How do trematode clones differ by fitness-related traits and interact
within the host?
Abstract
Polyclonal infections are widespread and provide evidence of
facilitation, competition, and neutral interactions between parasite
clones, even within the same host-parasite system. The outcome of
co-infections is usually assessed by parasite infection intensities,
while other important fitness-related traits, e.g. larval growth rates,
are often ignored. We studied both infectivity and the growth rate of
different clones of the common trematode Diplostomum
pseudospathaceum in the fish host (Salvelinus malma) and tested
how these fitness-related traits changed in double-clone infections
compared to single-clone ones. We found that the growth rates of the
parasite’s clones were more variable than their infectivity. The
relationships of these D. pseudospathaceum traits with host mass
were clone-specific. Some clones demonstrated higher infection
intensities and growth rates in larger fish. It hints that
specialization on different size groups of hosts may occur in this
parasite species. In addition, we found positive density-dependent
growth (Allee effect), rarely reported for parasites. Interestingly, it
was observed only in mixed infections and we discuss the reasons for it.
In double-clone infections, both evidence of facilitation and
competition between D. pseudospathaceum clones were found. The
outcome of co-infections varied not only between genotype combinations
but also between tested traits. Clones either ‘cooperated’ when
infecting the host or competed when growing. There were no clone pairs,
in which interactions changed their type with time or were observed
constantly during parasite development.