Physiological changes in brushtail possums, Trichosurus vulpecula, transferred from the wild to captivity

Pharmacokinetics of a topical application of moxidectin in bare-nosed wombats (Vombatus ursinus)

Sarcoptic mange is a debilitating disease that affects bare-nosed wombats (Vombatus ursinus). One of the drugs currently used for treatment is moxidectin, as it has a relatively high efficacy against endo and ectoparasites and side effects are uncommon in domestic species, thus it is considered a relatively safe drug to use at the recommended doses. Developing further understanding of the pharmacokinetics of moxidectin will aid in developing treatment regimens for sarcoptic mange in wombats. Here we analyzed the pharmacokinetic parameters of using 100 ml of moxidectin (5 g/l) applied topically. We found that mean peak plasma concentration was 0.50 ng/ml and half-life was 8 days. Moxidectin was excreted in scats with the mean peak concentration of 2461.43 ng/g (on a dry matter basis). Our study has provided the pharmacokinetic parameters of a commonly used treatment for sarcoptic mange in wombats. There were no adverse side effects recorded in the wombats after applying moxidectin topically. This study replicated real-world conditions using topical application on free-living wombats. The relatively low plasma concentration suggests the drug is not accumulating in the blood stream and is excreted via scats.

The Cranial Morphology of the Black-Footed Ferret: A Comparison of Wild and Captive Specimens

The black-footed ferret (Mustela nigripes), a North American mustelid species, was once found abundantly throughout the Midwest until the extreme decline in prairie dogs (Cynomys spp.), the black-footed ferret's primary food source, brought the species to near-extinction. Subsequently, the Black-Footed Ferret Recovery Program was created in the 1980s with a goal of bringing all remaining individuals of the species into captivity in order to breed the species back to a sustainable population level for successful reintroduction into the wild. While many components of the ferrets' health were accounted for while in captivity-especially those affecting fecundity-this study aims to assess the effects that captivity may have had on their cranial morphology, something that has not been widely studied in the species. In a previous study, we showed that the captive ferrets had significant oral health problems, and here we aim to document how the captive diet also affected their skull shape. For this study, 23 cranial measurements were taken on the skulls of 271 adult black-footed ferrets and 53 specimens of two closely related species. Skulls were divided based on sex, species, captivity status and phase of captivity and compared for all measurements using stepwise discriminant analysis as well as principal component analysis derived from the combined variables. We found that there are significant differences between captive and wild specimens, some of which are larger than interspecific variation, and that a diet change in the captive specimens likely helped decrease some of these differences. The results suggest that captivity can cause unnatural cranial development and that diet likely has a major impact on cranial morphology.

Chronic captivity stress in wild animals is highly species-specific

Wild animals are brought into captivity for many reasons-conservation, research, agriculture and the exotic pet trade. While the physical needs of animals are met in captivity, the conditions of confinement and exposure to humans can result in physiological stress. The stress response consists of the suite of hormonal and physiological reactions to help an animal survive potentially harmful stimuli. The adrenomedullary response results in increased heart rate and muscle tone (among other effects); elevated glucocorticoid (GC) hormones help to direct resources towards immediate survival. While these responses are adaptive, overexposure to stress can cause physiological problems, such as weight loss, changes to the immune system and decreased reproductive capacity. Many people who work with wild animals in captivity assume that they will eventually adjust to their new circumstances. However, captivity may have long-term or permanent impacts on physiology if the stress response is chronically activated. We reviewed the literature on the effects of introduction to captivity in wild-caught individuals on the physiological systems impacted by stress, particularly weight changes, GC regulation, adrenomedullary regulation and the immune and reproductive systems. This paper did not review studies on captive-born animals. Adjustment to captivity has been reported for some physiological systems in some species. However, for many species, permanent alterations to physiology may occur with captivity. For example, captive animals may have elevated GCs and/or reduced reproductive capacity compared to free-living animals even after months in captivity. Full adjustment to captivity may occur only in some species, and may be dependent on time of year or other variables. We discuss some of the methods that can be used to reduce chronic captivity stress.

The role of glucocorticoids in the vertebrate response to weather

Changes in the environment related to inclement weather can threaten survival and reproductive success both through direct adverse exposure and indirectly by decreasing food availability. Glucocorticoids, released during activation of the hypothalamic-pituitary-adrenal axis as part of the stress response, are an important candidate for linking vertebrate coping mechanisms to weather. This review attempts to determine if there is a consensus response of glucocorticoids to exposure to weather-related stimuli, including food availability, precipitation, temperature and barometric pressure. The included studies cover field and laboratory studies for all vertebrate taxa, and are separated into four exposure periods, e.g., hours, days, weeks and months. Each reported result was assigned a score based on the glucocorticoid response, e.g., increased, no change, or decreased. Short-term exposure to weather-related stimuli, of up to 24 h, is generally associated with increased glucocorticoids (79% of studies), suggesting that these stimuli are perceived as stressors by most animals. In contrast, the pattern for exposures longer than 24 h shows more variation, even though a majority of studies still report an increase (64%). Lack of glucocorticoid increases appeared to result from instances where: (1) prolonged exposure was a predictable part of the life history of an animal; (2) environmental context was important for the ultimate effect of a stimulus (e.g., precipitation limited food availability in one environment, but increased food in another); (3) prolonged exposure induced chronic stress; and (4) long-term responses appeared to reflect adaptations to seasonal shifts, instead of to short-term weather. However, there is a strong bias towards studies in domesticated laboratory species and wild animals held in captivity, indicating a need for field studies, especially in reptiles and amphibians. In conclusion, the accumulated literature supports the hypothesis that glucocorticoids can serve as the physiological mechanism promoting fitness during inclement weather.

Limitations in the isolation and stimulation of splenic mononuclear cells in a dasyurid marsupial, Phascogale calura

OBJECTIVE

Marsupials suffer from an increasing number of stressors in this changing world. Functional studies are thus needed to broaden our understanding of the marsupial immune system. The red-tailed phascogale (Phascogale calura) is a small Australian marsupial previously used in descriptive immunological studies. Here, we aimed to develop functional assays by isolating and stimulating blood and spleen mononuclear cells in vitro.

RESULTS

While peripheral blood mononuclear cell (PBMC) were relatively easy to isolate, only 105 mononuclear cells (> 90% purity and > 75% viability) could be recovered from the spleen, independently of the sex and age of the animal or the centrifugation time and speed tested. The pores of the mesh sieve used for tissue homogenization might have been too big to yield a single cell suspension. Nevertheless, in spite of the overall low number of cells recovered, PBMC and splenic mononuclear cells were successfully activated in preliminary trials with phytohemaglutinin. This activation state was evidenced by a change in shape and the presence of small cell aggregations in the mitogen-stimulated cultures. A non-radioactive colorimetric assay was also performed to confirm cell proliferation in these wells. This work highlights the importance of developing and reporting detailed methodological protocols in non-traditional research species.

Chronic stress and the introduction to captivity: How wild house sparrows (Passer domesticus) adjust to laboratory conditions

The conditions of captivity can cause chronic stress in wild animals. Newly-captured animals may experience weight loss, elevated glucocorticoid hormones, increased heart rate, increased resting adrenomedullary activation, and an altered heart rate response to acute stressors. As captivity conditions persist, chronic stress may decrease as animals adjust to the stressors of captivity. In this study, house sparrows (Passer domesticus) were captured from the wild, fitted with heart rate transmitters in a minor surgical process, and individually housed in an indoor bird facility. Mass, baseline corticosterone, resting heart rate, resting adrenomedullary activation, and the acute heart rate response to a sudden noise were measured over the course of the first 6 weeks of captivity. Birds lost weight during the first weeks of captivity, which was regained by week 5. Baseline corticosterone peaked at day 7, decreased sharply by day 11, and continued to decrease throughout the 6 weeks. Although heart rate in the first 24 h could not be collected, daytime heart rate decreased from day 1 through day 20, where it reached a stable plateau. Daytime heart rate variability decreased through the entire 6 weeks, which may indicate a gradual shift from sympathetic to parasympathetic nervous system regulation of heart rate. The acute heart rate response to a sudden noise lasted longer at day 6 than earlier or later in captivity. In conclusion, the data indicate that the different physiological systems associated with chronic stress adjust to captivity over different timelines.

Oral health correlates of captivity

The predominant diet fed to captive carnivores in North America consists of ground meat formulated to provide full nutritional requirements. However, this ground meat diet completely lacks the mechanical properties (i.e., toughness and hardness) of the foods these animals would consume in the wild. The goal of this study is to evaluate the effect of captivity on oral health by comparing the prevalence of periodontal disease and dental calculus accumulation in wild and captive lions and tigers (Panthera leo and Panthera tigris), and to also correlate oral health with cranial morphology in these specimens. To achieve this, 34 adult lion and 29 adult tiger skulls were scored for the presence and extent of dental calculus and periodontal disease. These oral health scores were also compared to cranial deformations examined in a previous study. We found that the occurrence and severity of calculus buildup and periodontal disease was significantly higher in captive felids compared to their wild counterparts. Further, higher calculus accumulation occurred on the posterior teeth when compared to the anterior teeth, while an opposite trend for periodontal disease was observed. We also found a significant correlation between oral health and cranial morphology of lions and tigers. The results suggest that food mechanical properties are significant factors contributing to oral health in felids.

Corticosterone stress response shows long-term repeatability and links to personality in free-living Nazca boobies

The concept of "coping styles", or consistently different responses to stressors, is of broad interest in behavioral ecology and biomedicine. Two critical predictions of this concept are individual consistency of neurophysiological and behavioral responses (relative to population variability) and a negative relationship between aggression/proactivity and hypothalamic-pituitary-adrenal axis reactivity. Recent studies failed to provide strong support for these predictions, especially outside of strictly controlled conditions, and long-term measures to test the first prediction are rare. Here, we demonstrate individual repeatability across 2-3years of maximum circulating corticosterone concentration [CORT] and area under the [CORT] response curve (AUCI) during a standard capture-restraint test in wild, free-living adult Nazca boobies (Sula granti). We also show that the stress response predicts the personality traits aggression and anxiety in these birds (measured in the wild); however, the strength of these results was weak. Maximum [CORT] and AUCI showed higher repeatability between years than baseline [CORT]. After controlling breeding status, sex, mass, date sampled, and their interactions, baseline [CORT] was most closely related to personality traits, followed by AUCI, and then maximum [CORT]. The direction of these relationships depended on whether the testing context was social or non-social. [CORT] parameters had little to no relationship with cross-context plasticity in personality traits. Our results generally affirm two critical predictions of coping styles, but match the emerging trend that these relationships are weak in the wild, and may depend on testing context.

Measures of physiological stress: a transparent or opaque window into the status, management and conservation of species?

Conservation physiology proposes that measures of physiological stress (glucocorticoid levels) can be used to assess the status and future fate of natural populations. Increases in glucocorticoids may reflect a more challenging environment, suggesting that the influence of human activities on free-living animals could be quantified by measuring glucocorticoids. Biomedical studies suggest that chronic increases in glucocorticoids can have detrimental effects on survival and reproduction, which could influence the viability of populations. Here, we discuss the use of measurements of glucocorticoids in conservation physiology. We first provide an overview of the different methods to quantify glucocorticoids and their utility in conservation physiology. We then discuss five questions we think are essential for conservation physiologists to address. We highlight how intrinsic (e.g. sex, reproductive status, age, recent experiences) and ecological factors (e.g. predation, food availability, snowfall) can, by themselves or through their interactions with anthropogenic disturbances, affect the physiological stress response and mask any general patterns about the effects of anthropogenic disturbances on glucocorticoids. Using a meta-analysis, we show that anthropogenic disturbances are consistently associated with increased glucocorticoids regardless of the type of human disturbance. We also show that males may be more sensitive to anthropogenic disturbances than females and that faecal glucocorticoids, but not baseline plasma glucocorticoids, consistently increase in response to anthropogenic disturbances. Finally, we discuss how increases in glucocorticoids in free-living animals can sometimes enhance survival and reproduction. Unfortunately, our literature analysis indicates that this observation has not yet gained traction, and very few studies have shown that increases in glucocorticoid levels resulting from anthropogenic disturbances decrease survival or reproduction. We think that the use of measures of glucocorticoids in conservation physiology has tremendous potential, but there are still a number of methodological concerns, in addition to several crucial questions that should be addressed.

Assessing stability of body weight in the brushtail possum (Trichosurus vulpecula)

When conducting controlled laboratory studies with non-traditional laboratory animals it is important that methods for determining body weight stability are reliable. This helps ensure the health and welfare of animals when they are maintained during periods of free feeding or food restriction. This study compared different methods for determining body weight stability in six common brushtail possums (Trichosurus vulpecula) maintained on a free-feeding diet under laboratory conditions. A criterion of five consecutive weighings with less than ±2.5% change across days and no more than two consecutive days of weight loss or weight gain was judged to be the most suitable criteria for determining stability. It is important to study non-traditional animals, especially endangered or pest species, under controlled laboratory conditions and to have robust methods for establishing body weight stability.

Effects of natural weathering conditions on faecal cortisol metabolite measurements in the greater bilby (Macrotis lagotis)

Natural weathering conditions can influence faecal cortisol metabolite (FCM) measurements in wildlife if fresh faeces cannot be collected immediately following defaecation. In this study, we evaluated this issue in a threatened Australian marsupial, the greater bilby (Macrotis lagotis). Fresh (<12 h since defaecation) faecal samples (n = 19 pellets per bilby) were collected one morning from seven adult bilbies kept in captivity. One control faecal sample (Day 1) from each bilby was immediately frozen. The remaining faecal pellets were randomly positioned outdoors. Subsequently, we froze one faecal pellet every 24 h for 19 days. FCM levels in bilby faeces were quantified using an enzyme-immunoassay. Mean FCM levels showed variation (daily mean coefficients of variation [CV %]) of 56.83–171.65% over 19 days. Overall, FCM levels were affected by exposure time; however, multiple comparisons showed that no significant change in FCM occurred after environmental exposure (no significant difference in mean FCM between control (Day 1) with any of the exposure days (Days 2–19). Individuals and sex also affected FCM levels. We found no correlation between mean daily CVs with daily minimum–maximum temperatures or rainfall. Our results indicate that FCM in bilby faeces is fairly stable to long-term environmental exposure (19 days). In future, freshly excreted bilby faeces (where the sample maintains a distinct odour for 9–13 days) should be used to study FCM levels in wild bilbies.

Haematology and serum biochemistry of adult free-ranging mountain brushtail possums (Trichosurus cunninghami), including correlations with season, sex, age, habitat type and disease status

For many wildlife species only limited data are available on haematology and blood biochemistry for free-ranging populations because these are often difficult to obtain. We collected blood samples from wild adult mountain brushtail possums (Trichosurus cunninghami) in the Strathbogie Ranges, Victoria (Australia), over two years, to provide reference values for haematological and some serum biochemical parameters (serum protein, sodium, chloride, potassium, urea, creatinine, creatine kinase and cortisol) for free-ranging animals. We also investigated patterns associated with sex, season, age, habitat type and disease status, including a form of skin disease (rumpwear – one of the major diseases of brushtail possums) and parasite loads. Values for several blood parameters correlated with sex, and most also changed significantly with season. Eosinophil counts increased significantly with the number of strongyle eggs in faeces, and packed cell volume decreased significantly with increasing numbers of ticks. Surprisingly, there was a significant negative relationship between mean population serum cortisol concentrations and the prevalence of rumpwear. Serum sodium and chloride concentrations were significantly lower in possums with moderate to severe rumpwear; however, the biological significance of this is unclear. While there is a growing body of data on the blood parameters of marsupials, these are mainly derived from captive animals, or single sample sets from wild populations, thus are unlikely to accurately reflect the changing status of wild animals/populations across seasons and under varying environmental conditions and parasite loads. More comprehensive, longer-term data from free-ranging marsupial populations, such as those presented here, provide extremely important reference data to aid in determining the health status of wild populations and interpreting data collected from individuals.

Non-invasive assessment of stress in captive numbats, Myrmecobius fasciatus (Mammalia: Marsupialia), using faecal cortisol measurement

Annual patterns of faecal cortisol metabolite (FCM) secretion were examined in six captive numbats (Myrmecobius fasciatus). The use of enzyme-immunoassay for the measurement of FCM in the numbat faeces was validated using an adrenocorticotropic hormone (ACTH) challenge and the resultant FCM measurements represent the first description of adrenal endocrinology in this species. Total overall, baseline and peak FCM mean concentrations varied according to individual, but not gender. For males, mean baseline and overall FCM secretion was higher in spring in summer (compared to winter and autumn) and was elevated during the breeding season. For females, mean baseline FCM secretion did not differ by season or breeding season, but mean overall FCM secretion was elevated during the breeding season. Thus, male (but not female) numbats display an annual change in FCM secretion that is strongly linked to their seasonal pattern of reproduction. Significant FCM elevations (n=178) were observed in response to 20 different stressors, with these stressors being allocated to one of six categories: ANIM, ENVIRO, HAND, HEALTH, MAN and UNK. The mean proportion of positive responses to each category varied according to category, season and breeding season, but did not vary by individual or gender. ANIM and HEALTH stressors elicited a higher response rate than all other categories and an increase in the number of ANIM, ENVIRO, and HEALTH stressors were observed during the breeding season. Although there were multiple stressors within the captive environment that the numbats reacted to, this did not translate into a welfare issue.

Assessing acute effects of trapping, handling, and tagging on the behavior of wildlife using GPS telemetry: a case study of the common brushtail possum

Trapping, handling, and deployment of tracking devices (tagging) are essential aspects of many research and conservation studies of wildlife. However, often these activities place nonhuman animals under considerable physical or psychological distress, which disrupts normal patterns of behavior and may ultimately result in deleterious effects on animal welfare and the validity of research results. Thus, knowledge of how trapping, handling, and tagging alter the behavior of research animals is essential if measures to ameliorate stress-related effects are to be developed and implemented. This article describes how time-stamped location data obtained by global-positioning-system telemetry can be used to retrospectively characterize acute behavioral responses to trapping, handling, and tagging in free-ranging animals used for research. Methods are demonstrated in a case study of the common brushtail possum, a semiarboreal phalangerid marsupial native to Australia. The study discusses possible physiological causes of observed effects and offers general suggestions regarding simple means to reduce trapping-handling-and-tagging-related stress in field studies of vertebrates.

Hypothalamus-pituitary-adrenal axis activity and the subsequent response to chronic stress differ depending upon life history stage

The hypothalamus-pituitary-adrenal (HPA) axis is modulated seasonally in many species, and chronic stress can alter HPA functioning. However, it is not known how these two factors interact - are there particular life history stages when animals are more or less vulnerable to chronic stress? We captured wild house sparrows (Passer domesticus) in Massachusetts during six different life history stages: early and late winter, pre-laying, breeding, late breeding, and molt. At each time point, we tested HPA function by measuring baseline and stress-induced corticosterone (CORT), negative feedback in response to an injection of dexamethasone, and maximum adrenal response through an injection of adrenocorticotropic hormone. We then brought birds into captivity as a model for chronic stress, and repeated the four tests 5 days later. At capture, all HPA variables varied seasonally. Birds showed increased negative feedback during breeding and late winter compared to pre-laying. Furthermore, birds during the late breeding period had down-regulated their HPA axis, perhaps in preparation for molt. After 5 days of captivity, house sparrows lost ∼11% of initial body mass, although birds lost more weight during molt and early winter. Overall, captive sparrows showed elevated baseline CORT and increased negative feedback, although negative feedback did not show a significant increase during any individual life history stage. During most of the year, adrenal sensitivity was unaffected by captivity. However, during late breeding and molt, adrenal sensitivity increased during captivity. Taken together, these data provide further support that HPA function naturally varies throughout the year, with the interesting consequence that molting birds may potentially be more vulnerable to a chronic stressor such as captivity.

Interpreting indices of physiological stress in free-living vertebrates

When vertebrate physiological ecologists use the terms 'stress' or 'physiological stress', they typically mean the level of hypothalamus-pituitary-adrenal (HPA-) axis activation. Measurements of stress hormone concentrations (e.g. glucocorticoids in blood, urine or faeces), leukocytes (e.g. the neutrophil-lymphocyte ratio or heterophil equivalent), immunofunction (e.g. innate, cell-mediated or humoral immunity measures) and regenerative anaemia (e.g. mean erythrocyte volume and red blood cell distribution width) have all been used to estimate HPA-axis activity in free-living vertebrates. Stress metrics have provided insights into aspects of autecology or population regulation that could not have been easily obtained using other indices of population wellbeing, such as body condition or relative abundance. However, short- and long-term stress (often problematically termed acute and chronic stress, respectively) can interact in unpredictable ways. When animals experience trapping and handling stress before blood, faeces and/or urine is sampled, the interaction of short- and long-term stress can confound interpretation of the data, a fact not always acknowledged in studies of stress in free-living vertebrates. This review examines how stress metrics can be confounded when estimates of HPA-axis activation are collected for free-living vertebrates and outlines some approaches that can be used to help circumvent the influence of potentially confounding factors.

Within seasons and among years: when are corticosterone levels repeatable?

Hormones play a central role in integrating internal and external cues to help mediate life-history decisions as well as changes in behavior and physiology of individuals. Describing the consistency of endocrine traits within and among individuals is an important step for understanding whether hormonal traits are dependable predictors of phenotypes that selection could act upon. However, few long-term field studies have investigated the individual consistency of hormonal traits. Glucocorticoid hormones mediate homeostatic responses to environmental variation as well as stress responses to acute, unpredictable disturbances. We characterized the repeatability of plasma corticosterone concentrations in two species of free-living passerines across multiple years. We found repeatability in baseline corticosterone concentrations in both sexes of great tits (Parus major) and in female tree swallows (Tachycineta bicolor) within the breeding season but no repeatability of this trait among seasons or across years. Stress-induced levels of corticosterone were only assessed in great tits and were not repeatable in either sex. Our data suggest that in line with their function in mediating responses of individuals to longer-term and acute demands, both baseline and stress-induced plasma corticosterone concentrations are rather plastic traits. However, individuals may differ in their degree of trait plasticity and hence in behavioral and physiological responses to a variety of organismal challenges.

Does habitat fragmentation cause stress in the agile antechinus? A haematological approach

Although the vertebrate stress response is essential for survival, frequent or prolonged stress responses can result in chronic physiological stress, which is associated with a suite of conditions that can impair survivorship and reproductive output. Anthropogenic habitat fragmentation and degradation are potential stressors of free-living vertebrates, and in theory could result in chronic stress. To address this issue, we compared haematological indicators of stress and condition in agile antechinus (Antechinus agilis) populations in 30 forest fragments and 30 undisturbed, continuous forest sites (pseudofragments) in south-eastern Australia over 2 years. In peripheral blood, the total leucocyte count was lower and the neutrophil/lymphocyte ratio and percentage of eosinophils in the total leucocyte population was higher in fragment than pseudofragment populations, indicating that fragment populations were probably experiencing higher levels of stress hormone-mediated and/or parasite infection-related chronic physiological stress. The total erythrocyte count and haematocrit were higher and mean erythrocyte haemoglobin content was lower in fragment than pseudofragment populations. This suggests that fragment populations showed possible signs of regenerative anaemia, a syndrome associated with elevated hypothalamus-pituitary-adrenal axis mediated stress. However, mean erythrocyte volume was also lower in fragments, and red blood cell distribution width did not differ between the study populations, findings which were not consistent with this diagnosis. Whole blood and mean cell haemoglobin concentrations were similar in fragment and pseudofragment populations. We suggest that where anthropogenic activity results in habitat fragmentation and degradation, chronic stress could contribute to a decline in agile antechinus populations. The broader implication is that chronic stress could be both symptomatic of, and contributing to, decline of some vertebrate populations in anthropogenically fragmented and degraded habitats.

From process to pattern: how fluctuating predation risk impacts the stress axis of snowshoe hares during the 10-year cycle

Predation is a central organizing process affecting populations and communities. Traditionally, ecologists have focused on the direct effects of predation--the killing of prey. However, predators also have significant sublethal effects on prey populations. We investigated how fluctuating predation risk affected the stress physiology of a cyclic population of snowshoe hares (Lepus americanus) in the Yukon, finding that they are extremely sensitive to the fluctuating risk of predation. In years of high predator numbers, hares had greater plasma cortisol levels at capture, greater fecal cortisol metabolite levels, a greater plasma cortisol response to a hormone challenge, a greater ability to mobilize energy and poorer body condition. These indices of stress had the same pattern within years, during the winter and over the breeding season when the hare:lynx ratio was lowest and the food availability the worst. Previously we have shown that predator-induced maternal stress lowers reproduction and compromises offspring's stress axis. We propose that predator-induced changes in hare stress physiology affect their demography through negative impacts on reproduction and that the low phase of cyclic populations may be the result of predator-induced maternal stress reducing the fitness of progeny. The hare population cycle has far reaching ramifications on predators, alternate prey, and vegetation. Thus, predation is the predominant organizing process for much of the North American boreal forest community, with its indirect signature--stress in hares--producing a pattern of hormonal changes that provides a sensitive reflection of fluctuating predator pressure that may have long-term demographic consequences.

High possum mortality on urban roads: implications for the population viability of the common brushtail and the common ringtail possum

Animal–vehicle collisions impact wildlife populations and in the northern suburbs of Sydney, both the common brushtail possum (Trichosurus vulpecula) and the common ringtail possum (Pseudocheirus peregrinus) are killed in large numbers. Over a two-year period almost 600 road-killed possums were observed from 217 road surveys covering over 7800 km, equating to 5.45 possums per week over the 36-km study area. Surveys were conducted along roads where the environment ranged from low-rise suburban to continuous sclerophyll forest. Significantly more ringtail possums were observed as road-kill, outnumbering brushtail possums by almost three to one. No sex bias was found amongst road-killed ringtail possums; however, seasonal trends and weight fluctuations were significant, with both males and females being at their lowest weights during the autumn breeding season. For brushtail possums a bias towards young males was observed. Sex and weight of road-killed brushtail possums were comparable to live-trap data from a previous study in the same location. In areas of such high possum mortality, wildlife managers may need to take action to mitigate possum road-kill.

Mitogen-induced responses in lymphocytes from platypus, the Tasmanian devil and the eastern barred bandicoot

OBJECTIVE

As the platypus (Ornithorhynchus anatinus), the Tasmanian devil (Sarcophilus harrisi) and the eastern barred bandicoot (Perameles gunni) are currently at risk of serious population decline or extinction from fatal diseases in Tasmania, the goal of the present study was to describe the normal immune response of these species to challenge using the lymphocyte proliferation assay, to give a solid basis for further studies.

METHODS

For this preliminary study, we performed lymphocyte proliferation assays on peripheral blood mononuclear cells (PBMC) from the three species. We used the common mitogens phytohaemagglutinin (PHA), concanavalin A (ConA), lipopolysaccharide (LPS) and pokeweed mitogen (PWM).

RESULTS

All three species recorded the highest stimulation index (SI) with the T-cell mitogens PHA and ConA. Tasmanian devils and bandicoots had greater responses than platypuses, although variability between individual animals was high.

CONCLUSION

For the first time, we report the normal cellular response of the platypus, the Tasmanian devil and the eastern barred bandicoot to a range of commonly used mitogens.

Seasonal glucocorticoid responses to capture in wild free-living mammals

We determined baseline and capture-induced glucocorticoid concentrations during two different seasons in three species of wild free-living rodents: brown lemmings ( Lemmus trimucronatus), golden-mantled ground squirrels ( Spermophilus saturatus), and yellow-pine chipmunks ( Tamias amoenus). Initial blood samples were obtained within 3 min of capture, so that initial glucocorticoid levels reflect baseline titers of undisturbed animals. Animals were held for an additional 30 min, when a second blood sample was taken to measure stress-induced glucocorticoid titers. The primary glucocorticoid differed in each species. Lemmings secreted extremely large amounts of corticosterone (as high as 8,000 ng/ml). These high concentrations were accompanied by high corticosterone-binding globulin capacity and resistance to negative feedback. Squirrels and chipmunks secreted a mixture of cortisol and corticosterone (10–400 ng/ml). In males of all three species and female squirrels and chipmunks, glucocorticoid levels were significantly elevated 30 min after capture. Baseline and 30-min glucocorticoid levels differed seasonally in each species. Levels were higher during summer (with no snow cover) than in spring (with ∼60% snow cover) in female lemmings, higher during breeding than before hibernation in squirrels, and higher postreproductively than during breeding in chipmunks. Together, these data indicate that glucocorticoid responses to stress in these free-living species are similar to those in laboratory species, but the magnitude of the response appears to depend on life-history features specific to each species.

Culture and Stimulation of Tammar Wallaby Lymphocytes

We describe the culture and stimulation of lymphocytes from the model marsupial, the tammar wallaby (Macropus eugenii). We also describe the capacity of tammar wallaby lymphocytes isolated from blood, spleen and lymph nodes to produce soluble immunomodulatory factors. Culture conditions were optimized for mitogen-driven stimulation using the plant lectin phytohaemagglutinin (PHA). Products secreted by stimulated cells were harvested and crudely fractionated before they were added back to freshly isolated lymphocytes. Using the 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) assay, both stimulatory and inhibitory bioactive factors were detected in serum-free supernatants harvested from mitogen-treated peripheral blood mononuclear cells. This paper describes the capacity of leukocytes of the tammar wallaby to respond to mitogenic stimulation and to produce soluble, low-molecular-weight bioactive molecules that possess cytokine-like activity.

Adrenal and white cell count responses to chronic stress in gestating and postpartum females of the viviparous skink Egernia whitii (Scincidae)

This study investigates the relationships between plasma corticosterone concentrations and white cell counts in captive females of the viviparous lizard Egernia whitii during two phases of the reproductive cycle. Gestating and postpartum females were captured in the field and held in the laboratory for 4 weeks. Plasma corticosterone and progesterone concentrations and white blood cell counts were examined in blood samples taken at capture and after 24 h, 1 week, and 4 weeks in captivity. At 24 h after capture, plasma corticosterone concentrations in both groups had increased significantly compared with initial values but then returned to initial concentrations after 1 week in captivity and remained low in the 4 week samples. Plasma progesterone concentrations remained elevated in the gestating females until the week 4 sample, just prior to parturition. The hormone data suggest that capture and captivity did not represent a significant long-term stressor to these animals. The increase in plasma corticosterone concentration was associated with heterophilia in the differential leucocyte count in both groups of females. Lymphocyte numbers decreased only in gestating females, suggesting that reproductive status may influence the interaction between adrenal activity and immune function.

Faecal corticosteroid levels as an indicator of well-being in the tammar wallaby, Macropus eugenii

Faecal corticosteroid levels were measured in five female tammar wallabies, Macropus eugenii, at Macquarie University, NSW, Australia, to assess their reliability as indicators of well-being in this species. Animals were challenged with a change in conditions over the course of approximately 1 week, comprising movement from group yards to isolation in individual yards, in order to impose a disturbance to homeostasis ("stress"). Faecal samples were collected in 24-h intervals during the study period and analysed for corticosteroid concentration. The use of enzyme immunoassay for the measurement of corticosteroids in marsupial faecal pellets was validated. We observed a significant increase in faecal corticosteroids upon isolation and movement. Faecal corticosteroids remained above initial levels in all five animals throughout the study period, suggesting that faecal corticosteroid concentrations may be a useful indicator of a change in animal well-being. Faecal corticosteroid levels did not correlate with serum cortisol levels, implying that the use of noninvasive methods in a representative marsupial, the tammar wallaby, has the potential to provide information that is not readily apparent using blood-based protocols. Faecal corticosteroid analysis therefore has the potential for application in monitoring the well-being of captive and managed marsupial populations, as part of an integrated system of measures of animal health and well-being.

Establishing and maintaining an operant research facility with brushtail possums (Trichosurus vulpecula)

The common brushtail possum (Trichosurus vulpecula) is a readily accessible marsupial that has been shown to adapt relatively well to captivity. The aim of this paper is to outline the husbandry procedures, experimental equipment, and methodologies used successfully within our possum colony since 1995.

Adaptation of wild-caught Tasmanian devils (Sarcophilus harrisii) to captivity: evidence from physical parameters and plasma cortisol concentrations

This study assessed whether capture and transferral into captivity represents a significant stressor to Tasmanian devils. Four male and four female devils were captured in the wild and housed for 6 months in captivity in male–female pairs. Blood samples were collected for cortisol assay at capture, every 24 h for the first 4 days, and then monthly; body weight and tail width were monitored weekly. In the males, mean plasma cortisol concentrations were highest (49 ± 9.19 ng mL–1) at the time of initial capture; cortisol concentrations declined significantly after 48 h in captivity (9.2 ± 5.96 ng mL–1) and did not change significantly over the months in captivity. Females exhibited a different pattern: plasma cortisol concentrations were highest (74.0 ± 3.24 ng mL–1) in the initial sample, but mean concentrations remained elevated in samples taken at 24, 48 and 96 h after initial capture, and did not exhibit a significant decline (to 20.65 ± 8.95 ng mL–1) until 4 weeks after capture. During the first 2 months in captivity, the male devils lost ~8.7% of their original body weight, and females lost 10.6% during this same period. However, body weights then rose during the rest of the experiment. These results suggest that Tasmanian devils experience elevated plasma cortisol concentrations in response to capture and transfer into captivity. However, these high concentrations are not maintained during 6 months in captivity, suggesting that the animals are not chronically stressed.

Normal levels of immunocompetence in possums (Trichosurus vulpecula) exposed to different laboratory housing conditions post capture

Specific and non-specific immunological tests were used to monitor aspects of the immune response in captive possums. The tests included total and differential white blood cell counts, lymphocyte transformation assay, and enzyme linked immunosorbant assay. The level of free cortisol present in possum plasma samples was evaluated as an endocrine marker for stress. Four different housing conditions were used to test whether stress could be managed or avoided in captive animals. Animals were caged individually or as groups in pens. Bacille Calmette-Gurein (BCG) and tetanus toxoid immunization was used to evoke primary cell mediated and antibody responses in test animals. The results indicated that there was no significant difference in immunological responses or endocrine parameters in animals held under any of the housing conditions. The results infer that wild possums adapt quickly post-capture to novel housing conditions and produce representative patterns of immunity when held in housing conditions and fed ad libitum.

Are serum cortisol levels a reliable indicator of wellbeing in the tammar wallaby, Macropus eugenii?

Serum corticosteroid levels were measured in six female tammar wallabies (Macropus eugenii) at Macquarie University, NSW, Australia, to assess their reliability as indicators of wellbeing in this species. Animals were challenged with a change in conditions over the course of approximately 3 weeks, comprising (i) isolation and movement; (ii) altered feeding routine, in order to impose a disturbance to homeostasis ("stress"). Blood samples were collected five times during the study period, and analysed for corticosteroid concentration and a number of haematological and biochemical measures. The use of enzyme immunoassay for the measurement of corticosteroids in marsupial serum was validated. We found that there was no significant change in serum corticosteroid concentrations in response to either of the changed conditions suggesting that serum corticosteroid concentrations are not reflective of a change in wellbeing. Cortisol was the dominant serum corticosteroid, with concentrations up to 50 times higher than corticosterone. Significant differences were observed in aspartate amino-transferase, alanine amino-transferase, haemoglobin, total erythrocyte count and mean corpuscular haemoglobin concentration over the period of study. However, no significant correlations emerged to justify any of these measures, or serum corticosteroid levels, as reliable indicators of compromised wellbeing in the tammar wallaby.

Effects of sex steroids, sex, and sexual maturity on cortisol production: an in vitro comparison of chinook salmon and rainbow trout interrenals

Sex steroids appear to be responsible for hyperactivation of the hypothalamus-pituitary-interrenal (HPI) axis that occurs in mature semelparous Pacific salmon as a prelude to post-spawning (programmed) death. This study was undertaken to examine the direct effects of sex steroids on interrenal activity of semelparous (chinook salmon) and iteroparous (rainbow trout) salmonids using an in vitro incubation system. In addition, phenotypic sex differences in cortisol production by interrenals of sexually mature (spawning) rainbow trout and chinook salmon were investigated. Interrenal tissue from juvenile and sexually mature chinook salmon and rainbow trout was incubated for 48 h in culture medium containing either no steroid (controls), 1 microM estradiol (E2) or 1 microM 11-ketotestosterone (11-KT). This tissue was then challenged for 3h with either pregnenolone, dibutyryladenosine 3('):5(')-cyclic monophosphate (dbcAMP) or forskolin, or synthetic human adrenocorticotropic hormone (ACTH(1-24)). Sex differences in in vitro interrenal cortisol production were assessed using separate tissue pools challenged with the same agents. Cortisol in media was measured by radioimmunoassay. E2 suppressed the ability of juvenile chinook salmon interrenals to utilize pregnenolone as substrate for cortisol synthesis. In mature female chinook salmon the suppressive effect of E2 was less pronounced, but was observed as a reduced response of interrenals to both pregnenolone and dbcAMP. E2 did not affect ACTH(1-24) stimulated cortisol production. Immature and mature rainbow trout interrenals were both relatively insensitive to E2. 11-KT did not affect cortisol production by juvenile chinook salmon and juvenile or mature rainbow trout, and had only minor effects in male and female spawning chinook salmon. In mature chinook salmon and rainbow trout, the interrenals of females were more responsive to ACTH stimulation and showed a greater utilization of pregnenolone as a substrate than interrenals of males. Mature female rainbow trout were also more responsive to dbcAMP stimulation than males. The results of this study suggest that the onset of sexual maturation and gonadal steroid production may contribute to sexually dimorphic cortisol responses in vitro.

Seasonal changes in plasma glucocorticoid concentrations in free-living vertebrates

The vertebrate stress response helps animals respond to environmental dangers such as predators or storms. An important component of the stress response is glucocorticoid (GC) release, resulting from activation of the hypothalamic-pituitary-adrenal axis. After release, GCs induce a variety of behavioral and physiological changes that presumably help the animal respond appropriately to the situation. Consequently, GC secretion is often considered an obligatory response to stressful situations. Evidence now indicates, however, that free-living species from many taxa can seasonally modulate GC release. In other words, the magnitudes of both unstressed and stressed GC concentrations change depending upon the time of year. This review examines the growing evidence that GC concentrations in free-living reptiles, amphibians, and birds, but not mammals, are commonly elevated during the breeding season. This evidence is then used to test three hypotheses with different focuses on GC's energetic or behavioral effects, as well as on GC's role in preparing the animal for subsequent stressors. These hypotheses attempt to place annual GC rhythms into a physiological or behavioral context. Integrating seasonal differences in GC concentrations with either different physiological states or different life history stages provides clues to a new understanding of how GCs actually help in survival during stress. Consequently, understanding seasonal modulation of GC release has far-reaching importance for both the physiology of the stress response and the short-term survival of individual animals.

Ontogeny of the immune system of the brushtail possum, Trichosurus vulpecula

The numbers and distribution of T and B cells in the thoracic thymus, spleen and intestinal tissue and the proliferation of T lymphocytes were examined during pouch life and in the adult to determine when the developing brushtail possum reaches immunological maturity. CD3-positive cells were observed in the thoracic thymus at day 2 post-partum indicating that the thymus produces T lymphocytes at or soon after birth. By day 25 the thymus was fully populated with CD3-positive T lymphocytes and they were observed in distinct regions of the cortex and medulla. By day 48 post-partum, B and T lymphocytes were identified in the follicles and parafollicular areas of the spleen. Although the numbers of T and B cells in the spleen increased significantly from day 25 to day 100 post-partum (P < 0.005), fewer cells were present at day 150 post-partum than in the adult (P < 0.05). Peyer's patches were not observed in the intestines up to day 73 post-partum. However, both T and B cells were observed in the intestinal lymph nodes. Although the T lymphocytes at weaning showed a proliferative response, the response was not as great as that observed in the adult possum. Thus, the immune system of the possum is not fully developed at weaning but continues its development after pouch life.

Reproductive capability of brushtail possums (Trichosurus vulpecula) transferred from the wilds of Brisbane, Adelaide, and Armidale into captivity in Brisbane

The transfer of animals from the wild into captivity is an important strategy for the conservation of species that are under threat of extinction. To determine the reproductive capability of animals following transfer from the wild, brushtail possums relocated from Brisbane, Adelaide, and Armidale into captivity in Brisbane were monitored. Seventy five percent of the Brisbane possums (N = 80) gave birth during the months from March to May following transfer from the suburbs of Brisbane and 75% of the young born reached weaning. Thirteen adult females and four adult male brushtail possums were relocated from Adelaide into captivity in Brisbane in June 1994. Four young were born in Brisbane, however none survived to weaning and all the relocated possums had died 2 years after their transfer from Adelaide. Seventeen adult females and seven adult male possums were transferred from Armidale to Brisbane in July 1996. In the first year, 1997, four young were born in Brisbane and none survived to weaning. In the second year, three young were born and survived to weaning. Two years after their transfer, one adult male and three adult females from Armidale and three juvenile possums were housed in the Brisbane enclosures. As the Brisbane, Adelaide, and Armidale possums received the same photoperiod and environmental conditions, some factor must have inhibited breeding activity in the Adelaide possums and to a lesser extent in the Armidale possums. The ability of the Armidale possums to give birth and wean their young after 2 years in Brisbane would suggest that relocated possums require up to 2 years in order to adjust sufficiently to their new environment to reproduce. However, the failure of the Adelaide possums to reproduce successfully after a similar period of time in Brisbane suggests that certain environmental differences inhibit the ability of different populations of possums to adjust to a new environment. J. Exp. Zool. 284:783-788, 1999. Copyright 1999 Wiley-Liss, Inc.