Data: Canonical host-pathogen tradeoffs subverted by mutations with dual benefits

Host-parasite coevolution is expected to drive the evolution of genetic
diversity because the traits used in arms races, namely host range and
parasite resistance, are hypothesized to trade off with traits used in
resource competition. We therefore tested data for several tradeoffs among
93 isolates of bacteriophage and 51 Escherichia coli genotypes that
coevolved during a laboratory experiment. Surprisingly, we found multiple
tradeups (positive trait correlations) but little evidence of several
canonical tradeoffs. For example, some bacterial genotypes evaded a
tradeoff between phage resistance and absolute fitness, instead evolving
simultaneous improvements in both these traits. This was surprising
because our experimental design was predicted to expose resistance-fitness
tradeoffs by culturing E. coli in a medium where the phage
receptor, LamB, is also used for nutrient acquisition. On reflection, LamB
mediates not one but many tradeoffs, allowing for more complex trait
interactions than just pairwise tradeoffs. Here, we report that
mathematical reasoning and laboratory data highlight how tradeups should
exist whenever an evolutionary system exhibits multiple interacting
tradeoffs. Does this mean that coevolution should not promote genetic
diversity? No, quite the contrary: we deduce that whenever positive trait
correlations are observed in multi-dimensional traits, other traits may
tradeoff and so provide the right circumstances for diversity maintenance.
Overall, this study reveals there are predictive limits when data only
account for pairwise trait correlations and it argues that a wider range
of circumstances than previously anticipated can promote genetic and
species diversity.