禁食时间对雌性长爪沙鼠免疫功能的影响

动物的免疫系统是防御细菌、病毒等病原体侵害的重要途径,对其生存很重要,而食物短缺是影响动物免疫的重要因素。前期研究发现,禁食3天可抑制雌性长爪沙鼠T细胞介导的免疫功能,而禁食时长可能在影响动物免疫中起重要作用。为此,本实验主要测定不同的禁食时间如何影响雌性长爪沙鼠的免疫功能,该问题的解决有助于理解它们在野外面临食物短缺时的生存状况。将55只成年雌鼠随机分为8组,分别禁食1 d、2 d 、3 d和自由取食,每种处理又分别注射磷酸缓冲液和植物血凝素（PHA）。结果发现,随禁食时间的延长,PHA反应（指示T细胞介导的免疫功能）逐渐受到抑制,胸腺和脾脏逐渐萎缩,表明禁食时间对长爪沙鼠的免疫功能影响显著。同样,随饥饿时间增加,长爪沙鼠的体脂、血糖和血清瘦素水平逐渐下降,并且与PHA反应呈正相关,但白细胞总数和皮质酮水平不受禁食时间的影响。结果表明,禁食时间长短能显著影响雌性长爪沙鼠的免疫功能,随禁食时间的延长,长爪沙鼠T细胞介导的免疫功能逐渐受抑制,这可能与体脂和葡萄糖含量下降有关,血清瘦素逐渐降低也可能是其免疫受抑制的原因。     

Indirect Costs of Parasitism are Shaped by Variation in the Type of Immune Challenge and Food Availability

Parasites can inflict indirect fitness costs to their hosts by eliciting costly immune responses. These costs depend on the type and amount of immunostimulants presented to the host immune system but also on the amount of resources available to fuel host immune responses. Here, we investigated how the relative costs of two different types of immune challenge are modulated by variation in food availability. We injected nestling tawny owls (Strix aluco) with either 10 μg of phytohaemagglutinin (PHA) or 20 μg of lipopolysaccharide (LPS), and subsequently raised them under two different food regimes (food-restricted vs. ad libitum). After controlling for food consumption, we found that LPS-injected nestlings lost more body mass than PHA-injected ones only when food-restricted. We also found that body mass gain of owlets fed ad libitum decreased with the intensity of the skin swelling response against LPS, but not PHA. These experimental and correlative results suggest that nestling tawny owls suffered greater immune costs when treated with LPS than PHA, and that variation in the costs of two different types of immune challenge can be exacerbated under conditions of low food availability. Our study highlights the importance of taking into consideration the interplay between host immunity and nutrition in the study of indirect costs of parasitism.     

Mhc polymorphisms fail to explain the heritability of phytohaemagglutinin-induced skin swelling in a wild passerine

Genetic estimates of the variability of immune responses are rarely examined in natural populations because of confounding environmental effects. As a result, and because of the difficulty of pinpointing the genetic determinants of immunity, no study has to our knowledge examined the contribution of specific genes to the heritability of an immune response in wild populations. We cross-fostered nestling house sparrows to disrupt the association between genetic and environmental effects and determine the heritability of the response to a classic immunological test, the phytohaemagglutinin (PHA)-induced skin swelling. We detected significant heritability estimates of the response to PHA, of body mass and tarsus length when nestlings were 5 and 10 days old. Variation at Mhc genes, however, did not explain a significant portion of the genetic variation of nestling swelling to PHA. Our results suggest that while PHA-induced swelling is influenced by the nest of origin, the importance of additive genetic variation relative to non-additive genetic variation and the genetic factors that influence the former in wild populations still need to be identified for this trait.     

Correlates of cell-mediated immunity in nestling house sparrows

Cell-mediated immunity is an important vertebrate defense against pathogens, but components of this response may vary in quality. Such variation could arise through the effects of ecology on optimal immunocompetence. We used injections of phytohaemagglutinin (PHA) to measure the factors influencing T-cell proliferation in nestling house sparrows (Passer domesticus). Bivariate analyses revealed positive associations with nestling mass and size, but no effect of ectoparasites. The response to PHA was, however, strongly affected by brood identity. A mixed model with brood identity as a random factor and nestling mass, size, number of ectoparasites, parental feeding rate, clutch size, brood size at hatching, and date uncovered significant positive correlations between PHA response and both nestling mass and the brood size at hatching. Because many of these variables are related hierarchically, we used path analysis to explore the relationships in more detail. We found that a nestling immune response was affected by several indirect paths. Brood size at hatch had both positive and negative paths, and date in the season had several indirect negative effects through its effect on brood size and nestling mass. The approach used and the results obtained offer some new ideas for incorporating immune responses into life history theory.     

Short-term fluctuations in cellular immunity of tree swallows feeding nestlings

We examined cellular immunity of adult tree swallows feeding nestlings under variable weather conditions. Birds received an injection of phytohaemagglutinin (PHA), which causes a local swelling, reflecting the strength of T-cell-mediated immunocompetence. There was a negative relationship between the immune response and the number of nestlings in the brood (range 3-6 young) which suggests that parental effort suppresses the immune function. However, there was also a strong effect of ambient temperature and food abundance (aerial insects) on immune response. Parents that received the PHA injection during cold weather and at low food abundance showed a suppressed immune response compared to birds treated during more favourable conditions. They also lost more body mass during the 24 h inoculation period, and their offspring showed reduced growth. When controlling for ambient temperature and food abundance in a multivariate analysis, there was no longer any significant effect of brood size on the parents' immune response. Three of 39 pairs deserted their broods after PHA injection. All three desertions took place when the mean ambient temperature fell below 13°C. The PHA response is known to have both heritable and environmental components; our study emphasizes its condition-dependency. Previous studies of other passerine birds have shown that high levels of parental effort may have an immunosuppressive effect. Our study indicates that weather conditions may override the effects of natural variation in parental effort, and that the PHA response is particularly influenced by short-term fluctuations in energy balance.     

No effect of blood sampling or phytohaemagglutinin injection on postfledging survival in a wild songbird

The injection of phytohaemagglutinin (PHA) and sampling of blood are widely used in studies of wild vertebrates to assess components of immune and endocrine function and health state and to obtain genetic material. Despite the pervasive use of these techniques in the life sciences, their potential effects on survival are rarely considered. For example, whether injection of the immunogen PHA into body parts critical for locomotion (e.g., the prepatagium, or wing web, in birds) affects survival has not been tested. Here, we test whether injection of PHA into the wing web and blood sampling from nestling house wrens affects their subsequent recruitment and survival as breeding adults. Capture‐mark‐recapture analysis on a large sample of young (N = 20,152 fledglings from 3959 broods) treated over 10 years revealed that neither PHA injection nor blood sampling affected individual survival and detection probability. Recruitment as a breeder varied among years, but this variation was not attributable to sampling effort, or the percent of all adults identified at the nest during a given year. Variation in the percent of adults identified was primarily attributable to the effect of nest depredation on our ability to capture nesting pairs. Our results indicating lack of an effect of blood sampling and immune stimulation on survival are encouraging, but we recommend further work to assess the potential negative effects of all commonly used techniques on the survival of study subjects in the wild, including the potential costs associated with mounting various immunological responses.     

Studies on the methodology and evaluation of the lymphocyte transformation microtest

Optimum experimental conditions for the lymphocyte transformation microtest in healthy persons are described. The dependence of PHA stimulation on duration of culture, additions of serum and PHA concentration is investigated. A function of normal distribution pattern can be set up by determining the lymphocyte stimulability with four different PHA concentrations in the optimal stimulation range. With this function, the area under the curve, steepness, position and height of the maximum can be calculated. These parameters should serve for better interpretation of cellular immunity.     

Genetic and environmental variation in immune response of collared flycatcher nestlings

This paper aims at partitioning genetic and environmental contribution to the phenotypic variance in nestling immune function measured with the hypersensitivity test after inoculation with phytohaemagglutinin. A cross-fostering experiment with artificial enlargement of some broods was conducted. Variation in nestling immune response was related to their common origin, which suggests heritable component of cell-mediated immunity. A common rearing environment also explained a significant part of variation. However, deterioration of rearing conditions as simulated by enlargement of brood size did not affect nestling immunocompetence, although it affected nestling body mass. Variation in body mass explained some of the variation in immune response related to rearing environment, which means that growth is more sensitive to the shifts in rearing conditions than the development of immune function. Heritable variation in immune response suggests that there should be potential for selection to operate and the micro evolutionary changes in immunity of flycatcher nestlings are possible.     

Hatching asynchrony and brood reduction influence immune response in Common Kestrel Falco tinnunculus nestlings

The onset of incubation before the end of laying imposes asynchrony at hatching and, therefore, a size hierarchy in the brood. It has been argued that hatching asynchrony might be a strategy to improve reproductive output in terms of quality or quantity of offspring. However, little is known about the mediating effect of hatching asynchrony on offspring quality when brood reduction occurs. Here, we investigate the relationship between phenotypic quality and hatching asynchrony in Common Kestrel Falco tinnunculus nestlings in Spain. Hatching asynchrony did not increase breeding success or nestling quality. Furthermore, hatching asynchrony and brood reduction had different effects on nestlings’ phytohaematogglutinin (PHA)‐mediated immune response and nestling growth. In asynchronous and reduced broods (in which at least one nestling died), nestlings showed a stronger PHA‐mediated immune response and tended to have a smaller body size compared with nestlings raised in synchronous and reduced broods. When brood reduction occurred in broods hatched synchronously, there was no effect on nestling size, but nestlings had a relatively poor PHA‐mediated immune response compared with nestlings raised in asynchronous and reduced broods. We suggest that resources for growth can be directed to immune function only in asynchronously hatched broods, resulting in improved nestling quality, as suggested by their immune response. We also found that males produced a greater PHA‐mediated immune response than females only in brood‐reduced nests without any effect on nestling size or condition, suggesting that females may trade off immune activities and body condition, size or weight. Overall, our results suggest that hatching pattern and brood reduction may mediate resource allocation to different fitness traits. They also highlight that the resolution of immune‐related trade‐offs when brood reduction occurs may differ between male and female nestlings.     

Growing old with the immune system: a study of immunosenescence in the zebra finch (<Emphasis Type="Italic">Taeniopygia guttata)</Emphasis>

Immunosenescence has not received much attention in birds and the few existing studies indicate that the occurrence of immunosenescence and/or its extent may differ between species. In addition, not much information is available on the immunosenescence patterns of different immune parameters assessed simultaneously in both sexes within a single species. The present study reports the results on immunosenescence in innate immunity and both cellular and humoral acquired immunity of both sexes in a captive population of zebra finch (Taeniopygia guttata) using three age groups (approximately 0.2, 2.5 and 5.1 years). Both male and female finches showed an inverse U-shaped pattern in cellular immune function with age, quantified by a PHA response. Males showed stronger responses than females at all ages. In contrast, an increase with age in humoral immunity, quantified through total plasma immunoglobulin Y levels, was found in both sexes. However, our measurements of innate immunity measured through the bacteria-killing ability against Escherichia coli gave inconclusive results. Still, we conclude that both cellular and humoral acquired immunity are susceptible to immunosenescence, and that the sexes differ in cellular immunity.     

Stress,immunocompetence and leukocyte profiles of pied flycatchers in relation to brood size manipulation

The two main trade-offs considered determining reproductive patterns in iteroparous organisms are the one between current and future reproduction, and the one between the number and quality of offspring. Recently, it has been suggested that these trade-offs may be mediated by stress-induced reduction in immunocompetence. To test the hypothesis that stress reduces immune function, we investigated the effects of brood size manipulation on stress hormone levels, leukocyte profiles and immune responses against challenge with novel antigens in nestling and parent male pied flycatchers ( Ficedula hypoleuca). In male parents, heterophil (H) and lymphocyte (L) numbers, as well as H/L ratio increased with experimentally enlarged brood size, and corticosterone levels tended to do so, indicating that high parental work load altered their stress level and physiological state. Despite this, we found no effects on humoral immune responsiveness, measured as antibody production against diphtheria-tetanus vaccine. In nestlings, heterophil numbers and H/L ratio increased in enlarged broods, whereas T-cell-mediated immune responsiveness, measured against phytohemagglutinin (PHA), decreased in enlarged broods. The results support the view that growth-stress-induced immunosuppression may be an important physiological pathway mediating the trade-off between the number and viability of offspring. The difference in the observed immune-related responses between nestlings and males may be because we measured different aspects of the immune system (cellular vs humoral). However, it may also be a result of males lowering their own costs by feeding less, (and their mate possibly compensate by feeding more), whereas nestlings cannot escape the costs of increased intra-brood competition.     

Cross-fostering reveals an effect of spleen size and nest temperatures on immune responses in nestling European starlings

Immunocompetence may be a good measure of offspring quality, however, factors affecting variation in immune responses are not clear. Research suggests that immune function can vary due to differences in genetics, development conditions and individual quality. Here, I examined factors affecting variation in immune response among nestling European starlings through a split-nest cross-fostering brood manipulation that included two important covariates: spleen size and nest temperatures. Immunocompetence was assessed via a cell-mediated immune response to phytohaemagglutinin (PHA). This paper provides the first direct evidence that individuals with large spleens also mount strong immune responses. Exposure to PHA did not cause splenomegaly, as there was no difference in spleen size between control birds and those injected with PHA. Offspring immune function was affected by common origin and by rearing environment, though rearing environment appeared to exert its influence only through nest temperatures. A comparison of the immune performance of siblings reared in their home nest versus those reared in other nests revealed a strong effect of maternal quality. As the difference in natal clutch size increased, the magnitude of the difference in immune performance between home-reared nestlings versus out-reared nestlings increased. Overall, nestling immune function appears to be determined by the combination of genetic, maternal and environmental effects.     

Nestling cell-mediated immune response, body mass and hatching date as predictors of local recruitment in the pied flycatcher Ficedula hypoleuca

Offspring body mass and hatching date have been proposed as useful correlates of post-fledging survival and recruitment probability in studies of avian populations. However, these links may be mediated by underlying physiological variables which are frequently not reported. One of these is nestling immune function, which can be measured with several field-friendly protocols like the phytohemagglutinin (PHA) inoculation assay used to estimate cell-mediated immune response (CMI). Here we show in a population of pied flycatchers Ficedula hypoleuca subjected to a long-term study in central Spain that nestling CMI as measured with PHA is dependent on dose injected, body mass, hatching date and maternal moult state. Nestlings recruited during the first two or three years after hatching had a higher CMI but did not differ in mass or hatching date with respect to non-recruited nestlings. Nestling immunocompetence as measured with the PHA assay is a better predictor of local recruitment probability than mass or hatching date in our study population, and should be considered in future studies of determinants of offspring survival chances and fitness in avian populations.     

MC1R-dependent, melanin-based colour polymorphism is associated with cell-mediated response in the Eleonora's falcon

Colour polymorphism in vertebrates is usually under genetic control and may be associated with variation in physiological traits. The melanocortin 1 receptor (Mc1r) has been involved repeatedly in melanin-based pigmentation but it was thought to have few other physiological effects. However, recent pharmacological studies suggest that MC1R could regulate the aspects of immunity. We investigated whether variation at Mc1r underpins plumage colouration in the Eleonora's falcon. We also examined whether nestlings of the different morphs differed in their inflammatory response induced by phytohemagglutinin (PHA). Variation in colouration was due to a deletion of four amino acids at the Mc1r gene. Cellular immune response was morph specific. In males, but not in females, dark nestling mounted a lower PHA response than pale ones. Although correlative, our results raise the neglected possibility that MC1R has pleiotropic effects, suggesting a potential role of immune capacity and pathogen pressure on the maintenance of colour polymorphism in this species.     

Immune function and survival of great tit nestlings in relation to growth conditions

Life history theory predicts a trade-off between number and quality of offspring. Reduced quality with increasing brood size may arise from a decrease in body condition or in immunocompetence that would be important in fighting off virulent parasites by immunologically naive offspring. We tested the effect of rearing conditions on immune function of nestling great tits (Parus major) by reducing or increasing broods by two hatchlings. In the middle of the nestling period (on day 8), nestlings from enlarged broods developed lower T cell responses [as measured from the cutaneous swelling reaction to injection with phytohaemagglutinin (PHA)] and tended to have lower total leukocyte and lymphocyte concentrations in their peripheral blood than nestlings from reduced broods. Brood size manipulation affected the PHA response of nestlings most strongly in small clutches, suggesting that nestling immune function was dependent on their parents’ condition, as estimated by original clutch size. Intra-brood differences in nestling mortality were unrelated to immune parameters, but nestlings in broods without mortality had a stronger PHA response, higher concentration of lymphocytes and higher body mass on day 15 than nestlings in broods with mortality. These results support the prediction that the immune function of altricial birds is affected by rearing conditions, and that growth and immune parameters are related to inter-brood differences in nestling survival. Received: 1 February 1999 / Accepted: 19. July 1999     

Immunocompetence of nestling great tits in relation to rearing environment and parentage

Theoretical models of host–parasite coevolution assume a partially genetic basis to the variability in susceptibility to parasites among hosts, for instance as a result of genetic variation in immune function. However, few empirical data exist for free-living vertebrate hosts to support this presumption. In a cross-fostering experiment with nestling great tits, by comparing nestlings of the same origin we investigated (i) the variance in host resistance against an ectoparasite due to a common genetic origin, (ii) the effect of ectoparasite infestation on cell-mediated immunity and (iii) the variance in cell-mediated immunity due to a common genetic origin. Ectoparasitic hen fleas can impair the growth of nestling great tits and nestling growth was therefore taken as a measure of host susceptibility. A common origin did not account for a significant part of the variation in host susceptibility to fleas. There was no significant overall effect of fleas on nestling growth or cell-mediated immunity, as assessed by a cutaneous hypersensitivity response. A common rearing environment explained a significant part of the variation in cell-mediated immunity among nestlings, mainly through its effect on nestling body mass. The variation in cell-mediated immunity was also related to a common origin. However, the origin-related variation in body mass did not account for the origin-related differences in cell-mediated immunity. The results of the present study thus suggest heritable variation in cell-mediated immunity among nestling great tits.     

Ectoparasites and reproductive trade-offs in the barn swallow (Hirundo rustica)

Parents are predicted to trade offspring number and quality against the costs of reproduction. In altricial birds, parasites can mediate these costs because intensity of parasitism may increase with parental effort. In addition, parasites may mediate a trade-off between offspring number and quality because nestlings in large broods may have reduced anti-parasite immune defence. In this study, we experimentally analysed the effect of brood size on infestation by an ectoparasitic mite in nests of barn swallows (Hirundo rustica). Nests with an enlarged brood had larger prevalence and intensity of infestation than those with a reduced brood. Importantly, each nestling in enlarged broods was exposed to a larger number of mites, even when measured on a per nestling basis, than in reduced broods. Nestlings in enlarged broods had smaller body mass and T-cell-mediated immune response compared to reduced broods. T-cell-mediated immune response and feather growth were negatively correlated with per nestling intensity of infestation in enlarged but not in reduced broods. The results suggest that nestlings in enlarged broods have depressed immunity leading to larger per nestling mite infestation. Hence, exposure to parasites of offspring and parents increases with brood size, and parasitism can thus mediate trade-offs between reproduction and number and quality of the progeny in the barn swallow.     

Cell-mediated immunosenescence in birds

The phytohaemagglutinin (PHA) skin test response, used to assess cell-mediated immunity, is known to vary with many social and energetic factors, but the effects of age have received little attention. We found that the PHA response of immature birds was lower than those of the youngest breeding adults and were decreased in adults. Whenever possible, age should be included as a covariate when the PHA skin test is used to assess immunocompetence in ecological immunology. The rate of decline in PHA response differed between species and was inversely correlated with survival. The decrease in the PHA response averaged 57% over an average 80% of the maximum life span, but the absolute rate varied with species lifespan such that the short-lived species showed a greater loss per year than the long-lived species. This link between declining immune function and survival may reflect differences in resource partitioning between species, and suggests that selection may act on investment in immune function to influence maximum life span.     

Parasite-mediated growth patterns and nutritional constraints in a cavity-nesting bird

1. Trade-offs between growth and immunity of nestling birds can be influenced by parasites, but the magnitude of these effects may depend on availability of critical dietary nutrients. Owing to their importance for both immune system function and growth, dietary carotenoids have the potential to mediate parasite-induced developmental strategies of avian hosts. 2. The effects of ectoparasitic blow flies Protocalliphora spp. and dietary carotenoids (lutein and zeaxanthin) on immune function and patterns of growth in nestling mountain bluebirds Sialia currucoides were investigated by combining parasite removal and carotenoid supplementation treatments in a 2 x 2 design. 3. Supplemental carotenoids enhanced nestlings' T-cell-mediated immune response following intradermal injection of phytohaemagglutinin. 4. The effect of carotenoid supplementation on rate of mass gain depended on whether broods were exposed to parasites: among parasitized broods, those receiving supplemental carotenoids gained mass more rapidly than nonsupplemented broods, whereas there was no effect of supplemental carotenoids on growth of mass in broods that had parasites removed. This suggests that additional dietary carotenoids allowed nestlings to compensate for the otherwise detrimental effects of parasites on mass gain. For length of the eighth primary feather at fledging, early and late broods differed in their response to parasitism: early broods showed an increase in feather length when parasites were removed, while nestlings in late broods had shorter feathers in the absence of parasites. We suggest that this may reflect within-season variation in parasite-mediated growth strategies of nestlings. 5. Maternal condition was positively associated with mass, condition and rate of feather growth of offspring under all conditions, and also influenced nestling immunocompetence, but only in the absence of parasites. 6. We conclude that dietary carotenoids alleviate some of the detrimental effects of parasites on nestling birds; however, parasites also appear to specifically influence other growth and resource allocation strategies, and possibly constrain maternal or genetic effects on offspring phenotype, irrespective of dietary carotenoid availability.     

Ecological immunology in a fluctuating environment: an integrative analysis of tree swallow nestling immune defense

Evolutionary ecologists have long been interested by the link between different immune defenses and fitness. Given the importance of a proper immune defense for survival, it is important to understand how its numerous components are affected by environmental heterogeneity. Previous studies targeting this question have rarely considered more than two immune markers. In this study, we measured seven immune markers (response to phytohemagglutinin (PHA), hemolysis capacity, hemagglutination capacity, plasma bactericidal capacity, percentage of lymphocytes, percentage of heterophils, and percentage of eosinophils) in tree swallow (Tachycineta bicolor) nestlings raised in two types of agro‐ecosystems of contrasted quality and over 2 years. First, we assessed the effect of environmental heterogeneity (spatial and temporal) on the strength and direction of correlations between immune measures. Second, we investigated the effect of an immune score integrating information from several immune markers on individual performance (including growth, mass at fledging and parasite burden). Both a multivariate and a pair‐wise approach showed variation in relationships between immune measures across years and habitats. We also found a weak association between the integrated score of nestling immune function and individual performance, but only under certain environmental conditions. We conclude that the ecological context can strongly affect the interpretation of immune defenses in the wild. Given that spatiotemporal variations are likely to affect individual immune defenses, great caution should be used when generalizing conclusions to other study systems.