Increasing prevalence of wildlife disease accentuates the need to uncover drivers of epidemics. Predators can directly influence disease prevalence via density-mediated effects (e.g., culling infected hosts leading to reduced disease prevalence). However, trait-mediated indirect effects (TMIEs) of predators can also strongly influence disease--but predicting a priori whether TMIEs should increase or decrease disease prevalence can be challenging, especially since a single predator may elicit responses that have opposing effects on disease prevalence. Here, we pair laboratory experiments with a mechanistic, size-based model of TMIEs in a zooplankton host, fungal parasite, multiple predator system. Kairomones can either increase or decrease body size of the host Daphnia, depending on the predator. These changes in size could influence key traits of fungal disease, since infection risk and spore yield increase with body size. For six host genotypes, we measured five traits that determine an index of disease spread (R 0). Although host size and disease traits did not respond to kairomones produced by the invertebrate predator Chaoborus, cues from fish reduced body size and birth rate of uninfected hosts and spore yield from infected hosts. These results support the size model for fish; the birth and spore yield responses should depress disease spread. However, infection risk did not decrease with fish kairomones, thus contradicting predictions of the size model. Exposure to kairomones increased per spore susceptibility of hosts, countering size-driven decreases in exposure to spores. Consequently, synthesizing among the relevant traits, there was no net effect of fish kairomones on the R 0 metric. This result accentuates the need to integrate the TMIE-based response to predators among all key traits involved in disease spread.

Lake and stream habitats pose a variety of challenges to fishes due to differences in variables such as water velocity, habitat structure, prey community, and predator community. These differences can cause divergent selection on body size and/or shape. Here, we measured sex, age, length, and eight different morphological traits of the blackstripe topminnow, Fundulus notatus, from 19 lake and stream populations across four river drainages in central Illinois. Our goal was to determine whether size and shape differed consistently between lake and stream habitats across drainages. We also considered the effects of age and sex as they may affect size and morphology. We found large differences in body size of age 1 topminnows where stream fish were generally larger than lake fish. Body shape mainly varied as a function of sex. Adult male topminnows had larger morphological traits (with the exception of body width) than females, in particular longer dorsal and anal base lengths. Subtle effects of habitat were present. Stream fish had a longer dorsal fin base than lake fish. These phenotypic patterns may be the result of genetic and/or environmental variation. As these lakes are human-made, the observed differences, if genetic, would have had to occur relatively rapidly (within about 100 years).

Parasites are generally thought of as being intimately tied to their hosts, yet many parasites produce free-living stages. This raises the question: what are parasites doing when they are not being parasitic? We studied the spatiotemporal dynamics of free-living infectious stages and asked whether these dynamics were correlated with infections in 2 focal host species. We used a common and virulent bacterial parasite, Spirobacillus cienkowskii, which infects Daphnia spp. Densities of free-living infective stages were high in a stratified, eutrophic lake (up to ~10 5 to 10 6 cells l -1 ), but also spatiotemporally variable. There was a positive correlation between the density of these freeliving stages and the prevalence of infected Daphnia on the subsequent sampling date. This suggests that free-living stages increase in environmental reservoirs prior to the start of epidemics in Daphnia. We also studied the ability of free-living stages to persist outside their hosts for long periods of time.In laboratory microcosms, we found that S. cienkowskii persisted under simulated environmental conditions for more than 2 mo, before declining to below our method's detection limit after approximately 3 mo. Overall, our study of a common parasite of Daphnia reveals the potential importance of free-living stages to epidemic dynamics, and suggests that it is important to consider environmental reservoirs when studying disease dynamics.KEY WORDS: Spores · Daphnia dentifera · Daphnia pulicaria · Curse of the pharaoh · qPCR · Environmental transmission · Pathogen Resale or republication not permitted without written consent of the publisher Editorial responsibility: Urania Christaki,