Song predicts immunocompetence in male European starlings (Sturnus vulgaris)

According to the immunocompetence handicap hypothesis, sexually selected characteristics predict immune function and this relationship is mediated by testosterone. In the present study, we investigated whether bird song could predict immunity in European starlings (Sturnus vulgaris). We recorded the singing and reproductive behaviours of 16 adult male starlings in an outdoor aviary and then assessed their cell-mediated and humoral immunity in vivo. The males were observed in groups of four for 2 h each day over a 4-day period. For each male, the number of songs produced was recorded and the average song-bout length was computed. Next, cell-mediated and humoral immunity were assessed via cutaneous swelling responses to the T-cell mitogen phytohaemagglutinin and antibody responses to a novel antigen, keyhole limpet haemocyanin. Song rate and song-bout length were positively correlated with cell-mediated and humoral immunity, respectively. Additionally, a negative relationship between plasma testosterone concentration and antibody response was observed. These data demonstrate that male starling song can be used as a predictor of immunocompetence, with more robust singers exhibiting enhanced immunity. Whether this relationship is mediated directly by testosterone requires further investigation.     

Experimental removal of the male parent negatively affects growth and immunocompetence in nestling great tits

Given the available empirical evidence on the benefits and costs associated with immune defence, a role for the immune system in the trade-off between current and future reproduction has been predicted. This hypothesis was studied in a free-living population of great tits (Parus major) by examining the effects of male removal on the immunocompetence, body condition, and recapture probability in the widowed females and their nestlings. Furthermore, we investigated whether growth and its relation to immunocompetence were affected in the nestlings. For a short-lived species such as the great tit, one could predict that widowed females will compensate for the lack of any male assistance in feeding of their chicks and that they consequently might jeopardize their own health. However, we did not find any negative effects of male removal on body mass or condition, nor on humoral immunocompetence against sheep red blood cells in the widowed females by the end of the feeding period. In contrast, we observed significantly reduced body mass and size as well as a reduced T-lymphocyte cell-mediated immune response (expressed as the thickness of the swelling to a subcutaneous injection with phytohemagglutinin) in the experimental nestlings compared to the control nestlings. In addition, the experimental nestlings showed a tendency for a reduced chance to be found breeding the following year. Furthermore, our results showed that in the experimental nestlings, which suffered from unfavourable growth conditions, tarsus length was inversely related to cell-mediated immunocompetence, whereas in control nestlings this relationship was significantly positive. The relationship between cell-mediated immunity and body condition was found to be significantly positive in the experimental nestlings while in control nestlings there was no relationship between both variables. The latter finding suggests different priorities of investment in body condition between different growth conditions.     

Female house wrens (Troglodytes aedon) increase the size, but not immunocompetence, of their offspring through extra-pair mating

House wrens are typically socially monogamous, but frequently engage in extra-pair matings leading to multisired broods. Because females do not appear to acquire direct material benefits from their extra-pair mates, we tested the hypothesis that female house wrens derive indirect genetic benefits, such as enhanced immunocompetence (cutaneous immune activity, humoral immunity, and plasma bactericidal activity) and condition (size and haematoserological traits) for their offspring, by mating polyandrously. We predicted that extra-pair young (EPY) should show greater immune responsiveness and better body condition than their within-pair maternal half-siblings (WPY). Contrary to our prediction, WPY had higher cutaneous immune activity than their EPY brood-mates in two of three years, and EPY and WPY did not differ in measures of innate and humoral immunity. WPY also had higher albumin to γ-globulin ratios than EPY; however, they were not in better condition based on other measures. EPY had consistently longer tarsi (a measure of long-bone size) than their WPY half-siblings, suggesting that females engage in extra-pair copulations with larger males. The benefits of large structural size in the study population is unknown, but based on evidence from other passerines, we suggest that structural size may be an important fitness-related trait in house wrens. We conclude that our results are not consistent with the hypothesis that females gain immune-related benefits for their offspring by engaging in extra-pair matings. Further study of the fitness consequences of differences in tarsus length is needed to determine whether females acquire size-related benefits for their offspring from extra-pair mates.     

Effects of testosterone on cell-mediated and humoral immunity in non-breeding adult European starlings

One of the primary assumptions of the immunocompetence hypothesisis that testosterone is immunosuppressive. Although many studiesin birds and mammals have supported this assumption, conflictingresults have been reported in a variety of species. We investigatedthe effects of testosterone manipulation on both cell-mediatedand humoral immunity in adult songbirds, European starlings(Sturnus vulgaris). Male and female starlings were wild-caught,housed in the laboratory, and implanted with either empty silasticcapsules or capsules containing testosterone. Six weeks after implantation, humoral immunity was assessed by injecting thebirds with a novel antigen, keyhole limpet hemocyanin, andmeasuring specific antibody responses 10 and 15 days latervia an enzyme-linked immunosorbant assay. Cell-mediated immunitywas assessed 7 weeks after implantation via intradermal injectionof the T-cell mitogen phytohemagglutinin into the wing web and measuring the degree of swelling 24 h later. Antibody responsesto antigenic challenge were significantly suppressed in testosterone-treatedfemales 10 days post-injection and in both sexes 15 days post-injection.Furthermore, there was a significant inverse relationship betweenindividual variability in antibody responsiveness and plasmatestosterone concentrations. Cell-mediated responses to phytohemagglutininstimulation were also significantly suppressed in testosterone-treatedmales compared to same-sex controls. Testosterone treatmentsignificantly increased plasma corticosterone concentrations compared to controls, and the possibility of this effect mediatingthe immunosuppressive effects of testosterone is discussed.The present study is among the first to demonstrate testosterone-inducedsuppression of both cell-mediated and humoral immunity in aspecies of songbird.     

Effects of forest patch size on physiological stress and immunocompetence in an area-sensitive passerine, the Eurasian treecreeper (Certhia familiaris): an experiment

We manipulated the primary brood size of Eurasian treecreepers (Certhia familiaris) breeding in different sized forest patches (0.5-12.8 ha) in moderately fragmented landscapes. We examined the effects of brood size manipulation (reduced, control, enlarged) and forest patch size on physiological stress (heterophil-lymphocyte ratios; H/L), body condition and cell-mediated immunocompetence (phytohaemagglutinin test). Nestlings' H/L ratios were negatively related to forest patch area in control and enlarged broods, whereas no effects were found in reduced broods. The effects of forest patch area were strongest in enlarged broods, which had, in general, twofold higher H/L ratios than control and reduced broods. The elevated H/L ratios were positively related to nestling mortality and negatively correlated with body-condition indices suggesting that the origin of stress in nestlings was mainly nutritional. Cell-mediated immunity of nestlings was not related to brood manipulation or to forest patch size. Also, the H/L ratios of adults were not related to brood manipulation or forest patch size. In addition, parental H/L ratios and body condition were not related to nestling H/L ratios. Our results suggest that during the breeding period the deleterious effects of habitat loss are seen explicitly in growing young.     

家蚕先天免疫基因 Bmimd 的克隆、表达及序列分析

昆虫的先天免疫应答由一组基因通过级联网络调控实现。果蝇 Drosophila 免疫缺陷(immune deficiency, imd)基因在体液免疫信号传递途径中起着重要的作用。我们利用生物信息学方法进行电子克隆,成功地找到了 imd 基因在家蚕 Bombyx mori 中的同源体,命名为 Bmimd。该基因全长1 092 bp,由 4 个外显子和 3 个内含子组成,开放阅读框(open reading frame, ORF)长 750 bp,编码 250 个氨基酸,预测蛋白质分子量为 28.6 kD。Bmimd 序列中含有一个致死结构域,经聚类分析表明该结构域与哺乳动物的受体相互作用蛋白(receptor interacting protein, RIP)相似。将该基因亚克隆到 PET-50b 载体进行原核表达,表达出了带有 2 个 6×His tag 和 1 个 Nus·Tag 标签的重组蛋白。Western blotting 结果表明 Bmimd 蛋白在 5 龄 4 天家蚕的头、脂肪体 、生殖腺、表皮和中肠中都有表达,但丝腺中没有检测到表达。     

Bill colour and immunocompetence in the European blackbird

The level of expression of secondary sexual characters has been suggested to signal male ability to resist parasitic infestations. To test this idea, several studies have examined the link between sexual signals and immunocompetence in birds. However, most of them have used only a single aspect of immune response to evaluate immunocompetence. We investigated the relation between bill colour and immunocompetence in captive male European blackbirds, Turdus merula, during the breeding season by assessing both cell-mediated and humoral components of the immune system. The blackbird is a sexually dimorphic species with bill colour varying from yellow to orange in males. Humoral immunity was assessed by measuring both primary and secondary responses to sheep red blood cell inoculation. Cell-mediated immunity was estimated with a delayed cutaneous hypersensitivity response to an injection of a mitogen (phytohaemagglutinin). No relation was found between male bill colour and the primary humoral response. However, males with orange bills showed a lower secondary humoral response but a higher cell-mediated immune response than males with yellow bills. Thus, the relation between immunocompetence and a secondary sexual trait may differ markedly depending on which component of the immune system is under consideration. We discuss our results in relation to mechanisms involved in sexual selection. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour      

Age, parasites, and condition affect humoral immune response in tropical pythons

Mounting an immune response has been suggested to be physiologicallycostly because of metabolic requirements of immune cells specificallyand upregulation of the immune system in general. We investigatedsuch costs in free-living water pythons (Liasis fuscus), immunizedwith a harmless antigen, keyhole limpet hemocyanin. In the presentstudy, we analyze the independent effects of age, blood parasiteload, and body condition on the ability to mount a humoral immuneresponse (level of antibody production to novel antigens). Pythonhumoral immune response decreased with increasing body length/age,decreased with increasing blood parasite load, and decreasedwith declining body condition. The results suggest an energetictrade-off between immunocompetence and other energetically costlyprocesses.     

Immune response of male barn swallows in relation to parental effort, corticosterone plasma levels, and sexual ornamentation

Life-history theory posits trade-offs between fitness components. Reproduction negatively affects physiology and immune systemfunctioning, and the effect of this form of stress may be mediatedby glucocorticosteroids. We manipulated brood size of barnswallows (Hirundo rustica) to study the effect of stress arisingfrom reproductive effort on corticosterone levels of males.We also measured T-cell—mediated immunocompetence by intradermally injecting birds with phytohemagglutinin, whichis mitogenic to T-lymphocytes. The results confirmed the predictionof a negative effect of parental effort on lymphoproliferativeresponse. We found no covariation between immune response andcorticosterone levels. Males with long tails, an ornament currentlyunder directional sexual selection, had a relatively large T-cell response to the mitogen, consistent with models of parasite-mediated sexual selection predicting higher levels of immune defensein highly ornamented males. In addition, males with large sexualornaments had relatively low corticosterone levels at the endof the parental period. These results can be reconciled withthe hypothesis proposing a trade-off between parental activitiesand adaptive immunity and suggest that highly ornamented malesare less exposed or less susceptible to stress arising fromparental effort.     

Testosterone, immunocompetence, and honest sexual signaling in male red grouse

The expression of sexual ornaments has been suggested to reliablyindicate individual quality, such as the ability to cope withparasites and diseases. The Immunocompetence Handicap Hypothesis(IHH) states that testosterone-dependent ornaments honestlysignal such quality because of physiological costs associatedwith testosterone, such as impaired immune function. We testedpredictions of the IHH both correlatively and experimentallyin red grouse Lagopus lagopus scoticus. Male grouse exhibitsupra-orbital red combs whose size is testosterone-dependent.We found that comb size was not correlated to infection intensityby two parasites (coccidia and the nematode Trichostrongylustenuis), but it was significantly positively correlated withcondition and T-cell-mediated immunity (the ability to mounta primary inflammatory response). We manipulated testosteroneby means of implants and re-caught males after a month to investigatethe effects on comb size, condition, immunity, and parasiteload. Males implanted with testosterone had increased comb size,lost more condition, and had lower T-cell-mediated immunitythan control males. Increased testosterone also resulted ina significant increase in coccidia infection intensity but hadno effect on T. tenuis burden. The results are consistent withpredictions of the IHH and suggest that comb size honestly indicatesimmunocompetence and males' ability to cope with certain parasites.Females could thus benefit from choosing mates based on theexpression of this sexual trait.     

Evidence for the signaling function of egg color in the pied flycatcher Ficedula hypoleuca

A recent hypothesis proposes that the bright colors, especiallyblue and green, of many avian eggs may function as signals offemale or offspring phenotypic quality or condition to malesin species with biparental care, inducing them to allocate moreeffort to their offspring. The pigment determining blue andgreen egg colors is an antioxidant whose availability for eggshellcoloring may be limited. To test the signaling function on aspecies with blue eggs, the pied flycatcher Ficedula hypoleuca,we measured egg color with a spectrophotometer on the day oflaying and obtained two principal components from their reflectancespectra that together explained 99% of variation and representedshell lightness, and hue and saturation, respectively. We alsomeasured female immunocompetence during the nestling periodthrough the response to phytohemagglutinin as a measure of cell-mediatedimmunity and the response to a tetanus vaccination as a measureof humoral immunity. The total amount of immunoglobulins inblood of females and of nestlings before fledging was also estimated.Mean within-clutch egg darkness was positively associated withboth measures of female immunocompetence, while better femalecondition was associated with colors tending away from intermediateand toward short wavelengths. Ageing female laid lighter eggs.The mean within-brood level of nestling IgY was also associatedwith mean within-clutch egg colors tending away from intermediateand toward short wavelengths. Mean egg darkness decreased linearlyduring the laying sequence, suggesting pigment limitation. Maleswere observed frequently visiting nests during the laying period,allowing them to observe eggs before the start of incubation.These results support the signaling hypothesis for explainingbright colors of avian eggs.     

Do male ornaments signal immunity in the common yellowthroat?

Male ornaments may advertise genetic benefits to females choosingmates. These benefits may come in the form of genes for resistanceto parasites and disease. Thus, females that prefer more ornamentedmales as mates may receive genes for enhanced immune systemfunction for their offspring. The common yellowthroat (Geothlypistrichas) is the only species to date in which a male plumageornament (size of the black facial mask) is known to be relatedto extrapair mating, and extrapair young are more immunocompetentthan their within-pair half-sibs (at least in colder years).To investigate whether male mask size signals superior immunefunction, we examined male ornaments (mask and bib size andcolor) in relation to measures of overall health (hematocrit)and immune system function (plasma immunoglobulin G [IgG] concentrationand cutaneous immune activity). We also investigated the rolethat testosterone may play in mediating the relationship betweenornaments and immunity. Male mask size was correlated positivelywith IgG level, suggesting that male mask size may indicatehumoral immunity. However, mask size was correlated negativelywith hematocrit and cutaneous immune activity (our measure ofnestling immunocompetence). Bib size and color were not relatedto these indices of immune function or health. Plasma testosteronelevel was neither related to immune function or health nor tothe expression of male ornaments. These results suggest thatthere might be a trade-off between immune system components,as well as between immunity and the production or advertisementof male ornaments.     

Habitat-specific effects of a food supplementation experiment on immunocompetence in Eurasian Magpie Pica pica nestlings

Parasite pressure and nutrition are two of the most important factors affecting the trade-off between nestling growth and immune development. During development, energy and nutrients are often limited, and nestlings should only dedicate differentially more valuable resources to their immune system when the associated benefits are high (i.e. in situations of an increased risk of parasitism). In this study, we manipulated nutritional condition of Eurasian Magpie Pica pica nestlings by providing a food supplement. Additionally, the study area was subdivided into two categories of habitat (irrigated and arid) based on the presence of irrigation canals. Nestling diet composition was more varied in the irrigated compared with in the arid habitat. In addition, nestlings of the irrigated habitat showed a significantly higher infestation of both ectoparasites and blood parasites and a significantly higher cell-mediated immunity, but lower tarsus length compared with nestlings of the arid habitat. Food supplementation to nestlings did not affect tarsus length, but increased nestling cell-mediated immunity in the arid habitat only. Based on the recent demonstrated trade-off between growth and immunocompetence in nestlings, we suggest that differences between habitats in nestling diet and parasite prevalence may have caused different priority rules in the allocation of resources between both fitness traits.     

Genetic diversity predicts pathogen resistance and cell-mediated immunocompetence in house finches

Evidence is accumulating that genetic variation within individual hosts can influence their susceptibility to pathogens. However, there have been few opportunities to experimentally test this relationship, particularly within outbred populations of non-domestic vertebrates. We performed a standardized pathogen challenge in house finches (Carpodacus mexicanus) to test whether multilocus heterozygosity across 12 microsatellite loci predicts resistance to a recently emerged strain of the bacterial pathogen, Mycoplasma gallisepticum (MG). We simultaneously tested whether the relationship between heterozygosity and pathogen susceptibility is mediated by differences in cell-mediated or humoral immunocompetence. We inoculated 40 house finches with MG under identical conditions and assayed both humoral and cell-mediated components of the immune response. Heterozygous house finches developed less severe disease when infected with MG, and they mounted stronger cell-mediated immune responses to phytohaemagglutinin. Differences in cell-mediated immunocompetence may, therefore, partly explain why more heterozygous house finches show greater resistance to MG. Overall, our results underscore the importance of multilocus heterozygosity for individual pathogen resistance and immunity.     

Sexual advertisement and immune function in an arachnid species (Lycosidae)

A simple version of the immunocompetence handicap hypothesizesthat through condition-dependence, the size of the sexual traitmay be positively related to immune function at the populationlevel. In the present study, we investigated the relationshipbetween sexual advertisement and immune function in a naturalpopulation of male wolf spiders, Hygrolycosa rubrofasciata (Araneae:Lycosidae). Males of H. rubrofasciata have a costly and condition-dependentacoustic signal, courtship drumming. In the mating season, malesdrum against dry leaves while wandering around the habitat searchingfor receptive females. Males increase their mating success byincreasing their drumming rate and mobility. We used drummingrate and mobility measured without female proximity as estimatesof sexual advertisement. As estimates of male immune function,we used encapsulation rate and lytic activity. Encapsulationrate is a common challenging technique, which measures immuneresponse against multicellular parasites. Lytic activity isa monitoring technique, which measures immune response againstpathogens. Our results show that males with higher drummingrate had higher encapsulation rate. This suggests that femalesmight use drumming rate as a signal for choosing males withgood immunocompetence. Moreover, our results show that maleswith higher mobility had higher lytic activity. As females aremore likely to encounter those males that have higher mobility,this might also select males with better immune function. Ourresults suggest that the immunocompetence handicap might workalso among spiders, although we could not assess the causalityof the relationship between sexual selection and immune functionin this correlational study.     

Immunocompetence and helminth community of the white-toothed shrew, <Emphasis Type="Italic">Crocidura russula</Emphasis> from the Montseny Natural Park,Spain

Host immunocompetence assessed by spleen size and response to phytohaemagglutinin (PHA) injection may give some indications on the control of parasite infection and on host mediation effect, through immunity, on parasite community structure. We investigated the helminth community and immunocompetence of the white-toothed shrew in a small area to test the relationship between immunocompetence and intensity of helminth infection. At the proximate level and if spleen mass and PHA response reflect the level of immunocompetence, we expected that individuals with a large spleen or a high PHA response should harbour a lower parasite load than individuals with relatively small spleen or low PHA response. In addition, we predicted that the structure of the helminth community should be mediated by the host’s immune defence. Spleen mass was linked to helminth infection. Nematodes and cestodes were negatively associated within hosts. PHA response was not related to total helminth intensity of infection but was negatively related to cestode intensity and positively to nematode intensity. This result suggests either a differential modulating effect on immunity by the two groups of worms or the existence of an antagonistic association between nematodes and cestodes mediated by the immune response of the host.     

Reproduction and population density affect humoral immunity in bank voles under field experimental conditions

Density dependence is a common feature in the dynamics of animal populations. Availability of food resources critical to immunity is likely to be one of the mechanisms mediating the effect of population density on individual fitness. The ability to mount an immune response to an antigen is also affected by levels of immunosuppressive hormones associated with reproduction or mediating the response to ecological and social stress. We assessed variation in condition and intensity of humoral immune response to a T-cell-dependent antigen in bank voles (Clethrionomys glareolus) by experimentally altering population density before immunisation. Consistent with our prediction, males had lower humoral immunocompetence in the breeding than in the non-breeding season. Contrary to our expectation, males did not show enhanced immunocompetence and females showed depressed humoral immune response under experimentally lowered population density. Variation of immune response in relation to population density depended on sex, with females but not males showing lower immune response under experimentally reduced density. We conclude that humoral immunity of bank voles was affected by reproduction and social environment rather than by population density. Received: 2 November 1999 / Accepted: 22 March 2000     

The response of the regional lymph node of guinea-pigs to primary and challenge infection with the nematode, Trichostrongylus colubriformis

Responses characteristic of both cell-mediated immunity and the production of humoral antibodies occurred in the regional lymph node (mesenteric) of guinea-pigs following primary and challenge infection with the nematode Trichostrongylus colubriformis. In addition, depletion of lymphocytes in the paracortical areas and pronounced infiltration with basophil and eosinophil leucocytes were observed. All these changes were chronologically related to parasite rejection.     

Immunity and the expression of a secondary sexual trait in a horned beetle

Resource-based trade-offs are known to be important in determininginvestment in both sexual ornamentation and immunity in insects.Because of the strict resource limitation experienced duringmetamorphosis, we predict that if insects are trading off ornamentsize and immunity this should be most apparent immediately aftereclosion and that the relationship between sexual ornament sizeand immunity should change with maturation feeding because ofthe changing patterns of resource availability during this process.We therefore present an investigation into the relationshipbetween morphology, sex, and two measures of immune response(phenoloxidase [PO] activity and encapsulation ability) in thehorned beetle Euoniticellus intermedius, immediately after eclosionand after maturation feeding. Both measures increased with maturation,with sex differences in PO activity becoming discernable aftermaturation feeding. PO activity was positively correlated withhorn length in male beetles both on eclosion and after maturationfeeding, and encapsulation ability was positively correlatedwith elytra length. We conclude that resource limitation inthe pupating insect does have effects on immunity but that thisresource limitation does not translate into a measurable trade-offbetween horn length and immunity. The correlation between hornlength and PO activity may arise because both horn length andPO activity are correlated with the same elements of the animal'sbiology that allow some animals both to grow a long horn andto sustain a higher level of PO activity.     

Selenium Supplementation Restores Innate and Humoral Immune Responses in Footrot-Affected Sheep

Dietary selenium (Se) alters whole-blood Se concentrations in sheep, dependent upon Se source and dosage administered, but little is known about effects on immune function. We used footrot (FR) as a disease model to test the effects of supranutritional Se supplementation on immune function. To determine the effect of Se-source (organic Se-yeast, inorganic Na-selenite or Na-selenate) and Se-dosage (1, 3, 5 times FDA-permitted level) on FR severity, 120 ewes with and 120 ewes without FR were drenched weekly for 62 weeks with different Se sources and dosages (30 ewes/treatment group). Innate immunity was evaluated after 62 weeks of supplementation by measuring neutrophil bacterial killing ability. Adaptive immune function was evaluated by immunizing sheep with keyhole limpet hemocyanin (KLH). The antibody titer and delayed-type hypersensitivity skin test to KLH were used to assess humoral immunity and cell-mediated immunity, respectively. At baseline, FR-affected ewes had lower whole-blood and serum-Se concentrations; this difference was not observed after Se supplementation. Se supplementation increased neutrophil bacterial killing percentages in FR-affected sheep to percentages observed in supplemented and non-supplemented healthy sheep. Similarly, Se supplementation increased KLH antibody titers in FR-affected sheep to titers observed in healthy sheep. FR-affected sheep demonstrated suppressed cell-mediated immunity at 24 hours after intradermal KLH challenge, although there was no improvement with Se supplementation. We did not consistently prevent nor improve recovery from FR over the 62 week Se-treatment period. In conclusion, Se supplementation does not prevent FR, but does restore innate and humoral immune functions negatively affected by FR.