Nutritive Support for Critical Exotic Patients

Malnutrition and need for nutritive support are both very common in exotic animals requiring critical care. Assessment and monitoring of body condition, weight, protein absorption, and catabolic loss is recommended to help guide restorative therapy. Several critical care diets are available based on digestive strategy. Fluid requirements and evaporative water loss can vary based on taxa; ectoderms suffer evaporative losses at a greater magnitude than endotherms. Enteral and parenteral nutrition strategies can be appropriate for patients, with natural history and anatomic and physiologic differences considered as much as possible.

Contrasting patterns at interspecific and intraspecific levels in scorpion body size across a climatic gradient from rainforest to dryland vegetation

Body size is believed to be one of the most fundamental functional traits in animals and is evolutionarily conserved in order to guarantee the survival of the species. Besides the phylogenetic backgrounds, body size patterns might be a product of environmental filters, especially within fine taxonomic levels (i.e., within species or geographical lineages). Here, we evaluated the responses of scorpion body size at different organizational levels (inter and intraspecific) along a dry-wet climatic gradient in Brazilian forests. Scorpions were collected from 20 localities in northeastern Brazil, covering 12 sites of dry forests and eight sites in rainforest environments. As a proxy for body size, we measured the carapace length of 368 adult scorpions belonging to 11 species and applied linear mixed-effects models to investigate the potential effects of climatic features and geographical tendencies in this trait at inter- and intraspecific levels. Our findings suggest the existence of a longitudinal pattern of body size in scorpions with species becoming larger in an east-west direction (i.e., towards the continent); such geographical tendency was also detected for one of the three species analyzed at the population level. In addition, the warmer temperature had a negative effect on body size in scorpions at inter- and intraspecific levels. Based on these findings, we assert that body size in scorpions is not affected solely by their phylogenetic history, but also by the physiological constraints imposed by the environment, which becomes more evident across climatic gradients.

Post-feeding thermophily in a scorpion is associated with rapid digestion and recovery of maximal nocturnal activity

A postprandial increase in metabolic rate is typical in all studied animal groups. The phenomenon, termed specific dynamic action (SDA), is understudied in terrestrial arthropods, and arachnids in particular. To the best of our knowledge, this is the first report of SDA properties in scorpions, which are temperature-dependent as in other poikilotherms. Metabolic rates of scorpions are low compared with similarly-sized arthropods, and as they often feed on relatively large prey the cost of digestion is expected to be notable. This prompted us to study the extent of SDA and its characteristics in scorpions at two different ecologically-relevant temperatures. We also hypothesized that post-feeding behavioral thermoregulation would reflect benefits to the scorpion energy balance. On average, fed adult Hottentotta judaicus (Buthidae) expressed a 3 °C increase in preferred surface temperature, although we did not find evidence for lower costs of digestion at higher temperatures. However, SDA duration was significantly shorter at 30 compared with 25 °C. Fast processing of their meal at 30 °C was correlated with recovery of elevated nocturnal metabolic rates, which are not digestion-related. This suggests that post-feeding choice of higher temperatures accelerates digestion and recovery of other elevated metabolic states such as locomotion and lower sensory threshold, which may enhance foraging success.

Low temperatures induce physiological changes in lipids, fatty acids and hydrocarbons, in two rare winter scorpions of genus Urophonius (Scorpiones, Bothriuridae)

Different organisms (mainly poikilotherms) are subject to environmental fluctuations that could affect their normal physiological functioning (e.g., by destabilization of biomembranes and rupture of biomolecules). As a result, animals regulate their body temperature and adapt to different environmental conditions through various physiological strategies. These adaptations are crucial in all organisms, although they are more relevant in those that have reached a great adaptive diversity such as scorpions. Within scorpions, the genus Urophonius presents species with winter activity, being this a peculiarity within the Order and an opportunity to study the strategies deployed by these organisms when facing different temperatures. Here, we explore three basic issues of lipid remodeling under high and low temperatures, using adults and juveniles of Urophonius achalensis and U. brachycentrus. First, as an indicator of metabolic state, we analyzed the lipidic changes in different tissues observing that low temperatures generate higher quantities of triacylglycerols and fewer amount of structural lipids and sphyngomielin. Furthermore, we studied the participation of fatty acids in adaptive homeoviscosity, showing that there are changes in the quantity of saturated and unsaturated fatty acids at low temperature (mainly 16:0, 18:0, 18:1 and 18:2). Finally, we observe that there are quantitative and qualitative variations in the cuticular hydrocarbons (with possible water barrier and chemical recognition function). These fluctuations are in some cases species-specific, metabolic-specific, tissue-specific and in others depend on the ontogenetic state.

Intraspecific variation in metabolic rate and its correlation with local environment in the Chinese scorpion Mesobuthus martensii

Scorpions are well known for their reduced resting metabolic rate (RMR) in comparison to typical arthropods. Since RMR is a key physiological trait linked with evolutionary fitness, it is expected that there may exist intraspecific RMR variation given the ecological and geographical heterogeneities across the distributional range of a species. Nevertheless, it is unclear whether RMR variation exists among scorpion populations. Here, we compared the RMR (VCO₂) of 21 populations of the Chinese scorpion Mesobuthus martensii (Scorpiones: Buthidae) at 25°C after at least 3 months of laboratory acclimation. The following results were obtained. First, there was significant difference in RMR between sexes when body-weight effects were factored out. Second, significant local variation in RMR was detected by analyses of both variance and covariance, with one population showing significantly reduced RMR and another significantly increased RMR. Third, regression analysis indicated that the local mean temperature and mean annual days of rainfall were the two significant factors associated with the aforementioned inter-population difference in RMR. The implication of such an association was discussed.

Summary: Metabolic rate variation is observed between the two sexes and among populations in the Chinese scorpion, with the latter being correlated negatively with local mean temperature and positively with annual days of rainfall.

Terrestrial locomotion energy costs vary considerably between species: no evidence that this is explained by rate of leg force production or ecology

Inter-specifically, relative energy costs of terrestrial transport vary several-fold. Many pair-wise differences of locomotor costs between similarly-sized species are considerable, and are yet to be explained by morphology or gait kinematics. Foot contact time, a proxy for rate of force production, is a strong predictor of locomotor energy costs across species of different size and might predict variability between similarly sized species. We tested for a relationship between foot contact time and metabolic rate during locomotion from published data. We investigated the phylogenetic correlation between energy expenditure rate and foot contact time, conditioned on fixed effects of mass and speed. Foot contact time does not explain variance in rate of energy expenditure during locomotion, once speed and body size are accounted for. Thus, perhaps surprisingly, inter-specific differences in the mass-independent net cost of terrestrial transport (NCOT) are not explained by rates of force production. We also tested for relationships between locomotor energy costs and eco-physiological variables. NCOT did not relate to any of the tested eco-physiological variables; we thus conclude either that interspecific differences in transport cost have no influence on macroecological and macrophysiological patterns, or that NCOT is a poor indicator of animal energy expenditure beyond the treadmill.

Does the Treadmill Support Valid Energetics Estimates of Field Locomotion?

SYNOPSIS

Quantifying animal energy expenditure during locomotion in the field is generally based either on treadmill measurements or on estimates derived from a measured proxy. Two common proxies are heart rate (ƒH) and dynamic body acceleration (accelerometry). Both ƒH and accelerometry have been calibrated extensively under laboratory conditions, which typically involve prompting the animal to locomote on a treadmill at different speeds while simultaneously recording its rate of oxygen uptake (V̇o2) and the proxy. Field estimates of V̇o2 during locomotion obtained directly from treadmill running or from treadmill-calibrated proxies make assumptions about similarities between running in the field and in the laboratory. The present study investigated these assumptions, focusing on humans as a tractable species. First we investigated experimentally if and how the rate of energy expenditure during treadmill locomotion differs to that during field locomotion at the same speeds, with participants walking and running on a treadmill, on tarmac, and on grass, while wearing a mobile respirometry system. V̇o2 was substantially higher during locomotion in both of the field conditions compared with on a level treadmill: 9.1% on tarmac and 17.7% on grass. Second, we included these data in a meta-analysis of previous, related studies. The results were influenced by the studies excluded due to particulars of the experiment design, suggesting that participant age, the surface type, and the degree of turning during field locomotion may influence by how much treadmill and field locomotion V̇o2 differ. Third, based on our experiments described earlier, we investigated the accuracy of treadmill-calibrated accelerometry and ƒH for estimating V̇o2 in the field. The mean algebraic estimate errors varied between 10% and 35%, with the ƒH associated errors being larger than those derived from accelerometry. The mean algebraic errors were all underestimates of field V̇o2, by around 10% for fH and varying between 0% and 15% for accelerometry. Researchers should question and consider how accurately a treadmill-derived proxy calibration of V̇o2 will estimate V̇o2 during terrestrial locomotion in free-living animals.

Phylogenetic comparisons of pedestrian locomotion costs: confirmations and new insights

The energetic costs for animals to locomote on land influence many aspects of their ecology. Size accounts for much of the among-species variation in terrestrial transport costs, but species of similar body size can still exhibit severalfold differences in energy expenditure. We compiled measurements of the (mass-specific) minimum cost of pedestrian transport (COT_min, mL/kg/m) for 201 species - by far the largest sample to date - and used phylogenetically informed comparative analyses to investigate possible eco-evolutionary differences in COT_min between various groupings of those species. We investigated number of legs, ectothermy and endothermy, waddling, and nocturnality specifically in lizards. Thus, our study primarily revisited previous theories about variations in COT_min between species, testing them with much more robust analyses. Having accounted for mass, while residual COT_min did not differ between bipedal and other species, specifically waddling bipeds were found to have relatively high COT_min. Furthermore, nocturnal lizards have relatively low COT_min although temperature does not appear to affect COT_min in ectotherms. Previous studies examining across-species variation in COT_min from a biomechanical perspective show that the differences between waddling birds and nonwaddling species, and between nocturnal lizards and other ecotherms, are likely to be attributable to differences in ground reaction forces, posture, and effective limb length.

Terrestrial movement energetics: current knowledge and its application to the optimising animal

The energetic cost of locomotion can be a substantial proportion of an animal's daily energy budget and thus key to its ecology. Studies on myriad species have added to our knowledge about the general cost of animal movement, including the effects of variations in the environment such as terrain angle. However, further such studies might provide diminishing returns on the development of a deeper understanding of how animals trade-off the cost of movement with other energy costs, and other ecological currencies such as time. Here, I propose the ‘individual energy landscape’ as an approach to conceptualising the choices facing the optimising animal. In this Commentary, first I outline previous broad findings about animal walking and running locomotion, focusing in particular on the use of net cost of transport as a metric of comparison between species, and then considering the effects of environmental perturbations and other extrinsic factors on movement costs. I then introduce and explore the idea that these factors combine with the behaviour of the animal in seeking short-term optimality to create that animal's individual energy landscape – the result of the geographical landscape and environmental factors combined with the animal's selected trade-offs. Considering an animal's locomotion energy expenditure within this context enables hard-won empirical data on transport costs to be applied to questions about how an animal can and does move through its environment to maximise its fitness, and the relative importance, or otherwise, of locomotion energy economy.

The interactions between temperature and activity levels in driving metabolic rate: theory, with empirical validation from contrasting ectotherms

The rate of change in resting metabolic rate (RMR) as a result of a temperature increase of 10 °C is termed the temperature coefficient (Q10), which is often used to predict how an organism's total MR will change with temperature. However, this method neglects a potentially key component of MR; changes in activity level (and thus activity MR; AMR) with temperature may significantly alter the relationship between MR and temperature. The present study seeks to describe how thermal effects on total MR estimated from RMR-temperature measurements can be misleading when the contribution of activity to total MR is neglected. A simple conceptual framework illustrates that since the relationship between activity levels and temperature can be different to the relationship between RMR and temperature, a consistent relationship between RMR and total MR cannot be assumed. Thus the thermal effect on total MR can be considerably different to the thermal effect on RMR. Simultaneously measured MR and activity from three ectotherm species with differing behavioural and physiological ecologies were used to empirically examine how changes in temperature drive changes in RMR, activity level, AMR and the Q10 of MR. These species exhibited varied activity- and MR-temperature relationships, underlining the difficulty in predicting thermal influences on activity levels and total MR. These data support a model showing that thermal effects on total MR will deviate from predictions based solely on RMR; this deviation will depend upon the difference in Q10 between AMR and RMR, and the relative contribution of AMR to total MR. To develop mechanistic, predictive models for species' metabolic responses to temperature changes, empirical information about the relationships between activity levels, MR and temperature, such as reported here, is required. This will supersede predictions based on RMR alone.

Effects of within-generation thermal history on the flight performance of Ceratitis capitata: colder is better

The influence of thermal history on temperature-dependent flight performance was investigated in an invasive agricultural pest insect, Ceratitis capitata (Diptera: Tephritidae). Flies were exposed to one of four developmental acclimation temperatures (Tacc: 15, 20, 25, 30°C) during their pupal stage and tested at these temperatures (Ttest) as adults using a full-factorial study design. Major factors influencing flight performance included sex, body mass, Ttest and the interaction between Ttest and Tacc. Successful flight performance increased with increasing Ttest across all acclimation groups (from 10% at 15°C to 77% at 30°C). Although Tacc did not affect flight performance independently, it did have a significant interaction effect with Ttest. Multiple comparisons showed that flies which had been acclimated to 15°C and 20°C performed better than those acclimated to 25°C and 30°C when tested at cold temperatures, but warm-acclimated flies did not outperform cold-acclimated flies at warmer temperatures. This provides partial support for the 'colder is better' hypothesis. To explain these results, several flight-related traits were examined to determine whether Tacc influenced flight performance as a consequence of changes in body or wing morphology, whole-animal metabolic rate or cytochrome c oxidase enzyme activity. Although significant effects of Tacc could be detected in several of the traits examined, with an emphasis on sex-related differences, increased flight performance could not be explained solely on the basis of changes in any of these traits. Overall, these results are important for understanding dispersal physiology despite the fact that the mechanisms of acclimation-related changes in flight performance remain unresolved.

Gas exchange patterns and water loss rates in the Table Mountain cockroach, Aptera fusca (Blattodea: Blaberidae)

The importance of metabolic rate and/or spiracle modulation for saving respiratory water is contentious. One major explanation for gas exchange pattern variation in terrestrial insects is to effect a respiratory water loss (RWL) saving. To test this, we measured V·CO2 and V·H2O in a previously unstudied, mesic cockroach, Aptera fusca, and compared gas exchange and water loss parameters among the major gas exchange patterns (continuous, cyclic, discontinuous gas exchange (DGE)) at a range of temperatures. Mean V·CO2, V·H2O, and V·H2O per unit V·CO2 did not differ among the gas exchange patterns at all temperatures (p>0.09). There was no significant association between temperature and gas exchange pattern type (p=0.63). Percentage of RWL (relative to total water loss) was typically low (9.79±1.84%) and did not differ significantly among gas exchange patterns at 15°C (p=0.26). The method of estimation had a large impact on the %RWL and of three techniques investigated (traditional, regression, hyperoxic switch), the traditional method generally performed best. In many respects, A. fusca has typical gas exchange for what might be expected from other insects studied to date (e.g. V·CO2, V·H2O, RWL and CWL). However, we found for A. fusca that V·H2O expressed as a function of metabolic rate was significantly higher than the expected consensus relationship for insects, suggesting it is under considerable pressure to save water. Despite this, we found no consistent evidence supporting the conclusion that transitions in pattern type yield reductions in RWL in this mesic cockroach.