Reference levels for corticosterone and immune function in farmed saltwater crocodiles (Crocodylus porosus) hatchlings using current Code of Practice guidelines

Exposure to ecologically relevant estrogen levels do not influence morphology or immune parameters in hatchling American alligators (Alligator mississippiensis)

Human activity has increased concentrations of endocrine-disrupting contaminants (EDCs) in many ecological systems. Many EDCs are xenoestrogens, which imitate naturally derived estrogen like estradiol 17-β (E2). These pollutants can critically affect a broad range of biological functions, particularly in organisms inhabiting aquatic environments. E2 and associated receptors are involved in regulating innate immune responses, where documentation of exogenous E2 on immune parameters is important for understanding health consequences. In this study, we explore the impact of environmentally relevant concentrations of E2 on circulating glucocorticoid levels and several innate immune parameters in hatchling American alligators (Alligator mississippiensis). Twenty-three hatchling alligators were randomly placed in one of three groups that differed in dietary E2 concentration: control (no E2 exposure), low E2 (0.5 μg/kg E2), or high E2 (1 μg/kg E2) for 10 weeks. Following this period, several biomarkers were quantified to monitor the impact of E2: growth, change in body condition, white blood cell (WBC) counts, glucocorticoid levels, and general antibody response. Blood E2 concentrations were greater in individuals exposed to E2, but plasma corticosterone levels were reduced among the experimental groups. Morphology, growth, and immune parameters of E2 exposed animals did not differ from controls. These results suggest that acute exposure to increased environmental estrogen concentrations may alter plasma hormone concentrations but have little to no impact on immediate morphology or immune responses. Future studies may expand on this by monitoring biomarkers in wild populations across time, which will provide insight into how different ontogenetic stages are impacted by environmental contaminants.

Critical review of the phytohemagglutinin assay for assessing amphibian immunity

Infectious diseases are a major driver of the global amphibian decline. In addition, many factors, including genetics, stress, pollution, and climate change can influence the response to pathogens. Therefore, it is important to be able to evaluate amphibian immunity in the laboratory and in the field. The phytohemagglutinin (PHA) assay is an inexpensive and relatively non-invasive tool that has been used extensively to assess immunocompetence, especially in birds, and more recently in amphibians. However, there is substantial variation in experimental methodology among amphibian PHA studies in terms of species and life stages, PHA doses and injection sites, and use of experimental controls. Here, we compile and compare all known PHA studies in amphibians to identify knowledge gaps and develop best practices for future work. We found that research has only been conducted on a limited number of species, which may not reflect the diversity of amphibians. There is also a lack of validation studies in most species, so that doses and timing of PHA injection and subsequent swelling measurements may not effectively evaluate immunocompetence. Based on these and other findings, we put forward a set of recommendations to make future PHA studies more consistent and improve the ability to utilize this assay in wild populations, where immune surveillance is greatly needed.

Reptilian Innate Immunology and Ecoimmunology: What Do We Know and Where Are We Going?

Reptiles, the only ectothermic amniotes, employ a wide variety of physiological adaptations to adjust to their environments but remain vastly understudied in the field of immunology and ecoimmunology in comparison to other vertebrate taxa. To address this knowledge gap, we assessed the current state of research on reptilian innate immunology by conducting an extensive literature search of peer-reviewed articles published across the four orders of Reptilia (Crocodilia, Testudines, Squamata, and Rhynchocephalia). Using our compiled dataset, we investigated common techniques, characterization of immune components, differences in findings and type of research among the four orders, and immune responses to ecological and life-history variables. We found that there are differences in the types of questions asked and approaches used for each of these reptilian orders. The different conceptual frameworks applied to each group has led to a lack of unified understanding of reptilian immunological strategies, which, in turn, have resulted in large conceptual gaps in the field of ecoimmunology as a whole. To apply ecoimmunological concepts and techniques most effectively to reptiles, we must combine traditional immunological studies with ecoimmunological studies to continue to identify, characterize, and describe the reptilian immune components and responses. This review highlights the advances and gaps that remain to help identify targeted and cohesive approaches for future research in reptilian ecoimmunological studies.

Stress responses in captive Crocodylus moreletii associated with metal exposure

Environmental pollution by metals has repercussions on wildlife health. It is known that some metals can have an influence on the neuroendocrine stress response, and at the same time, metals have pro-oxidant effects that can overwhelm the antioxidant system and cause oxidative stress. This study evaluates the association of metals with neuroendocrine stress activity and biomarkers of oxidative stress in 42 captive female Morelet's crocodiles (Crocodylus moreletii). We measured five metals of ecotoxicological importance (Hg, Cd, Pb, Cu and Zn), and three biomarkers of the oxidative stress response in the liver: glutathione (GSH) and glutathione disulfide (GSSG) as markers for antioxidant system and thiobarbituric acid reactive substances (TBARS) for oxidative damage. We also measured one biomarker of the neuroendocrine response to stress: corticosterone (B) in blood plasma. The mean ± SD concentrations of metals in the liver expressed in μg/g (dw) were: Cd: 0.004 ± 0.003, Hg: 0.014 ± 0.019, Cu: 0.017 ± 0.013, Zn: 0.043 ± 0.035, Pb: 0.16 ± 0.256. The mean ± SD of GSH was 0.42 ± 0.35 nmol/mg protein, the mean ± SD of GSSG was 0.24 ± 0.20 nmol/mg protein, the mean ± SD concentrations of TBARS were 0.36 ± 0.21 nmol/mg protein, and the mean ± SD of B was 393.57 ± 405.14 pg/mL. Hg presented a significant negative relationship with corticosterone. Cd had a negative relationship with both GSH and GSSG; meanwhile, Zn showed a negative relationship with TBARS levels, could be a protective element against hepatic oxidative damage. Finally, B had negative relationship with oxidative damage. The connection found between Hg and the neuroendocrine stress response, as well as the correlations of Cd and Zn with oxidative damage and antioxidant activity should be studied further, given their toxicological importance and implications for the conservation of C. moreletii and other crocodilians.

Changes in antioxidant enzyme levels following capture in juvenile American Alligators (Alligator mississippiensis) are tissue dependent

Many parameters used to investigate stress in vertebrates are temporally sensitive. The act of capture and sampling can influence them, hindering their functionality for evaluating the effects of stressors. Consequently, the investigation and subsequent incorporation of less time sensitive parameters are necessary to better evaluate stressors affecting vertebrates. In this study, we investigated how capture stress and handling associated with sampling influences antioxidant status in American Alligators (Alligator mississippiensis, Daudin, 1802; hereafter Alligator), long-lived, top-trophic carnivores found in the southeastern United States, by measuring levels of two antioxidant enzymes in destructive (brain and pancreas) and nondestructive (tail scutes) tissues: superoxide-dismutase-1 (SOD1) and glutathione peroxidase-1 (GPX1). Capture stress had no effect on pancreatic SOD1 and no effect on brain and pancreatic GPX1 (all p > 0.05). However, brain SOD1, scute SOD1, and scute GPX1 were all impacted by capture stress. These disparate results illustrate that the influence of capture stress on antioxidant enzymes in Alligators is tissue and marker dependent, necessitating further investigation. Our results provide a firm foundation to further investigate oxidative status in crocodilians.

Welfare of Farmed Crocodilians: Identification of Potential Animal-Based Measures Using Elicitation of Expert Opinion

Simple Summary

This study focuses on an elicitation of expert opinion to identify a toolbox of animal-based measures that can be used to assess the welfare of farmed crocodilians. This is the initial step towards identifying an animal-based assessment protocol that could be used to support the international outcome-based standard developed by the crocodilian farming industry. Potential measures were identified and aligned with the four animal welfare principles and twelve criteria developed by Welfare Quality^®, focusing primarily on practical measures that could be used for monitoring farm processes or during external verification activities. The proposed measures were presented to a panel made up of animal welfare specialists (farmers, veterinarians and scientists) for judgment and scoring. Twenty-eight experts scored the proposed measures for validity (that being the relevancy to the welfare criterion and usefulness as a measure) and feasibility (that being how easy it is to observe and assess, for example, during an on-farm animal welfare assessment or routine monitoring). Future studies, involving the preliminary testing of the measures on a commercial crocodile farm, are planned to confirm validity and establish the reliability of the identified measures.

Abstract

Animal-based measures are the measure of choice in animal welfare assessment protocols as they can often be applied completely independently to the housing or production system employed. Although there has been a small body of work on potential animal-based measures for farmed crocodilians, they have not been studied in the context of an animal welfare assessment protocol. Potential animal-based measures that could be used to reflect the welfare state of farmed crocodilians were identified and aligned with the Welfare Quality^® principles of good housing, good health, good feeding and appropriate behaviour. A consultation process with a panel of experts was used to evaluate and score the potential measures in terms of validity and feasibility. This resulted in a toolbox of measures being identified for further development and integration into animal welfare assessment on the farm. Animal-based measures related to ‘good feeding’ and ‘good health’ received the highest scores for validity and feasibility by the experts. There was less agreement on the animal-based measures that could be used to reflect ‘appropriate behaviour’. Where no animal-based measures were deemed to reliably reflect a welfare criterion nor be useful as a measure on the farm, additional measures of resources or management were suggested as alternatives. Future work in this area should focus on the reliability of the proposed measures and involve further evaluation of their validity and feasibility as they relate to different species of crocodilian and farming system.

Short-term capture stress and its effects on corticosterone levels and heat shock proteins in captive American Alligators (Alligator mississippiensis)

Heat shock proteins (HSPs) are important mediators of the normal cellular function and the cellular stress response. As such, HSPs are often utilized to measure the effects of stressors on organisms in vivo. However, multiple variables can influence their expression, including time or season, confounding results. To investigate the utility of HSPs in measuring effects of stressors in a top-trophic carnivore, we captured 20 American Alligators (Alligator mississippiensis (Daudin, 1802)), placed them in burlap sacks for 2 h and collected blood samples over four time points (baseline, 1 and 2 h after placement into burlap sacks, and 24 h after initial capture) to measure plasma corticosterone (the main crocodilian glucocorticoid) and levels of HSP60, HSP70, and HSP90. Time point significantly affected plasma corticosterone levels in Alligators (p < 0.0001), with levels significantly elevated at 1, 2, and 24 h, relative to baseline (all p < 0.05). However, capture stress did not affect HSP60, HSP70, or HSP90 in red blood cells (all p > 0.05). Our results suggest HSPs may be important biomarkers for investigating the impacts of stressors on captive and wild crocodilians, as they are not acutely elevated by capture or handling stress.

Identification and characterization of microRNAs (miRNAs) and their transposable element origins in the saltwater crocodile, Crocodylus porosus

MicroRNAs (miRNAs) are 18-24 nucleotide regulatory RNAs. They are involved in the regulation of genetic and biological pathways through post transcriptional gene silencing and/or translational repression. Data suggests a slow evolutionary rate for the saltwater crocodile (Crocodylus porosus) over the past several million years when compared to birds, the closest extant relatives of crocodilians. Understanding gene regulation in the saltwater crocodile in the context of relatively slow genomic change thus holds potential for the investigation of genomics, evolution, and adaptation. Utilizing eleven tissue types and sixteen small RNA libraries, we report 644 miRNAs in the saltwater crocodile with >78% of miRNAs being novel to crocodilians. We also identified potential targets for the miRNAs and analyzed the relationship of the miRNA repertoire to transposable elements (TEs). Results suggest an increased association of DNA transposons with miRNAs when compared to retrotransposons. This work reports the first comprehensive analysis of miRNAs in Crocodylus porosus and addresses the potential impacts of miRNAs in regulating the genome in the saltwater crocodile. In addition, the data suggests a supporting role of TEs as a source for miRNAs, adding to the increasing evidence that TEs play a significant role in the evolution of gene regulation.

Mosquito-Independent Transmission of West Nile virus in Farmed Saltwater Crocodiles (Crocodylus porosus)

West Nile virus, Kunjin strain (WNV_KUN) is endemic in Northern Australia, but rarely causes clinical disease in humans and horses. Recently, WNV_KUN genomic material was detected in cutaneous lesions of farmed saltwater crocodiles (Crocodylus porosus), but live virus could not be isolated, begging the question of the pathogenesis of these lesions. Crocodile hatchlings were experimentally infected with either 10⁵ (n = 10) or 10⁴ (n = 11) TCID₅₀-doses of WNV_KUN and each group co-housed with six uninfected hatchlings in a mosquito-free facility. Seven hatchlings were mock-infected and housed separately. Each crocodile was rotationally examined and blood-sampled every third day over a 3-week period. Eleven animals, including three crocodiles developing typical skin lesions, were culled and sampled 21 days post-infection (dpi). The remaining hatchlings were blood-sampled fortnightly until experimental endpoint 87 dpi. All hatchlings remained free of overt clinical disease, apart from skin lesions, throughout the experiment. Viremia was detected by qRT-PCR in infected animals during 2–17 dpi and in-contact animals 11–21 dpi, indicating horizontal mosquito-independent transmission. Detection of viral genome in tank-water as well as oral and cloacal swabs, collected on multiple days, suggests that shedding into pen-water and subsequent mucosal infection is the most likely route. All inoculated animals and some in-contact animals developed virus-neutralizing antibodies detectable from 17 dpi. Virus-neutralizing antibody titers continued to increase in exposed animals until the experimental endpoint, suggestive of persisting viral antigen. However, no viral antigen was detected by immunohistochemistry in any tissue sample, including from skin and intestine. While this study confirmed that infection of saltwater crocodiles with WNV_KUN was associated with the formation of skin lesions, we were unable to elucidate the pathogenesis of these lesions or the nidus of viral persistence. Our results nevertheless suggest that prevention of WNV_KUN infection and induction of skin lesions in farmed crocodiles may require management of both mosquito-borne and water-borne viral transmission in addition to vaccination strategies.

Systemic Granulomatous Pathology in Two Captive Alligator Mississippiensis

The literature in this field cites various ubiquitous fungal and bacterial microorganisms as etiologic agents in severely stressed captive alligators and crocodiles. This study reports two cases of Alligator mississippiensis with bacterial and fungal disease. Two adult American alligators have been submitted for post-mortem investigations. Necropsy, cytology (MGG), and histopathology investigations (HE, HEA, PAS, Gram, Giemsa, Ziehl Neelsen) were carried out. Pleural and pericardial swabs were subjected to microbiological examination. The main lesions detected involved the lower respiratory system and were characterized by thoracic serosanguineous effusions, pleural and pulmonary nodules (1 – 80 mm), accompanied by edema. Similar nodules observed also in the liver, spleen and myocardium, suggested a systemic disease. Additionally, cutaneous, gingival and gastrointestinal erosions and ulcers were found. Cytoarchitecture findings in the major organs revealed lymphoid depletion, multifocal to coalescing necrotic areas with coccoid aggregates and rod shaped bacteria intermixing fungal structures, boarded by heterogeneous inflammatory infiltrates, composed by epithelioid macrophages, lymphocytes and heterophils. The microbiological examination revealed the presence of Aeromonas hydrophila, A. caviae, Serratia marcescens, Pantoea agglomerans, Proteus vulgaris, haemolitic and non-haemolitic E. coli, Citrobacter freundii, Rhizopus/Absidia from pleural and pericardial cavities, concluding that death occurred following a bacterial and fungal pneumonia, with secondary spreading of microorganisms. Along with the low immune response, severe stress was the main possible cause, as a result of environmental temperature changes during the winter, as well as other husbandry issues.

Examining the Effects of Chronic Selenium Exposure on Traditionally Used Stress Parameters in Juvenile American Alligators (Alligator mississippiensis)

Environmental contaminants, such as the trace element selenium (Se), are a continuing concern to species worldwide due to their potential pathophysiological effects, including their influence on the stress response mediated through glucocorticoids (GCs; stress hormones). Environmental concentrations of Se are increasing due to anthropogenic activities, including the incomplete combustion of coal and subsequent disposal of coal combustion wastes. However, most studies examining how Se affects GCs have been focused on lower trophic organisms. The objectives of this study were to investigate the effects of long-term Se exposure on traditionally used stress parameters and to identify which of these parameters best indicate Se accumulation in liver and kidney of the American alligator (Alligator mississippiensis), a top trophic carnivore found in the southeastern United States and known to inhabit Se-containing areas. Alligators were divided into three dietary treatments and fed prey spiked with 1000 or 2000 ppm of selenomethionine (SeMet) or deionized water (control treatment) for 7 weeks. Following the 7-week treatment protocol, blood and tissue samples were obtained to measure plasma corticosterone (CORT; the main crocodilian GC), tail scute CORT, the ratio of peripheral blood heterophils (H) to lymphocytes (L) as H/L ratio, and body condition. To evaluate which parameter best indicated Se accumulation in the liver and kidney, principal component and discriminant analyses were performed. The only parameter significantly correlated with liver and kidney Se concentrations was scute CORT. Our results suggest that measurement of CORT in tail scutes compared with plasma CORT, H/L ratios, and body condition is the best indicator of Se-exposure and accumulation in crocodilians.

Diving beyond Aerobic Limits: Effect of Temperature on Anaerobic Support of Simulated Predator Avoidance Dives in an Air-Breathing Ectotherm

Diving optimality models predict air breathers to routinely dive within aerobic limits, but predator avoidance dives may be an exception. Lengthening submergence times during a predation threat may enhance survival probability, and we therefore hypothesized that predator avoidance dives in juvenile estuarine crocodiles (Crocodylus porosus) would be partially anaerobically fueled. We also predicted that reliance on anaerobic metabolism would increase at elevated temperatures to offset the faster depletion of body oxygen stores. Crocodiles were maintained at 28° and 34°C for 60 d and subsequently underwent simulated predator avoidance dive trials at two test temperatures (28° and 34°C). Blood was sampled immediately on surfacing to measure plasma lactate concentrations relative to nondiving (control) values. Aerobic dive limits (cADL; min) were also calculated using known body mass and oxygen storage relationships and rates of diving oxygen consumption and compared with observed dive durations. Postdive plasma lactate levels were elevated beyond resting levels at both test temperatures, indicating that aerobic thresholds were surpassed during simulated predator avoidance dives. Similarly, ≥90% of dive durations exceeded cADLs at both test temperatures. Postdive plasma lactate concentrations were independent of water temperature and thermal acclimation treatment. Together, these findings suggest that reliance on anaerobiosis during simulated predator avoidance dives is important regardless of temperature.

Quantification of plasma corticosterone in juvenile farmed saltwater crocodiles (Crocodylus porosus) using current Australian Code of Practice guidelines

Saltwater crocodiles (Crocodylus porosus) across three size categories (hatchlings, grower and harvest-size) were repeatedly blood sampled on two farms in the Northern Territory, Australia to determine reference plasma corticosterone (CORT; crocodilian stress hormone) levels. The mean CORT values for hatchlings (<1 year old), growers (1-3 years) and harvest-size individuals (2 + years) were 1.65 ± 0.15 ng/ml, 2.73 ± 0.21 ng/ml and 2.19 ± 0.16 ng/ml, respectively. No inter-farm differences within the hatchling or harvest-size crocodiles were detected, but growers on Farm 2 had significantly lower plasma CORT than those on Farm 1. However, the grower growth rate coefficients were the same across both farms so the repeated blood sampling design most likely contributed to the difference in CORT values rather than any management procedures. Plasma corticosterone levels significantly increased with time of day. Substantial variation in plasma CORT was observed at each sampling which is not unprecedented in the literature but requires further elucidation. Irrespective, as CORT values were generally low, our results suggest that the farming environment and husbandry practices, as implemented under the Australian industry Code of Practice, are effective as baseline animal welfare measures although they should be viewed as a foundation for further welfare research and not considered static.

Corticosterone in American alligator (Alligator mississippiensis) tail scutes: Evaluating the feasibility of using unconventional samples for investigating environmental stressors

Baseline plasma corticosterone (CORT) concentrations have been widely used to investigate the effects of stressors in wild and captive crocodilians. However, collecting baseline plasma CORT samples from wild crocodilians may be particularly difficult due to the capture and handling protocols used for large individuals. Thus, it may prove beneficial to use recently modified techniques for extracting CORT deposited in keratinized and non-keratinized tissues to better quantify the effects of long-term stress in crocodilians. In this study, we investigated the feasibility of using American alligator (Alligator mississippiensis) tail scute tissues to quantify CORT by collecting blood and tail scutes from 40 alligators before and after a short-term handling stressor. The objective of the current study was to better understand CORT deposition in crocodilian scutes and whether short-term increases in CORT could be detected. We found that CORT can be reliably extracted from alligator scute tissue and quantified using a commercially available enzyme immunoassay. However, there was a significant increase in scute CORT concentrations following an alligator being exposed to a short-term stressor (p = 0.017), although the magnitude of change was less than observed in plasma samples from the same individuals (p = 0.002). Furthermore, our results indicate that there was a significant effect of body condition on an alligator's post-stressor CORT concentration (p = 0.02). While our study is among the first to experimentally examine the usefulness of tissue CORT in crocodilians, a combination of field and laboratory experiments are needed to better understand deposition rates of CORT in scute tissues and to further validate the usefulness of tissue glucocorticoids for evaluating the effects of stress.

Dietary Selenomethionine Administration and Its Effects on the American Alligator (Alligator mississippiensis): Oxidative Status and Corticosterone Levels

Selenium (Se) is an essential nutrient which in excess causes toxicity. The disposal of incompletely combusted coal, which often is rich in Se, into aquatic settling basins is increasing the risk of Se exposure worldwide. However, very few studies have looked at the physiological effects of Se exposure on long-lived, top trophic vertebrates, such as the American alligator (Alligator mississippiensis). During a 7-week period, alligators were fed one of three dietary treatments: mice injected with deionized water or mice injected with water containing 1000 or 2000 ppm selenomethionine (SeMet). One week after the last feeding alligators were bled within 3 min of capture for plasma corticosterone (CORT). A few days later, all alligators were euthanized and whole blood and tail tissue were harvested to measure oxidative damage, an antioxidant-associated transcription factor, and antioxidant enzymes [glutathione peroxidase-1 (GPX1), superoxide dismutase-1 (SOD1), and SOD2] by Western blotting. There was a dose-dependent increase in baseline CORT levels in alligators administered SeMet. Except for blood SOD2 levels, SeMet treatment had no effect (p > 0.05 for all) on oxidative status: oxidative damage, GPX1, SOD1, and muscle SOD2 levels were similar among treatments. Our results illustrate that high levels of Se may act as a stressor to crocodilians. Future studies should investigate further the physiological effects of Se accumulation in long-lived, top-trophic vertebrates.

Effects of selenium exposure on the hematology, innate immunity, and metabolic rate of yellow-bellied sliders (Trachemys scripta scripta)

Selenium (Se) is a naturally occurring essential element that can be toxic to vertebrates at high concentrations. Despite studies that have documented that wild reptile species can accumulate copious amounts of Se, little is known regarding specific toxicologic effects of Se. In this study, 70 juvenile yellow-bellied sliders (Trachemys scripta scripta) were exposed to one of three seleno-L-methionine (SetMet) treatments (control, n = 24; 15 mg/kg, n = 23; and 30 mg/kg, n = 23) via weekly oral gavage for 5 weeks. At the conclusion of the experiment, kidney, liver, muscle, and blood samples were collected for quantitative Se analysis. Turtles in the SeMet treatment groups accumulated significantly higher amounts of Se in all tissue types relative to controls (all p < 0.001). Turtles in the 30 mg/kg SeMet group also accumulated significantly higher amounts of Se compared to the 15 mg/kg group (all p < 0.001). Although toxicity thresholds for reptiles have not been established, Se concentrations in liver tissue from both SeMet treatment groups exceeded reported avian toxicity thresholds for liver tissue. Neither oxygen consumption nor innate bactericidal capacity were impacted by SeMet exposure. However, turtles in the 30 mg/kg SeMet group exhibited anemia, which has been reported in other vertebrates exposed to Se. Furthermore, juvenile T. s. scripta in the 30 mg/kg SeMet group experienced 17% mortality compared to 0% in the 15 mg/kg treatment and control groups. To our knowledge, this study is the first to report dose-dependent Se-associated anemia and mortality in a chelonian species.

Physiological mechanisms constraining ectotherm fright-dive performance at elevated temperatures

Survival of air-breathing, diving ectotherms is dependent on their capacity to optimise the time available for obligate underwater activities, such as predator avoidance. Submergence times are thermally sensitive, with dive durations significantly reduced by increases in water temperature, deeming these animals particularly vulnerable to the effects of climate change. The physiological mechanisms underlying this compromised performance are unclear but are hypothesised to be linked to increased oxygen demand and a reduced capacity for metabolic depression at elevated temperatures. Here, we investigated how water temperature (both acute and chronic exposures) affected the physiology of juvenile estuarine crocodiles (Crocodylus porosus) performing predator avoidance dives (i.e. fright-dives). Diving oxygen consumption, ‘fright’ bradycardia, haematocrit and haemoglobin (indicators of blood oxygen carrying capacity) were assessed at two test temperatures, reflective of different climate change scenarios (i.e. current summer water temperatures, 28°C, and ‘high’ climate warming, 34°C). Diving oxygen consumption rate increased threefold between 28 and 34°C (Q10=7.4). The capacity to depress oxygen demand was reduced at elevated temperatures, with animals lowering oxygen demand from surface levels by 52.9±27.8% and 27.8±16.5% (means±s.e.m.) at 28°C and 34°C, respectively. Resting and post-fright-dive haematocrit and haemoglobin were thermally insensitive. Together these findings suggest decrements in fright-dive performance at elevated temperatures stem from increased oxygen demand coupled with a reduced capacity for metabolic depression.

Accumulation of coal combustion residues and their immunological effects in the yellow-bellied slider (Trachemys scripta scripta)

Anthropogenic activities such as industrial processes often produce copious amounts of contaminants that have the potential to negatively impact growth, survival, and reproduction of exposed wildlife. Coal combustion residues (CCRs) represent a major source of pollutants globally, resulting in the release of potentially harmful trace elements such as arsenic (As), cadmium (Cd), and selenium (Se) into the environment. In the United States, CCRs are typically stored in aquatic settling basins that may become attractive nuisances to wildlife. Trace element contaminants, such as CCRs, may pose a threat to biota yet little is known about their sublethal effects on reptiles. To assess the effects of CCR exposure in turtles, we sampled 81 yellow-bellied sliders (Trachemys scripta scripta) in 2014-2015 from CCR-contaminated and uncontaminated reference wetlands located on the Savannah River Site (Aiken, SC, USA). Specific aims were to (1) compare the accumulation of trace elements in T. s. scripta claw and blood samples between reference and CCR-contaminated site types, (2) evaluate potential immunological effects of CCRs via bacterial killing assays and phytohaemagglutinin (PHA) assays, and (3) quantify differences in hemogregarine parasite loads between site types. Claw As, Cd, copper (Cu), and Se (all p ≤ 0.001) and blood As, Cu, Se, and strontium (Sr; p ≤ 0.015) were significantly elevated in turtles from CCR-contaminated wetlands compared to turtles from reference wetlands. Turtles from reference wetlands exhibited lower bacterial killing (p = 0.015) abilities than individuals from contaminated sites but neither PHA responses (p = 0.566) nor parasite loads (p = 0.980) differed by site type. Despite relatively high CCR body burdens, sliders did not exhibit apparent impairment of immunological response or parasite load. In addition, the high correlation between claw and blood concentrations within individuals suggests that nonlethal tissue sampling may be useful for monitoring CCR exposure in turtles.

Dietary Selenomethionine Administration in the American Alligator (Alligator mississippiensis): Hepatic and Renal Se Accumulation and Its Effects on Growth and Body Condition

Selenium (Se) is an essential trace nutrient, but in excess, it can induce toxicity. Incomplete combustion of coal produces coal combustion wastes, which are enriched in Se and often disposed of in aquatic basins. While a multitude of studies have investigated Se accumulation in vertebrates, few studies have examined its effects on longer-lived top trophic carnivores, such as the American alligator (Alligator mississippiensis). In this study, alligators were fed one of three Dietary Treatments: mice injected with water (controls) or water supplemented with 1000 or 2000 ppm selenomethionine (SeMet). Dietary Treatment significantly affected Se levels in both the liver (p < 0.0001; raw mean ± SE: 1000 ppm group, 35.20 ± 6.32 ppm; 2000 ppm group, 49.97 ± 4.00 ppm) and kidney (p < 0.0001; raw mean ± SE: 1000 ppm group, 101.60 ± 8.64 ppm; 2000 ppm, 96.38 ± 5.81 ppm), which were significantly higher in alligators fed SeMet than in controls. Post-treatment head length, used to control for size variation, was negatively related to both kidney (p = 0.0142) and liver (p = 0.0010) Se concentrations. Dietary treatment with SeMet significantly reduced body condition (1000 ppm, p < 0.0029; 2000 ppm, p = 0.0075), but it significantly increased growth (1000 ppm, p < 0.0001; 2000 ppm, p = 0.0316). Body condition and growth remained unchanged in control alligators (p > 0.05). Our results demonstrate alligators are capable of accumulating high levels of Se through trophic transfer. The positive effects of accumulation on growth may demonstrate Se essentiality, whereas the negative effects on condition may demonstrate toxicity. Accumulation also was associated with mortality, further demonstrating toxicity. Future studies should further investigate the physiological effects of Se accumulation in long-lived, top-trophic carnivores.

Chronic Ingestion of Coal Fly-Ash Contaminated Prey and Its Effects on Health and Immune Parameters in Juvenile American Alligators (Alligator mississippiensis)

Coal-burning power plants supply approximately 37 % of the electricity in the United States. However, incomplete combustion produces ash wastes enriched with toxic trace elements that have historically been disposed of in aquatic basins. Organisms inhabiting such habitats may accumulate these trace elements; however, studies investigating the effects on biota have been primarily restricted to shorter-lived, lower-trophic organisms. The American alligator (Alligator mississippiensis), a long-lived, top-trophic carnivore, has been observed inhabiting these basins, yet the health or immune effects of chronic exposure and possible accumulation remains unknown. In this study, we investigated how chronic dietary ingestion of prey contaminated with coal combustion wastes (CCWs) for 25 months, and subsequent accumulation of trace elements present in CCWs, affected juvenile alligator immune function and health. Alligators were assigned to one of four dietary-treatment groups including controls and those fed prey contaminated with CCWs for one, two, or three times a week. However, no effect of Dietary Treatment (p > 0.05) was observed on any immune parameter or hematological or plasma analyte we tested. Our results suggest that neither exposure to nor accumulation of low doses of CCWs had a negative effect on certain aspects of the immune and hematological system. However, future studies are required to elucidate this further.

Hepatic and renal trace element concentrations in American alligators (Alligator mississippiensis) following chronic dietary exposure to coal fly ash contaminated prey

Little is known about the propensity of crocodilians to bioaccumulate trace elements as a result of chronic dietary exposure. We exposed 36 juvenile alligators (Alligator mississippiensis) to one of four dietary treatments that varied in the relative frequency of meals containing prey from coal combustion waste (CCW)-contaminated habitats vs. prey from uncontaminated sites, and evaluated tissue residues and growth rates after 12 mo and 25 mo of exposure. Hepatic and renal concentrations of arsenic (As), cadmium (Cd) and selenium (Se) varied significantly among dietary treatment groups in a dose-dependent manner and were higher in kidneys than in livers. Exposure period did not affect Se or As levels but Cd levels were significantly higher after 25 mo than 12 mo of exposure. Kidney As and Se levels were negatively correlated with body size but neither growth rates nor body condition varied significantly among dietary treatment groups. Our study is among the first to experimentally examine bioaccumulation of trace element contaminants in crocodilians as a result of chronic dietary exposure. A combination of field surveys and laboratory experiments will be required to understand the effects of different exposure scenarios on tissue residues, and ultimately link these concentrations with effects on individual health.

Unexpected lower testosterone in faster growing farmed saltwater crocodile (Crocodylus porosus) hatchlings

Agricultural production of the saltwater crocodile (Crocodylus porosus) is an emergent industry in northern Australia with many of the factors affecting production remaining unknown. In this study, we sought to expand upon our previous findings of reference corticosterone and immune function by reporting baseline sex hormone levels [testosterone (TEST) and estradiol (ESTR)] and their association with growth. This was achieved by sampling 253 hatchling crocodiles repeatedly at 3, 6, and 9months of age. Sampling age had a significant effect on both TEST (p<0.001) and ESTR (p<0.001) suggesting climatic/abiotic factors have an influence even in prepubescent crocodiles. Stress, as measured by plasma corticosterone, had no detectable effect on plasma ESTR or TEST levels. Unexpectedly however, TEST was higher in slower-growing crocodiles, which is contrary to what has been reported for the American alligator. ESTR was not associated with growth.

Evaluating the effect of sample type on American alligator (Alligator mississippiensis) analyte values in a point-of-care blood analyser

The assessment of wildlife health has been enhanced by the ability of point-of-care (POC) blood analysers to provide biochemical analyses of non-domesticated animals in the field. However, environmental limitations (e.g. temperature, atmospheric humidity and rain) and lack of reference values may inhibit researchers from using such a device with certain wildlife species. Evaluating the use of alternative sample types, such as plasma, in a POC device may afford researchers the opportunity to delay sample analysis and the ability to use banked samples. In this study, we examined fresh whole blood, fresh plasma and frozen plasma (sample type) pH, partial pressure of carbon dioxide (PCO2), bicarbonate (HCO3 (-)), total carbon dioxide (TCO2), base excess (BE), partial pressure of oxygen (PO2), oxygen saturation (sO2) and lactate concentrations in 23 juvenile American alligators (Alligator mississippiensis) using an i-STAT CG4+ cartridge. Our results indicate that sample type had no effect on lactate concentration values (F 2,65 = 0.37, P = 0.963), suggesting that the i-STAT analyser can be used reliably to quantify lactate concentrations in fresh and frozen plasma samples. In contrast, the other seven blood parameters measured by the CG4+ cartridge were significantly affected by sample type. Lastly, we were able to collect blood samples from all alligators within 2 min of capture to establish preliminary reference ranges for juvenile alligators based on values obtained using fresh whole blood.

Providencia rettgeri septicaemia in farmed crocodiles

Bacterial septicaemia is a major cause of morbidity and mortality in farmed saltwater crocodiles (Crocodylus porosus) in the Northern Territory. Providencia rettgeri is the most common aetiological agent. Efficacy of antibiotic treatment is dubious and there are high levels of resistance to antibiotics commonly used by farms, underlining the need for exploration of new approaches to managing the disease.