Implications and Avenues for Future Work
Our findings provide several avenues for future work that may further clarify the onset of epidemics in this system. While the constant temperatures of our study are a strength in that they allow us to disentangle the role of temperature on this system from other seasonal dynamics, it remains unclear how temperature changes (i.e. the speed of warming in the Spring or daily/seasonal fluctuations) may impact these dynamics. As climate change is predicted to cause more extreme temperature fluctuations in addition to warming in most of the areasD. magna and P. ramosa inhabit, and previous work has shown that daily fluctuations in temperature and heatwaves differentially impact the performance of D. magna and another of its parasites, the microsporidium Ordospora colligata (Kunze et al. 2022), this question remains important for future work to address. Identifying which steps of P. ramosa infection (Ebert et al. 2016) are limited by temperature could also further clarify this parasite’s relationship to temperature. D. magna exposure toP. ramosa is slower at lower temperature due to slower D. magna filtering/metabolism, however we have controlled for this effect by running the experiment longer at lower temperatures, yet differences in infection by temperature persist. Previous work shows spore activation and attachment are possible at all our tested temperatures (Duneau et al. 2011). Penetration of the host cuticle and reproduction within the host are remaining candidates for which step(s) are limited by infection and remain an interesting avenue for future work. Furthermore, identifying if sexual offspring have a different behaviour and/or physiology that makes them less likely to be infected than asexual offspring would also be important. Future work may focus on how temperature affects later stages of the epidemic. Additionally, a longer-term study that examines selection for resistance in a population could determine whether rapid warming would alter the diversity of phenotypes and genotypes in the population.