Differences between thermal preference and thermal performance in a wintry spider Mecicobothrium thorelli: are the spiders under evolutionary pressures on their seasonal activity?

Abstract

Thermal preference and thermal performance are used to describe the thermal biology of an ectothermic organism through parameters, i.e., estimating locomotor performance by maximum running speed. In this study, we assessed the thermal preference and locomotor performance of the spider Mecicobothrium thorelli Holmberg, 1882, a wintry mygalomorph spider endemic to the native mountainous grasslands of central Argentina and Uruguay. The preferred temperatures of the 72.4% of the individuals were in the range of 10-20°C. The highest frequencies of preferred temperatures were 10-15 °C in males and 15-20°C in females. The sprint speed showed significant differences between all the temperatures evaluated and showed the highest speeds at 25 °C and the lowest at 3 °C. The optimal temperature was 26.09 °C which was significantly higher than the preferred temperature in both males and females. We concluded that M. thorelli selects a wide range of temperatures and prefers to stay in medium and low temperatures, which are correlated with winter activity in the wild. However, the species showed maximum speed at higher temperatures which implies that spiders would perform even better in nature and maximize their locomotion by being active during a warmer period.