Resolving the paradox of the ambush feeding cyclopoid copepod Apocyclops royi being microphageous

Abstract

Abstract The cyclopoid copepod Apocyclops royi is assumed to be an ambush feeder that passively waits for its prey and captures it by a fast surprise attack. This feeding strategy requires an acute sensibility to hydromechanical signals generated by moving prey. However, A. royi in long-term cultures is able to survive microphageously fed solely on Baker’s yeast (Saccharomyces cerevisae), a small, non-motile prey. In this study, we investigate the feeding behavior of A. royi and how it senses S. cerevisae cells. Using high-speed video, we find that A. royi still exhibits an ambush feeding behavior when fed S. cerevisae. Moreover, we characterize the distance and the duration of attack jumps and evaluate the sensitivity of A. royi to fluid disturbances by filming its escaping behavior when caught in a suction flow simulating a predator, e.g. a fish larva. We demonstrate that its sensitivity to fluid disturbances is very similar to that of other copepod species. Thus, we find that remote detection of S. cerevisae cells due to hydromechanical signals is unlikely as the particles are small (3.8 ± 1.3 μm) and non-motile, and that A. royi likely senses S. cerevisae cells by randomly touching them with setae on their first antennae.