Abstract Marine viruses affect Bacteria, Archaea and eukaryotic organisms and are major
components of the marine food web. Most studies have focused on their role as predators
and parasites, but many of the interactions between marine viruses and their hosts are much
more complicated. A series of recent studies has shown that viruses have the ability to
manipulate the life histories and evolution of their hosts in remarkable ways, challenging our
understanding of this almost invisible world.