The effects of sex, age and commensal way of life on levels of fecal glucocorticoid metabolites in spiny mice (Acomys cahirinus)

Sounds of danger and post-traumatic stress responses in wild rodents: ecological validity of a translational model of post-traumatic stress disorder

In the wild, animals face a highly variable world full of predators. Most predator attacks are unsuccessful, and the prey survives. According to the conventional perspective, the fear responses elicited by predators are acute and transient in nature. However, the long-term, non-lethal effects of predator exposure on prey behavioral stress sequelae, such as anxiety and post-traumatic symptoms, remain poorly understood. Most experiments on animal models of anxiety-related behavior or post-traumatic stress disorder have been carried out using commercial strains of rats and mice. A fundamental question is whether laboratory rodents appropriately express the behavioral responses of wild species in their natural environment; in other words, whether behavioral responses to stress observed in the laboratory can be generalized to natural behavior. To further elucidate the relative contributions of the natural selection pressures influences, this study investigated the bio-behavioral and morphological effects of auditory predator cues (owl territorial calls) in males and females of three wild rodent species in a laboratory set-up: Acomys cahirinus; Gerbillus henleyi; and Gerbillus gerbillus. Our results indicate that owl territorial calls elicited not only "fight or flight" behavioral responses but caused PTSD-like behavioral responses in wild rodents that have never encountered owls in nature and could cause, in some individuals, enduring physiological and morphological responses that parallel those seen in laboratory rodents or traumatized people. In all rodent species, the PTSD phenotype was characterized by a blunting of fecal cortisol metabolite response early after exposure and by a lower hypothalamic orexin-A level and lower total dendritic length and number in the dentate gyrus granule cells eight days after predator exposure. Phenotypically, this refers to a significant functional impairment that could affect reproduction and survival and thus fitness and population dynamics.

Validation of Enzyme Immunoassays via an Adrenocorticotrophic Stimulation Test for the Non-Invasive Quantification of Stress-Related Hormone Metabolites in Naked Mole-Rats

Small size in mammals usually restricts long-term, frequent monitoring of endocrine function using plasma as a matrix. Thus, the non-invasive monitoring of hormone metabolite concentrations in excreta may provide an invaluable approach. The aim of the current study was to examine the suitability of enzyme immunoassays (EIAs) for monitoring responses to stressors in the naked mole-rat (Heterocephalus glaber, NMR) using urine and feces as hormone matrices. A saline control administration, and a high- and low-dose adrenocorticotropic hormone (ACTH) challenge were performed on six male and six female disperser morph NMRs. The results revealed that a 5α-pregnane-3β,11β,21-triol-20-one EIA detecting glucocorticoid metabolites (GCMs) with a 5α-3β-11β-diol structure is the most suitable assay for measuring concentrations in male urine samples, whereas an 11-oxoaetiocholanolone EIA detecting GCMs with a 5β-3α-ol-11-one structure appears the most suitable EIA for quantifying GCMs in female urine. An 11-oxoaetiocholanolone EIA detecting 11,17 dioxoandrostanes was the most suitable EIA for quantifying GCMs in the feces of both sexes. There were sex-related differences in response to the high- and low-dose ACTH challenge. We recommend using feces as a more suitable matrix for non-invasive GCM monitoring for NMRs which can be valuable when investigating housing conditions and other welfare aspects.

Evaluation of stress response in black-tailed prairie dogs (Cynomys ludovicianus) in arid regions from colonies in Chihuahua Mexico

Among all the regulatory homeostatic networks in vertebrates, the activation of the hypothalamic-pituitaryadrenal axis during the stress response, has gained considerable attention, and the measurement of fecal glucocorticoids (FGC) has become an invaluable tool to assess adrenocortical activity related to stressful events in wild and captive animals. However, the use of FGC requires the validation of measurement techniques and the proper selection of the specific hormone according to the study species. The main objective of this study was to identify the dominant glucocorticoid (GC) hormone in the stress response of black-tailed prairie dogs (Cynomys ludovicianus) in an arid grassland of Chihuahua, Mexico. A capture stress challenge in the field was developed to determine if the levels of glucocorticoids (cortisol and corticosterone) both in serum and fecal samples could be attributed to stress in Cynomys ludovicianus. The samples were analysed with the technique of liquid phase radioimmunoassay , and this study showed that both cortisol and corticosterone are present at measurable levels in serum and fecal samples of black-tailed prairie dogs. We found that both GCs were present in similar concentrations in serum, however, corticosterone concentration in fecal samples was higher than cortisol. Likewise, biochemical validations performed in this study to test the assay reached acceptable levels of reliability. Therefore, we confirm that fecal analysis can be implemented as a method to measure stress responses in wild prairie dogs.

Hidden but Potentially Stressed: A Non-Invasive Technique to Quantify Fecal Glucocorticoid Levels in a Fossorial Amphisbaenian Reptile

To understand wildlife responses to the changing environment, it is useful to examine their physiological responses and particularly their endocrine status. Here, we validated an enzyme immunoassay (EIA) to non-invasively quantify fecal corticosterone metabolites (FCM) in the fossorial amphisbaenian reptile Trogonophis wiegmanni from North Africa. We supplemented animals assigned to the treatment group with corticosterone dissolved in oil applied non-invasively on the skin for several days, while control groups received the oil-alone solution. Fresh feces were collected at the end of the supplementation period, and FCM levels were quantified by an EIA. Basal FCM levels were similar for both treatments and increased at the end of the test, but FCM increased significantly more in corticosterone-treated animals. A further examination of FCM levels in a wild population of this amphisbaenian did not find overall sexual, size or seasonal differences but showed a high range of variation among individuals. This suggests that different uncontrolled intrinsic or local environmental variables might increase the circulating glucocorticoid levels of different individuals. Our results confirmed the suitability of EIA for analyzing physiological changes in FCM in this amphisbaenian species. This technique may be useful for understanding and remediating the little-explored potential stressors of the soil environment that may negatively affect the health state of fossorial reptiles.

Sex, not social behavior, predicts fecal glucocorticoid metabolite concentrations in a facultatively social rodent, the highland tuco-tuco (Ctenomys opimus)

Social relationships may influence circulating glucocorticoid levels, particularly in group-living species in which individuals regularly engage in interactions with conspecifics. The effects of such interactions appear to vary, with greater social contact being associated with increased glucocorticoid concentrations in some species but decreased concentrations in others. These distinct responses raise intriguing questions regarding relationships among social behavior, individual phenotypes, and glucocorticoid physiology. To explore such relationships in a free-living mammal with a dynamic social organization, we quantified variation in baseline glucocorticoids in a population of highland tuco-tucos (Ctenomys opimus) from Jujuy Province, Argentina. These subterranean rodents are facultatively social, with lone and group-living individuals regularly occurring within the same population. To assess potential endocrine correlates of this behavioral variability, we examined differences in baseline fecal glucocorticoid metabolite (fGCm) concentrations as a function of social group size and composition as well as several metrics of social behavior derived from social network analyses. Despite marked variability in social relationships among the 37 (12 male, 25 female) free-living tuco-tucos sampled, none of the measures of social behavior examined were significant predictors of variation in fGCm concentrations. In contrast, individual variation in glucocorticoid metabolites was best explained by sex, with males having higher fGCm concentrations than females. These analyses provide the first characterization of the glucocorticoid physiology of highland tuco-tucos and underscore the potential importance of intrinsic phenotypic factors (e.g., sex) in shaping glucocorticoid variation in free-living mammals.

Effects of ectoparasite infestation during pregnancy on physiological stress and reproductive output in a rodent-flea system

Biotic and abiotic stressors impose various fitness costs on individuals across a variety of taxa. In vertebrates, these stressors typically trigger complex neuroendocrine responses that stimulate glucocorticoid (GC) secretion from the adrenal cortex. Short-term elevation of GCs can be adaptive as it shifts energy toward physiological processes that cope with acute stressors; however, chronic increases in GC levels could have detrimental effects on fitness. Parasitism can be considered an important biotic stressor in nature and a possible cause of reproductive failure that could substantially affect an individual's fitness. Thus, we aimed to test the effects of parasitism and maternal stress, as measured by GCs, during pregnancy and the relationship between these variables and measures of reproductive output using a rodent-flea system. Female Egyptian spiny mice (Acomys cahirinus) were randomly assigned to flea (Parapulex chephrenis) infested or uninfested treatments before and during pregnancy. The offspring of these females were flea-free. Feces were collected at five time points during the experiment to determine maternal fecal glucocorticoid metabolite (FGCM) concentrations. Overall, infested females had lower FGCM levels during gestation but higher FGCM levels post-parturition and larger mass changes than uninfested females. Additionally, models related to pup quality and quantity often included some measure of maternal investment or body condition moderating relationships between infestation and stress. This suggests that flea parasitism or high GC levels alone might not significantly impact host reproduction but rather females can experience different effects depending on their level of investment, which could be limited by body condition and/or the number of pups present in a litter.

Relationship between exploratory activity and adrenocortical activity in the black rat (Rattus rattus)

The relationship between physiological and behavioral stress markers is documented in several rodent species. However, there is no information regarding the role of adrenocortical activity in behavior of the black rat (Rattus rattus). Therefore, we hypothesize that the adrenocortical activity of black rats varies between individuals and is related to some of the behaviors in a novel environment. To test this hypothesis, we (i) validated a method for quantifying glucocorticoid metabolites from feces (fGCMs) with an enzyme immunoassay (EIA); (ii) examined variation and diurnal rhythms of feces and GCM production; and (iii) examined the relationship between GCM levels and exploratory behavioral traits. We fulfilled the first aim (i) by successfully performing an ACTH challenge test to validate the use of a 5α-pregnane-3β,11β,21-triol-20-one EIA for measuring fGCMs. Second (ii) we detected considerable consistent interindividual variability in production of both feces and glucocorticoids. The peak production of feces occurred in the first hour of the dark cycle, the peak of fGCMs occurred approximately 3 h later. Lastly, (iii) there was no clear relationship between behavior in the hole board test and GCMs. Grooming, a typical behavioral stress marker, was negatively associated with stress reactivity, while head-dipping in the hole-board test (traditionally considered an exploratory behavior independent of stress) was not correlated with the GCMs. This study offers a first look at GCMs in the black rat, successfully validates a method for their measurement and opens possibilities for future research of the relationship between glucocorticoids and exploratory behavior in this species.

Non-Invasive Monitoring of Adrenocortical Activity in Three Sympatric Desert Gerbil Species

Simple Summary

In this era, characterized by remarkable anthropogenic impacts on wildlife, it is crucial to monitor the health of wild animal populations while minimizing the interference to them. To this end, for a better understanding of the eco-physiology of wild animals, the adrenocortical activity can be non-invasively evaluated by measuring glucocorticoid metabolites excreted in feces. However, to ensure that the endocrine information is reliable, the experimental assays should be first validated and the causes for the major variability among individuals should be considered. Here we validated an enzyme immunoassay for measuring fecal corticosterone metabolites (FCM) in three wild gerbil species and emphasized the differences among them. These are endangered species, which play a key role in psammophilic communities, and provide a model system for various aspects in ecology. Thus, this work constitutes the first step toward using the FCMs of these species as indicators for individual and community stress.

Abstract

The study of the endocrine status can be useful to understand wildlife responses to the changing environment. Here, we validated an enzyme immunoassay (EIA) to non-invasively monitor adrenocortical activity by measuring fecal corticosterone metabolites (FCM) in three sympatric gerbil species (Gerbillus andersoni, G. gerbillus and G. pyramidum) from the Northwestern Negev Desert’s sands (Israel). Animals included into treatment groups were injected with adrenocorticotropic hormone (ACTH) to stimulate adrenocortical activity, while control groups received a saline solution. Feces were collected at different intervals and FCM were quantified by an EIA. Basal FCM levels were similar in the three species. The ACTH effect was evidenced, but the time of FCM peak concentrations appearance differed between the species (6–24 h post-injection). Furthermore, FCM peak values were observed sooner in G. andersoni females than in males (6 h and 18 h post-injection, respectively). G. andersoni and G. gerbillus males in control groups also increased FCM levels (18 h and 48 h post-injection, respectively). Despite the small sample sizes, our results confirmed the EIA suitability for analyzing FCM in these species as a reliable indicator of the adrenocortical activity. This study also revealed that close species, and individuals within a species, can respond differently to the same stressor.

Measuring fecal metabolites of endogenous steroids using ESI-MS/MS spectra in Taiwanese pangolin, (order Pholidota, family Manidae, Genus: Manis): A non-invasive method for endangered species

Pangolins are 'keystone species' driven towards extinction due to a lack of profound awareness and illegal trade. The drivers urge for immediate development in the understanding of demographics and reproductive dynamics of this species. In this study, we developed and validated a quantitative method to measure pangolin fecal extracts using the electrospray (ESI-MS/MS) interface in positive ionization mode. The method aids in the measurement of hormones from the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axis, making it a possibly appropriate technique to understand the cross-talk between the axes. The study aims to measure the relative abundance of adrenal and gonadal hormones such as corticosterone, cortisol, estrone, estradiol-17β, progesterone, testosterone, and a number of its metabolites. From the dried fecal extract, the principal metabolite identified from the estrogen family was estradiol-17β, whereas the gestagen family revealed that the pregnane series is predominated in 5α-configuration. On the other hand, epiandrosterone was seen as the dominant form in the male fecal extracts. Additionally, the glucocorticoids are excreted majorly as corticosterone, but traces of cortisol are also present in both the male and female fecal samples. The physiological validation confirmed that the ESI-MS/MS technique is suitable to determine physiologically caused differences in the fecal steroid concentrations. Physiologically, the age structure in pangolin is not responsible for causing differences within gender. However, the results revealed that glucocorticoids might vary between the sexes, i.e., males have a higher relative abundance of glucocorticoids over females. Therefore, our studies show that some of the main adrenal and gonadal metabolites can be predicted by exploiting MS/MS, which can steer research to potentially assess the reproductive status of captive and free-ranging pangolin species.

On the ground and in the heights: Does exploratory activity differ in commensal and non-commensal spiny mice?

Human settlements represent a specific environment where commensal animals are exposed to different selective pressures than their wild-living conspecifics. Despite the importance of commensal rodents for human health and economy, little is known about how a transition to a commensal way of life changes the behaviour of the animals. We tested twelve populations of spiny mice (Acomys spp.) in two open field-type tests - a vertical test and a hole board test. In the vertical test, a wire mesh for climbing was offered to spiny mice. We used a multipopulation approach using two commensal and ten non-commensal spiny mouse populations to account for inter-population variability. We aimed to investigate whether there are differences in behaviour of commensal and non-commensal populations with special regard to their exploratory activity both on the ground and on the wire mesh. We found that all non-commensal populations behaved similarly despite their long separate evolutionary histories. Contrary, the commensal populations were less exploratory on the ground in both tests. We concluded that this change was associated with their transition to commensalism. This shows that selective pressures of the commensal environment are able to induce noticeable changes in behaviour after a very short evolutionary time.

Assessment of the Stress Response in North American Deermice: Laboratory and Field Validation of Two Enzyme Immunoassays for Fecal Corticosterone Metabolites

Simple Summary

If we want to employ stress physiology in the management and conservation of wildlife populations, we need robust methods to quantify stress physiology in the field. Although this is typically done with blood glucocorticoids (GCs), scientists now increasingly use fecal cortisol/corticosterone metabolites (FCMs), which are metabolized GCs excreted in feces. However, immunoassays to measure FCMs need to be validated for each species. North American deermice (Peromyscus maniculatus; hereafter deermice) are commonly used in laboratory and field studies. Although a corticosterone radioimmunoassay (RIA) has been validated for deermice, there are no validated enzyme immunoassays (EIAs), which do not require radioactive materials. Through laboratory and field experiments, we validated two EIAs for measuring FCMs in deermice. Researchers can now use these EIAs to evaluate stress physiology in deermice without the need for radioactive materials.

Abstract

Stress physiology is commonly employed in studies of wildlife ecology and conservation. Accordingly, we need robust and suitable methods to measure stress physiology in the field. Fecal cortisol/corticosterone metabolites (FCMs) are now increasingly being used to non-invasively evaluate adrenocortical activity; a measure of stress physiology. However, immunoassays that measure FCMs must be appropriately validated prior to their use and factors that can influence FCMs, such as trap-induced stress, must be considered. Deermice (Peromyscus maniculatus) are widely used in scientific studies so that developing methods that appropriately measure their adrenocortical activity is critical. In the laboratory, we tested the suitability of two enzyme immunoassays (EIAs; a corticosterone EIA, and a group-specific 5α-pregnane-3β,11β,21-triol-20-one EIA) in deermice by challenging individuals with dexamethasone and adrenocorticotropic hormone (ACTH). We found that dexamethasone suppressed FCM levels within ~10 h post injection whereas ACTH increased FCM levels within ~2 h post injection. In the field, we found that FCM levels generally increased with more time in trap confinement when using both EIAs. Although we acknowledge low sample sizes (N = 4), our results validated the two EIAs for use with FCMs from deermice.

Model systems for regeneration: the spiny mouse, Acomys cahirinus

The spiny mouse, Acomys spp., is a recently described model organism for regeneration studies. For a mammal, it displays surprising powers of regeneration because it does not fibrose (i.e. scar) in response to tissue injury as most other mammals, including humans, do. In this Primer article, we review these regenerative abilities, highlighting the phylogenetic position of the spiny mouse relative to other rodents. We also briefly describe the Acomys tissues that have been used for regeneration studies and the common features of their regeneration compared with the typical mammalian response. Finally, we discuss the contribution that Acomys has made in understanding the general principles of regeneration and elaborate hypotheses as to why this mammal is successful at regenerating.

Commensalism outweighs phylogeographical structure in its effect on phenotype of a Sudanian savanna rodent

The murid rodent Praomys daltoni is widespread in Sudanian savanna and woodlands of West Africa, and previous study of mitochondrial DNA variability suggested that it encompasses the phenotypically (small, grey-bellied) and ecologically (commensal) distinct form, Praomys derooi. Here, we comprehensively examined the genetic and morphological diversity within the complex. Six mitochondrial lineages showed a fine-scale phylogeographical pattern, whereas delimitation based on nuclear loci pooled four of them into a single widespread unit. A newly discovered lineage from southern Mauritania stands apart from the rest of the complex and might represent an unrecognized species. At the same time, the internal position of P. derooi (C2 mitochondrial lineage) was confirmed by the multilocus analysis. The magnitude of genetic distances between major phylogeographical lineages was typical for interspecific divergence in other clades of Praomys, despite the little differences among them in morphology (skull and upper molar row shapes). The most pronounced morphological shift was associated with a transition to commensalism, especially in P. derooi, but also in other lineages. This makes the whole complex a suitable model for the study of phenotypic novelty, the evolution of commensalism and conditions for ecological speciation.

Flea infestation, social contact, and stress in a gregarious rodent species: minimizing the potential parasitic costs of group-living

Both parasitism and social contact are common sources of stress that many gregarious species encounter in nature. Upon encountering such stressors, individuals secrete glucocorticoids and although short-term elevation of glucocorticoids is adaptive, long-term increases are correlated with higher mortality and deleterious reproductive effects. Here, we used an experimental host-parasite system, social rodents Acomys cahirinus and their characteristic fleas Parapulex chephrenis, in a fully-crossed design to test the effects of social contact and parasitism on stress during pregnancy. By analysing faecal glucocorticoid metabolites, we found that social hierarchy did not have a significant effect on glucocorticoid concentration. Rather, solitary females had significantly higher glucocorticoid levels than females housed in pairs. We found a significant interaction between the stressors of parasitism and social contact with solitary, uninfested females having the highest faecal glucocorticoid metabolite levels suggesting that both social contact and infestation mitigate allostatic load in pregnant rodents. Therefore, the increased risk of infestation that accompanies group-living could be outweighed by positive aspects of social contact within A. cahirinus colonies in nature.

Excretion and measurement of corticosterone and testosterone metabolites in bank voles (Myodes glareolus)

The bank vole is a commonly used model species in behavioral and ecophysiological studies. Thus, presenting a validated method for noninvasive monitoring of corticosterone and testosterone secretion is of high relevance. Here, we evaluated the effect of time of day and an ACTH challenge test on measured fecal corticosterone (FCM) and testosterone (FTM) metabolites in both sexes. Furthermore, we performed radiometabolism experiments for both steroids and sexes to study metabolism and excretion of ³H-corticosterone and ³H-testosterone. FCM and FTM were analysed with a 5α-pregnane-3β,11β,21-triol-20-one enzyme immunoassay (EIA) and a testosterone (measuring 17β-hydroxyandrostanes) EIA, respectively. Males had significantly higher FCM levels than females and their main excretion route was via the feces (∼72%), whereas females excreted nearly equal portions in both feces and urine. For testosterone the main excretion route was via the feces in both sexes (∼80%). The time course of excretion was similar in both sexes, but for the first time a significant difference between injected steroids was found: Corticosterone was excreted faster than testosterone, both in urine (median of peak levels: 4h vs 6h) and feces (6h vs 8h). Several metabolites were present in the feces and the tested EIAs reacted with some of them. Time of day had a significant effect on measured fecal steroid metabolites. As expected, males had significantly higher FTM levels than females. ACTH administration significantly increased FCM values; peaks were observed 4-8h after injection. In conclusion, both tested EIAs proved suited for a noninvasive measurement of glucocorticoids and androgens in bank voles.

Validation of an enzyme immunoassay for assessing adrenocortical activity and evaluation of factors that affect levels of fecal glucocorticoid metabolites in two New World primates

Non-invasive methods to assess stress hormone output via fecal glucocorticoid metabolites (FGCMs) have become a powerful tool in behavioral studies and conservation biology because they allow exploring the link between behavior, an animal's socio-ecological environment and its adrenocortical activity. However, FGCM levels are influenced by numerous other factors which often confound their interpretation. Thus, before applying these methods, knowledge on the impact of these factors is important. In this study we investigated the effect of (1) time of day, (2) age, (3) sex and (4) female reproductive state on FGCM levels in brown spider monkeys (Ateles hybridus) and red howler monkeys (Alouatta seniculus). Initially, we validated a 11β-hydroxyetiocholanolone enzyme immunoassay for monitoring the physiological stress response via fecal analysis in both species. We determined FGCM levels in fecal samples collected from two and six groups of wild spider monkeys (n=461 samples) and howler monkeys (n=166 samples), respectively. Our analyses revealed a strong effect of time of day on FGCM levels in spider monkeys, but no effect in howler monkeys. Adults of both species had significantly higher FGCM levels than subadults. In neither of the two species we found a sex-effect on FGCM output. Reproductive condition strongly affected FGCM levels in female spider monkeys which showed increasing concentrations with progressing gestation. This was not investigated in female howler monkeys due to an insufficient sample size. Our data indicate that the influence of the tested factors on fecal glucocorticoid metabolite output is species-specific, and that these variables need to be considered when interpreting FGCM levels in the species.

Review: Minimally invasive sampling media and the measurement of corticosteroids as biomarkers of stress in animals

Cook, N. J. 2012. Review: Minimally invasive sampling media and the measurement of corticosteroids as biomarkers of stress in animals. Can. J. Anim. Sci. 92: 227–259. The measurement of corticosteroid hormones is commonly used as a biomarker of an animal's response to stress. The difficulties in obtaining blood samples and the recognition of the stressor effect of blood sampling are primary drivers for the use of minimally invasive sample media. In mammals these include saliva, feces, urine, hair, and milk. In birds, samples include excreta, feathers, egg yolk and albumin. In fish, corticosteroids have been measured in excreta and swim-water. Each of these sample media incorporate corticosteroids in accordance with the processes by which they are formed, and this in turn dictates the periods of adrenocortical activity that each sample type represents. Cortisol in saliva represents a time-frame of minutes, whereas the production of feces may be hours to days depending on the species. The longest time-integrations are for hair and feathers which could be over a period of many weeks. The sample media also determines the structural changes that may occur via processes of conjugation to glucuronides and sulfides, metabolic conversion via enzymatic action, and bacterial breakdown. Structural changes determine the optimum methodologies used to measure corticosteroid hormones. In most sample media, measurement of a specific corticosteroid is a requirement depending on the species, e.g., cortisol in most mammals, or corticosterone in birds. However, in samples involving products of excretion, methodologies that measure a broad range of structurally related compounds are probably optimal. The utility of minimally invasive sample media as biomarkers of stress responses depends on the degree to which the corticosteroid content of the sample represents adrenocortical activity. Commonly, this involves comparisons between corticosteroid concentrations in blood plasma with concentrations in the alternative sample media. This review focuses on the methodological and biological validation of corticosteroid measurements in minimally invasive samples as biomarkers of adrenocortical responses to stress.

Characterizing adrenocortical activity in zoo-housed southern three-banded armadillos (Tolypeutes matacus)

Improving the husbandry in the southern three-banded armadillo (Tolypeutes matacus) through gaining knowledge of its stress physiology is imperative to maintaining a healthy, zoo-housed population. Our objectives were to: 1) validate the use of fecal hormone analysis for monitoring adrenocortical activity using both an adrenocorticotropic hormone (ACTH) challenge and biological events; and 2) characterize longitudinal adrenocortical activity in male and female southern three-banded armadillos. An ACTH injection was given intra-muscularly to one male (4IU/kg; 5.6IU total) and one female (5.5IU/kg; 8IU total) southern three-banded armadillo. Fecal samples were collected 1 day pre- and continued 5 days post-ACTH to capture the physiological response measured by elevated fecal glucocorticoid metabolites (FGM) to validate these techniques. Additionally, natural and routine events, including pairing individuals for breeding and veterinary procedures/handling, were used to biologically validate these techniques. To characterize adrenocortical activity, fecal samples (∼3025 total; n=275/animal/yr) were collected from 11 (5 males; 6 females) southern three-banded armadillos 5-7 times a week for 1 year at Lincoln Park Zoo (Chicago, IL). A cortisol enzyme immunoassay was used for FGM analysis. The ACTH challenge in the male resulted in a twofold increase of FGM (1123.2±36.2 ng/g dry feces) above baseline (675.7±10.0 ng/g dry feces) at approximately 54-94h post- injection. The female exhibited a twofold increase (1635.4 ng/g dry feces) over baseline FGMs (608.5±12.3 ng/g dry feces) approximately 30h post-injection. Reproductive behaviors and veterinary procedures resulted in elevated FGM concentrations from all individuals except for one male. The longitudinal characterization demonstrated that sex and season did not influence (P<0.05) FGM concentrations. Individuals were highly variable with mean FGM concentration of 2010.1±862.4 ng/g dry feces (range, 816.3-7889.1 ng/g dry feces). Mean FGM baseline concentration was 878.5±201.8ng/g dry feces (range, 475.2-1955.5 ng/g dry feces) with a mean elevated FGM concentrations of 2694.3±1111.4 ng/g dry feces (range, 1110.3-10,683.3 ng/g dry feces). This study provides the foundation for future research on how the environment directly affects the adrenocortical activity in this species of armadillo.

Comparing adult hippocampal neurogenesis in mammalian species and orders: influence of chronological age and life history stage

Adult hippocampal neurogenesis is a prominent event in rodents. In species with longer life expectancies, newly born cells in the adult dentate gyrus of the hippocampal formation are less abundant or can be completely absent. Several lines of evidence indicate that the regulatory mechanisms of adult neurogenesis differ between short- and long-lived mammals. After a critical appraisal of the factors and problems associated with comparing different species, we provide a quantitative comparison derived from seven laboratory strains of mice (BALB, C57BL/6, CD1, outbred) and rats (F344, Sprague-Dawley, Wistar), six other rodent species of which four are wild-derived (wood mouse, vole, spiny mouse and guinea pig), three non-human primate species (marmoset and two macaque species) and one carnivore (red fox). Normalizing the number of proliferating cells to total granule cell number, we observe an overall exponential decline in proliferation that is chronologically equal between species and orders and independent of early developmental processes and life span. Long- and short-lived mammals differ with regard to major life history stages; at the time points of weaning, age at first reproduction and average life expectancy, long-lived primates and foxes have significantly fewer proliferating cells than rodents. Although the database for neuronal differentiation is limited, we find indications that the extent of neuronal differentiation is subject to species-specific selective adaptations. We conclude that absolute age is the critical factor regulating cell genesis in the adult hippocampus of mammals. Ontogenetic and ecological factors primarily influence the regulation of neuronal differentiation rather than the rate of cell proliferation.

Fecal cortisol metabolite levels in free-ranging North American red squirrels: Assay validation and the effects of reproductive condition

Patterns in stress hormone (glucocorticoid: GC) levels and their relationship to reproductive condition in natural populations are rarely investigated. In this study, we (1) validate an enzyme-immunoassay to measure fecal cortisol metabolite (FCM) levels in North American red squirrels (Tamiasciurus hudsonicus), and (2) examine relationships between FCM levels and reproductive condition in a free-ranging red squirrel population. Injected radiolabeled cortisol was entirely metabolized and excreted in both the urine (mean+/-SE; 70.3+/-0.02%) and feces (29.7+/-0.02%), with a lag time to peak excretion in the feces of 10.9+/-2.3h. Our antibody reacted with several cortisol metabolites, and an adrenocorticotropic injection significantly increased FCM levels above baseline levels at 8h post-injection. Relative to baseline levels, manipulation by handling also tended to increase FCM levels at 8h post-manipulation, but this difference was not significant. FCM levels did not differ significantly between samples frozen immediately and 5h after collection. Reproductive condition significantly affected FCM levels in free-ranging females (pregnant>lactating>post-lactating>non-breeding) but not males (scrotal testes vs. abdominal testes). Among females with known parturition dates, FCM levels increased during gestation, peaked at parturition, and declined during lactation. The difference between pregnant and lactating females was therefore dependent upon when the fecal samples were obtained during these periods, suggesting caution in categorizing reproductive stages. This study demonstrates the utility of fecal hormone metabolite assays to document patterns of glucocorticoid levels in free-ranging animals.

Assessment of the stress response in Columbian ground squirrels: laboratory and field validation of an enzyme immunoassay for fecal cortisol metabolites

Stress responses play a critical role in the ecology and demography of wild animals, and the analysis of fecal hormone metabolites is a powerful noninvasive method to assess the role of stress. We characterized the metabolites of injected radiolabeled cortisol in the urine and feces of Columbian ground squirrels and validated an enzyme immunoassay for measuring fecal cortisol metabolites (FCM) with a 5 alpha-3beta,11 beta-diol structure by stimulation and suppression of adrenocortical activity and by evaluation of the circadian pattern of FCM excretion. In addition, we also evaluated the impact of capture, handling, and acclimation to the laboratory on FCM. Cortisol is highly metabolized, with virtually none being excreted, and of the radiolabeled cortisol injected, 31% was recovered in urine and 6.5% in feces. The lag time between cortisol injection and its appearance in urine and feces was 4.5 +/- 0.82 (SE) h and 7.0 +/- 0.53 (SE) h, respectively. FCM levels varied over the day, reflecting circadian variation in endogenous cortisol. Dexamethasone decreased FCM levels by 33%, and ACTH increased them by 255%. Trapping and housing initially increased FCM levels and decreased body mass, but these reversed within 3-7 d, indicating acclimation. Finally, FCM levels were modestly repeatable over time (r=0.57) in wild, live trapped, nonbreeding animals, indicating that FCMs provide a measure of the squirrel's stress-axis state. This assay provides a robust noninvasive assessment of the stress response of the Columbian ground squirrel and will facilitate an integration of its life history and physiology.