The role of phytoplankton in the diet of the bladderwort Utricularia australis R.Br. (Lentibulariaceae)

Abstract

It is becoming more apparent that the aquatic carnivorous plants Utricularia (Lentibulariaceae) can capture and utilise a wide range of small aquatic organisms. Although they can take up nutrients directly from the water by rootless shoots, much of their overall nutrition comes from prey caught in their traps. Most of the early literature was focused mainly on animal prey, hence the term carnivorous to describe Utricularia spp., but more recently the contribution of other microorganisms and detritus to their diet is being realised. Specifically, the importance of the phytoplankton in traps as prey is proving interesting. However, most investigations have focused on the trap communities with few comparisons to phytoplankton as potential prey, which could reveal the occurrence of feeding selectivity. The eurytopic species Utricularia australis was surveyed across 12 sites in central Italy in lentic waterbodies ranging from oligotrophic to eutrophic. Phytoplankton communities outside the traps were composed of 135 taxa from 21 orders belonging to eight phyla and the algal community in the traps comprised 124 taxa from 17 orders belonging to eight phyla, recorded from all sampling sites. Among the 12 sites phytoplankton communities were highly diverse; however, communities inside and outside the traps at each site were very similar. This similarity indicated that feeding was not selective. Algal movements are not able to elicit a trap response, yet around 70% of the traps contained phytoplankton only (no animal prey). Therefore, regular spontaneous trap firing, known to occur in U. australis, is thought to be responsible for the similarities in trap and plankton algal communities. At two sites, a Euglenophyte (Lepocinclis sp.) and a Cryptophyte (Chilomonas sp.) proliferated, which were otherwise very rare in the phytoplankton community. This is indicative of favourable growth conditions in the traps and possibly of commensal relationships. It seems that the diet requirements of U. australis are met by having a highly varied prey spectrum.

Biological control of Aedes mosquito larvae with carnivorous aquatic plant, Utricularia macrorhiza

“…Bladderworts can exist for extended periods without prey, adaptively shift to carnivory, and increase predatory efficiency as prey density increases. When plants are maintained in the absence of prey for long periods, it can impact the number of bladders [70][71][72][73]. Englund & Harms [88] demonstrated that the investment in predatory biomass (bladders) increases at high prey densities.…”

“…albopictus using cuttings of U. macrorhiza that had been stored 6 months without prey. Because the period without prey is known to alter the number of bladder traps in several species of Utricularia [70][71][72][73], we separated replicates based on the number of months the plants had been stored. However, the initial number of bladders used in experimental cups was standardized to 100 bladders.…”

Picky carnivorous plants? Investigating preferences for preys’ trophic levels – a stable isotope natural abundance approach with two terrestrial and two aquatic Lentibulariaceae tested in Central Europe

“…30 % prey-derived total plant nitrogen transferred to immature tissues. Another proportion of N is gained from capturing pollen, phytoplankton and other plant material (Koller- Peroutka et al, 2015;Ellwood et al, 2019) and even their own mutualistic microfauna (Richards, 2001). The remaining nitrogen supply is then received from the surrounding water medium (Friday and Quarmby, 1994).…”

“…We assume the enriched nitrogen is taken up by these plants and translocated to their tissue, resulting in enriched δ 15 N values for these autotrophic reference plants. A bladderless Utricularia species would represent an optimal reference, allowing for the determination of phytoplankton-derived nutrients in the nutrient supply of aquatic Utricularia, which are frequently identified inside the bladders (Koller- Peroutka et al, 2015;Ellwood et al, 2019). At least in temperate central Europe, the main issue is the existence of such submersed non-rooting plants.…”

“…ex J.Ellis). Temperate aquatic Utricularia establishes suction bladders to trap prey (Meyers and Strickler, 1979;Knight and Frost, 1991;Reifenrath et al, 2006;Peroutka et al, 2008;Jobson et al, 2018), which is described to be composed mostly of crustaceans and mosquito larvae (Jobson and Morris, 2001;Richards, 2001), but also algae and pollen due to an autonomous firing of the bladders (Peroutka et al, 2008;Adamec, 2011Adamec, , 2018Koller-Peroutka et al, 2015;Ellwood et al, 2019). Utricularia plants often form a mutualism with microfauna to attract microcrustaceans, thereby increasing trapping success and taking advantage of by-products of this microfauna (Albert et al, 2010).…”