We tried to explain this asymmetry with something that no movie director has tried before to convince Hollywood - a mathematical model! We simulated a number of factors that might have been different between the water fleas from the oldest layer and the most recent layer, as this was essentially the only difference between the treatments. Crucially, the water fleas from the recent layer can be regarded as experienced hosts with respect to the parasite, while water fleas from the oldest layer are actually naive hosts. The model revealed that Red Queen dynamics most likely stabilize due to an accumulation of resistance alleles over time. The gain in experience from naive hosts in the past to experienced hosts in the present hence seems modulated by a larger arsenal of genes enhancing the host performance in its coevolution with the parasite.
Michael J. Fox encounters the Red Queen
Ellen Decaestecker, Herbert de Gersem, Yannis Michalakis & Joost Raeymaekers (in press). Damped long-term host–parasite Red Queen coevolutionary dynamics: a reflection of dilution effects?