Meeting Abstract
Bladderworts are a carnivorous plant genus (Utricularia) containing several aquatic species; the latter form hundreds of millimeter-sized underwater traps to capture zooplankton prey. The large number of very small traps makes these plants ideal model organisms to study predator-prey interactions in a batch mode (mesocosm). In a laboratory microcosm we pit dozens to hundreds of prey against dozens to hundreds of predators in a small volume (mason jars) for a brief period (hours to days). We monitor the progress and outcome in terms of prey size and type, as well as trap age, size, capture rate, and capture efficiency. To this end, we have developed assays involving machine vision, fluorescence imaging, and sound recording. We can now address such questions as ‘how energetically expensive are active traps?’ and ‘how do prey size or predator size affect capture rate and capture success?’. An individual trap becomes active at the growing end of the plant, then captures and digests dozens of prey items before dying at the senescing end of the plant. We found that young traps have high rates of unsuccessful or spontaneous fires and that the majority of prey items are caught by mature, large traps. Using the volume of water inspired as a measure of the energy expended by traps, we found that small traps spend the most energy despite catching the fewest prey. This finding is contrary to the expectation that energy expenditure should correspond to capture success. The volume of water pumped is furthermore a proxy for the oxidative stress of respiration, which is believed to be a central factor in bladderworts’ extremely small genome and high rate of molecular evolution.
