For Immediate Release
September 5, 2002


GARDEN SCIENTISTS ANSWER A LONG-STANDING QUESTION ABOUT CARNIVOROUS PLANT EVOLUTION

Venus' flytrap  Photo by Kenneth M.  CameronConfirming one of Charles Darwin’s hunches, scientists at The New York Botanical Garden have discovered that two species of carnivorous plants living half a world apart—one on land and one in water—are each other’s closest relatives. This surprising finding, published in the September issue of The American Journal of Botany, resulted from the first DNA analysis to examine the link between the terrestrial Venus’ flytrap (Dionaea muscipula), found only in the southern United States, and the aquatic Old World waterwheel plant (Aldrovanda vesiculosa).

“Our results answer a long-standing question about the evolution of carnivorous plants,” says senior author Kenneth M. Cameron, Ph.D. “We show that Venus’ flytrap’s characteristic ‘snap-trap’ design evolved only once in the history of plants, not twice as some scientists had previously believed.” Cameron is the Assistant Curator of The New York Botanical Garden’s Lewis B. and Dorothy Cullman Program for Molecular Systematic Studies.

The Venus’ flytrap, which Darwin called “one of the most wonderful plants in the world,” resembles a set of open jaws that snap shut when an insect lands on them. Only one other plant—the aquatic waterwheel—has this mechanism, but for hundreds of years, scientists weren’t sure how the two were related.


Darwin’s Insight
When Carolus Linnaeus, the founder of modern taxonomy, was naming plants in the 1700s, he surmised that the waterwheel’s whorls of snap-traps were little air balloons that helped the rootless plant float in water. (Indeed, his name for the species, Aldrovanda vesiculosa, attests to the idea of air vesicles). Darwin was the first scientist to make the connection with carnivorous plants, describing the waterwheel as “a miniature, aquatic Dionaea [Venus’ flytrap].” Darwin carefully studied live specimens of the plant and strongly suspected that it used its “air balloons” to capture tiny marine animals.

Botanists subsequently proved that waterwheel’s whorls did indeed consist of prey-catching snap-traps, but many still believed the plant’s resemblance to Venus’ flytrap was coincidental. For much of the 20th century, botanists debated exactly how carnivorous plants had evolved, and in what order. Many researchers concluded that the snap-traps of Venus’ flytrap and waterwheel were an example of convergent evolution—nature’s way of creating the same mechanism twice in unrelated organisms.

The sole phylogenetic systematic study of waterwheel’s relationship to other carnivorous plants, conducted at the University of North Carolina in 1994, suggested that waterwheel was most closely related to the sundew. (Phylogenetic systematics is a taxonomic system that links organisms based on shared characteristics.) This seemed logical, because its flowers strongly resemble those of the sundew. The sundew, however, uses sticky globules called “flypaper traps” instead of snap-traps to capture its prey. The North Carolina study implied that the sundew’s flypaper mechanism may have evolved from the waterwheel’s snap-traps.

Cameron thought this was unlikely, since other evidence suggested that the trigger hairs on a Venus’ flytrap were themselves derived from flypaper trap tentacles. So he found himself asking the classic evolutionary question: which came first?


A New Genetic Approach to the Question

To settle the issue, Cameron and his team at The New York Botanical Garden conducted the first molecular evolutionary study of this question based on carnivorous plants’ genetic similarities, rather than on their outward appearances. Working with DNA sequences from each genus of carnivorous plants, the researchers constructed a family tree by comparing several genes. The basic idea was that the greater the genetic similarity between two plants, the more closely they are likely to be related.

Taken all together, the team’s results showed that Venus’ flytrap and waterwheel were each other’s closest relative, strongly supporting the idea that these plants have a common ancestor and that snap-traps evolved only once in the history of plants. Data on these plants’ genetic relationship with other carnivorous plant species also showed, as Cameron had suspected, that snap-traps evolved from flypaper traps, not the other way around.

Intriguingly, field botanists have reported that when Venus’ flytrap’s habitat becomes flooded, the plant is still able to grow and capture prey. “Thus,” says Cameron, “it isn’t hard to imagine a common terrestrial ancestor adapting to life in the water and, over time, evolving into the waterwheel plant.”

Cameron’s co-authors are Kenneth J. Wurdack, Ph.D., and Richard W. Jobson, Ph.D. Funding for the research was provided by the Lewis B. and Dorothy Cullman Foundation.

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Scientific Research at The New York Botanical Garden’s International Plant Science Center
The New York Botanical Garden is a public garden and research institution dedicated to the documentation and preservation of the Earth’s plant biodiversity. The Garden’s International Plant Science Center is one of the most accomplished, intensive, and distinguished botanical science programs in the world. It includes the Institute of Economic Botany for research, teaching, and publication in the field of economic botany—the relationship between plants and people; and the Institute of Systematic Botany for the research and documentation of plant diversity, plant taxa, and evolutionary relationships. The collections in its William and Lynda Steere Herbarium and The LuEsther T. Mertz Library are the most extensive resources of their kind in the Western Hemisphere. The Lewis B. and Dorothy Cullman Program for Molecular Systematics Studies and The Plant Genomics Consortium are becoming widely recognized as major contributors to our understanding of the origin and evolution of plants, and are headquartered in the Plant Research Laboratory. To disseminate the results of its research, as well as that of the international botanical community, the institution operates The New York Botanical Garden Press, the largest scholarly publications program of any botanical garden in the world. The Graduate Studies Program links the Garden with five universities to train future scientists. The New York Botanical Garden, founded in 1891, is located on 250 acres in New York City’s Bronx borough.

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CONTACT INFORMATION:
Researcher:
Dr. Kenneth M. Cameron
Assistant Curator
Lewis B. and Dorothy Cullman Program for Molecular Systematic Studies
The New York Botanical Garden
(718) 817-8179 or kcameron@nybg.org

Public Relations:
Lisa Stillman
Director of Media Relations
The New York Botanical Garden
(718) 817-8815 or lstillman@nybg.org


Image: Dionaea muscipula Venus’ flytrap; photo by Kenneth M. Cameron



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