Temperature-dependent transmission and latency ofHolospora undulata, a micronucleus-specific parasite of the ciliateParamecium caudatum

Abstract

Transmission of parasites to new hosts crucially depends on the timing of production of transmission stages and their capacity to start an infection. These parameters may be influenced by genetic factors, but also by the environment. We tested the effects of temperature and host genotype on infection probability and latency in experimental populations of the ciliate Paramecium caudatum, after exposure to infectious forms of its bacterial parasite Holospora undulata. Temperature had a significant effect on the expression of genetic variation for transmission and maintenance of infection. Overall, low temperature (10 8C) increased levels of (multiple) infection, but arrested parasite development; higher temperatures (23 and 30 8C) accelerated the onset of production of infectious forms, but limited transmission success. Viability of infectious forms declined rapidly at 23 and 30 8C, thereby narrowing the time window for transmission. Thus, environmental conditions can generate trade-offs between transmission relevant parameters and alter levels of multiple infection or parasite-mediated selection, which may affect evolutionary trajectories of parasite life history or virulence.

Temporal variation in temperature determines disease spread and maintenance inParameciummicrocosm populations

“…Under exponential growth conditions, P. caudatum divides up to three times every 24 h and optimal growth temperatures generally range between 248C and 288C [24]. There is also evidence of within-species genetic variation in growth and survival at different temperatures [25]. Paramecium were maintained in a culture medium of dried organic lettuce supplemented with the bacterium Serratia marcescens as food [30].…”

“…There is evidence that infected Paramecium can sometimes benefit from a transient protection against heat and osmotic stress owing to a general stress response induced by infection ( [26][27][28] but see [29]). Parasite viability declines rapidly at higher temperature thus hindering transmission [25]. We therefore expected both host and parasite populations to be negatively affected by higher mean environmental temperatures in our experimental treatments.…”

“…Microcosm experiments are powerful in that they allow estimates of parasite epidemiology and host demography to be determined. Paramecium species [24] and this bacterial parasite are both sensitive to heat stress [25]. There is evidence that infected Paramecium can sometimes benefit from a transient protection against heat and osmotic stress owing to a general stress response induced by infection ( [26][27][28] but see [29]).…”

“…We therefore expected both host and parasite populations to be negatively affected by higher mean environmental temperatures in our experimental treatments. We also expected variable environments to be worse than constant environments, especially for the parasite as even very short periods at high temperatures can lead to declines in transmission [25]. Specifically, we identify: (i) how host and parasite are impacted by different constant mean temperatures; and (ii) how variable temperature environments with the same mean temperature impact host and parasite dynamics.…”

Reciprocal Interaction Matrix Reveals Complex Genetic and Dose-Dependent Specificity among Coinfecting Parasites

“…The role of environmental variation in maintaining genetic variation in parasites is, however, still generally poorly understood (but see Fels and Kaltz 2006;Laine 2007;Vale and Little 2009;Bryner and Rigling 2011). Since hosts represent the parasites' primary environment, a potentially important environmental factor modifying their fitness is the presence of coinfecting parasites.…”