The larvae of freshwater mussels in the order
Unionoida are obligate parasites on fishes. Because adult
mussels are infaunal and largely sessile, it is generally
assumed that the majority of gene flow among mussel populations
relies on the dispersal of larvae by their hosts. The
objective of this study was to compare the genetic diversity
and the degree of congruence between the population structures
of two related freshwater mussels Leptodea leptodon
and Leptodea fragilis and their fish host, Aplodinotus grunniens.
Host specificity in parasites has been shown to result
in greater congruence between the population structures of
the two interacting species, and assessing the congruence
of genetic structure of the endangered L. leptodon with its
sister species L. fragilis and their sole host is an important
step in understanding the impact of host dispersal on population
structure. Analysis of microsatellite data indicated that
despite its imperiled status, L. leptodon displayed greater
genetic diversity than the more common L. fragilis. However,
the population structures of all three species were
incongruent even in the presence of substantial gene flow.
Other factors such as habitat specificity may play a role in
generating the differences in population structure observed.