Insights into thermal preferences of copepods in nature using the horizontal gradient method

Abstract

The final thermal preferendum (FTP) and the lower and upper thresholds of temperatures avoided were defined for the first time for Cyclops vicinus Ulyanin, 1875 (Crustacea: Copepoda). The preferred temperature on day one had a modal value of 13.9C (range: 11-17C), which increased on Days 2 and 3 to 20.4C (range: 17-23C) and 20.2C (range: 17-22C), respectively, and then declined during Days 4 (19.1) to 7 (17.1C). The selection process occurs with overshoot. On days seven and eight after placement in the thermal gradient the preferred temperature stabilized at 17.1-17.5C. These temperatures are accepted as the FTP of individual C. vicinus. Cyclops vicinus avoided temperatures below 5C and above 29?. We can compare these thermal ranges observed under experimental conditions with the typical temperature values reported for field populations. This study provides a proof of concept of an approach that was used previously primarily for determining species specific thermal preferences in fish and then adapted for cladocerans. This laboratory approach using C. vicinus provides an example of how this method can be used to improve interpretation of copepod phenologies in nature.