Biomedical subjects

Camille Bonneaud

Publications and source records attributed to Camille Bonneaud.

6 recordsLinked to original sources

PubMed2006

Complex Mhc-based mate choice in a wild passerine.

The extreme polymorphism of the vertebrate major histocompatibility complex (Mhc) is famous for protecting hosts against constantly evolving pathogens. Mate choice is often evoked as a means of maintaining Mhc variability through avoidance of partners with similar Mhc alleles or preference for heterozygotes. Evidence for these two hypotheses mostly comes from studies on humans and laboratory mice. Here, we tested these hypotheses in a wild outbred population of house sparrows (Passer domesticus). Females were not more or less closely related to the males they paired with when considering neutral genetic variation. However, males failed to form breeding pairs when they had too few Mhc alleles and when they were too dissimilar from females at Mhc loci (i.e. had no common alleles). Furthermore, pairs did not form at random as Mhc diversity positively correlated in mating pairs. These results suggest that mate choice evolves in response to (i) benefits in terms of parasite resistance acquired from allelic diversity, and (ii) costs associated with the disruption of co-adapted genes.

Animals↗

PubMed2006

Major histocompatibility alleles associated with local resistance to malaria in a passerine.

Malaria parasites are a major cause of human mortality in tropical countries and a potential threat for wildlife, as witnessed by the malaria-induced extinction of naive Hawaiian avifauna. Identifying resistance mechanisms is therefore crucial both for human health and wildlife conservation. Patterns of malaria resistance are known to be highly polygenic in both humans and mice, with marked contributions attributed to major histocompatibility (Mhc) genes. Here we show that specific Mhc variants are linked to both increased resistance and susceptibility to malaria infection in a wild passerine species, the house sparrow (Passer domesticus). In addition, links between host immunogenetics and resistance to malaria involved population-specific alleles, suggesting local adaptation in this host-parasite interaction. This is the first evidence for a population-specific genetic control of resistance to malaria in a wild species.

Alleles↗

PubMed2005

An Mhc class I allele associated to the expression of T-dependent immune response in the house sparrow.

The major histocompatibility complex (Mhc) encodes for highly variable molecules, responsible for foreign antigen recognition and subsequent activation of immune responses in hosts. Mhc polymorphism should hence be related to pathogen resistance and immune activity, with individuals that carry either a higher diversity of Mhc alleles or one specific Mhc allele exhibiting a stronger immune response to a given antigen. Links between Mhc alleles and immune activity have never been explored in natural populations of vertebrates. To fill this gap, we challenged house sparrows (Passer domesticus) with two T-dependent antigens (phytohemagglutinin and sheep red blood cells) and examined both primary and secondary immune responses in relation to their Mhc class I genotypes. The total number of Mhc alleles had no influence on either primary or secondary response to the two antigens. One particular Mhc allele, however, was associated with an increased response to both antigens. Our results point toward a contribution of the Mhc, or of other genes in linkage disequilibrium with the Mhc, in the regulation of immune responses in a wild animal species.

Alleles↗

PubMed2004

Diversity of Mhc class I and IIB genes in house sparrows (Passer domesticus).

In order to understand the expression and evolution of host resistance to pathogens, we need to examine the links between genetic variability at the major histocompatibility complex ( Mhc), phenotypic expression of the immune response and parasite resistance in natural populations. To do so, we characterized the Mhc class I and IIB genes of house sparrows with the goal of designing a PCR-based genotyping method for the Mhc genes using denaturing gradient gel electrophoresis (DGGE). The incredible success of house sparrows in colonizing habitats worldwide allows us to assess the importance of the variability of Mhc genes in the face of various pathogenic pressures. Isolation and sequencing of Mhc class I and IIB alleles revealed that house sparrows have fewer loci and fewer alleles than great reed warblers. In addition, the Mhc class I genes divided in two distinct lineages with different levels of polymorphism, possibly indicating different functional roles for each gene family. This organization is reminiscent of the chicken B complex and Rfp-Y system. The house sparrow Mhc hence appears to be intermediate between the great reed warbler and the chicken Mhc, both in terms of numbers of alleles and existence of within-class lineages. We specifically amplified one Mhc class I gene family and ran the PCR products on DGGE gels. The individuals screened displayed between one and ten DGGE bands, indicating that this method can be used in future studies to explore the ecological impacts of Mhc diversity.

Alleles↗

PubMed2004

Terminal investment induced by immune challenge and fitness traits associated with major histocompatibility complex in the house sparrow.

The terminal investment hypothesis predicts that individuals should invest more in their present reproduction if they are less likely to survive to future reproductive events. Infections, which reduce viability, may be used by individuals as a cue of a diminishing residual reproductive value and could therefore theoretically trigger an intensification of breeding effort. We tested this hypothesis in a natural population of house sparrows (Passer domesticus). We manipulated the immune system of breeding females by injecting them with a vaccine against the Paramyxo virus, the agent of Newcastle disease. Females were captured and treated immediately after completion of their first clutch either with the vaccine (NDV) or with phosphate buffered saline (PBS). The entire clutch was subsequently removed. We also screened Mhc class I genes of females to assess possible genotype-by-immune treatment interactions on reproductive investment. Our results indicate that vaccinated females were more likely to lay replacement clutches and that the difference in number of eggs between first and replacement clutches was greater for NDV females than for controls. In addition, chick size, both in terms of tarsus length and body mass, was affected by immune activation but in interaction with nestling age and female body mass, respectively. Mhc genotype-by-immune treatment interactions were never significant; however, allelic diversity was positively correlated with nestling survival. These results show that immune system activation is potentially used as a cue of reduced survival prospect and appears to induce a costly terminal investment behavior, and Mhc diversity might be under selection in a natural population of house sparrows.

Animals↗

PubMed2003

Assessing the cost of mounting an immune response.

The evolution of parasite resistance has often been assumed to be governed by antagonistic selection pressures. Defense against pathogens, by mounting an immune response, confers evident benefits but may also incur costs, so that the optimal level of defense is expected to depend on the balance between benefits and costs. Although the benefits of immune surveillance are well known, estimates of costs are still equivocal. Here we studied the behavioral and physiological modifications associated with exposure to a nonreplicating antigen (lipopolysaccharide [LPS] of Escherichia coli) in a passerine species, the house sparrow (Passer domesticus). We further investigated whether the behavioral and physiological changes provoked by LPS induced measurable repercussions on life-history traits, such as the breeding effort and reproductive success. Finally, we tested whether the trade-off between immune activation and breeding effort was modulated by the workload required to feed the brood. Exposure to LPS reduced activity and increased body mass loss of captive individuals; similarly, LPS injection induced a dramatic drop in feeding rate and reproductive success of breeding females. However, this reduction depended on brood size, suggesting that the strength of the trade-off between immune activation and reproduction was affected by the workload required to feed the brood. Overall, this study stresses the magnitude of costs associated with mounting immune responses and the ecological and evolutionary consequences for natural populations.

Animals↗