New carnivorous plant discovered
Thomas Givnish from the University of Wisconsin-Madison recalls playing in the Pine Barrens of New Jersey as a child amidst an off white, yellow flower perched atop a long green, hairy, sticky-looking stem. Decades later, the previously documented, Triantha occidentalis has been re-designated as a carnivorous plant. As Harry Lewis reports, this particular species has stood innocuously next to roadsides and gone unnoticed, until now…
Tom - It has a very unusual kind of trap mechanism. Its flower stalks are sticky and this runs counter to a theory, actually to a theory I devised a number of years ago, that carnivorous plants should not place their traps next to their flowers less they eat their pollinators. But it turns out that this plant Triantha, found in Western north America, is able to do this because it's tentacles, its glandular hairs, have a relatively weak glue to them so they can catch nats and midges. But they're too weak to immobilise the larger much stronger bees and butterflies that act as pollinators.
Harry - How unique is it to find a carnivorous plant in this day and age?
Tom - It's quite unusual, but not unheard of. It's only the 12th lineage in which carnivory has been discovered in plants. By lineage I mean all the plants descended from some common ancestor.
Harry - Carnivorous plants, they're quite specific to where they grow in terms of location. So, what is the advantage of being carnivorous?
Tom - That's an excellent question. All carnivorous plants have costs, right? They have to construct digestive enzymes or lures like odours or showy leaves to trap prey. So, there has to be some countervailing advantage to those energetic costs. And I argue that the most likely advantage would be an increment to photosynthesis. Photosynthesis is sunlight; it's limited by nitrogen and sometimes phosphorus. And so carnivory should evolve when the energetic benefits through enhanced photosynthesis exceed the costs of carnivory. And the conclusion is simply put that carnivory should evolve when nutrients and nutrients alone are limiting.
Harry - And when discovering this new lineage, I'm sort of imagining you wading through bogs and rainforests in order to find it. Was that the case?
Tom - Not at all. This story began with Sean Graham who had been studying the relationships among plants related to the Philodendron family, the aroids. And he found that a particular gene ndhF had been lost. Sean recognised that a number of carnivorous plants have lost that gene, for reasons we don't understand even to this day. So he said, "Oh that's interesting." And he also recognised that has these sticky inflorescence stems and thought, "Hey, maybe this is a new carnivorous plant." So, he interested one of his star graduate students. Qianshi Lin in the project? Qianshi designed an elegant set of experiments in order to test whether the plant was indeed carnivorous. He first of all grew up fruit flies on a medium that included a lot of heavy nitrogen. So, it comes in two stable isotopes, the common one being N14 and a somewhat heavier one being N15. And he applied them to the leaves of the plant and to the tentacles. And he was able to show 64% of the nitrogen in the plant was coming from prey.
Harry - Which is really high isn't it, Tom?
Tom - Yes, for a plant to be recognised as being carnivorous you have to demonstrate two things first that the plant is able to take up mineral nutrients from dead animal bodies, and secondly, that it has some unequivocal adaptation for prey attraction or pre capture or prey digestion. And in the case of the bog asphodel the ability to take up nutrients from the prey, finally, he was able to show that it had specialised adaptations for prey digestion. So, it turns out that the leaf hairs secrete phosphatase, which is a digestive enzyme that is found in many, but not all carnivorous plants.