their energy intake year-round

The Good, the Bad, and the Ugly: Agonistic Behaviour in Juvenile Crocodilians

We examined agonistic behaviour in seven species of hatchling and juvenile crocodilians held in small groups (N = 4) under similar laboratory conditions. Agonistic interactions occurred in all seven species, typically involved two individuals, were short in duration (5–15 seconds), and occurred between 1600–2200 h in open water. The nature and extent of agonistic interactions, the behaviours displayed, and the level of conspecific tolerance varied among species. Discrete postures, non-contact and contact movements are described. Three of these were species-specific: push downs by C. johnstoni; inflated tail sweeping by C. novaeguineae; and, side head striking combined with tail wagging by C. porosus. The two long-snouted species (C. johnstoni and G. gangeticus) avoided contact involving the head and often raised the head up out of the way during agonistic interactions. Several behaviours not associated with aggression are also described, including snout rubbing, raising the head up high while at rest, and the use of vocalizations. The two most aggressive species (C. porosus, C. novaeguineae) appeared to form dominance hierarchies, whereas the less aggressive species did not. Interspecific differences in agonistic behaviour may reflect evolutionary divergence associated with morphology, ecology, general life history and responses to interspecific conflict in areas where multiple species have co-existed. Understanding species-specific traits in agonistic behaviour and social tolerance has implications for the controlled raising of different species of hatchlings for conservation, management or production purposes