Temperature modifies trait-mediated infection outcomes in a Daphnia-fungal parasite system

Abstract

One major concern related to climate change is that elevated temperatures will drive increases in parasite outbreaks. Increasing temperature is known to alter host traits and host-parasite interactions, but we know relatively little about how these are connected mechanistically – that is, about how elevated temperatures impact the relationship between epidemiologically relevant host traits and infection outcomes. Here, we used a zooplankton-fungus (Daphnia dentifera-Metschnikowia bicuspidata) disease system to investigate whether temperature interacted with host susceptibility traits in determining infection outcomes. We did this by exposing D. dentifera to M. bicuspidata or leaving them unexposed at either control (20°C) or warming temperatures (24°C) in a fully factorial design. We found that elevated temperatures altered the physical barrier and immune responses to parasites during the initial infection process, and that infected hosts at elevated temperatures suffered a greater reduction of fecundity and lifespan. Furthermore, the relationship between a key trait – gut epithelium thickness, which is a physical barrier – and the likelihood of terminal infection reversed at warmer temperatures. Together, our results highlight the complex ways that temperatures can modulate host-parasite interactions, and the importance of considering key host susceptibility traits when predicting disease dynamics in a warmer world.This article is part of the theme issue ‘Infectious disease and evolution in a changing world’.

Transgenerational plasticity in a zooplankton in response to temperature elevation and parasitism

“…This experiment used the "Standard" lab lines of D. dentifera and M. bicuspidata originally isolated from a lake in Barry County, Michigan. We describe the maintenance of the D. dentifera and M. bicuspidata used in this study in more detail elsewhere (Sun et al 2022a). Immediately prior to this experiment, D. dentifera were maintained in standardized conditions (a 16:8 photoperiod at 22°C) for three generations and fed three times a week with a phytoplankton food (Ankistrodesmus falcatus, 20,000 cells/mL).…”

“…This experiment relates to, but differs from, two other recent experiments. In the first (Sun et al 2022a), we focused on how temperature modified trait-mediated infection outcomes in the F0 generation and did not look across generations. In the second related experiment (Sun et al 2022b), we looked for evidence of transgenerational plasticity in the parasite (rather than in the host, which is the focus of the present study).…”

“…To determine host fitness, we checked all animals daily for mortality and counted the number of offspring produced, which were then removed from the beakers. Once the last infected individual was found dead, the unexposed animals were checked twice a week, since uninfected Daphnia live significantly longer than infected ones (Sun et al 2022a). Dead infected animals were kept individually in a 1.5 mL tube of 100 μL deionized water and stored in a refrigerator before determining spore yield.…”

Infectious disease ecology and evolution in a changing world

“…To better understand the impact of environmental temperatures on disease outbreaks, two papers focus on changes in mechanisms underpinning the ability of parasites to infect [18] and of hosts to resist [19]. In effect, these papers take care to start from the beginning, where the host and parasite first meet, using the planktonic crustacean Daphnia and its bacterial parasites.…”

“…In detailed experiments, Sun et al . [19] found that warming affected these defence traits differently, with consequences for infection outcomes. Disease spread can also depend on how temperature interacts with traits in host communities [20,21].…”