Abstract
Many infectious diseases display strong seasonal dynamics. When both
hosts and parasites are influenced by seasonal variables, it is unclear
if the start of epidemics is limited by host or parasite factors or
both. The Daphnia—Pasteuria host—parasite system exhibits seasonal
epidemics. We experimentally tested if low Spring temperatures limit the
onset of these epidemics. We used sediments from a natural population
containing parasite spores at five constant temperatures ranging from
10-20 oC. We added either Daphnia magna resting stages (ephippia),
juveniles from largely susceptible clonal cultures or juveniles from
largely resistant clonal cultures from the same population. The
acceleration of development with increasing temperature was much faster
for the parasite than for the host. This finding supports our hypotheses
that parasite outbreaks are limited by temperature, and not solely the
availability of hosts. These results imply that climate change could
lead earlier seasonal epidemics for this host-parasite system.