Data from: Host coevolution alters the adaptive landscape of a virus

The origin of new and complex structures and functions is fundamental for
shaping the diversity of life. Such key innovations are rare because they
require multiple interacting changes. We sought to understand how the
adaptive landscape led to an innovation whereby bacteriophage λ evolved
the new ability to exploit a receptor, OmpF, on Escherichia coli cells.
Previous work showed that this ability evolved repeatedly, despite
requiring four mutations in one virus gene. Here, we examine how this
innovation evolved by studying six intermediate genotypes of λ isolated
during independent transitions to exploit OmpF and comparing them to their
ancestor. All six intermediates showed large increases in their adsorption
rates on the ancestral host. Improvements in adsorption were offset, in
large part, by the evolution of host resistance, which occurred by reduced
expression of LamB, the usual receptor for λ. As a consequence of host
coevolution, the adaptive landscape of the virus changed such that
selection favouring four of the six virus intermediates became stronger
after the host evolved resistance, thereby accelerating virus populations
along the path to using the new OmpF receptor. This dependency of viral
fitness on host genotype thus shows an important role for coevolution in
the origin of the new viral function.