Phytohemagglutinin-induced skin swelling in birds: histological support for a classic immunoecological technique

Continuous white noise exposure during sleep and childhood development: A scoping review

BACKGROUND

White noise machines are widely used as a sleep aid for young children and may lead to poor hearing, speech, and learning outcomes if used incorrectly.

OBJECTIVE

Characterize the potential impact of chronic white noise exposure on early childhood development.

METHODS

Embase, Ovid MEDLINE, the Cochrane Central Register of Controlled Trials, Scopus, and Web of Science were searched from inception through June 2022 for publications addressing the effects of chronic noise exposure during sleep on early development in animals and children. PRISMA-ScR guidelines were followed. Among 644 retrieved publications, 20 met inclusion criteria after review by multiple authors. Seven studies evaluated animal models and 13 studies examined pediatric subjects, including 83 animal and 9428 human subjects.

RESULTS

White noise machines can exceed 91 dB on maximum volume, which exceeds the National Institute for Occupational Safety and Health noise exposure guidelines for a 2-h work shift in adults. Evidence suggests deleterious effects of continuous moderate-intensity white noise exposure on early development in animal models. Human subject data generally corroborates these models; however, studies also suggest low-intensity noise exposure may be beneficial during sleep.

CONCLUSIONS

Existing data support the limitation of maximal sound intensity and duration on commercially available white noise devices. Further research into the optimal intensity and duration of white noise exposure in children is needed.

Subclinical peripheral inflammation has systemic effects impacting central nervous system proteome in budgerigars

Regulation of neuroimmune interactions varies across avian species. Little is presently known about the interplay between periphery and central nervous system (CNS) in parrots, birds sensitive to neuroinflammation. Here we investigated the systemic and CNS responses to dextran sulphate sodium (DSS)- and lipopolysaccharide (LPS)-induced subclinical acute peripheral inflammation in budgerigar (Melopsittacus undulatus). Three experimental treatment groups differing in DSS and LPS stimulation were compared to controls. Individuals treated with DSS showed significant histological intestinal damage. Through quantitative proteomics we described changes in plasma (PL) and cerebrospinal fluid (CSF) composition. In total, we identified 180 proteins in PL and 978 proteins in CSF, with moderate co-structure between the proteomes. Between treatments we detected differences in immune, coagulation and metabolic pathways. Proteomic variation was associated with the levels of pro-inflammatory cytokine mRNA expression in intestine and brain. Our findings shed light on systemic impacts of peripheral low-grade inflammation in birds.

Quantification of Thermal Acclimation in Immune Functions in Ectothermic Animals

This short review focuses on current experimental designs to quantify immune acclimation in animals. Especially in the face of rapidly changing thermal regimes, thermal acclimation of immune function has the potential to impact host-pathogen relationships and the fitness of hosts. While much of the field of ecoimmunology has focused on vertebrates and insects, broad interest in how animals can acclimate to temperatures spans taxa. The literature shows a recent increase in thermal acclimation studies in the past six years. I categorized studies as focusing on (1) natural thermal variation in the environment (e.g., seasonal), (2) in vivo manipulation of animals in captive conditions, and (3) in vitro assays using biological samples taken from wild or captive animals. I detail the strengths and weaknesses of these approaches, with an emphasis on mechanisms of acclimation at different levels of organization (organismal and cellular). These two mechanisms are not mutually exclusive, and a greater combination of the three techniques listed above will increase our knowledge of the diversity of mechanisms used by animals to acclimate to changing thermal regimes. Finally, I suggest that functional assays of immune system cells (such as quantification of phagocytosis) are an accessible and non-taxa-specific way to tease apart the effects of animals upregulating quantities of immune effectors (cells) and changes in the function of immune effectors (cellular performance) due to structural changes in cells such as those of membranes and enzymes.

Peripheral inflammation-induced changes in songbird brain gene expression: 3' mRNA transcriptomic approach

Species-specific neural inflammation can be induced by profound immune signalling from periphery to brain. Recent advances in transcriptomics offer cost-effective approaches to study this regulation. In a population of captive zebra finch (Taeniopygia guttata), we compare the differential gene expression patterns in lipopolysaccharide (LPS)-triggered peripheral inflammation revealed by RNA-seq and QuantSeq. The RNA-seq approach identified more differentially expressed genes but failed to detect any inflammatory markers. In contrast, QuantSeq results identified specific expression changes in the genes regulating inflammation. Next, we adopted QuantSeq to relate peripheral and brain transcriptomes. We identified subtle changes in the brain gene expression during the peripheral inflammation (e.g. up-regulation in AVD-like and ACOD1 expression) and detected co-structure between the peripheral and brain inflammation. Our results suggest benefits of the 3'end transcriptomics for association studies between peripheral and neural inflammation in genetically heterogeneous models and identify potential targets for the future brain research in birds.

Blind date: female fossorial amphisbaenians prefer scent marks of large and healthy males

Selecting a good mate is a decision with important fitness consequences. For this reason, mate choice has promoted the evolution of sexual ornaments signaling the quality of an individual. In fossorial animals, inhabiting visually restricted underground environments, chemical senses should be very important for mate choice. We examined whether sexual chemical signals (substrate scent marks) produced by males of the Iberian worm lizard, Blanus cinereus, a strictly fossorial blind amphisbaenian, provide information to females on morphological traits and health state. We administered corticosterone (CORT) to males simulating a continuous stressor affecting their health. Females preferred settling at sites scent-marked by males in comparison with similar sites with female scent or unmarked sites, but the attractiveness of males' scent differed between individuals. Females preferred scent marks of larger/older males and with a higher immune response, while their body condition and CORT treatment were unrelated to female preferences. Chemical analyses showed that proportions of some compounds in precloacal secretions of males (used to produce scent marks) were correlated with the morphological (body size) and health state (immune response and body condition, but not CORT treatment) of these males. These results suggest that females may make site-selection decisions based on assessing the chemical characteristics of males' scent marks, which were reliably related to some of the traits of the male that produced the scent. Therefore, females might use chemical senses to increase the opportunities to find and mate with males of high quality, coping with the restrictions of the subterranean environment.

Critical review of the phytohemagglutinin assay for assessing amphibian immunity

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

Comparative immunocompetence and interspecies transmission of avian orthoavulavirus-1 in feral birds originating from rural and urban settings

Feral birds residing close to urban settings exhibit higher immunocompetence against environmental pathogens than their counterparts in rural areas. In this study, we comprehensively evaluated the immunocompetence of five specific feral bird species and investigated the potential for interspecies transmission and pathogenicity of Avian orthoavulavirus-1 (AOAV-1) originating from the Anseriformes order. The immunocompetence assessment involved administering the phytohemagglutinin (PHA) test to individual groups of birds from rural and urban settings, measuring patagium thickness at specific time intervals (12, 24, 36, 48, and 60 h) following the administration of 0.1 mL (1 mg/mL) of PHA. Urban birds displayed significantly enhanced mean swelling responses, particularly urban pigeons, which exhibited a significant difference in patagium thickness at all-time intervals except for 24 h (p = 0.000, p = 0.12). Similarly, rural and urban quails and crows showed substantial differences in patagium thickness at all-time intervals except for 12 h (p = 0.542, p = 0.29). For the assessment of interspecies transmission potential and pathogenicity, each feral bird group was separately housed with naive broiler birds (n = 10 each) and challenged with a velogenic strain of AOAV-1 isolate (Mallard-II/UVAS/Pak/2016) at a dose of 1 mL (108 EID50/mL). Urban birds demonstrated higher resistance to the virus compared to their rural counterparts. These findings highlight the specific immunocompetence of feral bird species and their potential contributions to AOAV-1 transmission and pathogenicity. Continuous monitoring, surveillance, and strict implementation of biosafety and biosecurity measures are crucial for effectively controlling AOAV-1 spillover to the environment and wild bird populations in resource-limited settings, particularly Pakistan.

Spatial Variation in the Inflammatory Response of House Sparrows in their Native Range

Characterizing spatial differences in wildlife immunity is the first step to identify environmental drivers of host defense and disease risks. The house sparrow (Passer domesticus) is a model system for ecoimmunology, but spatial differences in immunity have been largely restricted to the invasive range of this global species. We provide an initial test of spatial variation in immune response to phytohemagglutinin in the native range, finding that birds from Romania have greater inflammatory responses than birds from Egypt. Future broad surveys across the house sparrow native range could contextualize these differences and determine underlying drivers.

Adaptive plastic responses to metal contamination in a multistress context: a field experiment in fish

Wild populations often differ in their tolerance to environmental stressors, but intraspecific variability is rarely taken into account in ecotoxicology. In addition, plastic responses to multiple stressors have rarely been investigated in realistic field conditions. In this study, we compared the responses to metal contamination of gudgeon populations (Gobio occitaniae) differing in their past chronic exposure to metal contamination, using a reciprocal transplant experiment and an immune challenge mimicking a parasite attack to test for potential effects of multiple stressors across biological levels. We measured fish survival and traits involved in metal bioaccumulation, oxidative stress, immunity, cell apoptosis, and energy management to decipher underpinning physiological mechanisms across biological levels (i.e., gene expression, cell, organism). Fish from the two replicate High Contamination sites had higher survival when transferred into contaminated sites, suggesting a local adaptation to the contaminated site, possibly explained by higher levels of detoxification and antioxidant capacity but with potential higher apoptosis costs compared to their naïve counterparts. We found no evidence of co- or maladaptation to the immune stressor, suggesting no specific costs to face pathogens. In the emerging field of evolutionary ecotoxicology, this study underlines the need to consider intraspecific variability to better understand the effects of pollution in heterogeneous populations.

Do female bluethroats without extra-pair offspring have more MHC-compatible social mates?

Abstract

Genes of the major histocompatibility complex (MHC) are crucial for adaptive immunity in jawed vertebrates, and theory predicts that there should be mate choice for optimizing MHC constitution in the offspring. In a previous study, we demonstrated a non-random female choice of extra-pair males in the bluethroat (Luscinia svecica), yielding offspring that was closer to an intermediate MHC class II (MHCII) allele count than their within-pair halfsiblings. The present study tests whether social pairs with only within-pair young (WPY) in their brood, in the same study population, had a combined MHC-constitution closer to a presumed intermediate optimum, than social pairs with extra-pair young (EPY), with a corresponding pattern in their offspring. As expected, we found that WPY from pure WPY-broods were more MHC-optimal than WPY from mixed broods, but only in broods of young (second year) males. Correspondingly, there was a tendency for social pairs with only WPY in their brood to be more MHC-compatible than social pairs with EPY in their brood, when the male was young. Older bluethroat males have considerably larger testes than young males, and their higher sperm competitiveness could help them secure paternity in their own brood, also when they are not MHC-compatible. In other words, in the sexual conflict over paternity, females may be more likely to realise their preference for a MHC-compatible mate when paired to a young male. As a possible fitness indicator, immune responsiveness to an injected antigen (PHA) was elevated for offspring closer to “the golden mean” in MHCII allele count.

Significance statement

This study contributes to our understanding of MHC-based mate choice in extra-pair mating systems, by showing that female bluethroats (Luscinia svecica) with an MHCII-compatible social mate tend to have no extra-pair young in their brood, but only when the social male is young. This elucidates a possible sexual conflict, in which older social males are able to override female preferences and prevent other males from gaining paternity in their brood through higher sperm production. Studying systems in which extra-pair paternity occurs offers an insight into the genetic benefits of mate choice, as extra-pair males, in contrast to social males, generally contribute only sperm. Further, the strict and thorough genotyping scheme applied in this study enabled us to demonstrate a preference for “the golden mean” in MHC-diversity in a species with one of the highest MHC class II-diversity known to date.

A Call For More Ecologically And Evolutionarily Relevant Studies of Immune Costs

What are the relative costs and benefits of mounting immune responses? Practitioners of ecoimmunology have grappled with this central question since the field's inception with the main tension being how to make tractable methodological choices that maintain the ecological relevance of induced and measured immune costs. Here, we point out two methodological approaches that we feel are underrepresented in the field, describe risks associated with neglecting these methods, and suggest modern techniques that maximize both the diversity and ecological relevance of collected data. First, it is commonly assumed that frequently used and experimentally convenient immune stimulants will induce ecologically relevant immune responses in study organisms. This can be a dangerous assumption. Even if a stimulant's general immune response properties are well characterized, it is critical to also measure the type and scale of immune responses induced by live pathogens. Second, patterns of immune defenses evolve like other traits, thus a comparative approach is essential to understand what forces shape immune variation. Finally, we describe modern genetic and immunological approaches that will soon become essential tools for ecoimmunologists, and present case studies that exemplify the utility of our recommendations.

Neglected skin-associated microbial communities: a unique immune defense strategy of Bufo raddei under environmental heavy metal pollution

Amphibians defend against pathogens using skin microbial communities, in addition to innate and adaptive immunity. Despite skin microbial communities play a key role in the immune function of amphibians, few studies have focused on the changes in its composition and function. In the present study, we identified the variation in adaptive immunity, as well as the corresponding changes in skin microbiome of Bufo raddei living in a heavy metal polluted area. The adaptive immunity of B. raddei in heavy metal polluted area was significantly lower than that in relatively unpolluted area. Further, different skin bacterial communities were found in the two areas. In the heavy metal polluted area, Actinobacteria and Microbacterium were the dominant bacteria in the skin microbiome of B. raddei, which showed broad-spectrum antibacterial activity. Besides, the antibiotic synthesis was also increased in metabolic pathways. The present study suggested that the adaptive immunity of B. raddei was weakened under long-term heavy metal stress. However, the toads increased the abundance of bacteriostatic bacteria by regulating the composition of skin microbiome, which released a large number of bacteriostatic metabolites and enhanced the host resistance to external pathogens in turn.

Effects of an immune challenge on the thermal preferences of adult and newborn Liolaemus lizards from Patagonia, Argentina

Body temperature has relevant effects on the immune response. Here, we characterized the thermal biology and health condition of the viviparous lizard Liolaemus kingii from Patagonia (Argentina), by studying field body temperatures, presence of injuries or ectoparasites, body condition (BC), and individual immune response capacity with the phytohemagglutinin (PHA) skin-swelling assay. In addition, we analyzed the effects of injections of a bacterial endotoxin (lipopolysaccharide; LPS) on the preferred temperature (Tp) and BC of adult males and newborns. The PHA treatment caused detectable thickening at 2 and 20 hours post-assay in males, indicating a significant immune response related to an increase in cellular activity. LPS-challenged lizards thermoregulated accurately and at stable body temperatures within the 50% interquartile of Tp (Tset) over the 72-hour period while the control group showed a more variable and lower Tp. Exposure to LPS negatively affected the BC of newborns, whereas it did not affect the BC of adult males. LPS challenges, used as a proxy of pathogen exposures to study lizard behavioral thermoregulation, constitute a practical approach to assess the immunological constraints lizards from high-latitude regions may face due to global warming and anthropogenic disturbances.

Long-term sex-dependent inflammatory response of adult frogs to ammonium exposure during the larval stage

Among others, the global change involves a worldwide increase in cropland area, with the concomitant rise in nitrogenous fertilizer supplementation and species range alterations, including parasites and pathogens. As most animals rely on their immune systems against these infectious agents, studying the potential effects of nitrogenous compounds on animal immune response is vital to understand their susceptibility to infections under these altered circumstances. Being subjected to an alarming process of global declines, amphibians are the object of particular attention, given their sensitivity to these compounds, especially to ammonium. Moreover, whereas adults can actively avoid polluted patches, larvae are confined within their waterbodies, thus exposed to contaminants in it. In this work, we test whether chronic exposure to a sublethal dose of ammonium during the larval stage of Pelophylax perezi frogs, released from all contamination after metamorphosis, leads to impaired inflammatory response to phytohemagglutinin in adults. We also test whether such a response differs between agrosystem individuals as compared with conspecifics from natural habitats. We found negative carryover effects of chronic exposure of larvae to ammonium on adult inflammatory response, which could imply a greater susceptibility to pathogens and parasites. However, this damage is only true for males, which, according to the immunocompetence handicap hypothesis, could be a consequence of a testosterone-triggered impairment of male immune function. In disagreement with our prediction, however, we detected no differences in the inflammatory response of agrosystem frogs to phytohemagglutinin as compared with natural habitat conspecifics.

Population density mediates induced immune response, but not physiological condition in a well-adapted urban bird

Thriving under high population density is considered a major feature of urban exploiter species. Nevertheless, population density appears to be a surprisingly overlooked factor in urban ecology studies. High population numbers observed in urban species might promote pathogen transmission and negatively affect health or condition, thus requiring investments in immunocompetence. The feral pigeon Columba livia domestica is an example of a successful city-dweller, found in great abundance in large cities across the globe. We investigated the effects of population density on induced immune response (phytohaemagglutinin skin test) and body condition (blood haemoglobin concentration and size-corrected body mass) in 120 feral pigeons, captured along population density gradient in Łódź (central Poland). We found that stronger immune response was associated with higher population density, but was not related to physiological condition and physiological stress (heterophil/lymphocyte ratio). Moreover, condition indices were not associated with population density. However, since pigeon population density was highly correlated with the level of habitat urbanization, we cannot exclude that any density-dependent effects may be mediated by habitat variation. Our results indicate that urban environment, via population density, might exert different selective pressures on immunocompetence and body condition in this successful urban exploiter.

Induction of both local and systemic immunity by in vivo injection of PHA into ginbuna carp fin

Phytohemagglutinin (PHA) is a well-known mitogen inducing activation and proliferation of lymphocytes, particularly T lymphocytes in vitro. PHA has also been used in vivo for assessing cell-mediated immunity in non-mammalian vertebrates, particularly in birds. However, it has been suggested that local inflammation as a direct result of tissue damage could be responsible for skin swelling after PHA injection, in addition to induction of T lymphocyte mitogenesis. In order to understand the complex nature of this response in fish we investigated the accumulation of cell types chronologically in dorsal fin of ginbuna crucian carp Carassius auratus langsdorfii after PHA injection. Neutrophils appeared first and showed a peak response on day 1, decreasing gradually and followed by macrophages and blast cells while lymphocytes increased later with a peak response on day 5. The number of accumulated cells was significantly higher in PHA-injected fish than controls in most cases. Lymphocytes identified as CD4-1⁺and CD8α⁺ were significantly more abundant in PHA-injected fish than in control fish throughout the 7-day experimental period except on day 1, while the number of IgM⁺ lymphocytes was higher in PHA-injected fish only on day 1. In the blast cell fraction, the number of CD4-1⁺ lymphocytes was significantly higher in PHA-injected fish than in control fish throughout experimental period, except on day 1. We also document the migration of neutrophils from the kidney to the fin through blood, followed by granulopoiesis in the kidney. These results suggest that adaptive immunity as well as innate immunity was induced by in vivo stimulation with PHA.

Blood parasites in sympatric lizards: what is their impact on hosts’ immune system?

Assessment of parasites and their pathogenicity is essential for studying the ecology of populations and understanding their dynamics. In this study, we investigate the prevalence and intensity of infection of haemogregarines (phylum Apicomplexa) in two sympatric lizard species, Podarcis vaucheri and Scelarcis perspicillata, across three localities in Morocco, and their effect on host immune response. We used the Phytohaemagglutinin (PHA) skin testing technique to relate the level of immune response with parasite infection. Prevalence and intensity levels were estimated with microscopy, and 18S rRNA gene sequences were used to confirm parasite identity. All parasites belong to the haemogregarine lineage found in other North African reptiles. There were differences in prevalence between localities and sexes. Overall, infected lizards were larger than uninfected ones, although we did not detect differences in parasitaemia across species, sex or locality. The swelling response was not related to the presence or number of haemogregarines, or to host body size, body condition, sex or species. We found no evidence of impact for these parasites on the circulating blood cells or the hosts’ immune system, but more data is needed to assess the potential impact of mixed infections, and the possibility of cryptic parasite species.

Establishment of baseline cytology metrics in nestling American kestrels (Falco sparverius): Immunomodulatory effects of the flame retardant isopropylated triarylphosphate isomers

Avian populations must mount effective immune responses upon exposure to environmental stressors such as avian influenza and xenobiotics. Although multiple immune assays have been tested and applied to various avian species, antibody-mediated immune responses in non-model avian species are not commonly reported due to the lack of commercially available species-specific antibodies. The objectives of the present study were to advance methods for studying wild bird immune responses and to apply these to the evaluation of cytological responses after exposure of American kestrels, Falco sparverius, to a commercial flame retardant mixture containing isopropylated triarylphosphate isomers (ITP). Hatchlings were gavaged daily with safflower oil or 1.5 ug/g bw/day of ITP suspended in safflower oil, then bled on days 9, 17, and 21. The ITP treatment group (n = 18) and a subset of controls (Poly I:C treatment group; n = 10) were injected on days 9 and 15 with a synthetic analog of viral double-stranded RNA, polyinosinic:polycytidylic acid (Poly I:C), a toll-like receptor ligand and synthetic viral mimic, and responses compared to a sham injected control group (n = 8). The hypotheses tested whether kestrels showed immunological differences among treatment groups, genetic sex, and/or white blood cell (WBC) subpopulation type over time. A flow cytometry (FCM) gating strategy categorized heterophils (H), lymphocytes (L), and monocytes (M) and their proportions, and measured relative fluorescence in response to anti-chicken CD4 binding. Fluorescent cell surfaces and some granular/vacuolar inclusions were visualized by epifluorescence microscopy. A fourth subpopulation with higher levels of granularity than M but less than H became increasingly apparent with time and was gated along with the H subpopulation; its frequency of occurrence was lowest in the ITP group (P = 0.0023). The percentages of cells differed among treatment groups, days, and sexes (P = 0.0001). For both sexes, percentages of H and L were higher than M in control and Poly I:C. In the ITP group, L percentages were higher than H and M (P = 0.0457), and H and L were higher than M on days 9 and 21 (P = 0.0001). The ratios of H:L and H:WBC, indicators of robust immunity, were also higher on days 9 and 21 than on 17 (P = 0.0079). For each sex, the highest levels of activity measured by FCM geometric means (GEO) of fluorescence (indicative of antibody binding) were observed on day 9 (P = 0.0001 female, and P = 0.0011 male) in H over both L and M (P < 0.0001 for each). In males, GEO of the Poly I:C group was higher than that of the ITP group (P = 0.0374), with no difference observed among females over all days. By using a FCM algorithm for population comparisons of fluorescence to investigate binding within H, the T(x) scores indicated higher fluorescence in control and Poly I:C groups over ITP (P = 0.0001). Unlike chickens, Gallus gallus, which express CD4 primarily on L, kestrels bound the commercial antibody primarily within the gated H subpopulation, suggesting an immunophenotypic difference between taxa, despite a ~60% identity of Falco CD4 amino acid sequences with chicken CD4. The emergent cell subset within the gated H presented dendritic-like cell (DLC) morphological and functional properties, apparently serving as an effector cell. This study adds interpretive context to ecological investigations of infection and of potential immunomodulation by emerging compounds, whereby the early innate responses are mediated by the various cell subsets serving as useful quantitative markers of immunological condition. Data showed that dietary exposure to ITP was immunosuppressive for male and female kestrels over the course of the experiment, reducing DLC frequency compared to the Poly I:C controls. Heterophils and DLC were important in facilitating innate immunological responses.

Effects of harmful algal blooms on stress levels and immune functioning in wetland-associated songbirds and reptiles

Harmful algal blooms (HABs), caused primarily by nutrient input from agricultural runoff, are a threat to freshwater systems worldwide, and are further predicted to increase in size, frequency, and intensity due to climate change. HABs occur annually in the Western Basin of Lake Erie (Ohio, USA), and these blooms become toxic when dominated by cyanobacteria that produce the liver toxin microcystin. Although we are making substantial inroads toward understanding how microcystin affects human health, less is known about effects of microcystin on wildlife exposed to HABs. Wetland-associated songbirds (barn swallows, Hirundo rustica, and red-winged blackbirds, Agelaius phoeniceus) and reptiles (Northern watersnakes, Nerodia sipedon, and painted turtles, Chrysemys picta) were sampled from wetlands exposed to chronically high microcystin levels due to a prolonged HAB event, and from unexposed, control wetlands. Physiological stress levels and several measures of immune functioning were compared between the HAB-exposed and control populations. Physiological stress levels, measured as heterophil:lymphocyte ratios, were higher in barn swallows, red-winged blackbirds, and Northern watersnakes exposed to a chronic HAB compared to unexposed, control individuals, but painted turtles did not differ in physiological stress levels between HAB-exposed and control individuals. Neither barn swallows nor red-winged blackbirds differed in immune functioning between populations, but HAB-exposed watersnakes had higher bactericidal capacity than control snakes, and HAB-exposed painted turtles had lower bactericidal capacity than control turtles. These results suggest that even when HABs do not cause direct mortality of exposed wildlife, they can potentially act as a physiological stressor across several taxa, and furthermore may compromise immune functioning in some species.

Infection with Batrachochytrium dendrobatidis reduces salamander capacity to mount a cell-mediated immune response

The vertebrate immune system is a costly defense system that is responsible for preventing and eliminating parasites and pathogens. Theory predicts that hosts experience tradeoffs associated with immune deployment and other physiological functions. Although empirical evidence for immune-physiology tradeoffs are well documented in the literature, fewer studies have examined tradeoffs within the immune system in wild vertebrates. We explored the topic of concomitant immune challenges in amphibians by exposing salamanders (Plethodon cinereus) to a fungal pathogen Batrachochytrium dendrobatidis (hereafter "Bd") and then to phytohemagglutinin (hereafter "PHA"). We measured Bd infection using quantitative PCR and used measurements of the tail thickness at the PHA injection site as an estimate of skin swelling. We tested whether Bd reduced the salamander's capacity to mount an immune response towards PHA or whether Bd would stimulate immune activity and thereby increase the response towards PHA. Salamanders that were infected with Bd had a reduced skin-swelling when injected with PHA compared to noninfected salamanders, a result that is consistent with the hypothesis that Bd-infected salamanders have lower immunocompetence than noninfected salamanders. We also found that PHA-induced swelling response was negatively associated with Bd infection abundance (i.e., the infection burden of all exposed salamanders, including those that were exposed but not infected), indicating that salamanders with a higher infection abundance had the lowest swelling response to PHA. Our results suggest that individuals of P. cinereus might experience an energetic tradeoff between successfully fighting off Bd and mounting an immune response towards PHA.

Traffic noise disrupts vocal development and suppresses immune function

Noise pollution has been linked to learning and language deficits in children, but the causal mechanisms connecting noise to cognitive deficiencies remain unclear because experimental models are lacking. Here, we investigated the effects of noise on birdsong learning, the primary animal model for vocal learning and speech development in humans. We found that traffic noise exposure retarded vocal development and led to learning inaccuracies. In addition, noise suppressed immune function during the sensitive learning period, indicating that it is a potent stressor for birds, which is likely to compromise their cognitive functions. Our results provide important insights into the consequences of noise pollution and pave the way for future studies using birdsong as an experimental model for the investigation of noise-induced learning impairments.

The effect of avian brood parasitism on physiological responses of host nestlings

Avian obligate brood parasites lay their eggs in the nests of other species that may provide care for the foreign offspring. Brood parasitism often imparts substantial fitness losses upon host nestlings when they are raised alongside the typically more competitive, larger, and older parasitic chick(s). Whereas fitness costs due to reduced host offspring survival in parasitized broods have been studied in detail, the physiological changes in host nestlings caused by parasitic nestmate(s) are less well known. We compared prothonotary warbler (Protonotaria citrea) nestlings, a host of the nest-sharing brown-headed cowbird (Molothrus ater), in experimentally parasitized vs. non-parasitized broods. Our aim was to determine whether cohabitation with brood parasitic young impacted host nestling baseline corticosterone plasma concentrations, immune responses, body condition, and mortality. Corticosterone levels and body condition of host nestlings were similar between nests with or without a cowbird nestmate, whereas host immune responses were lower and nestling mortality was greater in parasitized broods, irrespective of variation in brood size or total brood mass. We detected no trade-offs of baseline corticosterone levels with either immune responses or with body condition. These results suggest that this host species' nestlings experience some adverse fitness-relevant physiological effects in parasitized broods, but are also resilient in other aspects when coping with brood parasitism.

Density-dependence of nestling immune function and physiological condition in semi-precocial colonial bird: a cross-fostering experiment

BACKGROUND

Nesting in large aggregations provides several important advantages for colonially breeding birds. However, it also imposes certain costs, associated with facilitated pathogen transmission and social stress. The cost-benefit ratio is not similar for all the birds in a colony and it might be mediated by nest density. To investigate the influence of nest density on cell-mediated immune function and on physiological condition of nestlings, we arranged a cross-fostering experiment in three breeding colonies of black-headed gulls Chroicocephalus ridibundus. First, we exchanged eggs between plots of high and low nest density. Afterwards, we performed phytohaemagglutinin (PHA) skin test and we measured blood haemoglobin concentration in nearly 350 nestlings from experimental (exchanged) and control (non-exchanged) groups.

RESULTS

We found that PHA response was lowest in high nest density control group, indicating that depressed immune function of offspring, likely caused by social stress, can be considered as a cost of colonial breeding. Contrastingly, body condition of nestlings was the poorest in low density control group.

CONCLUSION

Nestlings hatched and raised in high nest density plots did not have higher blood haemoglobin concentration in comparison to other study groups. Furthermore, they were affected with depressed cell mediated immune function, which is possibly driven by combined maternal (corticosteroid hormones deposited in yolk) and environmental (elevated social stress) effects. These results indicate that breeders from high nest densities do not benefit by rising offspring in better quality, in terms of immune function and body condition, although, in the light of previous studies, high nest densities are occupied by birds of higher individual quality, than low density areas. Our study provides a novel insight into the mechanisms of density-dependence that govern fitness of colonially nesting birds.

Seasonal variation in sex-specific immunity in wild birds

Whilst the immune system often varies seasonally and exhibits differences between males and females, the general patterns in seasonality and sex differences across taxa have remained controversial. Birds are excellent model organisms to assess these patterns, because the immune system of many species is well characterised. We conducted a meta-analysis using 41 wild bird species from 24 avian families to investigate sex differences and seasonal (breeding/non-breeding) variations in immune status, including white blood cell counts, phytohaemagglutinin (PHA) test, bacteria-killing ability (BKA), haemolysis and haemagglutination assays. We found male-biased macrophage concentration, BKA and haemolysis titers, but only during the breeding season. Sex-specific heterophil concentrations, heterophil/lymphocyte ratios and PHA responses differed between breeding and non-breeding, suggesting larger changes in males than in females. Importantly, sex differences in immune status are stronger during the breeding period than during the non-breeding period. Taken together, our study suggests that both seasonal variation and sex differences in immune system are common in birds, although their associations are more complex than previously thought.

Egg production, fertility, hatchability and immune responses of some chicken strains under high ambient temperatures

This experiment was designed to investigate and compare the egg production, fertility, hatchability and immune responses of some local developed Egyptian chicken strains under high ambient temperatures. A total of 108 (26 weeks old) laying hens of Matrouh, Silver Montazah, Mandarah and Inshas (9 hens × 3 replicates × 4 strains) were used to evaluate the impact of thermal stress (24-34ºC) during summer season (June, July and August) on egg production, fertility, hatchability and immune responses. The obtained results revealed that final body weight (FBW/g) and body weight change (BWC/g) among different chicken strains were not affected. The daily feed consumption (FC/g) and feed conversion ratio (FCR) for Silver Montazah and Inshas strains were significantly (p ≤ .05) higher than those of Matrouh and Mandarah strains. The mean egg production (EP/%) and egg mass (EM) for Silver Montazah and Inshas strains were significantly (p ≤ .05) higher than those of Matrouh and Mandarah strains. The highest percentages of hatchability of total eggs (HTE) and fertile eggs (HFE) were recorded in Inshas chickens, while the lowest value was recorded in Mandarah chickens. Also, the highest embryonic mortalities (p ≤ .05) and lowest chick weight at hatch (CWH/g) were recorded in Mandarah chickens compared with the other strains. The highest values for antibody titres against phytohemagglutinin-P (PHA-P) were recorded in Mandarah chickens, while the least values were recorded in Inshas chickens.

Synergetic effects of immune challenge and stress depress cortisol, inflammatory response and antioxidant activity in fish-eating Myotis

One of the most common tools in conservation physiology is the assessment of environmental stress via glucocorticoid measurement. However, little is known of its relationship with other stress-related biomarkers, and how the incidence of an immune challenge during long-term stress could affect an individual's overall stress response. We investigated here the relationship between basal and post-acute stress fecal cortisol metabolite (FC) with different antioxidant enzymes, oxidative damage and immune parameters in the fish-eating bat, Myotis vivesi We found that in both basal and post-stress conditions, FC was highly related with a number of antioxidant enzymes and immune parameters, but not to oxidative damage. We also assessed changes of FC through the seasons. Basal FC samples and stress reactivity after short-duration stress displayed similar levels during summer, autumn and early winter, but lower concentrations in late winter. Stress reactivity after long-duration stress was greater in summer and early winter. Finally, we tested the effect of a simultaneous exposure to a long, strong stress stimulus with an immune response stimulation by administrating adrenocorticotropic hormone (ACTH) and phytohemagglutinin (PHA) after 42 h. Results showed that when both stimuli were administrated, FC concentrations, inflammation and some antioxidant activity were lowered in comparison with the control and individual administration of the challenges. Our findings support the idea that animals maintain constant basal glucocorticoid levels when living in challenging environments, but response to acute stress differs seasonally and immune defense mechanisms and stress responses might be compromised when confronted with multiple challenges.

Eurythermic Sprint and Immune Thermal Performance and Ecology of an Exotic Lizard at Its Northern Invasion Front

AbstractThermal performance of immunity has been relatively understudied in ectotherms, especially in the context of invasive species or in relation to other fitness-related traits and thermoregulatory patterns in the field. For reptiles, thermal biology is a primary factor determining physiological performance and population viability, and suboptimal thermal conditions may limit the expansion of exotic species along the edges of their invasion fronts. This study examined thermoregulatory ecology and thermal performance of immunity and sprinting in a population of Mediterranean geckos (Hemidactylus turcicus) at the northern edge of their invasion front in a temperate zone of the United States. In the field, we quantified temperatures of geckos of varied age classes in relation to air, wall, and refugia temperatures. We also quantified temperature-dependent sprint performance and immune function in field-collected geckos to detail thermal performance patterns that may contribute to the capacity for this species to invade cool climates. Although body temperature (T_b) of wild-caught geckos correlated with wall temperature, average T_b exhibited wide distributions, suggesting eurythermy. Furthermore, the thermal performance of immune swelling responses to phytohemagglutinin injections and sprinting was optimized over a similarly wide temperature range that overlapped with the field T_b's that suggest eurythermy in this species. The wide thermal performance breadths in these traits could buffer against variation in factors such as pathogen exposure and environmental temperatures that could otherwise suppress functional performance. Thus, eurythermy of sprint and immune performance may facilitate the invasive potential of H. turcicus.

Dose- and time-dependent effects of an immune challenge on fish across biological levels

Due to global changes, fish are increasingly exposed to immune challenges associated with disease outbreaks in aquatic ecosystems. Adjustments in physiology and behavior are generally critical to maintaining homeostasis after an immune challenge, but there is limited knowledge on the specific thresholds and dynamics of responses across levels of biological organization in fish. In this study, we tested how different concentrations of an antigens mixture (phytohemagglutinin and lipopolysaccharide) affected innate immunity with potential consequences on oxidative stress, energy reserves, body condition, and behavior across time, using the common gudgeon (Gobio sp.) as model species. The immune challenge induced a transitory increase in lytic enzyme activity (i.e., lysozyme) and local immune response (i.e., skin swelling) 2 days after the antigen injection. The available energy stored in muscle was also reduced 4 days after injection, without inducing oxidative stress at the cellular level. Overall, the immune challenge induced limited costs at the molecular and cellular levels but had strong effects at the whole organism level, especially on behavior. Indeed, fish swimming activity and sociability were affected in a dose- and time-dependent manner. These results suggest that immune challenges have dose-dependent effects across levels of biological organization and that behavior is a key response trait to cope with pathogen-induced immune costs in the wild, although fitness consequences remain to be tested.

Ontogeny of leukocyte profiles in a wild altricial passerine

Ecophysiological studies have highlighted the relevance of the avian immune system in individual fitness prospects in the wild. However, studies on the ontogeny of avian immunity are scarce. We analyse age-related changes in the cellular constitutive immunity throughout nestling development, as well as its relationship with sex and brood size. We found that cellular constitutive immunity could be affected by age, sex, brood size, or daily rhythm. Early-stage nestlings relied more on cells of the innate immunity rather than on cells linked to the adaptive immune system. Cellular immunity may not be fully mature in fledglings, as reflected by differences in phagocytic cell counts with regard to adults. Beyond the age-dependent effects, agranulocyte cell counts were affected by sibling competition while granulocyte cell counts showed a daily rhythm. We also show that the heterophil to lymphocyte ratio was negatively related to body weight when nestlings become more independent. Our study contributes knowledge to the fields of developmental immunology and ecological immunology based on essential components of the cellular immune system.

Endurance and sprint training affect immune function differently in green anole lizards (Anolis carolinensis)

Limited resources must be partitioned among traits that enhance fitness. Although survival-related traits often trade off with reproduction, survival-related traits themselves may trade off with each other under energy limitations. Whole-organism performance and the immune system both enhance survival, yet are costly, but it is unclear how the two might trade off with each other under energy-limited conditions. Resources can be allocated to very different types of performance (e.g. aerobic endurance versus anaerobic sprinting), just as they can be allocated to different components of the immune system (e.g. innate versus acquired) to maximize survival. We forced allocation to different performance traits in green anole lizards (Anolis carolinensis) using specialized exercise training, to determine how different components of the immune system would be impacted by shifts in energy use. We measured immunocompetence in endurance-trained, sprint-trained and untrained control lizards by evaluating swelling response to phytohemagglutinin (cell-mediated immunity), antibody response to sheep red blood cells (acquired humoral immunity) and wound healing (integrated immunity). Endurance-trained lizards had reduced cell-mediated immunity, whereas sprint-trained lizards had reduced rates of wound healing. The acquired immune response was not affected by either type of training. Because each immune measure responded differently to the different types of training, our results do not support the hypothesis that simple energy limitation determines overall investment in immunity. Instead, different components of the immune system appear to be affected in ways specific to how energy is invested in performance.

On the winter enhancement of adaptive humoral immunity: hypothesis testing in desert hamsters (Phodopus roborovskii: Cricetidae, Rodentia) kept under long-day and short-day photoperiod

We tested the winter immunity enhancement hypothesis (WIEH) on male desert hamsters (Phodopus roborovskii) kept under long-day (LD) and short-day (SD) photoperiods. We assumed that under SD in a laboratory, the adaptive humoral immune responsiveness to the antigenic challenge would be enhanced due to the lack of winter physical stressors and food shortages and/or because of the action of an endogenous winter bolstering mechanism, while under LD the immune responsiveness would be suppressed by the activity of the reproductive system. The results support the WIEH in part. We did not find a difference in antibody production in response to sheep erythrocytes between SD and LD hamsters, but SD males had the lower number of granulocytes and the higher number of lymphocytes in white blood cell counts. Reproductive activity was lower in SD males. These males demonstrated an increase in their mass-specific resting metabolic rate, their mass-specific maximal metabolic rate and their level of cortisol. The result of a generalized linear model analysis indicates the negative effect on secondary immunoresponsiveness to sheep erythrocytes of mid-ventral gland size, the organ characterizing individual reproductive quality, and designates a tradeoff between antibody production and reproductive effort. The mass-independent maximal metabolic rate also negatively affected antibody production, indicating a tradeoff between maximal aerobic performance and the adaptive immune function. The higher stress in SD males seems to be the most likely reason for the lack of the effect of daylight duration on antibody production.

Physiological responses of host parents to rearing an avian brood parasite: An experimental study

Raising an obligate avian brood parasite is costly for host parents because it redirects valuable parental resources from one's own offspring to genetically unrelated young. The costs of raising a brood parasite may be mediated by physiological stressors for foster parents if it requires greater or biased parental effort compared to raising non-parasitized broods. For example, upregulating glucocorticoid hormones or reducing immune responses may mediate a trade-off between resource allocation to a current brood versus future reproductive opportunities, but published data on parasitized hosts' physiology are scarce. Here we used an experimental approach to test if host parents respond to the presence of brood parasitic young through dynamic changes in their own physiology. We conducted our experiments with parasitic brown-headed cowbirds (Molothrus ater) fostered into nests of host prothonotary warblers (Protonotaria citrea). Relative to parents caring for non-parasitized control broods, parasitism increased baseline corticosterone levels and reduced body mass in adult male, but not in female, hosts. Immune responses to a novel antigen were depressed in both parents of parasitized broods compared to parents of non-parasitized broods. Additionally, we found that immune function increased along the breeding season regardless of treatment. These experiments also confirmed prior observational data that parasitized adult males have reduced return rates to breeding sites in years subsequent to raising cowbirds. The findings demonstrate diverse physiological effects of parasitism on the foster parents in our particular host-brood parasite system, yet we found no evidence of individual trade-offs between endocrine and immune responses of adult hosts.

Decreased Cell-Mediated Immune Response in Bosk's Fringe-Toed Lizards (Acanthodactylus boskianus) Inhabiting an Industrialized Area in Southern Tunisia

Lizards increasingly are recognized as suitable contaminant biomonitors in terrestrial ecosystems. Previously, we have shown that Bosk's fringe-toed lizards (Acanthodactylus boskianus) living close to the Gabès-Ghannouche industrial complex for fertilizer and acid production in southern Tunisia were contaminated by heavy metals. However, the impact of this contamination on lizard health parameters has not been investigated. In this study, we used the phytohaemagglutinin (PHA) skin-swelling test to assess whether the proximity to the industrial complex was associated with notable changes in lizard cell-mediated immune response (CMI). Our results showed significantly lower CMI in lizards living close to the industrial complex compared to those occurring farther away in a similar coastal habitat. Overall, our findings are consistent with the idea of immunotoxic effects of metal contamination. They also stress the usefulness of the PHA approach as an efficient tool for the evaluation of contaminant-related immunosuppression in lizards.

Dietary Supplementation With Various Fat Oils Affect Phytohemagglutinin Skin Test in Broiler Chickens

The current study aimed to investigate the effect of different dietary supplemental oils on the immune status of broilers. One-day-old Cobb 500 broiler chicks were randomly distributed into eight batteries and fed eight experimental diets. There were 680 broilers, 85 birds per battery. The experimental oils were all used at 10% of the total diet. Each dietary treatment (TRT) contained one of the following essential oils: TRT 1 = control group that received a basal diet + soybean oil (SO); TRT 2 = basal diet as in TRT 1 + sunflower oil (SFO); TRT 3 = basal diet as in TRT 1 + canola oil (CO); TRT 4 = basal diet as in TRT 1 + flaxseed oil (FLO); TRT 5 = basal diet as in TRT 1 + fish oil (FO); TRT 6 = basal diet as in TRT 1 + mix of fish oil and soya oil (SO + FO); TRT 7 = basal diet as in TRT 1 + algal biomass oil (DHA); TRT 8 = basal diet as in TRT 1 + echium oil (EO). All samples were taken from 10 birds per treatment (n = 10). The immune parameters investigated involved measurement of weights of immune organs as a general indicator, hemocytometric measurements, intestinal microbial count and hindgut acidosis, hindgut volatile fatty acids, and cellular immune response using phytohemagglutinin test. The use of the different dietary treatments did not affect the general health status of the chickens, and the mortality was minimal with no signs of illness or outbreaks. The fact that both the control and the treatment diets were equally consumed would indicate that supplemental oil inclusions did not adversely affect the palatability of the diet by the chickens. At 3 weeks of age, there was no significant effect observed in the microbial counts of the intestine. However, at 5 weeks of age, the highest microbial count was significantly observed for broilers fed EO (7.30%), closely followed by SFO (6.95%), and the least microbial counts were observed for CO (5.63%). No significance was observed for lactic acid bacteria (LAB) and Salmonella. There was no significance observed for the effect of the dietary treatments on the hindgut volatile acid in the broilers. Wattle swelling changes were significant between dietary treatments. The results revealed that dietary FLO, FO, and DHA oils induced higher cellular response than the other treatments (P = 0.035), representing higher cellular response in these groups. In conclusion, supplemental oils rich in n−3 fatty acids may enhance the immune response in broiler chickens, represented by the intestinal microbial counts and the cellular immune response.

Prenatal aromatase inhibition alters postnatal immunity in domestic chickens (Gallus gallus)

In birds, exposure to exogenous testosterone during embryonic development can suppress measures of immune function; however, it is unclear whether these effects are due to direct or indirect action via aromatization. Estradiol (E₂) is synthesized from testosterone by the enzyme aromatase, and this conversion is a necessary step in many signaling pathways that are ostensibly testosterone-dependent. Many lines of evidence in mammals indicate that E₂ can affect immune function. We tested the hypothesis that some of the immunomodulatory effects observed in response to in ovo testosterone exposure in birds are mediated by conversion to E₂ by aromatase, by using fadrozole to inhibit aromatization of endogenous testosterone during a crucial period of embryonic immune system development in domestic chickens (Gallus gallus). We then measured total IgY antibody count, response to PHA challenge, mass of thymus and bursa of Fabricius, and plasma testosterone post-hatch on days 3 and 18. Because testosterone has a reputation for immunosuppression, we predicted that if modulation of an immune measure by testosterone is dependent on aromatization, then inhibition of estrogen production by fadrozole treatment would lead to elevated measures of that parameter. Conversely, if testosterone inhibits an immune measure directly, then fadrozole treatment would likely not alter that parameter. Fadrozole treatment reduced circulating E₂ in female embryos, but had no effect on males or on testosterone in either sex. Fadrozole-treated chicks had decreased day 3 plasma IgY antibody titers and a strong trend towards increased day 18 thymic mass. Furthermore, fadrozole treatment generated a positive relationship between testosterone and thymic mass in males, and tended to increase day 18 IgY levels for a given bursal mass in females. There was no effect on PHA response, bursal mass, or plasma testosterone at either age post-hatch. The alteration of several indicators of immune function in fadrozole-treated chicks implicates aromatization as a relevant pathway through which developmental exposure to testosterone can affect immunity in birds.

Combined effects of temperature increase and immune challenge in two wild gudgeon populations

In the context of global changes, aquatic ecosystems are increasingly exposed to multiple stressors that can have unexpected interactive effects on aquatic organisms. Among these stressors, the occurrence of heat waves and pathogens is changing rapidly in freshwater rivers, but their combined effects on fish health are still understudied. In this study, we experimentally tested the crossed effects of increased temperature (mimicking a heat wave) and a standardized immune challenge (mimicking a parasite attack) on wild gudgeon (Gobio occitaniae) physiology and behaviour across biological levels from molecules to the whole individual. We also investigated the potential variation of sensitivity among populations by comparing two wild populations from contrasted thermal regimes. Combined stressors (i.e. temperature increase and immune challenge) had contrasted effects on fish physiology and behaviour compared to single stressors, but only at the individual level. In particular, the immune challenge inhibited the effect of the temperature on fish behaviour (activity, exploration and foraging) but amplified the negative effect of temperature on fish survival. No interactions were found at other biological levels. This study thus shows that it is essential to consider biotic stressors such as pathogens to better anticipate the effects of global changes on aquatic organisms. In addition, there was a high variability of response between the two gudgeon populations, suggesting that future studies should take into account population variability to better predict the responses of aquatic wildlife to current and future stressors.

Evaluation of neurobehavioral abnormalities and immunotoxicity in response to oral imidacloprid exposure in domestic chickens (Gallus gallus domesticus)

Domestic chickens (Gallus gallus domesticus) were exposed to imidacloprid by gavage once daily for 7 consecutive days at 0, 0.03, 0.34, 3.42, 10.25, and 15.5 mg/kg/day (n = 20 per group; 5 6-week-old males, 5 6-week-old females, 5 9-week-old males, and 5 9-week-old females). The severity and duration of neurobehavioral abnormalities were recorded. Components of the innate and adaptive immune system were assessed with 7 standard functional assays. Temporary neurobehavioral abnormalities were observed in a dose-dependent manner, including muscle tremors, ataxia, and depressed mentation. Based upon mean clinical severity scores, the no observed adverse effect level (NOAEL) was 3.42 mg/kg/day, and the lowest observed adverse effect level (LOAEL) was 10.25 mg/kg/day. The effective dose value for the presence of any neurobehavioral abnormalities in 50% of the test group (ED₅₀) was 4.62 ± 0.98 mg/kg/day. The ED₅₀ for an adjusted score that included both severity and duration of neurobehavioral abnormalities was 11.24 ± 9.33 mg/kg/day. These ED₅₀ values are equivalent to a 1 kg bird ingesting 29 or 70 imidacloprid treated soybean seeds respectively. Immunotoxicity was not documented, possible causes include the assays were insensitive, relevant immune functions were not examined, or imidacloprid is not immunotoxic at this dosing schedule in this species. Neurobehavioral abnormalities were a more sensitive indicator of the sublethal effects of imidacloprid than immunotoxicity.

Chronic elevation of glucorticoids late in life generates long lasting changes in physiological state without a life history switch

Chronic stressors have profound impacts on phenotypes and life history strategies on the short term, but delayed effects of stress experienced late in life remain poorly investigated in wild populations. Here, we used a combined laboratory and field experiment to test if chronic stress late in life has immediate and delayed effects on physiological and demographic traits in the common lizard, Zootoca vivipara. We increased plasma corticosterone levels in adults and yearlings during three weeks of the post-reproductive season. We quantified immediate responses in the laboratory, delayed intra-generational effects in field enclosures one month and one year later during the next reproductive season, and delayed inter-generational effects in the first generation of offspring. Our phenotypic assays included metabolism, immune capacities, lipid metabolism and oxidative stress. Relative to placebos, lizards treated with corticosterone had higher body condition and lower oxidative damages but an increased skin swelling response directly after the manipulation. Delayed responses in field enclosures were of three types. First, we found catch-up growth for body mass such the placebos had similar body conditions one month after the laboratory manipulation. Second, we found persistent differences in oxidative damages during one month but not one year later. Third, during the next reproductive season, corticosterone-treated females had higher levels of plasma triglycerides, whereas corticosterone-treated individuals had a higher skin swelling response. We found no delayed inter-generational effects on demographic traits of offspring. Our study demonstrates the potential for long-lasting physiological consequences of chronic corticosterone enhancement despite no obvious changes in life history.

Experimentally enhanced performance decreases survival in nature

Superior locomotor performance confers advantages in terms of male combat success, survival and fitness in a variety of organisms. In humans, investment in increased performance via the exercise response is also associated with numerous health benefits, and aerobic capacity is an important predictor of longevity. Although the response to exercise is conserved across vertebrates, no studies have tested whether non-human animals that invest in increased athletic performance through exercise realize a survival advantage in nature. Green anole lizards respond to exercise training, and enhanced performance drives trade-offs with reproduction and immunocompetence. We released sprint-trained, endurance-trained and untrained-control male and female green anole lizards into an isolated, urban island in New Orleans, LA, USA and monitored their survival. Sedentary controls realized a significant survivorship advantage compared to trained lizards. Our results suggest that locomotor capacity is currently optimized to maximize survival in green anoles, and that forcing additional investment in performance moves them into a suboptimal phenotypic space relative to their current environmental demands.

Lack of statistical power as a major limitation in understanding MHC-mediated immunocompetence in wild vertebrate populations

Disentangling the sources of variation in developing an effective immune response against pathogens is of major interest to immunoecology and evolutionary biology. To date, the link between immunocompetence and genetic variation at the major histocompatibility complex (MHC) has received little attention in wild animals, despite the key role of MHC genes in activating the adaptive immune system. Although several studies point to a link between MHC and immunocompetence, negative findings have also been reported. Such disparate findings suggest that limited statistical power might be affecting studies on this topic, owing to insufficient sample sizes and/or a generally small effect of MHC on the immunocompetence of wild vertebrates. To clarify this issue, we investigated the link between MHC variation and seven immunocompetence proxies in a large sample of barn owls and estimated the effect sizes and statistical power of this and published studies on this topic. We found that MHC poorly explained variation in immunocompetence of barn owls, with small-to-moderate associations between MHC and immunocompetence in owls (effect size: .1 ≥ r ≤ .3) similar to other vertebrates studied to date. Such small-to-moderate effects were largely associated with insufficient power, which was only sufficient (>0.8) to detect moderate-to-large effect sizes (r ≥ .3). Thus, studies linking MHC variation with immunocompetence in wild populations are underpowered to detect MHC effects, which are likely to be of generally small magnitude. Larger sample sizes (>200) will be required to achieve sufficient power in future studies aiming to robustly test for a link between MHC variation and immunocompetence.

Immune response declines with age in a wild lizard

The immune system allows animals to survive the constant attacks of pathogens. Although it is essential for survival and fitness, the performance of the immune system can decline with age (a process known as immunosenescence), which may be responsible for the increased mortality of older individuals. Only a few studies have investigated the effect of age on the immune system in reptiles, and no evidence of immunosenescence has yet been reported in lizards. In a wild population of Dickerson’s collared lizards (Crotaphytus dickersonae), we evaluated the effect of age (estimated by skeletochronology) on the male’s immune response to a novel antigen (phytohaemagglutinin). We found a strong negative relationship between immune response and age, the first evidence of immunosenescence in a lizard. Our results show that immunosenescence can occur even in relatively short-lived reptiles and underline the importance of age on performance in fitness-related traits.

Do glucocorticoids or carotenoids mediate plumage coloration in parrots? An experiment in Platycercus elegans

Conspicuous coloration can indicate phenotypic quality, and may reflect exposure or vulnerability to stress, or access to essential nutrients such as pigments. Although the production of pigmented colours is well understood, much less is known about how structural colours are affected by physiological state. In this study, we tested whether glucocorticoids (corticosterone) predicted expression of plumage coloration in an Australian parrot, the crimson rosella (Platycercus elegans). Parrots provide an interesting and unique test, as they possess conspicuous coloration produced by distinctive pigments known as psittacofulvins, in addition to structural coloration. We have previously documented that coloration in P. elegans is condition-dependent and responds to dietary manipulation. Here, n = 21 P. elegans underwent a dietary manipulation (including food restriction or carotenoid supplementation) during which they moulted, and the change in reflectance was measured for three structural and three pigmentary plumage patches. Stress-induced corticosterone (10 min after handling) measured at the start of the experiment predicted change in coloration in two pigmentary patches (crown and front). We also found that change in stress-induced corticosterone during the experiment was associated with the change in coloration of the crown and two structural patches (cheek and epaulette). Baseline corticosterone (<3 min after handling) was not associated with any measure of coloration. We found no effects of dietary manipulation on baseline or stress-induced corticosterone, but carotenoid supplementation was associated with an increase in a measure of chronic stress (heterophil/lymphocyte ratio), and the corticosterone response to handling decreased over the course of the study. Our results suggest that corticosterone may be linked to colour expression more broadly than previously recognised, including psittacofulvin and structural coloration in parrots, and they confirm the independence of plumage pigmentation in parrots from carotenoid accumulation. Moreover, our study provides new insight into the stress responses of Psittaciformes, one of the most highly threatened avian orders.

Colony size affects nestling immune function: a cross-fostering experiment in a colonial waterbird

Elevated transmission rate of pathogens and parasites is considered one of the major costs of sociality in birds. However, greater risk of infection in colonial birds might be compensated by specific immune adaptations. Here, we predicted that nestlings raised in larger colonies should invest more in their immune function. To test this hypothesis, we manipulated colony size and conduced cross-fostering experiment in a colonial waterbird, the common tern Sterna hirundo. Establishment of different size colonies under uniform environmental conditions was induced by providing large and small patches of attractive nesting area for terns (floating rafts). Then, pairs of clutches were swapped between large and small tern colonies, and skin-swelling response to phytohaemagglutinin (PHA) was assessed for nestlings from experimental and control broods. Contrary to our expectations, we found a negative effect of foster colony size on nestling PHA response (nestlings raised in the larger colony had lower PHA response). In addition, nestling PHA response correlated negatively with heterophil/lymphocyte ratio used as a measure of physiological stress. This suggested that low PHA response of nestlings raised in the larger colony could be mediated by an elevated level of social stress. We suggest that depression of immune function via social stress may constitute a strong selective pressure against large colony size in the common tern, and possibly in other colonial species. We also recommend that this largely overlooked cost of sociality should be considered in the further studies on the evolution and ecology of avian coloniality.

Integrating time progression in ecoimmunology studies: beyond immune response intensity

Habitat alterations in agroecosystems may damage amphibian immune capacity. As agroecosystem extension is increasing worldwide, broader-context knowledge on the effects of agroecosystem stressful conditions on amphibian immune capacity is crucial for understanding and management of amphibian global declines. However, most studies on ecoimmunology assume synchronal among-group immune-response peaks, and focus on immune response after standardized time lapses, neglecting its progression. Herein, I compared inflamatory response short-term progression of agroecosystem and natural-habitat female and male natterjack toads Epidalea calamita, by measuring swelling response, once per hour, 6 h following an artificial immune challenge with innocuous antigen phytohemagglutinin. I also compared maximum magnitude of swelling response, irrespective of the moment when it was reached. Habitat differences arose only 3 h after challenge, when natural-habitat toads showed greater swelling response. Maximum magnitude of swelling response was similar in toads from both habitats. However, agroecosystem toads showed a delayed swelling response as compared with natural-habitat conspecifics, probably as a consequence of agroecosystem stressful conditions. Such a delay suggests a weaker immune capacity, and consequently impaired anti-pathogen performance. Regarding sex, swelling response magnitude did not differ between males and females. Female swelling response peaked earlier, but that of males was more sustained in time, which contradicts general across-taxa findings that males show impaired immune response. Interestingly, results suggest that measuring swelling response only after some standardized period following stimulation may be a simplistic approach and produce unrealistic results. Consequently, studies on ecoimmunology should implement swelling response progression in order to produce unbiased science.