Data from: The joint evolution of the Myxozoa and their alternate hosts: a cnidarian recipe for success and vast biodiversity

The relationships between parasites and their hosts are intimate, dynamic
and complex; the evolution of one is inevitably linked to the other.
Despite multiple origins of parasitism in the Cnidaria, only parasites
belonging to the Myxozoa are characterized by a complex life cycle,
alternating between fish and invertebrate hosts, as well as by
exceptionally high species diversity. This inspired us to examine the
history of reciprocal interactions and adaptive radiations in myxozoans
and their hosts by determining the degree of congruence between their
phylogenies and by timing the emergence of myxozoan lineages in relation
to their hosts. Recent genomic analyses suggested a common origin of
Polypodium hydriforme, a cnidarian parasite of acipenseriform fishes, and
the Myxozoa, and proposed fish as original hosts for both sister lineages.
We clearly demonstrate that the Myxozoa emerged long before fish populated
Earth and that phylogenetic congruence with their invertebrate hosts is
evident down to the most basal branches of the tree, indicating bryozoans
and annelids as original hosts and challenging previous hypothesis. We
provide evidence that, following invertebrate invasion, fish hosts were
acquired multiple times, leading to parallel cospeciation patterns in all
major phylogenetic lineages. We identify the acquisition of vertebrate
hosts that facilitate alternative transmission and dispersion strategies
as reason for the distinct success of the Myxozoa, and identify massive
host specification-linked parasite diversification events. The results of
this study transform our understanding of the origins and evolution of
parasitism in the most basal metazoan parasites known.