Résumé
Numerous theoretical and experimental studies have investigated
antagonistic coevolution between parasites and their hosts. Although
experimental tests of theory from a range of biological systems are
largely concordant regarding the influence of several driving processes,
we know little as to how mechanisms acting at the smallest scales
(individual molecular and phenotypic changes) may result in the emergence
of structures at larger scales, such as coevolutionary dynamics and local
adaptation. We capitalized on methods commonly employed in community
ecology to quantify how the structure of community interaction matrices,
so called ‘bipartite networks’, reflected observed coevolutionary
dynamics, and how phages from these communities may or may not have
adapted locally to their bacterial hosts. We found a consistent nested
network structure for two phage types, one previously demonstrated to
exhibit arms race coevolutionary dynamics and the other fluctuating
coevolutionary dynamics. Both phages increased their host ranges through
evolutionary time, but we found no evidence for a trade off with impact on
bacteria. Finally, only bacteria from the arms race phage showed local
adaptation, and we provide preliminary evidence that these bacteria
underwent (sometimes different) molecular changes in the wzy gene
associated with the LPS receptor, while bacteria coevolving with the
fluctuating selection phage did not show local adaptation and had partial
deletions of the pilF gene associated with Type IV pili. We conclude that
the structure of phage-bacteria interaction networks is not necessarily
specific to coevolutionary dynamics, and discuss hypotheses for why only
one of the two phages was, nevertheless, locally adapted.