Heatwaves at different stages of pregnancy: effects on behaviour and fecundity in female guppies (Poecilia reticulata)

Heatwaves are extreme weather events typically defined as periods of at least 5 days when the daily maximum temperature exceeds by 5°C the local maximum expected. Guppies (Poecilia reticulata) are a tropical species of live-bearing fish often used as a model organism in many studies. Knowing the worryingly increase in heatwave events in the last decades and the already existing proof of their lethal effects on many living organisms, guppies included, this study aimed to investigate the nonlethal effects of heatwaves on the behaviour and fecundity of female guppies. Moreover, few studies suggested the importance of investigating the timing of heatwaves during the reproductive cycle . For this reason, this project aimed at disentangling the effects of heatwaves striking during the early stages of pregnancy versus the late stages of pregnancy. The project involved the artificial simulation of heatwaves either at the start or at the end of the pregnancy, in a controlled environment and the implementation of three behavioural tests: a foraging test, an open field test to study the propensity of the females to explore and their anti-predator response to an alarm cue and a flow chamber test to measure the swimming endurance. Both the open field and the flow chamber tests were conducted once in the early stages of pregnancy and once during the late stages while foraging was measured during the heatwave. Toward the end of the pregnancy, females were isolated and monitored for the delivery of a brood, because the gestation time and the size of the brood were considered to study the effects of heatwaves of fecundity.