Trait-mediated indirect effects, predators, and disease: test of a size-based model

Area of Science:

• Ecology
• Epidemiology
• Evolutionary Biology

Background:

• Wildlife disease prevalence is rising, necessitating understanding of epidemic drivers.
• Predators impact disease via density-mediated and trait-mediated indirect effects (TMIEs).
• Predicting TMIEs' effects on disease dynamics is complex due to potentially opposing trait responses.

Purpose of the Study:

• To investigate how predator-induced TMIEs affect zooplankton host disease dynamics.
• To integrate host size changes and disease-specific traits to predict disease spread (R0).
• To examine the effects of kairomones from invertebrate (Chaoborus) and vertebrate (fish) predators on Daphnia-fungal interactions.

Main Methods:

• Laboratory experiments using a zooplankton host (Daphnia), a fungal parasite, and predator cues (kairomones).
• Mechanistic, size-based modeling of TMIEs across six host genotypes.
• Quantification of host traits (size, birth rate) and disease parameters (infection risk, spore yield, susceptibility) in response to kairomones.

Main Results:

• Chaoborus kairomones had no significant effect on host size or disease traits.
• Fish kairomones reduced host body size, birth rate, and infected host spore yield.
• Despite size-based predictions, fish kairomones increased host susceptibility to infection, leading to no net change in disease spread (R0).

Conclusions:

• TMIEs can have complex, non-additive effects on disease dynamics.
• Integrating all relevant host and disease traits is crucial for accurate prediction of predator impacts on epidemics.
• Understanding the interplay of multiple trait-mediated effects is essential for managing wildlife diseases.