Effetti delle ondate di calore sulla riproduzione di Pisaura mirabilis (Araneae)

Climate warming is influencing species' distributions and abundances, posing a threat to biodiversity. The frequency and intensity of extreme climatic events, such as heatwaves, characterised by temperatures exceeding local averages by 5 °C for at least five days, are becoming more frequent and intense. These posing serious risks to health, society, and the environment. Yet, their effects on population persistence are poorly understood. Heatwaves can affect species beyond survival, because even if temperatures are sublethal, they can impact reproduction and various biological functions. Individuals, for example, may become sterile at temperatures below their lethal limits. Ectothermic organisms are particularly vulnerable to temperature fluctuations due to their reliance on ambient temperature for body regulation. Understanding the impacts of heat stress on ectotherms is essential for assessing the ecological consequences of climate change and understand potential mechanisms that are driving the massive decline in arthropod numbers. The nursery web spider, Pisaura mirabilis, is ideal for studying the effects of heatwaves on reproduction and survival due to its wide distribution, ease of recognition and collection, and well-documented mating behaviours. In addition, the effect of heatwaves on spider reproductive behaviour remains largely unknow. The study aims to investigate the effects of heatwaves on the mating behaviour and fitness of male Pisaura mirabilis. Juvenile spiders were collected and raised to adulthood in a lab setting. Adult males were then assigned to either a control group at room temperature or heatwave treatment group exposed to a 5-day simulated heatwaves of 36 °C. Male Behaviours such as exploration, aggression, and behaviours expressed during mating trials with control females, such as courtship and mating were recorded and analyzed. Females' reproductive success was monitored by assessing brood size and eggs count. Our main findings show that heatwaves affect certain male individual behaviours and partially fitness, but we haven’t found effects on mating behaviours. We found significant effects concerning the body mass of the subjects, with an important role of female weight in both mating (duration and rate) and fitness results.