Parasite mediated mortality and host immune response explain age-related differences in blood parasitism in birds
An important pattern in host-parasite assem- blages is a higher intensity of parasites in juveniles than in adults, but the reasons for these differences remain obscure. Three non-mutually exclusive hypotheses have been proposed: (1) heavily parasitized juveniles die before being recruited into the...
| Autores: | , , |
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| Tipo de recurso: | artículo |
| Fecha de publicación: | 2003 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/36866 |
| Acceso en línea: | http://hdl.handle.net/10261/36866 |
| Access Level: | acceso abierto |
| Palabra clave: | Columba livia Haematozoa Haemoproteus columbae Parasite-host interaction Survival selection |
| Sumario: | An important pattern in host-parasite assem- blages is a higher intensity of parasites in juveniles than in adults, but the reasons for these differences remain obscure. Three non-mutually exclusive hypotheses have been proposed: (1) heavily parasitized juveniles die before being recruited into the adult population (‘selec- tion’ hypothesis); (2) the development of an acquired immunity by the host in front of the parasite reduces the intensity of the parasite in adult hosts (‘immunity’ hypothesis); and (3) differences in behavior makes adults less exposed to the parasite than juveniles (‘vector exposure’ hypothesis). Having rejected the ‘vector expo- sure’ hypothesis in a previous study, here we tested the ‘selection’ and ‘immunity’ hypotheses in feral pigeons (Columba livia) infected by the blood parasite Haemo- proteus columbae. In agreement with the ‘selection’ hypothesis, young (but not adult) pigeons that were highly parasitized had a lower probability of surviving until adulthood, independent of their body condition. However, selection was not strong enough to account for the observed differences in parasite intensity between age- classes, and after selection parasite intensity of survivors still remained 85% higher in juveniles than in adults. In contrast, the ‘immunity’ hypothesis offered a greater explanatory power. The intensity of blood parasites in young pigeons, but not in adults, decreased over time so dramatically that by the time they had become adults their intensities were indistinguishable from that typically seen in adults. Therefore, while selection against highly parasitized juveniles can contribute to some extent to a reduction in parasitism seen in the adult population, age- specific blood parasitism in feral pigeons is best explained as a transitory phase just before the host develops an effective immune response |
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