Genetic variation in the cellular response of Daphnia magna (Crustacea: Cladocera) to its bacterial parasite.
Linking measures of immune function with infection, and ultimately, host and parasite fitness is a major goal in the field of ecological immunology. In this study, we tested for the presence and timing of a cellular immune response in the crustacean Daphnia magna following exposure to its sterilizing endoparasite Pasteuria ramosa. We found that D. magna possesses two cell types circulating in the haemolymph: a spherical one, which we call a granulocyte and an irregular-shaped amoeboid cell first described by Metchnikoff over 125 years ago. Daphnia magna mounts a strong cellular response (of the amoeboid cells) just a few hours after parasite exposure. We further tested for, and found, considerable genetic variation for the magnitude of this cellular response. These data fostered a heuristic model of resistance in this naturally coevolving host-parasite interaction. Specifically, the strongest cellular responses were found in the most susceptible hosts, indicating resistance is not always borne from a response that destroys invading parasites, but rather stems from mechanisms that prevent their initial entry. Thus, D. magna may have a two-stage defence--a genetically determined barrier to parasite establishment and a cellular response once establishment has begun.
School of Biological Sciences, Institute of Evolutionary Biology, University of Edinburgh, Ashworth Labs, Edinburgh EH9 3JT, UK. stuart.auld@ed.ac.uk
Stuart K J R
SK
Auld
Jennifer A
JA
Scholefield
Tom J
TJ
Little
D000818:Animals; D003621:Daphnia / Q000235:genetics / Q000276:immunology / Q000382:microbiology* / Q000502:physiology*; D014644:Genetic Variation / Q000276:immunology; D005838:Genotype; D006434:Hemocytes / Q000166:cytology / Q000276:immunology / Q000648:ultrastructure; D006458:Hemolymph / Q000166:cytology / Q000276:immunology; D054884:Host-Pathogen Interactions; D007111:Immunity, Cellular / Q000276:immunology; D018613:Microscopy, Confocal; D015233:Models, Statistical; D058676:Pasteuria / Q000276:immunology / Q000502:physiology*