Research Article: Ecoimmunity in Darwin’s Finches: Invasive Parasites Trigger Acquired Immunity in the Medium Ground Finch (Geospiza fortis)

Date Published: January 6, 2010

Publisher: Public Library of Science

Author(s): Sarah K. Huber, Jeb P. Owen, Jennifer A. H. Koop, Marisa O. King, Peter R. Grant, B. Rosemary Grant, Dale H. Clayton, Laurent Rénia.

Abstract: 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.

Partial Text: Invasive parasites pose a serious threat to native animal populations, because hosts with no history of exposure may lack effective immune defenses. Invasive parasites are a particular threat to small, island populations [1], [2]. For example, introduced malaria (Plasmodium relictum) has exacerbated the decline of Hawaiian honeycreeper species, many of which are now extinct [3], [4]. Darwin’s finches have recently been exposed to two introduced parasites of high conservation priority: avian pox virus (Poxvirus avium) and the nest fly Philornis downsi (Figure 1A, 1B) [1], [2]. Both of these parasites have been shown to have negative effects on host fitness of Galápagos birds [5], [6], [7], [8], [9], [10]. If birds are able to mount an immune response to these novel pathogens, then they might ultimately be protected, to at least some degree, from the negative fitness consequences of parasitism. Alternatively, the physiological costs of an induced immune response to these parasites may exceed the benefits of mitigating parasite damage and contribute to negative fitness consequences. Indeed, these contrasting possibilities are a guiding force behind research within the field of ecological immunology [11].

Adult birds on Daphne Major had significantly higher levels of pox-binding antibodies than birds from El Garrapatero (mean±SE for Daphne Major = 0.63±0.09 optical density (OD); mean±SE for El Garrapatero = 0.20±0.02 OD; Mann Whitney U = 619.50; p<0.0001; Figure 1C). Higher levels of pox-binding and Philornis-binding antibodies in Darwin's finches exposed to these parasites confirms that these birds are capable of mounting parasite-specific adaptive immune responses to novel parasites. Importantly, these antibody responses are directed against parasites that represent distinct immunological demands (intracellular versus external), and which constitute a serious threat to Darwin's finches. From the perspective of vertebrate immunology, it is not unusual that G. fortis is able to develop antibodies against novel challenges. However, our data are unique in two respects. This study is the first demonstration, to our knowledge, of ectoparasite-specific antibodies in a wild bird population. This study is also the first demonstration of parasite-specific antibodies directed against two distinct classes of parasites (external and intracellular) in a wild bird population. Within the field of ecological immunology, these observations are important because they establish a definitive immunological link between actual parasites and an animal of ecological interest [16]. Source:


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