Assessing the costs and benefits of active traps in the carnivorous plant utricularia australis: effects of trap size and age
Carnivorous plants form traps, which require resources that would otherwise go to photosynthetically more active tissue. Added to this cost of trap construction can be the cost of setting and resetting the trap if the trap is active (such as a Venus flytrap). The carnivorous plants with the most active traps are in the genus Utricularia (bladderwort). A bladderwort trap can fire up to several hundred times over its lifespan. The cost of setting and resetting the trap arises from expelling water from the tap lumen. As lumen volume scales with trap size, active cost scales with trap volume. Given that cost scales with trap size, we expect that the increased cost of larger traps is balanced by increased benefits in the form of larger or more prey captured. In this study we explored the effects of trap size on active costs and prey capture success. We developed a new method to quantify the volume of water expelled from each trap using a fluorescent dye. We found that the volume of water expelled increased with increasing trap size and that larger traps catch more prey. We also found that age effects did not confound size effects. We conclude that in bladderworts, both costs and benefits of traps scale with trap volume. Furthermore, studies that explore the cost of active traps need to take into account trap size as a confounding factor.