Faster but not optimal: how temperature affects prey capture behaviour and physiology in the winter midget funnel-web spider Mecicobothrium thorelli Holmberg, 1882 (Araneae: Mecicobothriidae)

Temperature influences a variety of traits in ectotherms, including growth, metabolism, and behaviour and they have developed several strategies that includes behavioural and physiological adaptations to maintain their body function under varying thermal conditions. Mecicobothrium thorelli, a mygalomorph spider with small populations, low abundance, and winter activity, may be especially vulnerable to temperature changes, though this remains understudied. In this study, we aimed to assess the effect of different thermal ranges on prey capture behaviour and physiological traits on this species. The spiders were exposed to cold (5–10°C), medium (15–20°C), and warm temperatures (25–30°C), and we measure prey acceptance, prey detection latency, and prey attack speed by offering a prey and recording the behaviours using video. Additionally, spiders were acclimated to 5°C or 25°C for four weeks, and we measured the total content and composition of proteins and lipids. We found that M. thorelli accepted prey across all thermal ranges without distinction and demonstrated greatest ability to detect prey at moderated temperatures. Furthermore, the spiders were able to capture prey at all evaluated thermal ranges, but they exhibited a faster attack speed at warm temperatures. The content and composition of proteins and lipids did not show significant differences between low and high acclimation temperatures. Despite M. thorelli being more efficient at capturing prey at warm temperatures, medium and cold temperatures appear to be sufficient for feeding, and the spider is capable of maintaining similar levels of proteins and lipids at both low and warm temperatures. Those results are consistent with the winter temperatures at which this species carries out its main survival and reproduction activities.