The timings of host diapause and epidemic progression mediate host genetic diversity and future epidemic size in Daphnia-parasite populations

Epidemics commonly exert parasite-mediated selection and cause declines in host population genetic diversity. This could lead to evolution of resistance in the long-term and smaller subsequent epidemics. Alternatively, the loss of genetic diversity could increase host vulnerability to future disease spread and larger future epidemics. Matters are made more complex by the fact that a great many host organisms produce diapausing life stages in response to environmental change (often as a result of sexual reproduction) e.g., plant seeds and invertebrate resting eggs. These diapausing stages can disrupt the relationship between past epidemics, host genetic diversity and future epidemics because they allow host dispersal through time. Specifically, temporally dispersing hosts avoid infection and thus selection from contemporary parasites, and also archive genetic variation for the future. We studied 80 epidemics in 20 semi-natural populations of the temporally dispersing crustacean Daphnia m..., These data were collected from twenty semi-natural outdoor crustacean-bacteria host-parasite populations over the course of four years (a total of eighty epidemics). The host was Daphnia magna and the parasite was the sterilising bacterium, Pasteuria ramosa. These data comprise of Pasteuria epidemic size, timing of mid epidemic and epidemic scaling constant (rate of infection), total host investment in sexual (diapausing) resting eggs, timing of sex, and sex scaling constant (rate at which hosts invest in sexual reproduction/diapause), expected heterozygosity and fiuture epidemic size for each population. Both epidemic size/host investment in sex and timings of epidemics and host sex were determined using three-parameter logistic models fitted to data from each invividual epidemic. These data have been used in structural equation modelling.,