Automated measurement of upper thermal limits in small aquatic animals

Abstract

We present a method for automating the measurement of upper thermal limits in small aquatic organisms. Upper thermal limits are frequently defined by the cessation of movement at high temperature, with measurement being performed by manual observation. Consequently, estimates of upper thermal limits may be subject to error and bias, both within- and among-observers. Our method utilises video-based tracking software to record the movement of individuals when exposed to high, lethal temperature. We develop an algorithm in the R computing language that can objectively identify the loss of locomotory function from tracking data. Using independent experimental data we validate our approach by demonstrating the expected response in upper thermal limits to acclimation temperature. Our R-code and the tracking data used in its development is made available on figshare.