The dynamics of host-parasite interactions are highly temperature-dependent and may be modified by increasing frequency and intensity of climate-driven heat events. Here, we show that altered patterns of temperature variance lead to an almost order-of-magnitude shift in thermal performance of host and pathogen life history traits over and above the effects of mean temperature and, moreover, that different temperature regimes affect these traits differently. We found that diurnal fluctuations of ±3°C lowered infection rates and reduced spore burden compared to constant temperatures in our focal host Daphnia magna exposed to the microsporidium parasite Ordospora colligata. In contrast, a three-day heatwave (+6°C) did not affect infection rates, but increased spore burden (relative to constant temperatures with the same mean) at 16°C, while reducing burden at higher temperatures. We conclude that changing patterns of climate variation, superimposed on shifts in mean temperatures due to global warming, may have profound and unanticipated effects on disease dynamics.

Date of collection: 04/04/2019 to 08/05/2019

These datasets contain observations on host fecundity, infection status and severity of infection collected during an experiment on Daphnia magna and its parasite Odospora colligata at School of Natural Sciences at the Trinity College Dublin in spring 2019. In this study we compared two patterns of temperature variation, a diurnal temperature fluctuation (of ±3°C in a 12:12 cycle) and a heat wave (of +6°C with 3 days duration 20 days after exposure to the parasite), with a constant treatment, which had the same mean temperature over the whole experimental period. Data were analyzed using R version 3.6.1(R Core Team, 2018) interfacing with JAGS. A Beta Function was fitted to each of our different fitness estimates (that is, host fecundity, parasite infectivity and burden) for each of the three temperature regimes using a baysian framework.

MeanTempTreatments.csv: mean temperature of the different treatments, calculated from temperature logger data that can be found in all_raw_temperatures_hobo.csv.

            meanTemp: mean temperature over the duration of the experiment.

treatment: treatment information, either constant, pulse (or heatwave) or fluctuation corresponding to the used temperature regimes in the experiment.

SporesNoMaleNA.csv: observations on infection status and spore burden

no: unique sample number from 1 to 516.

treatment: the temperature regime used, abbreviations, CS = constant, PULSE = heat wave, FLU = fluctuating.

exposed: exposure to the parasite, U = unexposed (control), I = exposed.

temperature: target temperature (10, 13, 16, 19, 22, 25 and 28).  Note: for fluctuating regime this is the lower temperature.

meantemp: mean temperature, different from target temperature for fluctuation regime which alternates been the target temperature and 6℃ higher.

realtemp: measured mean temperature over the experimental period provided by temperature loggers see MeanTempTreatments.csv.

replicate: replicate number from 1 to 18.

death: date of death (last day 08/05/2019)

lastday: was the animal alive the last day of the experiment? Either 0 (dead) or 1 (alive). Used for spore analysis.

infect: infection status, either 0 (no parasite) or 1 (infected).

no_spore: number of spores observed in the dissected Daphnia gut.

size: size of the Daphnia measured under the binocular (for the real size this value

must be transformed by the magnification factor). Not used for the paper and is correlated with fecundity.

comment: gives additional information about the Daphnia during their live span.

sum_daphnia_noNA.csv: Daphnia data,

no: unique sample number from 1 to 516.

treat: the temperature regime used, abbreviations, CS = constant, PULSE = heat wave, FLU = fluctuating.

inf: exposure to the parasite, U = unexposed (control), I = exposed.

mean_temp: measured mean temperature over the experimental period provided by temperature loggers see MeanTempTreatments.csv.

temp: target temperature (10, 13, 16, 19, 22, 25 and 28)

treatment_id: unique treatment ID comprised of Infection status, temperature, treatment, replicate number

repl: replicate number from 1 to 18.

sum: sum of offspring produced over the experimental period.