When experimental selection for virulence leads to loss of virulence

Abstract

Information on virulence evolution is critical for understanding disease dynamics. Theory predicts that under certain evolutionary conditions virulence should increase; for example, during host-parasite coevolution. Although these theoretical predictions are supported by natural observations, tests of these hypotheses using experimental evolution have yielded confounding and contradictory results, with discrepancies often being seen among experiments. Here we provide a critical overview of experimental tests of hypotheses regarding virulence evolution and provide potential explanations for the contradictory results. We emphasise the key role of parasite transmission mechanisms that can explain many of the observed discrepancies among evolution experiments. Finally, we make suggestions for how evolution experiments could be conducted in the future to avoid potentially confounding factors.

Keywords: coevolution; experimental evolution; serial passage; trade-off hypothesis; transmission; virulence.