Temperature and resource conditions jointly influence the infection of Daphnia dentifera by the fungal parasite, Metschnikowia bicuspidata

Background/Question/Methods

Interactions between hosts and parasites are modulated by environmental conditions, such as temperature and resource availability. These conditions can alter host growth rate and tolerance as well as parasite growth rate and virulence. In natural systems, temperature and resource conditions vary over time and space, but it is difficult to predict how these will alter host-parasite interactions at the population level. To begin to understand this, we use a model host-parasite system: Daphnia dentifera, a commonly occurring freshwater cladoceran, and its fungal parasite, Metschnikowia bicuspidata. Using this system, we ask how temperature and resource conditions jointly, and independently, influence host traits and how these traits relate to the transmission potential of a parasite in individual hosts. In order to do this, we raise hosts in individual tubes across three levels of temperature and three levels of resources with and without infections by the parasite. This results in a fully factorial experiment where host birth rate is measured daily and host body size and parasite spore yield are measured after death of each host. These data provide us with host body size, lifespan, and birth rate as well as parasite prevalence and spore yield under different temperature and resource conditions.

Results/Conclusions

Preliminary results from a pilot study show that resource concentration and temperature have significant effects on host body size, host lifespan, and parasite spore yield. Resource and temperature both had positive effects on host body size, but temperature had a negative effect on host lifespan while resource concentration had a positive effect on lifespan. Overall, spore yield showed increases with increasing temperature, but spore yield was not significantly higher in the high resource treatment at intermediate and high temperatures. However, at low temperature, spore yield was the highest in the high resource treatment. While previous experiments have highlighted the importance of temperature in modulating host-parasite interactions, we show that resource conditions can also play a significant role in driving these patterns. Further experiments aim to clarify these patterns and compare infected individuals to uninfected individuals to measure host tolerance at different temperature and resource conditions. With increasing temperatures and anthropogenic influence that can cause eutrophication in freshwater ecosystems, it is important to understand how these changes will influence the transmission of parasitic organisms. Furthermore, this work adds to our understanding of the factors that can determine the thermal optimum of host-parasite interactions.