Plants that devour insects seem unusual at first glance. But on closer inspection, the evolutionary path to carnivory is not that far.
Many garden centers have a section with plants that catch insects. In most of the green carnivores, the prey falls into a hopper and ends up in the digestive juices. Others have sticky leaves, and still others wrap their catch as well. And as probably the most conspicuous representative there is the Venus flytrap (Dionaea muscipula), whose snap trap snaps shut in fractions of a second. While the typical garden center shopper might be wondering how to keep these plants in the home, we biologists are interested in something else: how did some plants come to catch and eat insects?
To do this, we look at the green hunters from the point of view of evolutionary biology. What could be the advantage that led to this lifestyle? To do this, we need to get out into nature and study where and under what conditions carnivorous plants live.
Here in Germany there are different species of sundew (Drosera) and butterwort (Pinguicula), all of which catch their prey with sticky leaves. They can be found, for example, in the Black Moor in the Rhön and in wet areas in the Harz Mountains or the Mecklenburg Lake District. Even if you look around the world, most carnivorous plants thrive in similar biotopes. The area of the Venus Flytrap is limited to a small swampy area in the US states of North and South Carolina. Other green carnivores even live entirely in the water. What these areas have in common is that they have plenty of light and water, but the soil lacks elements such as nitrogen or phosphorus. As every hobby gardener knows, these nutrients are essential for plant growth and are therefore the main component of many fertilizers. Insects, on the other hand, contain a lot of nitrogen and phosphorus thanks to their proteins and DNA. In a nutrient-poor environment, a plant that can catch and digest such animals uses the fly as a kind of organic fertilizer. In such locations, carnivores therefore have a distinct advantage over competitors who can only get their nutrients from the ground.
But how could this new trait have arisen? …