Three’s a crowd: The relationship among endoparasites, an epibiont and
their Daphnia host
Abstract
In freshwater communities, organisms interact in a variety of ways,
including predation, competition and parasitism. Parasites are
ubiquitous, playing an important role in shaping freshwater communities.
Endoparasites live within internal organs of their host, while
ectoparasites, also known as epibionts, are confined to the external
part of the host’s body. We conducted a series of experiments to examine
the relationship between endoparasites and epibionts using the
crustacean Daphnia magna as host, the rotifer Brachionus rubens as
epibiont and three species of endoparasites. First, we tested host
preference of the epibiont between Daphnia infected by endoparasites and
uninfected Daphnia. Epibiont were found to attach more to uninfected
Daphnia than to Daphnia infected by the yeast Metschnikowia bicuspidata.
On the other hand, epibionts attached more to Daphnia infected by the
microsporidium Hamiltosporidium tvaerminnensis than to uninfected
Daphnia. Second, we examined the effect of epibionts on the infection of
Daphnia by endoparasites. Infection prevalence tended to be higher,
though not significantly, in the presence of epibionts. For two of the
endoparasites, M. bicuspidata and H. tvaerminnensis, infection intensity
(i.e., parasite spore production) was higher in the presence of
epibionts. The infection intensity of M. bicuspidata and the bacterium
Pasteuria ramosa was affected by the time of death of the Daphnia (i.e.,
virulence). Finally, we examined the effects of endoparasites and
epibionts on the survival and offspring production of the Daphnia. Both
host survival and offspring production were negatively affected by the
endoparasites, while epibionts did not seem to affect the fitness of
their host.