Graham G. Thompson

Standard and maximal metabolic rates of goannas (Squamata: Varanidae)

Standard metabolic rate and maximal metabolic rate during forced exercise are examined for nine species of goanna (genus Varanus), with body mass varying from 10 to 3,750 g. At 35°C, the common pooled mass exponent for standard metabolic rate is 0.97 and at 25°C it is 0.89, with considerable variation between species (0.43-1.20). Standard metabolic rate at 35°C scales interspecifically with body mass0.92 and at 25°C with body mass087. The Q10 for standard metabolic rate is approximately 2.5 between 25° and 35°C. At 35°C, maximal metabolic rate scales intraspecifically with body mass0.79 and scales interspecifically with body mass0.72. Factorial metabolic scope ranges from nine for the larger species to 35 for the smaller species; it scales with body mass-0.99 at 35°C. The maximal metabolic rate of 6.36 mL O₂ g⁻¹ h⁻¹ for Varanus caudolineatus is the highest recorded for any squamate. Variations from the interspecific regression line appear to have some ecological significance. Varanus tristis (a widely foraging arboreal goanna) and Varanus eremius (a widely foraging terrestrial goanna) have a higher standard metabolic rate than Varanus acanthurus (a sedentary terrestrial goanna). The three arboreal goannas (Varanus caudolineatus, Varanus gilleni, and Varanus tristis) have a higher maximal metabolic rate than the terrestrial species (Varanus brevicauda, V. eremius, V. acanthurus, Varanus gouldii, Varanus rosenbergi, and Varanus panoptes).

Comparative Morphology of Western Australian Varanid Lizards (Squamata: Varanidae)

Varanid lizards, which vary considerably in body mass both interspecifically and intraspecifically, are generally considered to be morphologically similar. However, significant and non‐isometric variation in the relative appendage dimensions for 17 species of Western Australian goannas suggest that these lizards are not morphologically conservative. The first and second canonical variates clearly distinguish the two subgeneral Odatria and Varanus, and species are generally sexually dimorphic. The morphological variation observed among these 17 species of goanna is associated with foraging mode and ecology. However, no single or small group of morphological dimensions discriminates phylogenetic groups, sexes, or ecological groups, and body size is an important component in these analyses. J. Morphol. 233:127–152, 1997.

Water balance of field-excavated aestivating Australian desert frogs, the cocoon- forming Neobatrachus aquilonius and the non-cocooning Notaden nichollsi (Amphibia: Myobatrachidae)

SUMMARY Burrowed aestivating frogs of the cocoon-forming species Neobatrachus aquilonius and the non-cocooning species Notaden nichollsi were excavated in the Gibson Desert of central Australia. Their hydration state (osmotic pressure of the plasma and urine) was compared to the moisture content and water potential of the surrounding soil. The non-cocooning N. nichollsi was consistently found in sand dunes. While this sand had favourable water potential properties for buried frogs, the considerable spatial and temporal variation in sand moisture meant that frogs were not always in positive water balance with respect to the surrounding soil. The cocoon-forming N. aquilonius was excavated from two distinct habitat types, a claypan in which frogs had a well-formed cocoon and a dune swale where frogs did not have a cocoon. Cocoons of excavated frogs ranged in thickness from 19.4 μm to 55.61 μm and consisted of 81-229 layers. Cocooned claypan N. aquilonius were nearing exhaustion of their bladder water reserves and had a urine osmolality approaching that of the plasma. By contrast, non-cocooned N. aquilonius from the dune swale were fully hydrated, although soil moisture levels were not as high as calculated to be necessary to maintain water balance. Both species had similar plasma arginine vasotocin (AVT) concentrations ranging from 9.4 to 164 pg ml-1, except for one cocooned N. aquilonius with a higher concentration of 394 pg ml-1. For both species, AVT showed no relationship with plasma osmolality over the lower range of plasma osmolalities but was appreciably increased at the highest osmolality recorded. This study provides the first evidence that cocoon formation following burrowing is not obligatory in species that are capable of doing so, but that cocoon formation occurs when soil water conditions are more desiccating than for non-cocooned frogs.

Is body shape of varanid lizards linked with retreat choice

In our earlier analysis ofVaranusbody shape, size was a dominating factor with some qualitative phylogenetic patterns and grouping of species into ecological categories. With a phylogeny and an improved capacity to account for the effects of size, we have reanalysed our morphometric data for male Australian goannas (Varanus spp.) using an increased numberofspecimensandspeciestoexaminewhethervariationsinbodyshapecanbeaccountedforbyretreatchoice,asitcan for Western Australian Ctenophorus dragon lizards. After accounting for body size in the current analysis, four ecotypes basedonretreatchoice(i.e.thosethatretreattoobliquecrevicesbetweenlargerocksorrockfaces,thosethatretreattoburrows dug into the ground, those that retreat to spaces under rocks or in tree hollows, and those that retreat to trees but not tree hollows)accountedformuchofthevariationinbodyshape.Thereisaphylogeneticpatterntotheecotypes,butaccountingfor phylogeneticeffectsdidnotweakenthelinkbetweenbodyshapeandecotypebasedonretreatchoice.Thissuggeststhatthere are large differences in body shape among ecotypes, and shape is relatively independent of phylogeny. The strong link between shape and choice of retreat site in Varanus spp. is consistent with that for Ctenophorus spp. We speculate on why there might be a strong link between retreat choice and body shape for both Varanus and Ctenophorus.

Allometry of Clutch and Neonate Sizes in Monitor Lizards (Varanidae: Varanus)

Abstract This paper analyzes data from the published literature with the addition of some new information to explore the relationship between varanid body size and reproductive biology. Incubation time for varanid eggs is positively correlated with egg mass, neonate snout–vent length (SVL), and maximum adult snout–vent length (SVLmax). Incubation period of heavier eggs is proportionally less than for smaller eggs at 30 C. SVLmax is positively correlated with egg mass, clutch size, clutch mass, neonate body mass, and neonate SVL. Neonates of larger species have longer SVL but are smaller as a proportion of SVLmax than for smaller species. Clutch sizes are larger and more variable for larger species; however, clutch sizes for larger species relative to SVLmax are smaller than for smaller species. The intraspecific influence of maternal SVL on clutch size is greater than the interspecific influence of SVLmax on clutch size. These results suggest there are greater fitness advantages for smaller species having relatively larger offspring than for larger species, which concurs with results for snakes and other genera of lizards, as well as optimal offspring size theory. Reproductive output also appears to be influenced by maternal abdominal volume. Analysis of phylogenetically corrected data generally concurs with patterns evident in the nonphylogenetically corrected data. Body size has a much greater influence on reproductive output of Varanus than phylogeny.

Usefulness of funnel traps in catching small reptiles and mammals, with comments on the effectiveness of the alternatives

Funnel traps were used in conjunction with pit traps (PVC buckets and pipes), Elliott traps and cage traps at 10 sites in southern Western Australia to examine sampling bias of trap types. Funnel traps seldom catch small mammals but catch more of the medium-sized and large terrestrial, diurnal snakes and some of the widely foraging, medium-sized skinks, medium-sized dragon lizards and arboreal geckos that climb out of PVC pit traps. For pit traps, buckets catch more reptiles, particularly smaller ones, than pipes. However, pipes catch more mammals than buckets. Elliott traps catch the same suite of small mammals as pipes plus some of the large, trappable species, such as Rattus spp. Cage traps are useful for trapping Tiliqua spp. and medium-sized mammals such as possums and bandicoots that are unlikely to be caught in pit and funnel traps. Funnel traps, pit traps and cage traps should be used in surveys of small terrestrial vertebrates to determine species richness and relative abundance in Western Australia and probably elsewhere. However, as cage traps are mostly useful for catching Tiliqua spp. and medium-sized mammals, they need only be used in faunal surveys undertaken for environmental impact assessments specifically targeting these species.

Aerial and aquatic respiration of the Australian desert goby, Chlamydogobius eremius

Physiological, anatomical and behavioural adaptations enable the Australian desert goby, Chlamydogobius eremius, to live in mound springs and temporary aquatic habitats surrounding the south-eastern rim of the Lake Eyre drainage basin in the harsh inland of Australia. This study describes the desert gobys respiratory and metabolic responses to hypoxic conditions and its use of buccal air bubbles for gas exchange at the water surface. Oxygen consumption for C. eremius is significantly higher in water than in air under normoxic and hypoxic conditions. In water, total oxygen consumption (V(O(2))) increases from normoxic conditions (253 microl g(-1) h(-1)) to 8% ambient O(2) concentration (377 microl g(-1) h(-1)), then decreases with increasing hypoxia of 4% O(2) (226 microl g(-1) h(-1)) and at 2% O(2) (123 microl g(-1) h(-1)). In air (fish were moist but out of water), V(O(2)) progressively decreases from normoxic conditions to hypoxic conditions (21% O(2), V(O(2)) is 169 microl g(-1) h(-1) to 39 microl g(-1) h(-1) at 2% O(2)). These data indicate oxygen-conforming patterns with increasing hypoxia both in air and in water below 8% O(2). In water, opercular movement rates remain unchanged with increasing hypoxia (139 min(-1) at 21% O(2), 154 min(-1) at 8%, 156 min(-1) at 4% and 167 min(-1) at 2%) but in air, opercular movement rates are significantly lower than in water, corresponding with the lower metabolic rate (71 min(-1) at 21% O(2), 53 min(-1) at 8%, 96 min(-1) at 4% and 64 min(-1) at 2%). Chlamydogobius eremius can use a buccal air bubble for aerial O(2) uptake, most probably in response to increased aquatic hypoxia. In air, C. eremius relies more on the buccal bubble as an oxygen source with increasing hypoxia up to an ambient O(2) of 4% (7.1% of V(O(2)) at 21% O(2); 14.5% at 8% O(2); and 27.1% at 4% O(2)), then when the available supply of O(2) is further reduced, it decreases (15% of V(O(2)) at 2% O(2)) and respiration across the skin again makes a higher relative contribution. The Australian desert goby has a higher metabolic rate in higher salinities (336 microl g(-1) h(-1) in 35 ppt, 426 microl g(-1) h(-1) in 70 ppt) than in freshwater (235 microl O(2) g(-1) h(-1)), presumably because of the increased metabolic cost of osmoregulation. There was no significant difference in V(O(2)) for fish in air that had come from varying salinities.

Effects of body mass and temperature on standard metabolic rates for two Australian varanid lizards (Varanus gouldii and V. panoptes)

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Influence of pit-trap type on the interpretation of fauna diversity

We compare bias in the interpretation of sampled reptile and mammal assemblages caught using 20-L PVC buckets and PVC pipes (150 mm by 600 mm deep) when used as pit-traps. We report on 16 632 pipe- and 16 632 bucket-nights of pit-trap data collected over 11 survey periods spread over 2.5 years around Ora Banda in Western Australia. Buckets caught more reptiles and more of the common ‘small’ and ‘medium’-sized reptiles, whereas pipes caught more mammals and the larger of the small trappable mammals. The trappability of some families of reptiles and some mammal species differs between buckets and pipes. We conclude that different pit-trap types provide a bias in the interpretation of the sampled fauna assemblage. Differences in the interpretation of vertebrate faunal diversity were accentuated by low trapping effort but attenuated by high trapping effort. We recommend that both buckets and pipes be employed as pit-traps during fauna surveys (as well as alternatives such as funnel traps) to more fully document fauna assemblages being surveyed.

Lizard tricks: overcoming conflicting requirements of speed versus climbing ability by altering biomechanics of the lizard stride

SUMMARY Adaptations promoting greater performance in one habitat are thought to reduce performance in others. However, there are many examples of animals in which, despite habitat differences, such predicted differences in performance do not occur. One such example is the relationship between locomotory performance to habitat for varanid lizards. To explain the lack of difference in locomotor performance we examined detailed observations of the kinematics of each lizards stride. Differences in kinematics were greatest between climbing and non-climbing species. For terrestrial lizards, the kinematics indicated that increased femur adduction, femur rotation and ankle angle all contributed positively to changes in stride length, but they were constrained for climbing species, probably because of biomechanical restrictions on the centre of mass height (to increase stability on vertical surfaces). Despite climbing species having restricted stride length, no differences have been previously reported in sprint speed between climbing and non-climbing varanids. This is best explained by climbing varanids using an alternative speed modulation strategy of varying stride frequency to avoid the potential trade-off of speed versus stability on vertical surfaces. Thus, by measuring the relevant biomechanics for lizard strides, we have shown how kinematic differences among species can mask performance differences typically associated with habitat variation.