Successfully resisting a pathogen is rarely costly in Daphnia magna
1 University of Edinburgh, Institute of Evolutionary Biology, King's Buildings, Edinburgh, EH9 3JT, UK
2 University of Montpellier 2, Institut des Sciences de l'Evolution de Montpellier, Pl Eugène Bataillon, CC065, 34095 Montpellier cedex 05, France
3 Centre d'Ecologie Fonctionnelle et Evolutive (CEFE) - UMR 5175 1919 route de Mende, 34293 Montpellier, France
BMC Evolutionary Biology 2010, 10:355 doi:10.1186/1471-2148-10-355Published: 17 November 2010
A central hypothesis in the evolutionary ecology of parasitism is that trade-offs exist between resistance to parasites and other fitness components such as fecundity, growth, survival, and predator avoidance, or resistance to other parasites. These trade-offs are called costs of resistance. These costs fall into two broad categories: constitutive costs of resistance, which arise from a negative genetic covariance between immunity and other fitness-related traits, and inducible costs of resistance, which are the physiological costs incurred by hosts when mounting an immune response. We sought to study inducible costs in depth using the crustacean Daphnia magna and its bacterial parasite Pasteuria ramosa.
We designed specific experiments to study the costs induced by exposure to this parasite, and we re-analysed previously published data in an effort to determine the generality of such costs. However, despite the variety of genetic backgrounds of both hosts and parasites, and the different exposure protocols and environmental conditions used in these experiment, this work showed that costs of exposure can only rarely be detected in the D. magna-P. ramosa system.
We discuss possible reasons for this lack of detectable costs, including scenarios where costs of resistance to parasites might not play a major role in the co-evolution of hosts and parasites.