Ecoimmunity in Darwin's finches: invasive parasites trigger acquired immunity in the medium ground finch (Geospiza fortis) - PubMed (original) (raw)

Ecoimmunity in Darwin's finches: invasive parasites trigger acquired immunity in the medium ground finch (Geospiza fortis)

Sarah K Huber et al. PLoS One. 2010.

Abstract

Background: Invasive parasites are a major threat to island populations of animals. Darwin's finches of the Galápagos Islands are under attack by introduced pox virus (Poxvirus avium) and nest flies (Philornis downsi). We developed assays for parasite-specific antibody responses in Darwin's finches (Geospiza fortis), to test for relationships between adaptive immune responses to novel parasites and spatial-temporal variation in the occurrence of parasite pressure among G. fortis populations.

Methodology/principal findings: We developed enzyme-linked immunosorbent assays (ELISAs) for the presence of antibodies in the serum of Darwin's finches specific to pox virus or Philornis proteins. We compared antibody levels between bird populations with and without evidence of pox infection (visible lesions), and among birds sampled before nesting (prior to nest-fly exposure) versus during nesting (with fly exposure). Birds from the Pox-positive population had higher levels of pox-binding antibodies. Philornis-binding antibody levels were higher in birds sampled during nesting. Female birds, which occupy the nest, had higher Philornis-binding antibody levels than males. The study was limited by an inability to confirm pox exposure independent of obvious lesions. However, the lasting effects of pox infection (e.g., scarring and lost digits) were expected to be reliable indicators of prior pox infection.

Conclusions/significance: This is the first demonstration, to our knowledge, of parasite-specific antibody responses to multiple classes of parasites in a wild population of birds. Darwin's finches initiated acquired immune responses to novel parasites. Our study has vital implications for invasion biology and ecological immunology. The adaptive immune response of Darwin's finches may help combat the negative effects of parasitism. Alternatively, the physiological cost of mounting such a response could outweigh any benefits, accelerating population decline. Tests of the fitness implications of parasite-specific immune responses in Darwin's finches are urgently needed.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. Parasite-specific antibody response of Geospiza fortis.

(A) Medium ground finch, Geospiza fortis, with pox lesion in front of eye. (B) G. fortis nestling with Philornis downsi lesions in nostrils and ear. (C) Pox-binding antibody levels of adult birds on Daphne Major (n = 30) were higher than those of adult birds at El Garrapatero (n = 113) (Mann Whitney U = 619.50, p<0.0001). (D) _Philornis_-binding antibody levels of adult birds with active nests at El Garrapatero (n = 37) were higher than those of adult birds prior to nesting (n = 76) at the same site (U = 800, p<0.0001). Antibody response is measured as the optical density (OD) at 450nm. Bars indicate mean±standard error.

Figure 2. Western blot of serum dilutions developed for house sparrow IgY.

Western blot of serum dilutions from Darwin's finch (DF), house sparrow and chicken using antibody markers developed for house sparrow IgY. Lane 1: DF serum 1∶10. Lane 2: DF serum 1∶20. Lane 3: house sparrow serum 1∶10. Lane 4: house sparrow serum 1∶20. Lane 5 chicken serum 1∶10. Lane 6 chicken serum 1∶20. Image indicates cross reactivity of house sparrow IgY detection antibody with Darwin's finch IgY. The lack of binding to chicken serum indicates no cross-reactivity with that species.

Figure 3. Optimization of ELISAs for antigen and Darwin's finch serum.

Optical density (OD) values for optimization ELISAs of (A) Pox antigen dilutions and Darwin's finch serum at 1/500, (B) Philornis antigen dilutions and Darwin's finch serum at 1/500, (C) Darwin's finch serum dilutions and Pox antigen at 1/1000, and (D) Darwin's finch serum dilutions and Philornis antigen at 1/1000. Decreasing amounts of antigen (A,B) and antibody (C,D) result in decreasing optical density values, indicating specific antibody-antigen binding.

References

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Ecoimmunity in Darwin's finches: invasive parasites trigger acquired immunity in the medium ground finch (Geospiza fortis) - PubMed (original) (raw)