Multi-year time shift study of bacteria and phage dynamics in the phyllosphere

Coevolutionary dynamics shape diversity within and among populations but
are difficult to study directly. Time shift experiments, where populations
of species A from one point in time are experimentally challenged against
populations of species B from past, contemporary, and/or future time
points, and vice versa, are a particularly powerful tool to measure
coevolution. This approach has been primarily applied to study
host-parasite interactions and proven useful in directly measuring
coevolutionary change and distinguishing among coevolutionary models.
However, these data are only as informative as the time window over which
they were collected, and data from shorter coevolutionary windows might
conflict with data collected over longer time periods. Previous work on
natural microbial communities from horse chestnut tree leaves used time
shifts to uncover an apparent asymmetry, whereby hosts tended to be
resistant to phages from all earlier points in the growing season while
phages tended to be most infective on hosts from the recent past. Here we
extend the time window over which these infectivity and resistance ranges
are observed from within a growing season to across years and confirm that
the previously observed asymmetry holds over longer timescales.