Energetics of bluetongue lizards ( Tiliqua scincoides ) in a seasonal tropical environment

Abstract

We studied the physiological ecology of bluetongue lizards (Tiliqua scincoides) on the Adelaide River floodplain in tropical Australia to determine the seasonal patterns of energy expenditure and to determine the mechanisms by which seasonal differences were achieved. Field metabolic rates (FMR) were significantly lower in the dry season (37.6 kJ kg(-1) day(-1); n=9) than in the wet (127.3 kJ kg(-1) day(-1); n=7). Water flux was also lower in the dry season (6.8 ml kg(-1) day(-1); n=9) than in the wet (39.4 ml kg(-1) day(-1); n=7). Measurements of body temperatures (T(b)) and movements of free-ranging animals, and standard metabolic rate (SMR) of recently caught animals, allowed a detailed analysis of energy budgets for wet and dry seasons. In the dry, bluetongue lizards expended 90 kJ kg(-1) day(-1) less energy than in the wet season. Unlike some other lizards of the wet-dry tropics, SMR did not differ between seasons. About 5% of the seasonal difference in FMR was due to lower night time T(b) during the dry season, and about 7% was due to lower diurnal T(b). The remaining 88% of the decrease in energy expended in the dry season was due to a substantial decrease in other costs that may include reproduction, growth, digestion and activity. If we assume the animals fed daily and the costs of digestion are taken into account, the estimates are: 14% of the savings result from lower T(b) at night, 20% from lower T(b) in the day, and 66% result from decreased activity. It is therefore apparent that, unlike some agamid and varanid lizards that use a combination of behavioural and physiological mechanisms to conserve energy when food and water are limited, bluetongue lizards primarily use behavioural mechanisms to achieve a dramatic reduction in energy expenditure in the dry season.

The importance of lizards as frugivores and seed dispersers.

“…Several skinks (Scincidae) from arid regions consume plant material during dry periods when arthropods are scarce (Kuchling, 1970;Symon, 1979;Schleich et al, 1996). In general, insects are scarcer in dry seasons than in the wet seasons (Churchill, 1994;Griffiths and Christian, 1996;Christian et al, 2003), and such a seasonal scarcity of arthropod food may select for omnivory in lizards.…”

Habitat selection by bluetongue lizards (Tiliqua, Scincidae) in tropical Australia: a study using GPS telemetry

“…Most obviously, they can avoid otherwise-lethal ground temperatures, and maintain water balance [31]. In addition, they are hidden from such predators as snakes, varanid lizards, raptors, and dingoes [52].…”

“…In the tropics, where ambient temperatures are high all year round [27], reptiles are able to maintain high, stable temperatures without the need for overt thermoregulation: that is, their selection of habitats is more likely to be driven by the need to avoid overheating than to find basking sites [28,29]. Thus, tropical reptiles may select thermally distinctive microhabitats not to heat up, but to avoid overheating and water loss [30][31][32]. In the tropics, this 'heat avoidance' behavior probably predominates most of the year, whereas many temperate reptiles face similar thermal challenges for shorter periods (for example, during hot, dry summers [33]).…”

Differential peptide expression in the central nervous system of the land snail Theba pisana, between active and aestivated

“…Vertebrates that undergo aestivation include amphibians [2,8,28], reptiles [14,21,64] and fish [22]. Amongst invertebrates, aestivation is seen in pulmonate land snails [57], some earthworms and insects [9,10], sea sponges [36] and sea cucumbers [68], as well as the similar hypometabolic states of dauer or diapause being found in the insects and nematodes [24,41].…”