The effect of temperature and kairomone on Daphnia escape ability: a simple bioassay

Abstract

We propose a simple and sensitive bioassay for analyzing zooplankton escape behavior and present results of its testing on four Daphnia species under varying temperature, and in either the presence or absence of chemical cues of fish predation. In the assay, the animals are blindly transferred with a pipette through subsequent containers and their final distributions are compared. For testing the effects of a single factor, comparing distributions of the animals is a sensitive tool to detect differences in escape ability. We propose single-value measures to be used in larger experiments with multigroup comparisons in order to enable studying global effects and reduce the loss of statistical significance due to correction for multiple testing. Our results show that if escape ability is considered an important fitness component, among the tested species, which were D. longispina, D. lumholtzi, D. magna, and D. pulicaria, the last may be the most vulnerable to increased fish predation associated with increased lake water temperatures.