Abstract
The Red Queen hypothesis can explain the maintenance of host and parasite diversity. However, the Red Queen requires genetic specificity for infection risk (i.e., that infection depends on the exact combination of host and parasite genotypes) and strongly virulent effects of infection on host fitness. A European crustacean (Daphnia magna) – bacterium (Pasteuria ramosa) system typifies such specificity and high virulence. We studied the North American host Daphnia dentifera and its natural parasite Pasteuria ramosa, and also found strong genetic specificity for infection success and high virulence. These results suggest that Pasteuria could promote Red Queen dynamics with D. dentifera populations as well. However, the Red Queen might be undermined in this system by selection from a more common yeast parasite (Metschnikowia bicuspidata). Resistance to the yeast did not correlate with resistance to Pasteuria among host genotypes, suggesting that selection by Metschnikowia should proceed relatively independently of selection by Pasteuria.
Highlights
Genetic specificity between hosts and their parasites shapes the ecology and evolution of infectious disease [1,2]
We looked for genetic specificity for infection with Pasteuria in a natural North American host, Daphnia dentifera, using an established experimental design [7]
Metschnikowia’s capacity to disrupt Red Queen dynamics between D. dentifera and Pasteuria should be reduced if the host pays an activation cost of resistance to Metschnikowia We looked for evidence of an activation cost of resistance to Metschnikowia by comparing host fecundity, survival, and r in controls with hosts that were exposed to parasites but did not suffer infection
Summary
Genetic specificity between hosts and their parasites shapes the ecology and evolution of infectious disease [1,2]. Genetic specificity has the potential to influence disease phenomena in at least two ways It decreases the likelihood of invasion of parasites into genetically diverse host populations (i.e., the parasite will have a lower reproductive ratio R0 when all else is equal, [8]) because much of the host population resists infection. Specificity can drive Red Queen coevolutionary dynamics, where the frequencies of host and parasite genotypes cycle through time [14,15]. Such coevolutionary cycling can maintain genetic diversity in both host and parasite populations [15,16]
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