COS 240-4 - Infectivity of the parasite Metschnikowia bicuspidata is decreased by time spent as a transmission spore, but exposure to phycotoxins in the water column has no effect

Background/Question/Methods

Transmission from one host to another is an important life stage with huge consequences for parasite fitness. Parasite transmission stages can be impacted by biotic and abiotic factors that influence the parasite’s ability to successfully infect and/or grow in a new host. Secondary metabolites of bloom-forming algae, especially cyanotoxins, are expected to exacerbate disease in aquatic organisms by adding physiological stress to animals, potentially rendering them more susceptible to diseases. However, those same compounds that are toxic to metazoans can also harm microbes, including parasites. In this study, we examined whether cyanotoxins dissolved in water have a negative impact on the transmission spores of the fungal parasite Metschnikowia bicuspidata. This fungal parasite has a free-living transmission stage that remains in the water column until encountering a new host. We exposed transmission stages to 10μg/L & 30μg/L of microcystin-LR and anatoxin-a at different lengths of exposure (factorial design: anatoxin/microcystin/control x concentration x duration of exposure), ranging from 24 hours to 10 days. We removed the toxins and used those same transmission stages (“spores”) to infect one genotype of the common lake zooplankton Daphnia dentifera.

Results/Conclusions

We found that cyanotoxins did not impact infection prevalence and spore yield per infected host or host lifetime reproduction and survivorship at the tested concentrations. However, we found that spending longer as a transmission spore decreased a spore’s chances for successful infection: spores that were only incubated for 24 hours infected approximately 75% of exposed hosts, whereas spores incubated for 10 days infected less than 25% of exposed hosts. These results suggest that fitness and virulence of this parasite are not strongly influenced by cyanotoxins in the water column, but that other aspects of spending time in the water strongly influence parasite fitness in this case the parasites’ ability to infect new host.