How does community context influence epidemic size and evolution in host-parasite interactions?
A major focus of research in the Duffy Lab is on the ways in which ecological and evolutionary processes jointly influence host-parasite dynamics. A particular focus has been on how rapid evolution influences ecological host-parasite dynamics, and how ecological context influences evolution in host-parasite systems. In a series of papers (e.g., Duffy & Sivars-Becker 2007, Duffy et al. 2008, Duffy & Hall 2008, Duffy et al. 2009), we have shown that host populations can evolve rapidly in response to parasite epidemics, and that host evolution can alter ecological dynamics. More recently, we have shown that the ecological context of the host-parasite interaction (specifically, the predation and productivity environments) influences the size of epidemics which, in turn, influences evolution of host populations (Duffy et al 2012).
What are the direct and indirect effects of predators on host-parasite interactions?
We have previously shown that predators can have strong direct effects on host-parasite interactions (e.g., Duffy et al. 2005, Duffy & Hall 2008). In general, this should mean that populations with higher predation should have lower parasitism. But, sometimes we see the opposite pattern. Why might that be? Indirect effects of predators can help explain why predators might sometimes increase parasitism. We recently showed that an important invertebrate predator (the phantom midge Chaoborus) increases the susceptibility of Daphnia dentifera to a virulent yeast parasite, and that it increases the spore yield from some genotypes (Duffy et al. 2011). An interesting avenue for future research will be trying to quantify the relative magnitude of direct and indirect effects of predators on disease.
Evolution of Multi-Host Parasites and Effects on Invasive Species
We have recently begun studying multihost parasites; most parasites can infect multiple host species. While this can be challenging to study in many cases, Daphnia are well-suited to studies addressing how parasites deal with trying to infect multiple host species. Our work on multihost parasites has, to date, focused on the bacterial pathogen Pasteuria ramosa. This parasite can infect multiple host species (e.g., Duffy et al. 2010). In Georgia, Pasteuria appears to have shifted to infect a novel host, the invasive Daphnia lumholtzi. We will study how parasites evolve after shifting to a novel host and how parasitism influences the population dynamics of indigenous and non-indigenous hosts. This links with earlier work in which we asked how parasites might influence invasive species (Kestrup et al. 2011).