Temperature Alters Host Genotype-Specific Susceptibility to Chytrid Infection

Abstract

The cost of parasitism often depends on environmental conditions and host identity. Therefore, variation in the biotic and abiotic environment can have repercussions on both, species-level host-parasite interaction patterns but also on host genotype-specific susceptibility to disease. We exposed seven genetically different but concurrent strains of the diatom Asterionella formosa to one genotype of its naturally co-occurring chytrid parasite Zygorhizidium planktonicum across five environmentally relevant temperatures. We found that the thermal tolerance range of the tested parasite genotype was narrower than that of its host, providing the host with a “cold” and “hot” thermal refuge of very low or no infection. Susceptibility to disease was host genotype-specific and varied with temperature level so that no genotype was most or least resistant across all temperatures. This suggests a role of thermal variation in the maintenance of diversity in disease related traits in this phytoplankton host. The duration and intensity of chytrid parasite pressure on host populations is likely to be affected by the projected changes in temperature patterns due to climate warming both through altering temperature dependent disease susceptibility of the host and, potentially, through en- or disabling thermal host refugia. This, in turn may affect the selective strength of the parasite on the genetic architecture of the host population.

Warming accelerates termination of a phytoplankton spring bloom by fungal parasites

“…Field studies have shown that relatively cold winters inhibit the activity of chytrids and thereby provide the host with an opportunity to bloom. In contrast, warm winters seem to facilitate chytrids, preventing the host to form a bloom (Van Donk & Ringelberg, ; Ibelings et al ., ; Gsell et al ., ). Furthermore, laboratory experiments showed enhanced chytrid infections with increasing temperature over a range of 1–16 °C, but infection was inhibited at a temperature of 21 °C (Gsell et al ., ).…”

“…In contrast, warm winters seem to facilitate chytrids, preventing the host to form a bloom (Van Donk & Ringelberg, ; Ibelings et al ., ; Gsell et al ., ). Furthermore, laboratory experiments showed enhanced chytrid infections with increasing temperature over a range of 1–16 °C, but infection was inhibited at a temperature of 21 °C (Gsell et al ., ). Not only transmission rates and virulence of parasites are important, but also chytrid physiological characteristics that are affected by temperature can be important for its success.…”

“…Infections of phytoplankton blooms by chytrids are influenced by environmental conditions, including temperature, resource availability and other external stressors (Van Donk & Ringelberg, ; Bruning, ; Ibelings et al ., ; Gsell et al ., ; Van Den Wyngaert et al ., ). Transmission rates and virulence of parasites are expected to increase with increasing temperature (Marcogliese, ).…”

Fluctuating temperatures alter environmental pathogen transmission in a Daphnia–pathogen system

“…This is potentially mediated by the effects of temperature variability on pathogen emergence, development time, or transmission dynamics (Hernandez, Poole, & Cattadori, ; Karvonen, Rintamaki, Jokela, & Valtonen, ; Lafferty, ; Macnab & Barber, ; Paull & Johnson, ; Studer & Poulin, ), or differences in thermal tolerance ranges of host and pathogen species (Altizer et al., ; Lafferty & Kuris, ). If the thermal tolerance range of the host is broader than that of the pathogen, extreme hot or cold temperatures may provide a thermal refuge, where pathogen pressure is not as high (Gsell, de Senerpont Domis, Van Donk, & Ibelings, ; Marinkelle & Rodriguez, ; Schoebel, Tellenbach, Spaak, & Wolinska, ). Thermal variability may influence host behavior, feeding ecology, and survival of both host and pathogen species (Lafferty & Kuris, ), the net effect of which determines the resulting relationship between temperature variability and infection dynamics.…”

Prevalence of chytrid parasitism among diatom populations in the lower Columbia River (2009–2013)

“…shorter development time results in reduced zoospore production) and a reduction in the infective zoospore lifetime (Bruning & Ringelberg, ; Bruning, ,b). With the exception of 2010, peaks in I p occurred during late spring when temperatures were near the optimum for chytrid growth (16 °C; Gsell et al ., ). Summer temperatures exceeded this optimum window, possibly accounting for the decreased abundance of sporangia associated with diatom hosts.…”