Stunned by a Heatwave: Experimental Heatwaves Alter Juvenile Responsiveness to the Threat of Predation

Abstract

Heatwaves, increasingly prevalent in our rapidly changing climate, significantly impact animals with far-reaching ecological and evolutionary consequences. One of the first responses in animals to stress, including heat stress, is behavioural change, and this can directly influence fitness and survival. Changes in anti-predator behaviour are particularly critical, as they may compromise a prey's ability to evade predators, thus increasing predation risk and jeopardising survival. In the context of climate change, assessing anti-predator reactions under ecologically relevant heat stress is thus crucial, especially during the vulnerable life stage of development. This study investigated the effects of a heatwave on anti-predator responses in juvenile guppies (Poecilia reticulata). One-month-old guppies were subjected to a 5-day experimental heatwave (32°C) or a control temperature (26°C). After the treatment, all individuals were tested at a common temperature (26°C) for anti-predator behavioural responses and swimming performance, the latter serving as a proxy for physical condition. While heatwave exposure did not affect swimming performance, it significantly altered anti-predator responses. Heatwave-exposed juveniles exhibited a reduced freezing response and faster resumption of normal activity compared to control fish. Our findings demonstrate that heatwaves can modify prey's anti-predator behaviours during critical developmental stages. This suggests that heatwaves may increase predation risk, potentially impacting survival rates and reshaping predator-prey interactions in the face of ongoing climate change.

Keywords: Poeciliidae; climate change; heat stress; predation risk; prey behaviour.

FIGURE 1

Open field test. (A) View of the arena from above and (B) example output of a tracking, showing the swimming path of a juvenile fish.

FIGURE 2

Anti‐predator response to a visual predator cue. Boxplots showing the anti‐predator response of juvenile guppies, Poecilia reticulata , during 1 min following the visual stimulus, measured by three different variables: Total distance moved (A), freezing rate (B), and swimming speed (C). Controls are represented as blue circles and treated individuals (heatwave) as red triangles. Boxes represent the interquartile range (IQR), with whiskers extending to 1.5 times the IQR from the first and third quartiles.

FIGURE 3

Overall swimming speed response to the chemical stimulus. Boxplot showing the average swimming speed of juvenile guppies, Poecilia reticulata , from a control (blue circles) or a heatwave (red triangles) group, during the 10 min undisturbed phase (clean water; background in plot not shaded) and the 10 min predator phase (conspecific alarm cue present in the water; plot background shaded grey). Boxes represent the interquartile range (IQR), with whiskers extending to 1.5 times the IQR from the first and third quartiles.

FIGURE 4

Anti‐predator response to the olfactory alarm cue. The temporal response, in terms of distance moved (A), freezing rate (B), and swimming speed (C), of juvenile guppies, Poecilia reticulata, from a control (blue circles, n = 51) or a heatwave (red triangles, n = 52) treatment, to a conspecific olfactory alarm cue. Each variable is plotted as mean ± SE per 10 s of exposure during the 10‐min predator phase. The model's predicted slope (smoothed estimates based on the fitted model; thick transparent line) and confidence intervals (SE of the predicted values; shade around the slope) are also shown. (see Figure S2 for responses to exposure time in the undisturbed phase.)