Revising the Mantis Family Tree
When did the praying mantis develop an ability to mimic the bark of the tree where it hunts?
It’s the kind of question researchers ask all the time as they study biodiversity, evolution and countless other explorations. Owing to dogged research from a team led by Dr. Gavin Svenson, the Museum’s curator of invertebrate zoology, such questions can now be answered.
What Svenson and his team have accomplished is development of a new system to classify Empusidae and Hymenopodidae, plant-mimicking orders of the praying mantis family (Mantodea). Together, these orders account for a quarter of all known Mantodea species.
The new classification system was introduced in a paper published in 2015 in Systematic Entomology, a journal of The Royal Entomological Society. It’s important for several reasons:
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Far more accurate and useful to science than the previous system because it’s based on both molecular phylogenetics (that is, DNA research) as well as new morphological analyses.
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Provides a model that can be used to improve classification of other insect groups.
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Supports global collaboration and provides important training for a small community of scientists doing genetic research on Mantodea.
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Solidifies the Museum’s Department of Invertebrate Zoology under Svenson as a world-class center for Mantodea research.
Svenson is lead author of the paper that describes the research, titled "Of Flowers and Twigs: Phylogenetic Revision of the Plant-Mimicking Praying Mantises with a New Suprageneric Classification." His co-authors are Nate Hardy, an assistant professor in entomology and plant pathology at Auburn University; Haley Cahill Wightman, a graduate student in biology at Brigham Young University; and Frank Wieland, head of the zoology department at the Palatine Museum of Natural History-Pollichia Museum in Bad Durkheim, Germany.
MAKING CLASSIFICATION MORE USEFUL
Since humans began observing the environment around them, living things have been classified by morphology—observations of physical attributes and behaviors. The complex Mantodea family tree is no different. Since the mid-19th century, it’s been organized around a fundamental assumption: species that display similar characteristics likely evolved from a common ancestor.
But for a small order of insects (there are fewer than 2,500 Mantodea species compared to more than 350,000 of beetles) mantises are extraordinarily diverse. They live all over the globe and come in a wide variety of shapes, colors and sizes. A third of species are strongly sexually dimorphic—meaning there are significant physiological differences between males and females. Some have ears, many don’t. Some fly, while others are earthbound. Some are ambush hunters; others are cryptic—hiding and waiting for food to walk by; still others are generalist feeders, varying their method based on environmental factors. The list of observable variations is long.
To find such diversity among a relatively small number of species makes Mantodea an attractive organism for studying biodiversity and evolution, according to Svenson.
But it also makes morphological classification messy—and to some degree arbitrary. For instance, is a non-flying, bark-mimicking ambush-hunting mantis more like the nonflying, bark-mimicking cryptic feeder? Or is it more like the flying, leaf-mimicking ambush hunter? How can you do advanced evolutionary research if you don’t know how one specimen is related to another?
So Svenson and his team painstakingly collected specimens from around the world and used DNA to map the relationships between Mantodea species. While the old system assigned presumed relationships based on features or morphology, the new system aligns known genetic relationships—allowing discovery of how and when the descriptive characteristics developed. In effect, the scientifically desirable Mantodea order has been opened to meaningful study.
For example, that’s how Svenson can now say with confidence that the ability of certain mantids to blend in with tree bark has developed independently at least six different times.
The National Science Foundation funded the reclassification project with a $603,742 grant, and the Museum built a $150,000
DNA lab to support the effort.
A MODEL SYSTEM
Svenson is by no means alone in using genetics to reclassify animals and organisms. The National Science Foundation spends about $10 million a year to fund projects through its “Advancing Digitization of Biodiversity Collections” program.
“This is basic science—science for the sake of discovery,” Svenson says. “We don’t know how or when any of this will lead to the next great breakthrough. But that’s how science works. Big discoveries don’t happen in a predictable manner; they happen because people are working on basic science and things come together.”
But Svenson’s new classification system is more than good science. It’s good packaging.
In addition to laying out genetic relationships in a standard format, the system provides a library of images and detailed morphological descriptions based on 124 different characteristics. Included is a key that allows accurate identification of a specimen and easy correlation to its place on the phylogenetic tree. The usability of this system may make it a model for other reclassification projects.
COLLABORATION AND TRANSFER OF KNOWLEDGE
The project is also significant in the way it supports professional collaboration and training.
Referring to Frank Wieland, one of the paper’s co-authors, Svenson says, “We’re two of the few people working full-time on mantid evolution and classification. We were competing on the same system.”
When they met at a professional conference several years ago, they warily discussed how much work there was to do, and soon agreed to collaborate rather than compete. The new classification system is a result of that handshake.
In the past few years, more than a dozen researchers have published findings with Svenson as co-author, calling on his expertise in mantis genetics; several other such collaborations are in the works.
Even more meaningful, perhaps, is his work with students—a role he considers as important to science as the research itself.
“You gain a lot of knowledge, but you can’t possibly write enough papers to pass it all down. Part of what you learn is in the process, and people need to be present to experience that. Knowledge can be built and transferred more easily to the next generation if students are involved,” Svenson says.
To his knowledge, the Museum’s DNA lab is the only such facility being used by students to study mantises.
Even though the terms of the NSF grant have been met, Svenson is continuing to collect specimens and expects to reclassify 70 percent of praying mantis species over the next few years.
Ironically, while he is arguably the world’s leading authority in the subject, “my primary interest is not species description or building a database; it’s studying deeper evolutionary questions,” Svenson says. “But I couldn’t begin to answer those questions without a good classification system to work from. It’s a foundation of biological science, and if the system is built wrong, we don’t have any way of understanding or communicating the meaning of what we observe.”
This article was published in Explore Member Magazine, Volume 3, Number 4, Winter 2015/2016