Effect of temperature and thermal acclimation on locomotor performance of Macrobiotus harmsworthi Murray (Tardigrada, Macrobiotidae)

We investigated the effects of acute and acclimation temperature on the locomotor performance and behavior of the tardigrade Macrobiotus harmsworthi collected from Qinling Mountains in central China. Tardigrades were acclimated to either 10 or 25 °C for 2 weeks. Then we recorded their walking speed, percentage of time moving, and the maximum distance covered by continuous locomotion at either 10 or 25 °C as the rate parameters of locomotor performance. The walking speeds of M. harmsworthi varied from 1.98 to 4.8 mm min-1. The locomotor performance rates were significantly influenced by both acclimation temperature and performance temperature and by the interaction of the performance temperature and acclimation temperature. The data from our studies support the Beneficial Acclimation Hypothesis (BAH) which predicts that animals acclimated to a particular temperature have enhanced performance or fitness at that temperature in comparison with animals acclimated to other temperatures. The data, at least potentially, also support the Warmer is Better Hypothesis which predicts that organisms raised at high temperatures have higher relative fitness across all temperatures than do those raised at intermediate or cool temperatures. Some of the results from our studies testify the inference from the BAH that performance temperature that deviates from the acclimation temperature could cause the reduction of the locomotor performance rate.