Hematological condition indexes in greenfinches: effects of captivity and diurnal variation

Correlated evolution of oxidative physiology and MHC-based immunosurveillance in birds

Maintenance and activation of the immune system incur costs, not only in terms of substrates and energy but also via collateral oxidative damage to host cells or tissues during immune response. So far, associations between immune function and oxidative damage have been primarily investigated at intra-specific scales. Here, we hypothesized that pathogen-driven selection should favour the evolution of effective immunosurveillance mechanisms (e.g. major histocompatibility complex, MHC) and antioxidant defences to mitigate oxidative damage resulting from immune function. Using phylogenetically informed comparative approaches, we provided evidence for the correlated evolution of host oxidative physiology and MHC-based immunosurveillance in birds. Species selected for more robust MHC-based immunosurveillance (higher gene copy numbers and allele diversity) showed stronger antioxidant defences, although selection for MHC diversity still showed a positive evolutionary association with oxidative damage to lipids. Our results indicate that historical pathogen-driven selection for highly duplicated and diverse MHC could have promoted the evolution of efficient antioxidant mechanisms, but these evolutionary solutions may be insufficient to keep oxidative stress at bounds. Although the precise nature of mechanistic links between the MHC and oxidative stress remains unclear, our study suggests that a general evolutionary investment in immune function may require co-adaptations at the level of host oxidative metabolism.

Songbirds avoid the oxidative stress costs of high blood glucose levels: a comparative study

Chronically high blood glucose levels (hyperglycaemia) can compromise healthy ageing and lifespan at the individual level. Elevated oxidative stress can play a central role in hyperglycaemia-induced pathologies. Nevertheless, the lifespan of birds shows no species-level association with blood glucose. This suggests that the potential pathologies of high blood glucose levels can be avoided by adaptations in oxidative physiology at the macroevolutionary scale. However, this hypothesis remains unexplored. Here, we examined this hypothesis using comparative analyses controlled for phylogeny, allometry and fecundity based on data from 51 songbird species (681 individuals with blood glucose data and 1021 individuals with oxidative state data). We measured blood glucose at baseline and after stress stimulus and computed glucose stress reactivity as the magnitude of change between the two time points. We also measured three parameters of non-enzymatic antioxidants (uric acid, total antioxidants and glutathione) and a marker of oxidative lipid damage (malondialdehyde). We found no clear evidence for blood glucose concentration being correlated with either antioxidant or lipid damage levels at the macroevolutionary scale, as opposed to the hypothesis postulating that high blood glucose levels entail oxidative costs. The only exception was the moderate evidence for species with a stronger stress-induced increase in blood glucose concentration evolving moderately lower investment into antioxidant defence (uric acid and glutathione). Neither baseline nor stress-induced glucose levels were associated with oxidative physiology. Our findings support the hypothesis that birds evolved adaptations preventing the (glyc)oxidative costs of high blood glucose observed at the within-species level. Such adaptations may explain the decoupled evolution of glycaemia and lifespan in birds and possibly the paradoxical combination of long lifespan and high blood glucose levels relative to mammals.

Oxidative physiology is weakly associated with pigmentation in birds

The mechanistic link between avian oxidative physiology and plumage coloration has attracted considerable attention in past decades. Hence, multiple proximal hypotheses were proposed to explain how oxidative state might covary with the production of melanin and carotenoid pigments. Some hypotheses underscore that these pigments (or their precursors, e.g., glutathione) have antioxidant capacities or function as molecules storing the toxic excess of intracellular compounds, while others highlight that these pigments can act as pro-oxidants under specific conditions. Most studies addressing these associations are at the intraspecific level, while phylogenetic comparative studies are still scarce, though needed to assess the generality of these associations. Here, we tested whether plumage and bare part coloration were related to oxidative physiology at an interspecific level by measuring five oxidative physiology markers (three nonenzymatic antioxidants and two markers of lipid peroxidative damage) in 1387 individuals of 104 European bird species sampled during the breeding season, and by scoring plumage eumelanin, pheomelanin, and carotenoid content for each sex and species. Only the plasma level of reactive oxygen metabolites was related to melanin coloration, being positively associated with eumelanin score and negatively with pheomelanin score. Thus, our results do not support the role of antioxidant glutathione in driving variation in melanin synthesis across species. Furthermore, the carotenoid scores of feathers and bare parts were unrelated to the measured oxidative physiology parameters, further suggesting that the marked differences in pigmentation across birds does not influence their oxidative state.

THE EFFECT OF DEXAMETHASONE ON HEMATOLOGIC PROFILES, HEMOSPORIDIAN INFECTION, AND SPLENIC HISTOLOGY IN HOUSE FINCHES (HAEMORHOUS MEXICANUS)

Research on host response to infectious disease often involves pharmacological induction of immunosuppression, frequently through administration of dexamethasone. Reports on the effect of dexamethasone in birds are largely restricted to poultry and pigeons. This study describes changes in white blood cell (WBC) differentials, hemoparasite counts, splenic histology, and splenic CD3 immunoreactivity in House Finches (Haemorhous mexicanus). Experimental group birds (n=9) were treated with a daily intramuscular injection of 25 µg of dexamethasone for 8 d; a control group (n=9) received daily saline solution. Smears were made with blood collected immediately before the first dose (day 0) and on d 4, 8, and 9, and stained with modified Wright. The WBC differential counts were performed by three blinded observers, parasite counts by two blinded observers, and histology by one blinded observer. Dexamethasone-treated birds experienced relative heterophilia and lymphopenia on d 4 (P=0.008); heterophilia was also present at d 8 (P=0.018). Hemosporidian counts were significantly increased in dexamethasone-treated birds on d 4 and 8 (P=0.048 and P=0.031, respectively). In contrast with control birds, all dexamethasone-treated birds lacked histologically apparent splenic lymphoid follicles (P<0.001). No significant difference was observed in splenic CD3 immunoreactivity between groups. Our results indicate that dexamethasone has an effect on the hematologic profile of House Finches and suggest that it may be a useful method to induce immunosuppression in this species.

Daily and fasting variation in blood parameters and H/L ratio in house sparrows (Passer domesticus)

Fluctuations in food supply are frequent in nature during seasons, in different stages of annual cycle of animals and lately, climate change is a strong driving force that could affect food supply. An animal's capacity to resist fasting is, therefore, determined by its ability to store energy and control its allocation during periods of food restriction. Daily variations of metabolic substrates and their fluctuation during fasting are relevant to understand the acclimation to fasting. Since fasting is an ecological stressor, we investigated the daily variation of corticosterone levels in feeding and fasting in Passer domesticus Linnaeus, 1758 and its short-term effect on some biochemical parameters. We found daily variations in body mass, glucose, triglycerides, plasma total protein, uric acid and corticosterone. However, we did not find diurnal variations of hematocrit and the Heterophil:Lymphocyte ratio (H/L ratio). Moreover, we did not find sex-related differences in any parameter. Throughout fasting we found variations of glucose, triglycerides, total protein, uric acid, H/L ratio and corticosterone. During the photophase, biochemical and physiological responses to food deprivation contribute to the efficient use of resources in this small bird. In the course of fasting period corticosterone could be responsible of alterations of some blood parameters such as glucose.

Antibiotic treatment increases yellowness of carotenoid feather coloration in male greenfinches (Chloris chloris)

Carotenoid plumage coloration is an important sexually selected trait in many bird species. However, the mechanisms ensuring the honesty of signals based on carotenoid pigments remain unclear. It has recently been suggested that intestinal integrity, which is affected by gut parasites and microbiota and influences nutrient absorption and acquisition, mediates the relationship between carotenoid ornamentation and individual quality. Here, we test whether carotenoid plumage coloration in greenfinches (Chloris chloris) is affected by the treatment of an antibiotic or an antiparasitic drug. We captured wild greenfinches (N = 71) and administered anticoccidial medication toltrazuril (TOLTRA) to one group, antibiotic metronidazole (METRO) to the second group to target trichomonosis, and the third group received no medication. In the METRO group, feathers grown during the experiment had significantly higher chroma of yellow parts, but there was no effect of TOLTRA on feather chroma. The results suggest that METRO increased the efficiency of carotenoid modification or deposition to the feathers rather than nutrient acquisition and/or freed energy resources that could be invested in coloration. Alternatively, though not measured, METRO might have affected microbial community and host physiology as microbial metabolites can modulate mitochondrial and immune function.

Hematocrit, age, and survival in a wild vertebrate population

Understanding trade-offs in wild populations is difficult, but important if we are to understand the evolution of life histories and the impact of ecological variables upon them. Markers that reflect physiological state and predict future survival would be of considerable benefit to unraveling such trade-offs and could provide insight into individual variation in senescence. However, currently used markers often yield inconsistent results. One underutilized measure is hematocrit, the proportion of blood comprising erythrocytes, which relates to the blood's oxygen-carrying capacity and viscosity, and to individual endurance. Hematocrit has been shown to decline with age in cross-sectional studies (which may be confounded by selective appearance/disappearance). However, few studies have tested whether hematocrit declines within individuals or whether low hematocrit impacts survival in wild taxa. Using longitudinal data from the Seychelles warbler (Acrocephalus sechellensis), we demonstrated that hematocrit increases with age in young individuals (<1.5 years) but decreases with age in older individuals (1.5-13 years). In breeders, hematocrit was higher in males than females and varied relative to breeding stage. High hematocrit was associated with lower survival in young individuals, but not older individuals. Thus, while we did not find support for hematocrit as a marker of senescence, high hematocrit is indicative of poor condition in younger individuals. Possible explanations are that these individuals were experiencing dehydration and/or high endurance demands prior to capture, which warrants further investigation. Our study demonstrates that hematocrit can be an informative metric for life-history studies investigating trade-offs between survival, longevity, and reproduction.

Corticosterone levels correlate in wild-grown and lab-grown feathers in greenfinches (Carduelis chloris) and predict behaviour and survival in captivity

Level of corticosterone (CORT), which is a predominant glucocorticoid in birds, has become the main indicator for assessing the stress level of birds in ecological studies. Feather corticosterone (CORT_f) provides information about corticosterone levels during feather growth, however, the underlying causes of individual variation of CORT_f between individuals and individual persistency of CORT_f are not yet fully understood. Therefore, this study addresses individual consistency in CORT_f and the association of variation in CORT_f with behaviour that results in damage to tail feathers. We studied relations between CORT_f, plasma CORT, and behaviour in wild-caught male greenfinches in captivity. CORT_f in wild-grown feathers correlated positively with CORT_f in lab-grown feathers. CORT_f levels were about 20% lower in lab-grown feathers than in those grown in the wild. Four birds that died in captivity had significantly higher average CORT_f levels in wild-grown feathers than the survivors. Plasma CORT levels of two measurements taken in the lab seven days apart correlated positively, however, no correlations between plasma CORT and CORT_f were found. In order to study the link between CORT_f and behaviour, the extent of tail damage from flapping against cage bar was assessed. Contrary to our prediction, birds with higher CORT_f had less tail damage. This study adds to the evidence that CORT_f levels can be considered as informative markers of some persistent component of individual phenotypic quality that can predict survival under standardized laboratory conditions.

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.

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.

Safety assessment of antibiotic and probiotic feed additives for Gallus gallus domesticus

Antibiotics in feed select for resistant strains and is thus a threat to human health. In this study, the effect of a multi-strain probiotic and antibiotics on the growth and health of broilers was studied. Equal numbers of broilers received on a daily basis either a multi-strain probiotic or a combination of sulphadiazine, colistin and trimethoprim, whereas the control group received standard feed. The villi of immature broilers (19 days old) administered antibiotics had a larger surface area and their lymphocyte and basophil counts were higher compared to broilers from the probiotic and control groups. The cecal microbiomes of mature broilers (29 days old) that received probiotics had higher levels of Enterobacteriaceae, but lower numbers of Clostridiales, Brucellaceae, Synergistaceae, Erysipelotrichaceae and Coriobacteriaceae compared to the antibiotic-treated group. A decline in the bioluminescence of Listeria monocytogenes observed for broilers on probiotics suggested that the probiotic may be used to control bacterial infections. No significant differences in total red blood cell, haemoglobin and haematocrit content, and mean values for corpuscular volume, corpuscular haemoglobin and corpuscular haemoglobin numbers were recorded amongst broilers from the different treatment groups. This study provides valuable information on the health and performance of broilers when administered probiotics and antibiotics as additives.

Variation in the Markers of Nutritional and Oxidative State in a Long-Lived Seabird: Associations with Age and Longevity

Age-related declines in life-history traits have been widely observed in free-living animals. Several theories link senescence to oxidative stress. The aim of this study was to measure several widely used markers of oxidative and nutritional state in a long-lived seabird, the common gull (Larus canus), in order to assess the suitability of these markers for describing deterioration in physiological condition associated with chronological age and survival. Associations with longevity and individual consistency of these parameters over the years (repeatability) were also assessed. Senescence in fitness parameters was observed during the study period: in females, laying date and clutch mass were related to bird age in a curvilinear manner, with middle-aged birds breeding earlier and laying heavier eggs. The only parameter associated with aging processes was glutathione concentration in erythrocytes, which was lower in female birds with longer life spans. Of indexes of nutritional state, plasma triglyceride concentration showed a between-individual increase with age, suggesting selective mortality of birds with low levels. Additionally, total plasma protein levels of individual males increased with age. The mostly negative results of this study hint that the commonly used parameters of physiological condition and oxidative state used in this study do not adequately reflect an individual's long-term health condition. Alternatively, it is possible that in common gulls, senescence occurs in reproductive mechanisms but not in mechanisms responsible for maintaining an organism's redox balance, consistent with the idea that different aspects of an organism's physiological condition age at different rates. Significant interannual repeatability was detected in three plasma constituents-carotenoids, uric acid, and total protein-all of which can possibly be linked to variation in dietary habits.

Influence of dietary protein on serum metabolites and antioxidant status: A study in Chrysolophus amherstiae

This experiment was conducted to study the effect of feeding graded levels of dietary crude protein (CP) on serum biochemical profile of Lady Amherst's pheasants (LAP). Eighteen male LAP were randomly distributed into three groups of six each in an experiment based on completely randomized design. The CP content of the diets was 13.4%, 16.5%, and 19.1%, in groups I, II, and III, respectively. Serum concentrations of uric acid was lowest (P < 0.05) in group I. Relationship between serum concentration of uric acid and nitrogen intake was linear (R(2)  = 0.39, P < 0.01). Concentrations of other serum metabolites and enzymes were similar among the groups. Serum concentration of triiodothyronine (T3 ) was highest (P < 0.05) in group I, followed by groups II and III. Total antioxidant capacity (TAC) of serum was lower (P < 0.007), whereas serum concentration of malondialdehyde (MDA) was higher (P < 0.001) in group I as compared to groups II and III. Regression of serum concentration of TAC (R(2)  = 0.74, P < 0.01) and MDA (R(2)  = 0.39, P < 0.05) was polynomial. Heterophil to lymphocyte ratio was higher (P < 0.007) in group I as compared to groups II and III. Relationship between H/L ratio and nitrogen intake was polynomial (R(2)  = 0.69, P < 0.05). Cell mediated immune response measured as foot web index was similar among the groups. Based upon the results, it was concluded that a diet containing 16.5% crude protein would be optimum for improving antioxidant defense and the ability of Lady Amherst's pheasant to combat stress. Zoo Biol. 35:346-354, 2016. © 2016 Wiley Periodicals, Inc.

Population-Wide Failure to Breed in the Clark's Nutcracker (Nucifraga columbiana)

In highly variable environments, conditions can be so stressful in some years that entire populations forgo reproduction in favor of higher likelihood of surviving to breed in future years. In two out of five years, Clark’s nutcrackers (Nucifraga Columbiana) in the Greater Yellowstone Ecosystem exhibited population-wide failure to breed. Clark’s nutcrackers at the study site experienced substantial interannual differences in food availability and weather conditions, and the two nonbreeding years corresponded with low whitebark pine (Pinus albicaulis) cone crops the previous autumn (≤ an average of 8 ± 2 cones per tree versus ≥ an average of 20 ± 2 cones per tree during breeding years) and high snowpack in early spring (≥ 61.2 ± 5.5 cm versus ≤ 51.9 ± 4.4 cm during breeding years). The average adult body condition index during the breeding season was significantly lower in 2011 (-1.5 ± 1.1), a nonbreeding year, as compared to 2012 (6.2 ± 2.0), a breeding year. The environmental cues available to the birds prior to breeding, specifically availability of cached whitebark pine seeds, may have allowed them to predict that breeding conditions would be poor, leading to the decision to skip breeding. Alternatively, the Clark’s nutcrackers may have had such low body energy stores that they chose not to or were unable to breed. Breeding plasticity would allow Clark’s nutcrackers to exploit an unpredictable environment. However, if large-scale mortality of whitebark pines is leading to an increase in the number of nonbreeding years, there could be serious population-level and ecosystem-wide consequences.

The influence of biological rhythms on host-parasite interactions

Biological rhythms, from circadian control of cellular processes to annual cycles in life history, are a main structural element of biology. Biological rhythms are considered adaptive because they enable organisms to partition activities to cope with, and take advantage of, predictable fluctuations in environmental conditions. A flourishing area of immunology is uncovering rhythms in the immune system of animals, including humans. Given the temporal structure of immunity, and rhythms in parasite activity and disease incidence, we propose that the intersection of chronobiology, disease ecology, and evolutionary biology holds the key to understanding host-parasite interactions. Here, we review host-parasite interactions while explicitly considering biological rhythms, and propose that rhythms: influence within-host infection dynamics and transmission between hosts, might account for diel and annual periodicity in host-parasite systems, and can lead to a host-parasite arms race in the temporal domain.

Seasonal variations in health indices of free-ranging asymptomatic guinea fowls (Numida meleagris) in Zambia

OBJECTIVE

To determine the impact of seasonal variations on health indices of free-ranging asymptomatic guinea fowls (Numida meleagris) in Zambia.

METHODS

A time series analysis was carried out on a prospective cohort study over a 12 month period between March 2010 and February 2011 by examining a total 147 guinea fowls for haematological and morphometric data of selected organs.

RESULTS

There was a strong correlation in erythrocytic indices between packed cell volume and red blood cell counts (=0.824, P<0.001) as well as between packed cell volume and hemoglobulin (Hb) counts (r=0.648, P<0.001). Seasonal differences showed that erythrocytic indices were higher in the males than the females and that the difference was significantly higher (P<0.001) during the rainy season, which coincided with the breeding period when females were laying eggs. Increase in total plasma protein was positively correlated with overall body weight. Generally, females had higher body weights and total plasma protein levels than the males in the rain season. Of the 147 birds examined, 51% (n=147) had the bursa of Fabricius. For birds that had the bursa of Fabricius, the weights of bursae were higher (P<0.05) in the cold-dry season than the other seasons and no sex differences were observed. Spleen morphometric data did not show any seasonal nor sex differences.

CONCLUSIONS

Overall, data presented herein demonstrate that seasonal variations have a significant influence on health indices of free-ranging guinea fowls and that these factors could influence the susceptibility of this species of birds to disease infections at different times of the year.

Profile of whole blood gene expression following immune stimulation in a wild passerine

Background

Immunoecology aims to explain variation among hosts in the strength and efficacy of immunological defences in natural populations. This requires development of biomarkers of the activation of the immune system so that they can be collected non-lethally and sampled from small amounts of easily obtainable tissue. We used transcriptome profiling in wild greenfinches (Carduelis chloris) to detect whole blood transcripts that most profoundly indicate upregulation of antimicrobial defences during acute phase response. The more general aim of this study was to obtain a functional annotation of a substantial portion of the greenfinch transcriptome that would enable to gain access to more specific genomic tools in subsequent studies. The birds received either bacterial lipopolysaccharide or saline injections and RNA-seq transcriptional profiling was performed 12 h after treatment to provide initial functional annotation of the transcriptome and assess whole blood response to immune stimulation.

Results

A total of 66,084 transcripts were obtained from de novo Trinty assembly, out of which 23,153 could be functionally annotated. Only 1,911 of these were significantly upregulated or downregulated. The manipulation caused marked upregulation of several transcripts related to immune activation. These included avian-specific antimicrobial agents avidin and gallinacin, but also some more general host response genes, such as serum amyloid A protein, lymphocyte antigen 75 and copper-transporting ATPase 1. However, links with avian immunity for most differentially regulated transcripts remained rather hypothetical, as a large set of differentially expressed transcripts lacked functional annotation.

Conclusions

This appears to be the first large scale transcriptional profiling of immune function in passerine birds. The transcriptomic data obtained suggest novel markers for the assessment of the immunological state of wild passerines. Characterizing the function of those possible novel infection markers would assist future vertebrate genome annotation. The extensive sequence information collected enables to identify possible target and housekeeping genes needed to gain access to more specific genomic tools in future studies.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-533) contains supplementary material, which is available to authorized users.

Dexamethasone inhibits corticosterone deposition in feathers of greenfinches

Corticosterone (CORT) content of feathers is a potent source of information about activation of hypothalamus-pituitary-adrenal (HPA) axis during feather growth, which is used for assessment of well-being and stress history of individuals and populations in avian studies. However, little is known about factors affecting deposition of CORT into feathers and how feather CORT covaries with other markers of stress imposed upon individuals during feather growth. We addressed these questions by measuring CORT levels in feathers of wild-caught greenfinches (Carduelis chloris) brought into captivity. One tail feather was removed from all the birds upon arrival to the laboratory and the CORT levels of replacement feathers, grown in captivity were recorded. The birds were subjected to treatments of immune activation (by injection of phytohaemagglutinin) and synthetic glucocorticoid (dexamethasone, DEX) administration. Only DEX injection affected feather CORT levels. DEX-injected birds deposited on average 37% less of CORT in their feathers than saline-injected birds. Despite significant effects of DEX and immune activation treatments on differential leukocyte counts, we did not find any correlations between CORT and leukocyte hemoconcentrations or heterophil/lymphocyte ratios (a haematological index of stress), measured at three stages of feather growth. Our findings provide novel evidence that feather CORT levels are sensitive to manipulation of hormonal balance of birds, thereby supporting the diagnostic value of feather CORT measurements. However, we did not find any evidence about covariation between feather CORT and other markers of stress perceived during the period of feather growth. This calls for further research on information content of feather CORT, preferably in experiments manipulating more diverse array of psychological, immunological and abiotic stressors.

Effects of Endotoxin and Psychological Stress on Redox Physiology, Immunity and Feather Corticosterone in Greenfinches

Assessment of costs accompanying activation of immune system and related neuroendocrine pathways is essential for understanding the selective forces operating on these systems. Here we attempted to detect such costs in terms of disruption to redox balance and interference between different immune system components in captive wild-caught greenfinches (Carduelis chloris). Study birds were subjected to an endotoxin-induced inflammatory challenge and temporary exposure to a psychological stressor (an image of a predator) in a 2*2 factorial experiment. Injection of bacterial endotoxin resulted in up-regulation of two markers of antioxidant protection – erythrocyte glutathione, and plasma oxygen radical absorbance (OXY). These findings suggest that inflammatory responses alter redox homeostasis. However, no effect on markers of oxidative damage to proteins or DNA in erythrocytes could be detected. We found no evidence that the endotoxin injection interfered with antibody production against Brucella abortus antigen or the intensity of chronic coccidiosis. The hypothesis of within-immune system trade-offs as a cost of immunity was thus not supported in our model system. We showed for the first time that administration of endotoxin can reduce the level of corticosterone deposited into feathers. This finding suggests a down-regulation of the corticosterone secretion cascade due to an endotoxin-induced immune response, a phenomenon that has not been reported previously. Exposure to the predator image did not affect any of the measured physiological parameters.

On the methodological limitations of detecting oxidative stress: effects of paraquat on measures of oxidative status in greenfinches

Oxidative stress (OS) is widely believed to be responsible for generation of trade-offs in evolutionary ecology by means of constraining investment into a number of components of fitness. Yet the progress in understanding the true role of OS in ecology and evolution has remained elusive. Interpretation of current findings is particularly hampered by the scarcity of experiments demonstrating which of the many available parameters of oxidative status respond most sensitively to and are relevant for measuring OS. We addressed these questions in wild-caught captive greenfinches (Carduelis chloris) by experimental induction of OS by administration of the pro-oxidant compound paraquat with drinking water. Treatment induced 50% of mortality and a significant drop in body mass and an increase in oxidative DNA damage and glutathione levels in erythrocytes among the survivors of the high paraquat (0.2 g/L during 7 days) group. Three days after the end of the treatment, paraquat had no effect on peroxidation of lipids (plasma malondialdehyde), carbonylation of proteins (in erythrocytes), parameters of plasma antioxidant protection (TAC and OXY), uric acid or carotenoids. Our findings of an increase in one marker of damage and one marker of protection from the multitude of measured variables indicate that detection of OS is difficult even under most stringent experimental induction of oxidative insult. We hope that this study highlights the need for reconsideration of over-simplistic models of OS and draws attention to the limitations of detection of OS due to time-lagged and hormetic up-regulation of protective mechanisms. This study also underpins the diagnostic value of measurement of oxidative damage to DNA bases and assessment of erythrocyte glutathione levels.

Variation in body condition indices of crimson finches by sex, breeding stage, age, time of day, and year

Body condition indices are increasingly applied in conservation to assess habitat quality, identify stressed populations before they decline, determine effects of disturbances, and understand mechanisms of declines. To employ condition indices in this manner, we need first to understand their baseline variability and sources of variation. Here, we used crimson finches (Neochmia phaeton), a tropical passerine, to describe the variation in seven commonly used condition indices by sex, age, breeding stage, time of day, and year. We found that packed cell volume, haemoglobin, total plasma protein, and scaled mass were all significantly affected by an interaction between sex and breeding stage. Furcular fat varied by sex and breeding stage and also trended by year, scaled mass showed a positive trend with age and varied by time of day, and haemoglobin additionally varied by year. Pectoral muscle scores varied and heterophil to lymphocyte ratio trended only by year. Year effects might reflect a response to annual variation in environmental conditions; therefore, those indices showing year effects may be especially worthy of further investigation of their potential for conservation applications. Pectoral muscle scores and heterophil to lymphocyte ratio may be particularly useful due to the lack of influence of other variables on them. For the other indices, the large variation that can be attributed to individual covariates, such as sex and breeding stage, suggests that one should not interpret the physiological condition of an individual as measured by these indices from their absolute value. Instead, the condition of an individual should be interpreted relative to conspecifics by sex, breeding stage, and possibly age.

Coccidian infection causes oxidative damage in greenfinches

The main tenet of immunoecology is that individual variation in immune responsiveness is caused by the costs of immune responses to the hosts. Oxidative damage resulting from the excessive production of reactive oxygen species during immune response is hypothesized to form one of such costs. We tested this hypothesis in experimental coccidian infection model in greenfinches Carduelis chloris. Administration of isosporan coccidians to experimental birds did not affect indices of antioxidant protection (TAC and OXY), plasma triglyceride and carotenoid levels or body mass, indicating that pathological consequences of infection were generally mild. Infected birds had on average 8% higher levels of plasma malondialdehyde (MDA, a toxic end-product of lipid peroxidation) than un-infected birds. The birds that had highest MDA levels subsequent to experimental infection experienced the highest decrease in infection intensity. This observation is consistent with the idea that oxidative stress is a causative agent in the control of coccidiosis and supports the concept of oxidative costs of immune responses and parasite resistance. The finding that oxidative damage accompanies even the mild infection with a common parasite highlights the relevance of oxidative stress biology for the immunoecological research.

Carotenoid intake does not affect immune-stimulated oxidative burst in greenfinches

Carotenoid-based integument colouration is extremely widespread in the animal kingdom. It has been hypothesized that carotenoid colouration is used for communicating the health status of the bearers because carotenoids are efficient immunomodulators or antioxidants. However, the latter argument has been recently debated and the mechanisms by which carotenoids modulate immunity or oxidative balance are poorly known. We performed an experiment on wild-caught captive greenfinches, passerine birds with carotenoid-based plumage colouration, in order to test whether dietary carotenoid supplementation affects immune-stimulated oxidative burst of phagocytes in the whole blood and humoral immune response to a novel antigen, Brucella abortus (BA). Additionally, we tested whether immune stimulation with bacterial lipopolysaccharide (LPS) affects blood carotenoid levels. We thus tested the effects of carotenoids on the oxidative burst of phagocytes under neutral conditions and during in vivo immune challenge. LPS injection depleted plasma carotenoids, indicating involvement of these phytochemicals in the immune response. However, we did not find any evidence that manipulation of carotenoid intake had modulated anti-BA antibody production, LPS-stimulated oxidative burst of phagocytes, or basal levels of circulating reactive oxygen species. This indicates that carotenoid intake does not affect endogenous production of reactive oxygen species by immune cells. This finding is consistent with the view that carotenoids are unlikely to provide a direct link between oxidative stress and colouration. However, it remains to be tested whether the oxidative burst of phagocytes induced in our experiment actually inflicts oxidative damage and whether carotenoids play a role in the attenuation of such potential damages.

Does immune suppression during stress occur to promote physical performance?

Two adaptationist hypotheses have been proposed to explain why stress, particularly elevation of stress hormones (i.e., glucocorticoids), tends to suppress immune functions. One is that immune suppression represents efforts to minimize autoimmune responses to self-antigens released as organisms cope with stressors (i.e., the autoimmune-avoidance hypothesis). The other is that immune suppression occurs to promote a shunting of resources to life processes more conducive to survival of the stressor (i.e., the re-allocation hypothesis). Here in wild-caught house sparrows (Passer domesticus), we tested the second hypothesis, asking whether sustained elevation of baseline glucocorticoids, due to captivity, caused a greater rate of decline in immune functions than flight performance. A greater decline in immune functions than flight performance would support the re-allocation hypothesis. As in previous studies, we found that captivity tended to alter baseline corticosterone, suggesting that house sparrows experience captivity as a stressor. Captivity also affected several constitutive and induced innate immune metrics: bacterial (Escherichia coli) killing activity (BKA) of blood and oxidative burst of leukocytes both changed in a manner consistent with immune disregulation. In contrast, breast muscle size and vertical flight (hovering) duration improved over captivity. Collectively, these changes provide indirect support for the re-allocation hypothesis, although within individuals, changes in immune and physical performance were unrelated.

Oxidative stress and information content of black and yellow plumage coloration: an experiment with greenfinches

Carotenoid and melanin pigments in the plumage of birds are hypothesized to be sensitive to oxidative stress. We manipulated oxidative status of captive greenfinches (Carduelis chloris L.) by the administration of buthionine sulfoximine (BSO), a selective inhibitor of the synthesis of glutathione (GSH), an intracellular antioxidant. Half of the birds in the treated group, as well as in the control group, also received dietary carotenoid (lutein) supplementation. BSO treatment reduced erythrocyte GSH levels and caused oxidative damage as indicated by the increased concentration of plasma malondialdehyde (MDA), an end product of lipid peroxidation. BSO treatment also reduced the brightness (i.e. increased blackness) of the tips of tail feathers grown during the experiment. These results show that a low systemic GSH level is required for development of eumelanin plumage coloration and that such a low GSH level is also potentially dangerous for the organism. Carotenoid supplementation increased plasma carotenoid levels and chroma of the yellow parts of the feathers grown during the experiment. However, carotenoid supplementation did not reduce plasma MDA levels. Manipulation of GSH did not affect plasma carotenoids or carotenoid-based plumage coloration. These findings argue against the antioxidant function of lutein in vivo and carotenoid signaling of antioxidant status.