Data from: Predators and patterns of within-host growth can mediate both among-host competition and the evolution of transmission potential of parasites

Parasite prevalence shows tremendous spatiotemporal variation. Theory
indicates this variation might stem from life history characteristics of
parasites and key ecological factors. Here, we illustrate how the
interaction of an important predator and the schedule of
'transmission potential' of two parasites can explain parasite
abundance. A field survey showed that a non-castrating fungus
(Metschnikowia bicuspidata) commonly infected a dominant zooplankton host
(Daphnia dentifera), while a castrating bacterial parasite (Pasteuria
ramosa) was rare. This result seemed surprising given that the bacterium
produces many more infectious propagules (spores) than the fungus upon
host death. The fungus's dominance can be explained by the schedule
of within host growth of parasites (i.e., how transmission potential
changes over the course of infection) and spore release from 'sloppy
predators' (Chaoborus spp., who consume Daphnia prey whole, then
later regurgitate the carapace and parasite spores). In essence, sloppy
predators create a niche that the faster-schedule fungus currently
occupies. However, a selection experiment showed the slower-schedule
bacterium can evolve into this faster-schedule, predator-mediated niche
(but pays a cost in maximal spore yield to do so). Hence, our study shows
how parasite life history can interact with predation to strongly
influence the ecology, epidemiology, and evolution of infectious disease.
18 pages, 1 table, 5 figures; Appendix