Water balance and arginine vasotocin in the cocooning frog Cyclorana platycephala (hylidae)

Water Availability and Temperature as Modifiers of Evaporative Water Loss in Tropical Frogs

Water plays a notable role in the ecology of most terrestrial organisms due to the risks associated with water loss. Specifically, water loss in terrestrial animals happens through evaporation across respiratory tissues or the epidermis. Amphibians are ideal systems for studying how abiotic factors impact water loss since their bodies often respond quickly to environmental changes. While the effect of temperature on water loss is well known across many taxa, we are still learning how temperature in combination with humidity or water availability affects water loss. Here, we tested how standing water sources (availability) and temperature (26 and 36°C) together affect water loss in anuran amphibians using a Bayesian framework. We also present a conceptual model for considering how water availability and temperature may interact, resulting in body mass changes. After accounting for phylogenetic and time autocorrelation, we determined how different variables (water loss and uptake rates, temperature, and body size) affect body mass in three species of tropical frogs (Rhinella marina, Phyllobates terribilis, and Xenopus tropicalis). We found that all variables impacted body mass changes, with greater similarities between P. terribilis and X. tropicalis, but temperature only showed a notable effect in P. terribilis. Furthermore, we describe how the behavior of P. terribilis might affect its water budget. This study shows how organisms might manage water budgets across different environments and is important for developing models of evaporative water loss and species distributions.

Amphibian Behavior for the Exotic Pet Practitioner

Amphibians represent a diverse group of animals with highly varied behaviors depending on their anatomy, physiology, and ecological niche. Behavioral and welfare issues in amphibians are frequent in captive settings and warrant evaluation. Welfare criteria and clinical diagnostic assays when combined with a comprehension of the natural history of a species are useful tools to improve both the well-being of the individual animal and the population. Correction of environmental factors that affect behavior and, secondarily, survival and reproduction is important in captivity and for the conservation of wild populations.

Determination of the diet of the ghost bat (Macroderma gigas) in the Pilbara region of Western Australia from dried prey remains and DNA metabarcoding

The ghost bat (Macroderma gigas) is listed as Vulnerable in Australia, and is a difficult species to study in the wild. The published literature available on even the most basic aspects of its ecology is limited. This study describes an investigation into the diet of ghost bats occupying the Pilbara region of Western Australia, using identification of dried food remains recovered from beneath roosts in the 1980s and 1990s, and DNA metabarcoding of faecal pellets collected from roost sites during 2011–12. Ghost bat diet in the Pilbara region consists primarily of small mammal and bird species, with a lesser contribution from reptiles (geckoes and skinks) and amphibians. In total, 46 vertebrate taxa were identified, with 32 taxa identified from the dried food remains, and 21 taxa by DNA metabarcoding analysis of the faecal pellets. Only seven of the taxa identified were common to both collection methods, and 32 of those taxa identified represent new prey records for ghost bats in Western Australia, and 19 prey species that had not previously been reported from any other part of Australia. Knowledge of the diet of the ghost bat will provide land managers with important information necessary to ensure the continued survival of this species across its range.

A state of non-specific tension in living matter? Stress in Australian animals

Evidence of stress responses in Australian animals is reviewed through a series of case studies involving desert frogs and lizards, small carnivorous marsupials, desert wallabies, a dwarf kangaroo species, the quokka wallaby and a small nectarivorous bird. An operational definition of stress as "the physiological resultant of demands that exceed an animal's homeostatic capacities" is used to identify instances of stress responses in the field, and to gauge their intensity. Clear evidence of stress responses is found in small dasyurid marsupial carnivores, and desert agamid lizards, both of which are semelparous. Other instances of seasonal stress responses include the Rottnest Island quokka, the Barrow Island euro kangaroo and a small nectarivorous bird, the Silvereye. The review also highlights the high level of physiological adaptation of some desert wallabies, such as the Spectacled hare wallaby, which is able to maintain physiological homeostasis in the field when challenged by conditions of extreme drought. The importance of thermal and hygric refugia for the long-term survival or rock wallabies, which apparently lack any hormonal control of renal function, is also highlighted.

Endocrinology of osmoregulation and thermoregulation of Australian desert tetrapods: A historical perspective

Many Australian tetrapods inhabit desert environments characterised by low productivity, unpredictable rainfall, high temperatures and high incident solar radiation. Maintaining a homeostatic milieu intérieur by osmoregulation and thermoregulation are two physiological challenges faced by tetrapods in deserts, and the endocrine system plays an important role in regulating these processes. There is a considerable body of work examining the osmoregulatory role of antidiuretic hormones for Australian amphibians, reptiles and mammals, with particular contributions concerning their role and function for wild, free-living animals in arid environments. The osmoregulatory role of the natriuretic peptide system has received some attention, while the role of adrenal corticosteroids has been more thoroughly investigated for reptiles and marsupials. The endocrinology of thermoregulation has not received similar attention. Reptiles are best-studied, with research examining the influence of arginine vasotocin and melatonin on body temperature, the role of prostaglandins in heart rate hysteresis and the effect of melanocyte-stimulating hormone on skin reflectivity. Australian mammals have been under-utilised in studies examining the regulation, development and evolution of endothermy, and there is little information concerning the endocrinology of thermoregulation for desert species. There is a paucity of data concerning the endocrinology of osmoregulation and thermoregulation for Australian desert birds. Studies of Australian desert fauna have made substantial contributions to endocrinology, but there is considerable scope for further research. A co-ordinated approach to examine arid-habitat adaptations of the endocrine system in an environmental and evolutionary context would be of particular value.

Arginine vasotocin inhibits social interactions and enhances essential activities in male common lizards (Zootoca vivipara)

Arginine vasotocin (AVT) is known to play an important role in the regulation of social behavior in a number of vertebrate species. Nevertheless, the relationship between AVT and intraspecific interactions appears complex and in some cases contradictory. Moreover, AVT influences other behaviors, which are not primarily social including exploratory behavior, locomotion and thermoregulation. Some of these behavioral effects may be side-effects from a general influence of AVT on physiology. Indeed AVT can regulate metabolism and osmoregulation. Because most studies have been conducted using mammals and birds, its role in modulating behavior in other vertebrate groups is largely unknown. In this study we examined the effect of AVT on the social behavior of male common lizards, Zootoca vivipara. Moreover, considering the variety of pathways AVT could be involved in, we investigated its consequences on thermoregulatory behavior and physiological performance. In mid-June 2010, 74 males were captured from field sites (Mont-Lozère, South-eastern France) and kept in the laboratory for three weeks to obtain behavioral (reaction to conspecific odors, thermoregulation) and physiological (endurance, testosterone level) measurements. We demonstrated that injection of AVT reduced testosterone level and affected social behavior in different ways depending on the size of an individual. Specifically, small males injected with AVT were less attracted by conspecific odors than small control males, and no effect was detected in large males. Moreover, AVT promoted thermoregulatory behavior and enhanced endurance. These results are concordant with previous results obtained in this species in studies on stress suggesting that AVT may act through its influence on corticosterone secretion.

Metabolic and Kidney Diseases in the Setting of Climate Change, Water Shortage, and Survival Factors

Climate change (global warming) is leading to an increase in heat extremes and coupled with increasing water shortage, provides a perfect storm for a new era of environmental crises and potentially, new diseases. We use a comparative physiologic approach to show that one of the primary mechanisms by which animals protect themselves against water shortage is to increase fat mass as a means for providing metabolic water. Strong evidence suggests that certain hormones (vasopressin), foods (fructose), and metabolic products (uric acid) function as survival signals to help reduce water loss and store fat (which also provides a source of metabolic water). These mechanisms are intricately linked with each other and stimulated by dehydration and hyperosmolarity. Although these mechanisms were protective in the setting of low sugar and low salt intake in our past, today, the combination of diets high in fructose and salty foods, increasing temperatures, and decreasing available water places these survival signals in overdrive and may be accelerating the obesity and diabetes epidemics. The recent discovery of multiple epidemics of CKD occurring in agricultural workers in hot and humid environments may represent harbingers of the detrimental consequences of the combination of climate change and overactivation of survival pathways.

Cloning and expression of the epithelial sodium channel and its role in osmoregulation of aquatic and estivating African lungfish Protopterus annectens

The epithelial sodium channel (ENaC) is a sodium (Na(+))-selective aldosterone-stimulated ion channel involved in Na(+) transport homeostasis of tetrapods. We examined full-length cDNA sequences and tissue distributions of ENaCα, ENaCβ, and ENaCγ subunits in the African lungfish Protopterus annectens. Protopterus ENaC (pENaC) comprises 3 subunits: pENaCα, pENaCβ, and pENaCγ. pENaCα, pENaCβ, and pENaCγ subunits are closely related to α, β, and γ subunits of the Australian lungfish Neoceratodus forsteri ENaC (nENaC), respectively. Three ENaC subunit mRNAs were highly expressed in the gills and moderately expressed in the kidney and rectum of P. annectens. During estivation for 2-4weeks and 2-3months, plasma Na(+) concentration was relatively stable, but plasma urea concentration significantly increased in comparison with the control fish kept in a freshwater environment. Plasma aldosterone concentration and mRNA expression of the ENaCα subunit gradually and significantly decreased in the gills and kidney after 2months of estivation. Thus, aldosterone-dependent Na(+) absorption via ENaC probably exists in the epithelial cells of osmoregulatory organs of lungfish kept in fresh water, whereas plasma Na(+) concentration may be maintained by a mechanism independent of aldosterone-ENaC axis during estivation in lungfish.

RNA-seq dependent transcriptional analysis unveils gene expression profile in the intestine of sea cucumber Apostichopus japonicus during aestivation

The seasonal marine, the sea cucumber Apostichopus japonicus (Selenka, 1867), cycles annually between periods of torpor when water temperature is above about 25°C in summer and active life when temperature is below about 18°C. This species is a good candidate model organism for studies of environmentally-induced aestivation in marine invertebrates. Previous studies have examined various aspects of aestivation of A. japonicus, however, knowledge of the molecular regulation underpinning these events is still fragmentary. In the present study, we constructed a global gene expression profile of the intestine tissue of A. japonicus using RNA-seq to identify transcriptional responses associated with transitions between different states: non-aestivation (NA), deep-aestivation (DA), and arousal from aestivation (AA). The analysis identified 1245 differentially expressed genes (DEGs) between DA vs. NA states, 1338 DEGs between AA vs. DA, and 1321 DEGs between AA vs. NA using the criteria |Log2Ratio|≥1 and FDR≤0.001. Of these, 25 of the most significant DEGs were verified by real-time PCR, showing trends in expression patterns that were almost in full concordance between the two techniques. GO analysis revealed that for DA vs. NA, 24 metabolic associated processes were highly enriched (corrected p value<0.05) whereas for AA vs. NA, 12 transport and metabolism associated processes were significantly enriched (corrected p value<0.05). Pathways associated with aestivation were also mined, and indicated that most DEGs were enriched in metabolic and signal transduction pathways in the deep aestivation stage. Two up pathways were significantly enriched at the arousal stage (ribosome and metabolism of xenobiotics by cytochrome P450 pathway). A set of key DEGs was identified that may play vital roles in aestivation; these involved metabolism, detoxification and tissue protection, and energy-expensive processes. Our work presents an overview of dynamic gene expression in torpor-arousal cycles during aestivation of A. japonicus and identifies a series of candidate genes and pathways for further research on the molecular mechanisms of aestivation.