DOI: 10.5061/dryad.6mf734p
title: Data from: Can hot temperatures limit disease transmission? a test of mechanisms in a zooplankton-fungus system

description: 1. Thermal ecology theory predicts that transmission of infectious
 diseases should respond unimodally to temperature, i.e., be maximized at
 intermediate temperatures and constrained at extreme low and high
 temperatures. However, empirical evidence linking hot temperatures to
 decreased transmission in nature remains limited.2. We tested the
 hypothesis that hot temperatures constrain transmission in a
 zooplankton-fungus (Daphnia dentifera-Metschnikowia bicuspidata) disease
 system where autumnal epidemics typically start after lakes cool from
 their peak summer temperatures. This pattern suggested that maximally hot
 summer temperatures could be inhibiting disease spread. 3. Using a series
 of lab experiments, we examined the effects of high temperatures on five
 mechanistic components of transmission. We found that (1) high
 temperatures increased exposure to parasites by speeding up foraging rate
 but (2) did not alter infection success post-exposure. (3) High
 temperatures lowered parasite production (due to faster host death and an
 inferred delay in parasite growth). (4) Parasites made in hot conditions
 were less infectious to the next host (instilling a parasite ‘rearing’ or
 'trans-host' effect of temperature during the prior infection).
 (5) High temperatures in the free-living stage also reduce parasite
 infectivity, either by killing or harming parasites. 4. We then assembled
 the five mechanisms into an index of disease spread. The resulting
 unimodal thermal response was most strongly driven by the rearing effect.
 Transmission peaked at intermediate-hot temperatures (25-26°C) and then
 decreased at maximally hot temperatures (30-32°C). However, transmission
 at these maximally hot temperatures only trended slightly lower than the
 baseline control (20°C), which easily sustains epidemics in laboratory
 conditions and in nature. Overall, we conclude that while exposure to hot
 epilimnetic temperatures does somewhat constrain disease, we lack evidence
 that this effect fully explains the lack of summer epidemics in this
 natural system. This work demonstrates the importance of experimentally
 testing hypothesized mechanisms of thermal constraints on disease
 transmission. Furthermore, it cautions against drawing conclusions based
 on field patterns and theory alone.
description: Bootstrapped foraging
 rate estimatesBootstrapped foraging
 rate estimates fit by MLE from Shocket et al. 2018 (prior
 publication)MLE_f_points.csvData from transmission rate (beta + u measurement) assayData from transmission rate (beta + u measurement) assayUTC_BetaUAssay_Prev.csvSpore yield dataSpore yield data from two assays: transmission rate (beta + u measurement) assay and within-host parasite growth assayUTC_CombinedSporeYieldData.csvField data - temperature at epidemic start dateField data - temperature at epidemic start date (used for motivating figure 1)UTC_FieldDataWeightedStartTemps.csvData from free living spore effect assayData from free-living spore effect assayUTC_FreeLivingSporeAssay.csvData from foraging rate assay at 30 degreesData from foraging rate assay at 30 degreesUTC_HighTempForagingAssay.csvData from host juvenile growth rate assayData from host juvenile growth rate assayUTC_HostGrowthRateAssay.csvData from spore rearing effect assayData from spore rearing effect assayUTC_SporeRearingEffectAssay.csvData from within host parasite growth assayData from within host parasite growth assayUTC_WithinHostParasiteGrowthAssay.csvR Code for Figure 1 (motivating field pattern figure)R Code for Figure 1 (motivating field pattern figure)UTC_MotivatingFigure.RR code for rearing and free-living spore effectsR code for rearing and free-living spore effectsUTC_RearingFreeLivingSporeEffects.RR Code for spore yield and related traitsR Code for spore yield and related traitsUTC_SporeYieldGrowthTraits.RR code for transmission, infectivity, and foraging ratesR code for transmission, infectivity, and foraging ratesUTC_TransmissionandForagingAssays.RR code for transmission potentialR code for transmission potentialUTC_TransmissionPotential.R