New addition to the carnivorous plant community: Researchers report a previously undiscovered case of carnivory in a North American swamp plant: Triantha occidentalis gets more than half of its nitrogen from trapped insects, the studies show. The special thing about it is that the plant has to combine prey capture and pollination, because it catches and digests insects with its sticky flower stalks.
Plants are usually the victims – but some bizarre plants have turned the tables: the approximately 600 representatives of the carnivores hunt insects with ingenious trap systems. This gives them growth advantages in locations where the soil offers only a few nutrients, because the prey acts on them like “fertilizer tablets”. In order to catch insects, these rabid plants have developed different strategies: some set up pitfalls, others snap at their prey and the third group catches insects through sticky structures. The catch organs are usually special leaf structures. After a successful hunt, the carnivores absorb the nutrients of their victims by breaking them down through digestive fluids or by letting symbiotic microbes do this job.
Occasionally, researchers also discover new carnivores – but these are mostly species from well-known families such as the sundew family (Droseraceae). The plant that Qianshi Lin from the University of British Columbia in Vancouver and his colleagues are now presenting is a representative of a plant family from which no carnivory was previously known and its prey-catching concept is also special. Triantha occidentalis belongs to the common lily family (Tofieldiaceae), which in turn are assigned to the monocotyledonous frog-spoon-like (Alismatales). The white flowering perennial is widespread in wetlands in northwest North America. It was already known that its tall flower stems were covered in sticky hair. But such features can also serve as protection against enemies.
On the trail of prey nitrogen
The researchers only focused on the species following evidence from a genetic study of various representatives of the frog-spoon-like species – including T. occidentalis. It turned out that this species lacks a special genetic make-up that carnivorous plants have typically lost in the course of their evolution. The scientists then followed up on this trail by means of a systematic investigation. First of all, they were able to show that small mosquitoes actually get caught on the sticky hairs of the flower stalks of the plant. But does the plant actually incorporate its nutrients?
The researchers investigated this question by experimentally feeding the plants with special fruit flies. Some of the nitrogen in these insects was a special stable isotope that is easy to detect. After the feeding, the scientists were able to follow the path of the nitrogen isotope in the test plants. They then compared the results with the values for a known carnivorous plant as well as for a “normal” plant that occurs in the same habitat as T. occidentalis.
The investigation data and calculations confirmed that the nitrogen from the prey is actually absorbed and relocated by the plant. The bottom line is that T. occidentalis gets more than half of its nitrogen supply from insect trapping – similar to what is known from other carnivores, say the scientists. It is therefore the first known carnivore from the group of frog-spoon-like and also only the fourth case of a carnivore from the group of monocotyledons. Through further investigations, the scientists were also able to prove that T. occidentalis is one of the representatives that digest its prey directly and does not use microbes as helpers: the plant produces an enzyme called phosphatase, which can break down the nutrients in its prey, they showed Analyzes.
Pollinators are spared
“What is particularly interesting about this plant is that it catches its prey near its insect-pollinated flowers,” says Lin. “So there seems to be a conflict between carnivore and pollination, since the insects that are used for reproduction should not be killed”. But apparently the plant differentiates between victims and helpers: “Because its glandular hairs are not very sticky and can only catch mosquitoes and other tiny things, we believe that larger and stronger insects such as bees or butterflies, which act as their pollinators, are not caught “Says co-author Tom Givnish of the University of Wisconsin-Madison.
The researchers suspect that there are other carnivorous representatives of the genus Triantha in addition to T. occidentalis, as other species with sticky stems are known. Therefore, they now want to investigate this species in more detail. According to them, the study also shows a general potential: The fact that the way of life of T. occidentalis has gone unnoticed for so long suggests that even more cases of plant-based carnivores are waiting to be discovered, according to the scientists.
Source: University of Wisconsin – Madison, article: PNAS, doi: 10.1073 / pnas.2022724118