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.