Shared geographic histories and dispersal contribute to congruent phylogenies between amphipods and their microsporidian parasites at regional and global scales

In parasites that strongly rely on a host for dispersal, geographic
barriers that act on the host will simultaneously influence parasite
distribution as well. If their association persists over macroevolutionary
time it may result in congruent phylogenetic and phylogeographic patterns
due to shared geographic histories. Here, we investigated the level of
congruent evolutionary history at a regional and global scale in a highly
specialised parasite taxon infecting hosts with limited dispersal
abilities: the microsporidians Dictyocoela spp. and their amphipod hosts.
Dictyocoela can be transmitted both vertically and horizontally and is the
most common microsporidian genus occurring in amphipods in Eurasia.
However, little is known about its distribution elsewhere. We started by
conducting molecular screening to detect microsporidian parasites in
endemic amphipod species in New Zealand; based on phylogenetic analyses,
we identified nine species-level microsporidian taxa including six
belonging to Dictyocoela. With a distance-based cophylogenetic analysis at
the regional scale, we identified overall congruent phylogenies between
Paracalliope, the most common New Zealand freshwater amphipod taxon, and
their Dictyocoela parasites. Also, hosts and parasites showed similar
phylogeographic patterns suggesting shared biogeographic histories.
Similarly, at a global scale, phylogenies of amphipod hosts and their
Dictyocoela parasites showed broadly congruent phylogenies. The observed
patterns may have resulted from covicariance and/or codispersal,
suggesting that the intimate association between amphipods and Dictyocoela
may have persisted over macroevolutionary time. We highlight that shared
biogeographic histories could play a role in the codiversification of
hosts and parasites at a macroevolutionary scale.