Feather corticosterone is lower in translocated and historical populations of the endangered Laysan duck (Anas laysanensis).

Identifying reliable bioindicators of population status is a central goal of conservation physiology. Physiological stress measures are often used as metrics of individual health and can assist in managing endangered species if linked to fitness traits. We analysed feather corticosterone, a cumulative physiological stress metric, of individuals from historical, translocated, and source populations of an endangered endemic Hawaiian bird, the Laysan duck (Anas laysanensis). We hypothesized that feather corticosterone would reflect the improved reproduction and survival rates observed in populations translocated to Midway and Kure Atolls from Laysan Island. We also predicted less physiological stress in historical Laysan birds collected before ecological conditions deteriorated and the population bottleneck. All hypotheses were supported: we found lower feather corticosterone in the translocated populations and historical samples than in those from recent Laysan samples. This suggests that current Laysan birds are experiencing greater physiological stress than historical Laysan and recently translocated birds. Our initial analysis suggests that feather corticosterone may be an indicator of population status and could be used as a non-invasive physiological monitoring tool for this species with further validation. Furthermore, these preliminary results, combined with published demographic data, suggest that current Laysan conditions may not be optimal for this species.

It's cool to be stressed: body surface temperatures track sympathetic nervous system activation during acute stress.

The acute stress response can be considered the primary evolutionary adaptation to maximise fitness in the face of unpredictable environmental challenges. However, the difficulties of assessing physiology in natural environments mean that comparatively little is known about how response variation influences fitness in free-living animals. Currently, determining acute stress physiology typically involves blood sampling or cardiac monitoring. Both require trapping and handling, interrupting natural behaviour, and potentially biasing our understanding toward trappable species/individuals. Importantly, limits on repeated sampling also restrict response phenotype characterisation, vital for linking stress with fitness. Surface temperature dynamics resulting from peripheral vasomotor activity during acute stress are increasingly promoted as alternative physiological stress indicators, which can be measured non-invasively using infrared thermal imaging, overcoming many limitations of current methods. Nonetheless, which aspects of stress physiology they represent remains unclear, as the underlying mechanisms are unknown. To date, validations have primarily targeted the hypothalamic-pituitary-adrenal axis, when the sympathetic-adrenal-medullary (SAM) system is likely the primary driver of vasomotor activity during acute stress. To address this deficit, we compared eye and bill region surface temperatures (measured using thermal imaging) with SAM system activity (measured as heart rate variability via electrocardiogram telemetry) in wild-caught captive house sparrows (Passer domesticus) during capture and handling. We found that lower body surface temperatures were associated with increased sympathetic nervous system activation. Consequently, our data confirm that body surface temperatures can act as a proxy for sympathetic activation during acute stress, providing potentially transformative opportunities for linking the acute stress response with fitness in the wild.

Smart sensing flexible sutures for glucose monitoring in house sparrows.

There is a need for flexible chemical sensors for the ecological and physiological research of avian species such as house sparrows (Passer domesticus). Current methods in this field are invasive and require multiple physical interactions with the birds. Emerging research in flexible bioelectronics can enable realization of implantable devices that are mechanically compliant with the underlying tissues for continuous real-time sensing in situ. However, challenges still remain in forming an intimate flexible interface. One of the promising flexible bioelectronic platforms for tissue-embedded sensing is based on functionalizing surgical sutures or threads. Threads have three-dimensional flexibility, high surface-area-to-volume ratio, inherent wicking properties, and are easily functionalizable using reel-to-reel dip coating. Threads are ideal as they are lightweight, therefore, would not interfere with flight motion and would only require minimal interaction with the bird. However, the challenge remains in achieving a highly conductive yet flexible electrode for electrochemical sensing using materials such as gold. In this study, we address this issue through novel gold deposition directly on thread substrate followed by enzyme immobilization to realize flexible electrochemical glucose biosensors on medical-grade sutures. These sensors were calibrated and tested in a range that is wide enough to include the expected range of glucose concentration in house sparrows (0-8.55 mM). Glucose monitoring in house sparrows will provide insights into energy metabolism and regulation during stress responses. In addition, the stability, repeatability, and selectivity of the sensor were tested with final validation in a real bird. Our innovative gold-coated, thread-based flexible electrochemical glucose sensor can also be used in other small and large animals. This can also be extended to monitoring other metabolites in future.

A mathematical representation of the reactive scope model.

Researchers have long sought to understand and predict an animal's response to stressful stimuli. Since the introduction of the concept of homeostasis, a variety of model frameworks have been proposed to describe what is necessary for an animal to remain within this stable physiological state and the ramifications of leaving it. Romero et al. (Horm Behav 55(3):375-389, 2009) introduced the reactive scope model to provide a novel conceptual framework for the stress response that assumes an animal's ability to tolerate a stressful stimulus may degrade over time in response to the stimulus. We provide a mathematical formulation for the reactive scope model using a system of ordinary differential equations and show that this model is capable of recreating existing experimental data. We also provide an experimental method that may be used to verify the model as well as several potential additions to the model. If future experimentation provides the necessary data to estimate the model's parameters, the model presented here may be used to make quantitative predictions about physiological mediator levels during a stress response and predict the onset of homeostatic overload.

Long term stability of corticosterone in feathers.

Measuring corticosterone in feathers allows researchers to make long-term, retrospective assessments of physiology with non-invasive sampling. To date, there is little evidence that steroids degrade within the feather matrix, however this has yet to be determined from the same sample over many years. In 2009, we made a pool of European starling (Sturnus vulgaris) feathers that had been ground to a homogenous powder using a ball mill and stored on a laboratory bench. Over the past 14 years, a subset of this pooled sample has been assayed via radioimmunoassay (RIA) 19 times to quantify corticosterone. Despite high variability across time (though low variability within assays), there was no effect of time on measured feather corticosterone concentration. In contrast, two enzyme immunoassays (EIA) produced higher concentrations than the samples assayed with RIA, though this difference is likely due to different binding affinities of the antibodies used. The present study provides further support for researchers to use specimens stored long-term and from museums for feather corticosterone quantification, and likely applies to corticosteroid measurements in other keratinized tissues.

Tropical tree foliage supplementation in ruminants improves rumen fermentation and the bacterial profile and decreases methane production.

The main of this study was to evaluate the effect of supplementation of tropical tree foliage in ruminant diets on the in vitro fermentation, bacterial population, volatile fatty acids (VFAs), and enteric CH4 production. Seven experimental diets were evaluated: a control treatment of Pennisetum purpureum (T7) and six treatments of P. purpureum supplemented (30%) with the foliage of Neomillspaughia emargiata (T1), Tabernaemontana amygdalifolia (T2), Caesalpinia gaumeri (T3), Piscidia piscipula (T4), Leucaena leucocephala (T5), and Havardia albicans (T6). The T2, T7, and T5 treatments had the highest (p < 0.05) digestibility of dry matter. Overall, supplementation increased (p < 0.05) the concentrations of propionic and butyric acid and decreased acetic acid. Methanogenic bacteria decreased (p < 0.05) in T1, T2, T5, and T6. Ruminococcus albus decreased in T1, T2, T3, and T5 and Selenomonas ruminiantum increased in T3. Fibrobacter succinogenes increased, except in T5. Methane production decreased (p < 0.05) in T1, T4, T5, and T6. The supplementation with Leucaena leucocephala, Tabernaemontana amygdalifolia, Neomillspaughia emargiata, Piscidia piscipula, Havardia albicans, and Caesalpinia gaumeri is a potential alternative nutritional strategy for ruminants that results in positive changes in VFAs profile, a decrease on CH4 production and methanogenic bacteria, and changes on fibrolytic and non-fibrolytic bacteria composition.HIGHLIGHTSTropical tree foliage supplementation increased propionic and butyric acid and decreased acetic acid concentrations.Fibrolytic, non-fibrolytic, and Methanogenic bacteria were selectively modulated with the supplementation of tropical tree foliage.The enteric methane (CH4) production decreased with the supplementation of tree foliage.The supplementation of Tabernaemontana amygdalifolia and Leucaena leucocephala had the highest digestibility and is a potential alternative nutritional strategy for ruminants.

Sustainable use of wastes as reactive material in permeable reactive barrier for remediation of acid mine drainage: Batch and continuous studies.

The aim of this work was to evaluate the feasibility of the use of different industrial and agricultural wastes as reactive materials in Permeable Reactive Barriers (PRB) for Acid Mine Drainage (AMD) remediation. Sugar foam (SF), paper mill sludge (PMS), drinking water sludge (DWS) and olive mill waste (OMW) were evaluated in terms of pH neutralization and metal removal from AMD. Laboratory batch tests and continuous pilot scale up-flow columns containing 82% of Volcanic Slag (VS), as porous fill material, and 18% w/w of one of the industrial and agricultural wastes previously indicated, were tested. From the batch tests it was observed that the reactive material presenting the best results were the SF and the PMS. The results obtained in all the PRB were accurately described by a pseudo-first order model, presenting coefficient of determination higher than 0.96 in all the cases. During the continuous operation of the PRB, the porosity and hydraulic retention time (HRT) of most of the up-flow columns strongly decreased due to chemical precipitation and biofilm growth. The SF presented a significant number of fine particles that were washed out by the liquid flow, generating an effluent with very high total suspended solid concentration. Despite SF was the material with the highest alkalinity potential, the reduction of the HRT limited its neutralization and metal removal capacity. PMS and DWS presented the best pollutant removal yields in the continuous operation of the PRB, ranging from 55 to 99% and 55-95% (except in the case of the Mn), respectively. These results allowed the metal removal from the AMD. Additionally, these wastes presented very good biological sulphate reduction. Based on these results, the use of PMS and DWS as reactive material in PRB would allow to simultaneously valorise the industrial waste, which is very interesting within the circular economy framework, and to remove metals from the AMD by means of a low-cost and environmentally sustainable procedure.

A new species of Trichobius (Diptera: Streblidae) from Mexico and new record of Paratrichobius americanus.

A new species of Trichobius Gervais, 1844 (Diptera: Streblidae) is described from specimens collected in Jalisco, Mexico, from host bat Choeronycteris mexicana Tschudi. We place the new species within the "dugesii" group, because it shares certain characteristics with Trichobius urodermae Wenzel, 1966 T. angulatus Wenzel, 1976 and T. tiptoni Wenzel, 1976. However, it is easy to differentiate from all known species due to the chaetotaxy of the thorax, in which the prescutal and lateral setae are very long, while the discal setae are abruptly smaller and denser. It also possesses the metasternal lobe, which is very broad and translucent. We found a male of Paratrichobius americanus Peterson & Ross, 1972 on the same host individual, which expands the distribution area of P. americanus into Mexico because the unique holotype was collected in Arizona.

Chronic stress and captivity alter the cloacal microbiome of a wild songbird.

There are complex interactions between an organism's microbiome and its response to stressors, often referred to as the 'gut-brain axis'; however, the ecological relevance of this axis in wild animals remains poorly understood. Here, we used a chronic mild stress protocol to induce stress in wild-caught house sparrows (Passer domesticus), and compared microbial communities among stressed animals, those recovering from stress, captive controls (unstressed) and a group not brought into captivity. We assessed changes in microbial communities and abundance of shed microbes by culturing cloacal samples on multiple media to select for aerobic and anaerobic bacteria and fungi. We complemented this with cultivation-independent 16S and ITS rRNA gene amplification and sequencing, pairing these results with host physiological and immune metrics, including body mass change, relative spleen mass and plasma corticosterone concentrations. We found significant effects of stress and captivity on the house sparrow microbiomes, with stress leading to an increased relative abundance of endotoxin-producing bacteria - a possible mechanism for the hyperinflammatory response observed in captive avians. While we found evidence that the microbiome community partially recovers after stress cessation, animals may lose key taxa, and the abundance of endotoxin-producing bacteria persists. Our results suggest an overall link between chronic stress, host immune system and the microbiome, with the loss of potentially beneficial taxa (e.g. lactic acid bacteria), and an increase in endotoxin-producing bacteria due to stress and captivity. Ultimately, consideration of the host's microbiome may be useful when evaluating the impact of stressors on individual and population health.

The Effect of a Combined Fast and Chronic Stress on Body Mass, Blood Metabolites, Corticosterone, and Behavior in House Sparrows (Passer domesticus).

One aspect of the Reactive Scope Model is wear-and-tear, which describes a decrease in an animal's ability to cope with a stressor, typically because of a period of chronic or repeated stressors. We investigated whether wear-and-tear due to chronic stress would accelerate a transition from phase II to phase III of fasting. We exposed house sparrows (Passer domesticus) to three weeks of daily fasts combined with daily intermittent repeated acute stressors to create chronic stress, followed by two weeks of daily fasts without stressors. We measured circulating glucose, ß-hydroxybutyrate (a ketone), and uric acid in both fasted and fed states. We expected birds to be in phase II (high fat breakdown) in a fasted state, but if wear-and-tear accumulated sufficiently, we hypothesized a shift to phase III (high protein breakdown). Throughout the experiment, the birds exhibited elevated ß-hydroxybutyrate when fasting but no changes in circulating uric acid, indicating that a transition to phase III did not occur. In both a fasted and fed state, the birds increased glucose mobilization throughout the experiment, suggesting wear-and-tear occurred, but was not sufficient to induce a shift to phase III. Additionally, the birds exhibited a significant decrease in weight, no change in corticosterone, and a transient decrease in neophobia with chronic stress. In conclusion, the birds appear to have experienced wear-and-tear, but our protocol did not accelerate the transition from phase II to phase III of fasting.

Anaphylaxis to Vespa velutina nigrithorax: Pattern of Sensitization for an Emerging Problem in Western Countries.

OBJECTIVE: To define the sensitization pattern of patients with anaphylaxis to Vespa velutina nigrithorax (VVN). METHODS: We studied 100 consecutive Spanish patients with anaphylaxis to Hymenoptera venom and systematically determined specific IgE (sIgE) to whole venoms (Vespula species, Polistes dominula, Apis mellifera, Vespa crabro, and Dolichovespula maculata) and their molecular components (rApi m 1, rApi m 5, rApi m 10, rVes v 1, rVes v 5, rPol d 5, and cross-reactive carbohydrates). Specific IgE to VVN venom and its antigen 5 (nVesp v 5) were measured in a subsample. RESULTS: Seventy-seven patients had anaphylaxis to VVN. Of these, only 16 (20.8%) reported previous VVN stings, but were stung by other Hymenoptera. Positive sIgE (>0.35 kUA/L) to each of the whole venoms was detected in >70% of patients (Vespula species in 100%). The components showing >50% positivity were rApi m 5 (51.4%), rPol d 5 (80.0%), and rVes v 5 (98.7%). This pattern was similar to that of Vespula species anaphylaxis (n=11) but different from that of A mellifera anaphylaxis (n=10). Specific IgE to nVesp v 5 was positive in all patients (n=15) with VVN anaphylaxis and was correlated with sIgE to both rVes v 5 (R=0.931) and rPol d 5 (R=0.887). CONCLUSIONS: VVN has become the commonest cause of Hymenoptera anaphylaxis in our area. Most cases report no previous VVN stings. Their sensitization pattern is similar to that of patients with anaphylaxis to other Vespidae. Specific IgE to antigen-5 from VVN, Vespula species, and P dominula are strongly correlated in patients with VVN anaphylaxis.

Quantifying resilience of humans and other animals.

All life requires the capacity to recover from challenges that are as inevitable as they are unpredictable. Understanding this resilience is essential for managing the health of humans and their livestock. It has long been difficult to quantify resilience directly, forcing practitioners to rely on indirect static indicators of health. However, measurements from wearable electronics and other sources now allow us to analyze the dynamics of physiology and behavior with unsurpassed resolution. The resulting flood of data coincides with the emergence of novel analytical tools for estimating resilience from the pattern of microrecoveries observed in natural time series. Such dynamic indicators of resilience may be used to monitor the risk of systemic failure across systems ranging from organs to entire organisms. These tools invite a fundamental rethinking of our approach to the adaptive management of health and resilience.

Retinol-binding protein 4 (RBP4), a potential biomarker of frailty in HIV-infected people on stable antiretroviral therapy.

OBJECTIVES: A quantitative biomarker for identification of pre-frail and frail persons is still lacking. This study aimed to identify biomarker predictors of frailty in HIV-infected patients. METHODS: A cross-sectional study of HIV-infected patients who had been on antiretroviral therapy (ART) for at least 1 year and who presented an undetectable viral load (< 50 HIV-1 RNA copies/mL) at baseline was carried out. For each frail patient, up to four pre-frail and robust patients were randomly selected. The frailty status assessment was based on the five-item criteria described by Fried et al. Sociodemographic, anthropometric, biochemical and HIV-related characteristics were evaluated. Multiple potential biomarkers of frailty and a biological age biomarker were analysed. RESULTS: A total of 73 HIV-infected patients on ART for at least 1 year were evaluated. The patients were categorized as robust (n = 33), pre-frail (n = 32) and frail (n = 8) using the Fried criteria. All patients were on ART, with 100% undetectable viral load (< 50 copies/mL) at baseline. No significant differences in demographic, clinical or analytical characteristics were observed among patients in the different categories based on Fried criteria, with the exception of the veterans aging cohort study index (VACS). Similarly, no differences were observed in HIV-related characteristics, although nucleoside reverse transcriptase inhibitor (NRTI) use was less common in frail persons. The distribution of biomarker values varied according to frailty status, with frail persons having higher levels of interleukin (IL)-8, IL-18, CXC chemokine ligand 10 (CXCL10) and retinol-binding protein 4 (RBP4). In multivariable analysis, the assocation of frailty with RBP4 showed a tendency to statistical significance (odds ratio 1.0; 95% confidence interval 0.99-1.00; P < 0.05). CONCLUSIONS: Differential biomarker expression was present according to Fried status. Longitudinal studies will clarify the utility of these biomarkers as targets for diagnostic or therapeutic intervention.

Bacterial Cellulose-Chitosan Paper with Antimicrobial and Antioxidant Activities.

The production of paper-based bacterial cellulose-chitosan (BC-Ch) nanocomposites was accomplished following two different approaches. In the first, BC paper sheets were produced and then immersed in an aqueous solution of chitosan (BC-ChI); in the second, BC pulp was impregnated with chitosan prior to the production of paper sheets (BC-ChM). BC-Ch nanocomposites were investigated in terms of physical characteristics, antimicrobial and antioxidant properties, and the ability to inhibit the formation of biofilms on their surface. The two types of BC-Ch nanocomposites maintained the hydrophobic character, the air barrier properties, and the high crystallinity of the BC paper. However, BC-ChI showed a surface with a denser fiber network and with smaller pores than those of BC-ChM. Only 5% of the chitosan leached from the BC-Ch nanocomposites after 96 h of incubation in an aqueous medium, indicating that it was well retained by the BC paper matrix. BC-Ch nanocomposites displayed antimicrobial activity, inhibiting growth of and having a killing effect against bacteria Staphylococcus aureus and Pseudomonas aeruginosa and yeast Candida albicans. Moreover, BC-Ch papers showed activity against the formation of a biofilm on their surface. The incorporation of chitosan increased the antioxidant activity of the BC paper. Paper-based BC-Ch nanocomposites combined the physical properties of BC paper and the antimicrobial, antibiofilm, and antioxidant activities of chitosan.

Cortisol is the predominant glucocorticoid in the giant paedomorphic hellbender salamander (Cryptobranchus alleganiensis).

Corticosterone is widely regarded to be the predominant glucocorticoid produced in amphibians. However, we recently described unusually low baseline and stress-induced corticosterone profiles in eastern hellbenders (Cryptobranchus alleganiensis alleganiensis), a giant, fully aquatic salamander. Here, we hypothesized that hellbenders might also produce cortisol, the predominant glucocorticoid used by fishes and non-rodent mammals. To test our hypothesis, we collected plasma samples in two field experiments and analyzed them using multiple analytical techniques to determine how plasma concentrations of cortisol and corticosterone co-varied after 1) physical restraint and 2) injection with adrenocorticotropic hormone (ACTH), the pituitary hormone responsible for triggering the release of glucocorticoids from amphibian interrenal glands. Using liquid chromatography-mass spectrometry, we found that baseline and restraint-induced plasma concentrations of cortisol were more than five times those of corticosterone. We then demonstrated that plasma concentrations of both glucocorticoids increased in response to ACTH in a dose-dependent manner, but cortisol concentrations were consistently higher (up to 10-fold) than corticosterone. Cortisol and corticosterone concentrations were not correlated with one another at basal or induced conditions. The extremely low plasma concentrations of corticosterone in hellbenders suggests that corticosterone could simply be a byproduct of cortisol production, and raises questions as to whether corticosterone has any distinct physiological function in hellbenders. Our results indicate that hellbenders produce cortisol as their predominant glucocorticoid, supporting a small and inconclusive body of literature indicating that some other amphibians may produce appreciable quantities of cortisol. We hypothesize that the use of cortisol by hellbenders could be an adaptation to their fully aquatic life history due to cortisol's ability to fulfill both mineralocorticoid and glucocorticoid functions, similar to its functions in fishes. Given the large number of amphibian species that are fully aquatic or have aquatic life stages, we suggest that the broadly held assumption that corticosterone is the predominant glucocorticoid in all amphibians requires further scrutiny. Ultimately, multi-species tests of this assumption will reveal the ecological factors that influenced the evolution of endocrine adaptations among amphibian lineages, and may provide insight into convergent evolution of endocrine traits in paedomorphic species.

Recovery periods during repeated stress impact corticosterone and behavioral responses differently in house sparrows.

A number of studies have shown that chronic stress can negatively impact both physiology and behavior in a variety of organisms. What has yet to be extensively explored is whether these changes permanently alter an animal's functioning, or if they can be reversed. In this study, we used wild-caught house sparrows (Passer domesticus) to assess how recovery periods influence the physiological and behavioral impacts of an initial four days and subsequent four days of repeated stressors. Birds were randomly assigned to a recovery group and either experienced 0, 24, or 72 h of recovery between the two sets of stressors (cage rolling and cage tapping). We measured the regulation of the hypothalamic pituitary adrenal (HPA) axis by quantifying baseline and stress-induced corticosterone as well as negative feedback strength. We also assessed behavior using neophobia trials to measure how birds altered their approach towards novel objects and their overall activity. Both behavior and corticosterone responses were assessed before the experiment, after the recovery time, and following the final 4 days of stressors. We found that birds that experienced 24 h of recovery had reduced stress-induced corticosterone, but enhanced negative feedback relative to the pre-experiment sample. Additionally, 4 days of stressors was enough to significantly reduce approach latency towards novel objects; however, pre-experiment levels returned with longer periods of recovery. Finally, recovery time did not significantly influence responses to the second 4 days of stressors. Our results indicate that brief recovery periods partially ameliorate the hormonal and behavioral effects of repeated stress.

Recovery from repeated stressors: Physiology and behavior are affected on different timescales in house sparrows.

For decades, researchers across disciplines have been captivated by classifying, diagnosing, and avoiding the consequences of chronic stress. Despite the vast body of literature this has generated, we still lack the ability to predict which individuals or populations may be susceptible to stress-related pathologies. One critical unanswered question is whether the impacts of repeated stressors are reversible, or if instead they permanently alter an individual. In this study, we exposed house sparrows (Passer domesticus) to 6 days of random, repeated stressors, permitted them 0, 1, 3, or 6 days to recover, and then assessed changes in their body mass, hypothalamic-pituitaryadrenal (HPA) axis (baseline, stress-induced corticosterone, negative feedback strength), immune function, uric acid concentrations, DNA damage levels, and perch hopping activity. Body mass did not vary between groups after recovery. We found that the HPA axis and perch hopping were not significantly impacted by the 6 days of stressors, but that uric acid and DNA damage increased. Short recovery periods tended to negatively affect the HPA axis and reduced uric acid levels, but these were reversed with longer recovery periods. Following the recovery periods, the birds experienced an additional 6 days of random stressors and their responses were assessed again. All recovery times reduced perch hopping and immune function, but paradoxically, DNA damage was highest in the birds that had the longest amount of time to recover. These results show that recovery time affects responses to subsequent chronic stress in complex ways, and highlight the importance of multimodal, interdisciplinary approaches to studying stress physiology.

Profile repeatability: A new method for evaluating repeatability of individual hormone response profiles.

There is broad interest in determining repeatability of individual responses. Current methods calculate repeatability of individual points (initial and/or peak), time to peak value, or a single measure of the integrated total response (area under the curve), rather than the shape of the response profile. Repeatability estimates of response profiles using linear mixed models (LMM) generate an average repeatability for an aggregate of individuals, rather than an estimate of individual repeatability. Here we use a novel ad hoc method to calculate repeatability of individual response profiles and demonstrate the need for a more rigorous assessment protocol. Response profile repeatability has not been defined at the individual level. We do this using a new metric, Profile Repeatability (PR), which incorporates components of variance and the degree to which response profiles cross each other in a time series. Values range from 0 (no repeatability) to 1 (complete repeatability). We created synthetic data to represent a range of apparent time series repeatability, and 20 independent observers visually ranked those data sets by degree of repeatability. We also applied the method to real data on stress responses of European starlings Sturnus vulgaris. We then computed PR scores for the synthetic data and for real data from European starling corticosterone responses over time, and contrast the results to those from LMM. Finally, we assessed the sensitivity of PR to reductions in the number of time points in the corticosterone response, as well as reductions in the number of replicates per individual. We found the average PR scores for a group of individuals to be somewhat robust to reductions in points in the time series; however, the ranks of individuals (PR values relative to one another) could change substantially with reduction in the number of values in a time series. PR showed threshold sensitivity to losing replicate time series between 6 and 4 replicates. Surprisingly, human observers fell into two disparate groups when ranking repeatability of the synthetic data, and the PR score indicated that human observers may underestimate repeatability of data where replicates cross each other. In contrast to the average profile repeatability estimated using LMMs, our approach calculates individual repeatability. From our perspective, LMM does not provide a definitive idea of repeatability at the individual level; in essence, it concludes that suites of time series with low within-individual variance has high repeatability, regardless of replicate trajectories. LMM and PR have non-linear relationships between 0 and 1, but PR has greater discrimination for mid-values of repeatability. Consistent average group repeatability can be associated with substantial differences in individual ranks suggests that estimating individual repeatability is critical. The PR score should be useful in comparing repeatability of any type of nonlinear, including non-monotonic, response profiles over time, which are common in both physiology and behavior, and it demonstrates the specific needs for future improvements of a profile repeatability metric.

Stress, sleep, and sex: A review of endocrinological research in Octodon degus.

The Common Degu (Octodon degus) is a small rodent endemic to central Chile. It has become an important model for comparative vertebrate endocrinology because of several uncommon life-history features - it is diurnal, shows a high degree of sociality, practices plural breeding with multiple females sharing natal burrows, practices communal parental care, and can easily be studied in the laboratory and the field. Many studies have exploited these features to make contributions to comparative endocrinology. This review summarizes contributions in four major areas. First are studies on degu stress responses, focusing on seasonal changes in glucocorticoid (GC) release, impacts of parental care on offspring GC responses, and fitness consequences of individual variations of GC responses. These studies have helped confirm the ecological relevance of stress responses. Second are studies exploring diurnal circadian rhythms of melatonin and sex steroids. These studies have formed important work translating circadian biology from nocturnal laboratory rodents to diurnal humans. Third are studies that exploit the open nature of degu natural habitat, combined with laboratory studies, to explore the impact of testosterone on agonistic behavior. Studies have focused primarily on male:male, female:female, male:female, and parental behaviors. Fourth, are contributions to the study of female masculinization from male siblings in the uterus. These studies have focused on both the behavioral consequences of masculinization and the impact of those behaviors on fitness. Taken together, the studies reviewed here have formed a strong foundation for further studies in the degu so that future studies can address how endocrinological components underlie new mechanistic connections to the ecological effects on behavior and fitness.

DNA damage as an indicator of chronic stress: Correlations with corticosterone and uric acid.

Corticosterone does not change in consistent ways across species and contexts, making it challenging to use as an indicator of chronic stress. We assessed DNA damage as a potential metric that could be a more integrative stress measurement with direct links to health. We captured free-living house sparrows, took an immediate blood sample, and transferred them to the laboratory, exposing them to the chronic stress of captivity. Biweekly blood and weight samples were then taken for 4 weeks. We immediately assessed DNA damage in red blood cells using the comet assay and later quantified corticosterone. Uric acid was analyzed in a separate group of birds. We found that birds initially lost, but began to regain weight over the course of captivity. DNA damage peaked within the first 10 days of captivity, and mostly remained elevated. However, the cellular distribution of damage changed considerably over time; most cells showed low levels of damage early, a bimodal distribution of high and low DNA damage during the peak of damage, and a wide unimodal distribution of damage at the end of the 4 weeks. Furthermore, corticosterone increased and remained elevated and uric acid decreased and remained depleted over the same period. Although both a molecular (DNA damage) and an endocrine (corticosterone) marker showed similar response profiles over the 4 weeks, they were not correlated, suggesting they reflect different aspects of the underlying physiology. These data provide convincing preliminary evidence that DNA damage has potential to be an additional indicator of chronic stress.