New England Carnivorous Plant Society

How does a plant develop a taste for flesh? In the play Little Shop of Horrors, all it takes is a drop of human blood. But in real life, it takes much more. Now, a study of three closely related carnivorous plants suggests dextrous genetic shuffling helped them evolve the ability to catch and digest protein-rich meals.

Carnivorous plants have developed many devious ways to snare prey. Pitcher plants, for example, use "pitfall traps" that contain enzymes for digesting stray insects. Others-including the closely related Venus flytrap (Dionaea muscipula), the aquatic waterwheel plant (Aldrovanda vesiculosa), and the sundew (Drosera spatulata)-use moving traps. The sundew rolls up its sticky landing pad when mosquitoes get caught. And the Venus flytrap uses modified leaves, or pads, that snap shut when an insect lands-but only after the pads sense multiple touches on their trigger hairs.

To find out how these traps evolved, researchers led by computational evolutionary biologist Jörg Schultz and plant biologist Rainer Hedrich, both of the University of Würzburg, sequenced the genomes of the sundew, the aquatic waterwheel, and the Venus flytrap, which are all closely related. They then compared their genomes with those of nine other plants, including a carnivorous pitcher plant and noncarnivorous beetroot and papaya plants.

They found that the key to the evolution of meat eating in this part of the plant kingdom was the duplication of the entire genome in a common ancestor that lived about 60 million years ago, the team reports today in Current Biology. That duplication freed up copies of genes once used in roots, leaves, and sensory systems to detect and digest prey. For example, carnivorous plants repurposed copies of genes that help roots absorb nutrients, to absorb the nutrients in digested prey. "That root genes are being expressed in the leaves of carnivores is absolutely fascinating," says Kenneth Cameron, a botanist at the University of Wisconsin, Madison.

Hedrich and his colleagues conclude that carnivory evolved once in the ancestor of the three species and, independently, in the pitcher plant. Adding these two new origins to others already documented, the researchers conclude that meat eating has evolved at least six times.

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The Venus flytrap (Dionaea muscipula) takes only 100 milliseconds to trap its prey. Once their leaves, which have been transformed into snap traps, have closed, insects can no longer escape. Using biomechanical experiments and virtual Venus flytraps a team from Freiburg Botanical Garden and the University of Stuttgart has analyzed in detail how the lobes of the trap move. Freiburg biologists Dr. Anna Westermeier, Max Mylo, Prof. Dr. Thomas Speck and Dr. Simon Poppinga and Stuttgart structural engineer Renate Sachse and Prof. Dr. Manfred Bischoff show that the trap of the carnivorous plant is under mechanical prestress. In addition, its three tissue layers of each lobe have to deform according to a special pattern. The team has published its results in the Journal Proceedings of the National Academy of Sciences.

The diet of the Venus flytrap consists mainly of crawling insects. When the animals touch the sensory hairs inside the trap twice within about 20 seconds it snaps shut. Aspects such as how the trap perceives its prey and how it differentiates potential prey from a raindrop falling into the trap were already well known to scientists. However the precise morphing process of the halves of the trap remained largely unknown.

In order to gain a better understanding of these processes, the researchers have analyzed the interior and exterior surfaces of the trap using digital 3-D image correlation methods. Scientists typically use these methods for the examination of technical materials. Using the results the team then constructed several virtual traps in a finite element simulation that differ in their tissue layer setups and in the mechanical behavior of the layers.

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