# Energy availability influences the dynamics of thermal phenotypic plasticity

## TL;DR

Food availability affects how well organisms can adjust to heat, with fed individuals showing greater thermal tolerance than unfed ones.

## Contribution

The study reveals that energy availability influences the capacity but not the rate of thermal phenotypic plasticity.

## Key findings

- Thermal tolerance increases with acclimation duration, but more so in fed individuals.
- Food treatment primarily affects the capacity component of thermal plasticity.
- Laboratory estimates of thermal tolerance may be overly optimistic for wild organisms.

## Abstract

We tested whether food availability limits phenotypic plasticity in thermal tolerance in the amphipod Echinogammarus marinus. We shifted specimens from 10°C to an acclimation temperature of 20°C, and kept them there for different durations with and without food before measuring the time to immobilization at 30°C. Our results show that thermal tolerance increases with acclimation duration, but this response was about two times more pronounced in fed than in unfed individuals. We also decomposed the plastic response into a rate component (how fast the trait changes) and a capacity component (by how much it changes). This showed that the overall effect of food treatment on the temporal dynamics of thermal tolerance was primarily driven by the effect on capacity. We conclude that laboratory derived thermal tolerance data from experiments where ecological conditions are otherwise optimal may provide overly optimistic estimates of how well organisms deal with extreme events through phenotypic plasticity.

Summary: Energetic status influences plasticity capacity in thermal tolerance, but not plasticity rate. Therefore, the ability of wild organisms to deal with extreme events through plasticity may be less pronounced than that inferred from laboratory experiments.