Variation In Immunocompetence Research Articles

Experimental evolution reveals sex-specific dominance for surviving bacterial infection in laboratory populations of Drosophila melanogaster.

Males and females are subjected to distinct kinds of selection pressures, often leading to the evolution of sex‐specific genetic architecture, an example being sex‐specific dominance. Sex‐specific dominance reversals (SSDRs), where alleles at sexually antagonistic loci are at least partially dominant in the sex they benefit, have been documented in Atlantic salmon, rainbow trout, and seed beetles. Another interesting feature of many sexually reproducing organisms is the asymmetric inheritance pattern of X chromosomes, which often leads to distinct evolutionary outcomes on X chromosomes compared to autosomes. Examples include the higher efficacy of sexually concordant selection on X chromosomes, and X chromosomes being more conducive to the maintenance of sexually antagonistic polymorphisms under certain conditions. Immunocompetence is a trait that has been extensively investigated for sexual dimorphism with growing evidence for sex‐specific or sexually antagonistic variation. X chromosomes have been shown to harbor substantial immunity‐related genetic variation in the fruit fly, Drosophila melanogaster. Here, using interpopulation crosses and cytogenetic cloning, we investigated sex‐specific dominance and the role of the X chromosome in improved postinfection survivorship of laboratory populations of D. melanogaster selected against pathogenic challenge by Pseudomonas entomophila. We could not detect any contribution of the X chromosome to the evolved immunocompetence of our selected populations, as well as to within‐population variation in immunocompetence. However, we found strong evidence of sex‐specific dominance related to surviving bacterial infection. Our results indicate that alleles that confer a survival advantage to the selected populations are, on average, partially dominant in females but partially recessive in males. This could also imply an SSDR for overall fitness, given the putative evidence for sexually antagonistic selection affecting immunocompetence in Drosophila melanogaster. We also highlight sex‐specific dominance as a potential mechanism of sex differences in immunocompetence, with population‐level sex differences primarily driven by sex differences in heterozygotes.

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.

Immunocompetence and high metabolic rates enhance overwinter survival in the root vole, Microtus oeconomus.

Despite its presumed significance, the association between immune defence, energy expenditures and overwinter survival is rarely studied. We analysed individual variation in immunocompetence quantified as neutrophil-to-lymphocyte ratio (N/L), total white blood cells (WBC) and natural antibody levels, along with resting (RMR) and peak metabolic rates (PMR) and mortality during three consecutive winter seasons in a natural population of the root vole, Microtus oeconomus. In early winter, WBC count was negatively correlated with RMR, whereas N/L ratio was negatively correlated with swim-elicited PMR. We suggest that while the first correlation reflected the trade-off between energy allocation in immunocompetence and other metabolically demanding processes, the latter correlation stemmed from stress-induced immunosuppression elicited by the necessity to cope with swimming in frequently flooded habitat. In addition, the analysis carried out during the first year of study characterized by a high population density and prevalence of infestation with a blood parasite--Babesia spp., showed that its intensity was inversely correlated with the N/L ratio. In summary, our results suggest that elevated N/L ratio increases the winter survival of free-ranging rodents by increasing their ability to cope with parasitic infections.

Immunocompetence of the red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae, Scolytinae): Variation between developmental stages and sexes in populations in China

Immune defense imposes fitness costs as well as benefits, so organisms should optimize, not maximize, their immune function through their life cycle. We investigated this issue in the red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae, Scolytinae), which is a pine-killing invasive beetle in China, though it is usually considered as a secondary pest in its native range of North America. We hypothesized that pathogen pressure may affect these beetles differently throughout their life history. We measured the insect's immunocompetence throughout life, determining encapsulation ability and phenoloxidase activity in larval stages, pupae and adults. Pupae had the highest encapsulation ability, but encapsulation was not different between final instar larvae and adults. Phenoloxidase (PO) activity was highest in final instar larvae and pupae, followed by the second instar larvae and adults. Total phenoloxidase activity increased significantly from the second instar larval stage to pupae, and then decreased in adults. Although the second instar larvae had the lowest phenoloxidase activity, more than 90% of total PO existed in the hemolymph in the form of the active enzyme, as compared with pupae, in which over 60% of PO occurred as a proenzyme. Both active PO and total PO were much higher in females than in males, though no significant differences were detected between the encapsulation ability of male and female adults. This result suggests the existence of a sexual dimorphism of immunocompetence in D. valens adults. Variations in immunocompetence across developmental stages suggest that D. valens adopts diverse investment strategies in immunocompetence during different stages. Potential reasons for variation in immunocompetence among developmental stages and between the sexes of D. valens are discussed.

Palatability of passerines to parasites: within‐brood variation in nestling responses to experimental parasite removal and carotenoid supplementation

Asynchronous hatching of eggs in avian clutches produces a size hierarchy among nestlings that may lead to variation within broods in resistance to pathogens or parasites. In this study, we tested several predictions regarding variation in immunocompetence and distribution of parasites within avian broods by combining parasite removal and carotenoid supplementation treatments in nests of mountain bluebirds Sialia currucoides. Last‐hatched nestlings were less likely to invest carotenoids in an induced cell‐mediated immune response, suggesting they may be more susceptible to parasites; however, parasite removal disproportionately benefited middle‐ranked nestlings. This supports the hypothesis that some avian ectoparasites balance host resistance against nutritional benefits by preferentially parasitizing nestlings of intermediate quality and immunocompetence. We found no evidence that males positioned last in the hatching sequence were differentially affected by ectoparasites, and, contrary to some previous studies in other passerines, last‐hatched nestlings in asynchronously hatching broods were not less immunocompetent than their nest mates. In fact, junior nestlings exhibited weaker immune responses than their siblings in more synchronously hatching broods, and we suggest this may reflect environment‐dependent maternal effects that warrant further investigation. Overall, our results highlight the importance of understanding the feeding and host selection behaviour of ectoparasites, as well as the fitness consequences thereof, since many predictions related to within‐brood distribution of parasites require that parasites are able to discern the relative quality of available hosts.

Wolbachia Mediate Variation of Host Immunocompetence

BackgroundAfter decades during which endosymbionts were considered as silent in their hosts, in particular concerning the immune system, recent studies have revealed the contrary. In the present paper, we addressed the effect of Wolbachia, the most prevalent endosymbiont in arthropods, on host immunocompetence. To this end, we chose the A. vulgare-Wolbachia symbiosis as a model system because it leads to compare consequences of two Wolbachia strains (wVulC and wVulM) on hosts from the same population. Moreover, A. vulgare is the only host-species in which Wolbachia have been directly observed within haemocytes which are responsible for both humoral and cellular immune responses.Methodology/Principal FindingsWe sampled gravid females from the same population that were either asymbiotic, infected with wVulC, or infected with wVulM. The offspring from these females were tested and it was revealed that individuals harbouring wVulC exhibited: (i) lower haemocyte densities, (ii) more intense septicaemia in their haemolymph and (iii) a reduced lifespan as compared to individuals habouring wVulM or asymbiotic ones. Therefore, individuals in this population of A. vulgare appeared to suffer more from wVulC than from wVulM. Symbiotic titer and location in the haemocytes did not differ for the two Wolbachia strains showing that these two parameters were not responsible for differences observed in their extended phenotypes in A. vulgare.Conclusion/SignificanceThe two Wolbachia strains infecting A. vulgare in the same population induced variation in immunocompetence and survival of their hosts. Such variation should highly influence the dynamics of this host-symbiont system. We propose in accordance with previous population genetic works, that wVulM is a local strain that has attenuated its virulence through a long term adaptation process towards local A. vulgare genotypes whereas wVulC, which is a widespread and invasive strain, is not locally adapted.

In kittiwakes food availability partially explains the seasonal decline in humoral immunocompetence

Summary 1The immune system plays an important role in fitness, and interindividual variation in immunocompetence is due to several factors including food supply. 2Seasonal variation in food resources may therefore explain why immunocompetence in bird nestlings usually declines throughout the breeding season, with chicks born early in the season receiving more food than chicks born later, and thereby possibly developing a more potent immune system. Although there are studies supporting this hypothesis, none has been experimental. 3We performed an experiment in the kittiwake Rissa tridactyla by manipulating the food supply of pairs that were left to produce a first brood, and of pairs that were induced to produce a late replacement brood. 4If food supply mediates, at least partially, seasonal variations in chick immunocompetence, non-food-supplemented chicks would show a stronger seasonal decline in immunocompetence than food-supplemented chicks. 5Food supplementation improved humoral immunocompetence (the production of immunoglobulins Y), but not T-cell immunocompetence (phytohaemagglutinin, PHA response). T-cell immunocompetence of food-supplemented and non-food-supplemented chicks decreased through the season but to a similar extent, whereas the humoral immunocompetence of non-food-supplemented chicks decreased more strongly than that of food-supplemented chicks. 6Our results suggest that the seasonal decline in humoral immunocompetence can be explained, at least partly, by variations in food supply throughout the breeding season.

Covariance in species diversity and facilitation among non-interactive parasite taxa: all against the host

Different parasite taxa exploit different host resources and are often unlikely to interact directly. It is unclear, however, whether the diversity of any given parasite taxon is indirectly influenced by that of other parasite taxa on the same host. Some components of host immune defences may operate simultaneously against all kinds of parasites, whereas investment by the host in specific defences against one type of parasite may come at the expense of defence against other parasites. We investigated the relationships between the species diversity of 4 higher taxa of ectoparasites (fleas, sucking lice, mesostigmatid mites, and ixodid ticks), and between the species richness of ectoparasites and endoparasitic helminths, across different species of rodent hosts. Our analyses used 2 measures of species diversity, species richness and taxonomic distinctness, and controlled for the potentially confounding effects of sampling effort and phylogenetic relationships among host species. We found positive pairwise correlations between the species richness of fleas, mites and ticks; however, there was no association between species richness of any of these 3 groups and that of lice. We also found a strong positive relationship between the taxonomic distinctness of ecto- and endoparasite assemblages across host species. These results suggest the existence of a process of apparent facilitation among unrelated taxa in the organization of parasite communities. We propose explanations based on host immune responses, involving acquired cross-resistance to infection and interspecific variation in immunocompetence among hosts, to account for these patterns.

Ecological immunology: life history trade-offs and immune defense in birds

There has been considerable recent interest in the effects of life-history decisions on immunocompetence in birds. If immunocompetence is limited by available resources, then trade-offs between investment in life-history components and investment in immunocompetence could be important in determining optimal life-history traits. For this to be true: (1) immunocompetence must be limited by resources, (2) investment in life-history components must be negatively correlated with immunocompetence, and (3) immunocompetence must be positively correlated with fitness. To gather such empirical data, ecologists need to be able to measure immunocompetence. We review techniques used to measure immunocompetence and how they are applied by ecologists. We also consider the components of the immune system that constitute immunocompetence and evaluate the possible consequences of measuring immunocompetence in different ways. We then review the empirical evidence for life-history tradeoffs involving immune defense. We conclude that there is some evidence suggesting that immunocompetence is limited by resources and that investment in certain life-history components reduces immunocompetence. However, the evidence that immunocompetence is related to fitness is circumstantial at present, although consistent with the hypothesis that immunocompetence and fitness are positively correlated. We argue that future work needs to examine the fitness effects of variation in immunocompetence and suggest that artificial selection experiments offer a potentially important tool for addressing this issue.

Relationships between genetic change and infectious disease in domestic livestock

AbstractThe relations between genetic change in domestic livestock and infectious disease (including both its epidemiology and the animal's reaction to it) are examined. The overall picture is confusing because there are different, and seemingly unrelated, ways of considering the issue. An attempt is made to put these together into a more general framework. Four processes of particular interest are distinguished and discussed in more detail: (i) the way a population's genetic potential for immunocompetence can be changed by breeding, (ii) the way an animal's immunocompetence is influenced by that animal's production potential, in combination with the environmental resources that are available to it at a given time, (iii) the way the disease status of an animal (and a population of animals) is influenced by its immunocompetence, and (iv) the way the production level of an animal is influenced by activation of its immune system. Ultimately, all four processes influence the realised level of production.This comes down to four questions that need to be addressed: (i) can we use genetic variation in immunocompetence in animal breeding? (ii) does a higher production potential (today's direction of breeding) have a negative impact on immunocompetence? (iii) does improved immunocompetence result in improved health? and (iv) how large is the negative impact of disease on production?

Changes in serum protein and IgM concentration duringsmolting and early post-smolt period in vaccinated and unvaccinated Atlantic salmon ( Salmo salar L.).

During smolting the concentrations of serum protein and IgM were measured.A Vibrio salmonicida vaccine was given once or twice at various times to study the effect of smolting on vaccination. During smolting there was a decrease of both total serum proteins and totalserum IgM of 24%. After sea water transfer, the total serum protein concentration increased to levels similar to those before smolting and remained stable at this level throughout the observation period. The total IgM concentration increased immediately after sea water transfer and 4 weeks later it was similar to levels before sea water transfer. In September, 4 months after sea water transfer, the IgM concentration was twice the concentration before smolting. Weight and length were not affected by primary vaccination, while groups secondary vaccinated after sea water transfer were significantly smaller than those secondary vaccinated prior to sea water transfer. The observed decrease in total serum protein and IgM during the parr-smolt transformation and the subsequent increase of IgM after sea water transfer and in the autumn indicate a potential variation in immunocompetence, suggesting that the timing of vaccination with respect to developmental stage or smolt status has an impact on the immune response.

Immune Responsiveness in Patients With Choroidal Malignant Melanoma

We studied selective in vivo and in vitro immunologic factors of 25 patients with choroidal malignant melanoma. Immune profile factors did not show consistent differences between patients with melanoma and an age-matched control population. The studies were also non-contributory in delineating variations in immunocompetence with respect to melanoma cell types. Serial immune profiles failed to identify a change when clinical evidence of metastasis developed. When tested as a group, patients with melanoma in whom metastatic disease developed during the study showed significant depression of initial mitogen-induced lymphocyte blastogenesis. This depression was noted in advance of clinically recognized metastatic disease. This group had a wide range of responses that overlapped those of control patients, thus making the usefulness of these testing factors questionable for individual prognosis or for clinical monitoring.