“Venus flytrap rarely traps its pollinators”

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Elsa Youngsteadt, Rebecca E. Irwin, Alison Fowler, Matthew A. Bertone, Sara June Giacomini, Michael Kunz, Dale Suiter, and Clyde E. Sorenson (Apr 2018)

The DOI will be http://dx.doi.org/10.1086/696124

Venus flytrap pollinators now documented: Bees, beetles are key flower visitors. They stay clear of the snap-traps

Carnivorous plants are best known for their ability to digest insects and other prey as a source of nutrients. Like their more mundane cousins, however, these plants also often rely on insects as pollinators. Plants that eat their own pollinators would appear to be at a reproductive disadvantage, but the identity of pollinators and the extent of pollinator-prey overlap is unknown for most of the world’s 600 carnivorous plants. Now, thanks to a collaborative effort involving researchers from North Carolina State University, the North Carolina Botanical Garden, and the U.S. Fish and Wildlife Service, this key piece of natural history has been revealed for the Venus flytrap, the only terrestrial carnivorous plant with an active snap trap.

The new study shows that more than 98 species of insects and spiders visit Venus flytrap flowers in their native North Carolina. The most important of these—as determined by their abundance and the amount of flytrap pollen on their bodies—included a green sweat bee and two kinds of beetles. To see if the flytraps ever eat their pollinators, the researchers also gently pried open snap-traps of about 200 plants and removed their partly digested prey, primarily spiders and ants. The most important pollinators never appeared in traps, and few species were shared between flowers and traps. Those flower visitor species that were trapped turned out to be poor pollinators; examples include fire ants and buckeye butterflies, which were consumed as caterpillars but visited flowers as adults (and carried little pollen).

These results indicate that the Venus flytrap largely avoids pollinator-prey overlap, balancing its needs for prey and pollination. Future work will examine which plant traits are important for keeping these interactions separate; for example, the placement of flowers on tall stalks, or the different colors of flowers and traps, may help the plant recruit different invertebrates for different functions. The new study provides a foundation for examining how tradeoffs between potentially conflicting interactions have shaped the evolution of carnivorous plants.

Left, Venus flytrap in bloom, illustrating the spatial separation between traps and flowers. Photo credit: Clyde Sorenson. Right, two of the most important potential pollinators of Venus flytrap: Augochlorella gratiosa (top) and Typocerus sinuatus (bottom). Photo credits: Elsa Youngsteadt (top), Clyde Sorenson (bottom).

Abstract

Because carnivorous plants rely on arthropods as pollinators and prey, they risk consuming would-be mutualists. We examined this potential conflict in the Venus flytrap (Dionaea muscipula)), whose pollinators were previously unknown. Diverse arthropods from two classes and nine orders visited flowers; 56% of visitors carried D. muscipula pollen, often mixed with pollen of co-flowering species. Within this diverse, generalized community, certain bee and beetle species appear to be the most important pollinators, based on their abundance, pollen load size, and pollen fidelity. D. muscipula prey spanned four invertebrate classes and eleven orders; spiders, beetles, and ants were most common. At the family and species levels, few taxa were shared between traps and flowers, yielding a near-zero value of niche overlap for these potentially competing structures. Spatial separation of traps and flowers may contribute to partitioning the invertebrate community between nutritional and reproductive functions in D. muscipula.