The comparison of mechanically stimulated and spontaneous firings in traps of aquatic carnivorous Utricularia species

Firing and resetting of traps in aquatic Utricularia species are associated with water flows and trap volume changes. In this study, trap thickness was used as a measure of water flow and was monitored automatically using an electronic position sensor. Isolated traps from three aquatic Utricularia species were monitored over the course of 1-2 days to verify spontaneous firings (without any mechanical stimulation) and describe their basic characteristics. Isolated traps of three Utricularia species were initially fired by mechanical stimulation and allowed to naturally reset within a period of 24-48 h. Within this resting period, spontaneous firings were found in the traps of all species and in two trap age categories of U. vulgaris. The timing of spontaneous firings was found to be irregular. Spontaneous firings ranged between 0.29 and 2.4 during the 24-h resting period and the mean time between two spontaneous firings was highly variable within each species (319-891 min). There was no quantitative difference between spontaneous and mechanically stimulated firings of the traps. Spontaneous firings could explain how phytoplankton or detritus enters traps even when no prey species are present.