Aerobic and anaerobic metabolism during activity in the lizardDipsosaurus dorsalis

114

SUMMARY Amphisbaenians are legless reptiles that differ significantly from other vertebrate lineages. Most species dig underground galleries of similar diameter to that of the animal. We studied the muscle physiology and morphological attributes of digging effort in the Brazilian amphisbaenid Leposternon microcephalum (Squamata; Amphisbaenia), which burrows by compressing soil against the upper wall of the tunnel by means of upward strokes of the head. The individuals tested (<72 g) exerted forces on the soil of up to 24 N. These forces were possible because the fibres of the longissimus dorsi, the main muscle associated with burrowing, are highly pennated, thus increasing effective muscle cross-sectional area. The muscle is characterized by a metabolic transition along its length: proximal, medial and distal fibres are fast contracting and moderately oxidative, but fibres closer to the head are richer in citrate synthase and more aerobic in nature. Distal fibres, then, might be active mainly at the final step of the compression stroke, which requires more power. For animals greater than a given diameter,the work required to compress soil increases exponentially with body diameter. Leposternon microcephalum, and probably some other highly specialized amphisbaenids, are most likely constrained to small diameters and can increase muscle mass and effective muscle cross-sectional area by increasing body length, not body diameter.

Section: Discussionmentioning

confidence: 99%

Morphological and physiological specialization for digging in amphisbaenians, an ancient lineage of fossorial vertebrates

Navas

Antoniazzi

Carvalho

et al. 2004

114

“…This 'metabolic theory of ecology' has grown into a discipline of its own, emanating from the legendary astronomer Harlow Shapley's observation that walking speed in ants increased directly and predictably with temperature to the point that air temperature could be predicted to within 1°C from ant walking speed alone (Huey and Kingsolver, 2011) [see also Shapley (Shapley, 1966), cited in Huey and Kingsolver (Huey and Kingsolver, 2011)]. This close relationship between metabolic physiology, metabolic rate and temperature also applies in ectothermic reptiles (Bennett, 1982;Bennett and Dawson, 1976;Beyer and Spotila, 1994;Zari, 1991). This suggests that with increasing temperature comes an inevitable increase in metabolic rate and mitochondrial activity, and with that an increased production of reactive oxygen species (ROS), perhaps even at the cost of a reduced lifespan (Hollingsworth, 1969;Farmer and Sohal, 1987).…”

Section: Introductionmentioning

confidence: 99%

Net superoxide levels: steeper increase with activity in cooler female and hotter male lizards

Ballen

Healey

Wilson

et al. 2012

SUMMARYEctotherms increase their body temperature in response to ambient heat, thereby elevating their metabolic rate. An often inferred consequence of this is an overall upregulation of gene expression and energetic expenditure, and a concomitant increased production of reactive oxygen species (e.g. superoxide) and, perhaps, a shortened lifespan. However, recent work shows that this may be a superficial interpretation. For example, sometimes a reduced temperature may in fact trigger up-regulation of gene expression. We studied temperature and associated activity effects in male and female Australian painted dragon lizards (Ctenophorus pictus) by allowing the lizards to bask for 4h versus 12h, and scoring their associated activity (inactive versus active basking and foraging). As predicted, long-basking lizards (hereafter ʻhotʼ) showed heightened activity in both sexes, with a more pronounced effect in females. We then tested for sex-specific effects of basking treatment and activity levels on the increase in net levels of superoxide. In males, short-baskers (hereafter ʻcoldʼ) had significantly more rapidly decreasing levels of superoxide per unit increasing activity than hot males. In females, however, superoxide levels increased faster with increasing activity in the cold than in the hot basking treatment, and females earlier in the ovarian cycle had lower superoxide levels than females closer to ovulation. In short, males and females differ in how their levels of reactive oxygen species change with temperature-triggered activity.

“…Aerobic metabolism provides only a portion of the total energy used to sustain high levels of activity in lizards, and most of the available energy is derived from anaerobic metabolism (Bennett and Dawson, 1972;Bennett and Licht, 1972; but see Bennett, 1991 for a review). The relative proportion of aerobic and anaerobic pathways is however an important factor in these animals, and can be used for understating how the metabolic balance between two pathways influences muscle function.…”

Section: Enzyme Activities On Hindlimb and Head Musclesmentioning

confidence: 99%

Beyond body size: muscle biochemistry and body shape explain ontogenetic variation of anti-predatory behaviour in the lizard Salvator merianae (Squamata: Teiidae)

Barros

Carvalho

Abe

et al. 2016

Anti-predatory behaviour evolves under the strong action of natural selection because the success of individuals avoiding predation essentially defines their fitness. Choice of anti-predatory strategies is defined by prey characteristics as well as environmental temperature. An additional dimension often relegated in this multilevel equation is the ontogenetic component. In the tegu Salvator merianae, adults run away from predators at high temperatures but prefer fighting when it is cold, whereas juveniles exhibit the same flight strategy within a wide thermal range. Here, we integrate physiology and morphology to understand ontogenetic variation in the temperature-dependent shift of anti-predatory behaviour in these lizards. We compiled data for body shape and size, and quantified enzyme activity in hindlimb and head muscles, testing the hypothesis that morphophysiological models explain ontogenetic variation in behavioural associations. Our prediction is that juveniles exhibit body shape and muscle biochemistry that enhance flight strategies. We identified biochemical differences between muscles mainly in the LDH:CS ratio, whereby hindlimb muscles were more glycolytic than the jaw musculature. Juveniles, which often use evasive strategies to avoid predation, have more glycolytic hindlimb muscles and are much smaller when compared with adults 1-2 years old. Ontogenetic differences in body shape were identified but marginally contributed to behavioural variation between juvenile and adult tegus, and variation in antipredatory behaviour in these lizards resides mainly in associations between body size and muscle biochemistry. Our results are discussed in the ecological context of predator avoidance by individuals differing in body size living at temperature-variable environments, where restrictions imposed by the cold could be compensated by specific phenotypes.