Contact: dkenney@mbl.edu; 508-685-3525

WOODS HOLE, Mass. – It sounds like a “Just So Story” – “How the Insect Got its Wings” – but it’s really a mystery that has puzzled biologists for over a century. Intriguing and competing theories of insect wing evolution have emerged in recent years, but none were entirely satisfactory. Finally, a team from the Marine Biological Laboratory (MBL), Woods Hole, has settled the controversy, using clues from long-ago scientific papers as well as state-of-the-art genomic approaches. The study, conducted by MBL Research Associate Heather Bruce and MBL Director Nipam Patel, is published this week in Nature Ecology & Evolution.

Insect wings, the team confirmed, evolved from an outgrowth or “lobe” on the legs of an ancestral crustacean (yes, crustacean). After this marine animal had transitioned to land-dwelling about 300 million years ago, the leg segments closest to its body became incorporated into the body wall during embryonic development, perhaps to better support its weight on land. “The leg lobes then moved up onto the insect’s back, and those later formed the wings,” says Bruce.
 

Injection of CRISPR solution into crustacean embryos (Parhyale hawaiensis). Credit: Heather Bruce

Heather Bruce dissecting crustacean embryos, wearing an arthropod shirt of her own design. Credit: Eric Chen

 
One of the reasons it took a century to figure this out, Bruce says, is that it wasn’t appreciated until about 2010 that insects are most closely related to crustaceans within the arthropod phylum, as revealed by genetic similarities.

“Prior to that, based on morphology, everyone had classified insects in the myriapod group, along with the millipedes and centipedes,” Bruce says. “And if you look in myriapods for where insect wings came from, you won’t find anything,” she says. “So insect wings came to be thought of as ‘novel’ structures that sprang up in insects and had no corresponding structure in the ancestor -- because researchers were looking in the wrong place for the insect ancestor.”

“People get very excited by the idea that something like insect wings may have been a novel innovation of evolution,” Patel says. “But one of the stories that is emerging from genomic comparisons is that nothing is brand new; everything came from somewhere. And you can, in fact, figure out from where.”
 

Insects incorporated two ancestral crustacean leg segments (labeled 7 in red and 8 in pink) into the body wall. The lobe on leg segment 8 later formed the wing in insects, while this corresponding structure in crustaceans forms the tergal plate. Credit: Heather Bruce

 
Bruce picked up the scent of her now-reported discovery while comparing the genetic instructions for the segmented legs of a crustacean, the tiny beach-hopper Parhyale, and the segmented legs of insects, including the fruit fly Drosophila and the beetle Tribolium. Using CRISPR-Cas9 gene editing, she systematically disabled five shared leg-patterning genes in Parhyale and in insects, and found those genes corresponded to the six leg segments that are farthest from the body wall. Parhyale, though, has an additional, seventh leg segment next to its body wall. Where did that segment go, she wondered? “And so I started digging in the literature, and I found this really old idea that had been proposed in 1893, that insects had incorporated their proximal [closest to body] leg region into the body wall,” she says.

“But I still didn’t have the wing part of the story,” she says. “So I kept reading and reading, and I came across this 1980s theory that not only did insects incorporate their proximal leg region into the body wall, but the little lobes on the leg later moved up onto the back and formed the wings. I thought, wow, my genomic and embryonic data supports these old theories.”

It would have been impossible to resolve this longstanding riddle without the tools now available to probe the genomes of a myriad of organisms, including Parhyale, which the Patel lab has developed as the most genetically tractable research organism among the crustaceans.

 

Parhyale hawaiensis, shown here eating, has had its genome sequenced and is the most genetically tractable crustacean for biological research.
Credit: Heather Bruce

 

Citation: Heather S. Bruce and Nipam H. Patel (2020) Knockout of crustacean leg patterning genes suggests that insect wings and body wall evolved from ancient leg segments. Nature Ecol. Evol., DOI: 10.1038/s41559-020-01349-0

Homepage photo: An azure hawker dragonflly alights. Credit: Wikimedia

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The Marine Biological Laboratory (MBL) is dedicated to scientific discovery exploring fundamental biology, understanding marine biodiversity and the environment, and informing the human condition through research and education. Founded in Woods Hole, Massachusetts in 1888, the MBL is a private, nonprofit institution and an affiliate of the University of Chicago.

Contact: dkenney@mbl.edu; 508-685-3525

An octopus (O. bimaculoides) extends an arm to explore its environment. Credit: Michael LaBarbera

Amazingly, all eight arms could perform all four types of deformation (bend, twist, elongate, shorten) throughout their length. Moreover, each type of movement could be deployed in multiple orientations (e.g. left, right, up, down, 360º, etc.). Especially noteworthy was the clockwise and counterclockwise twisting that could occur throughout each arm during bending, shortening or elongating. This twisty strong arm is exceptionally flexible by any standard.

“Even our research team, which is very familiar with octopuses, was surprised by the extreme versatility of each of the eight arms as we analyzed the videos frame-by-frame,” said co-author and MBL Senior Scientist Roger Hanlon.  “These detailed analyses can help guide the next step of determining neural control and coordination of octopus arms, and may uncover design principles that can inspire the creation of next-generation soft robots.”

Engineers have long wished to design “soft robotic arms” with greater agility, strength and sensing capability. Currently, most robotic arms require hard materials and joints of many configurations, all of which have limitations. The octopus presents a novel model for future robotic designs. Octopus arms are similar in function to the human tongue and the elephant trunk; they are muscular hydrostats that use incompressible muscle in different arrangements to produce movement. The current study provides a basis for investigating motor control of the entire octopus arm. Soft, ultra-flexible robotic arms could enable many new applications, e.g., inspecting unstructured and cluttered environments such as collapsed buildings, or gentler medical inspection of alimentary or respiratory pathways.

Examples of arm deformation types in an octopus (O. bimaculoides). Credit: Roger Hanlon Laboratory/Marine Biological Laboratory

 
Citation: E.B. Lane Kennedy, Kendra C. Buresch, Preethi Boinapally, and Roger T. Hanlon (2020) Octopus Arms Exhibit Exceptional Flexibility. Scientific Reports, DOI: 10.1038/s41598-020-77873-7

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The Marine Biological Laboratory (MBL) is dedicated to scientific discovery – exploring fundamental biology, understanding marine biodiversity and the environment, and informing the human condition through research and education. Founded in Woods Hole, Massachusetts in 1888, the MBL is a private, nonprofit institution and an affiliate of the University of Chicago.

Ctenophore Pleurobrachia with ctenes (along left side of body) at different stages of their power stroke.

The study, published in Scientific Reports, found that small marine animals with multiple propulsers—including larval crabs, polychaete worms, and some types of jellyfish—don’t push themselves forward when they move their appendages, but instead create negative pressure behind them that pulls them through the water.

When the front appendage moves, it creates a pocket of low pressure behind it that may reduce the energy required by the next limb to move. “It is similar to how cyclists use draft to reduce wind drag and to help pull the group along,” says lead author Sean Colin of Roger Williams University, a Whitman Center Scientist at the MBL.

This publication builds on the team’s previous work, also conducted at the MBL, on suction thrust in lampreys and jellyfish. For the current study, they focused on small marine animals that use metachronal kinematics also known as “metachronal swimming,” a locomotion technique commonly used by animals with multiple pairs of legs in which appendages stroke in sequence, rather than synchronously.

“We came into this study looking for the benefits of metachronal swimming, but we realized the flow around the limbs looks very similar to the flow around a jellyfish or a fish fin,” said Colin. “Not only does the flow look the same, but the negative pressure is the same.”

For this study, the researchers worked with two crab species, a polychaete worm, and four species of comb jellies. All are smaller than a few millimeters in length. They found that the fluid flow created while swimming was the same as in the larger animals they had previously studied.

“Even at these really small scales, these animals rely on negative pressure to pull themselves forward through the water,” said Colin, who added that this could be a common phenomenon among animals.

“It’s not unique to the fish or the jellyfish we looked at. It’s probably much more widespread in the animal kingdom,” says Colin, who added that something like suction thrust has been observed in birds and bats moving themselves through the air. These creatures have the same degree of bend in their limbs (25-30 degrees) that the observed marine animals do.

Video by Emily Greenhalgh, MBL

 
Moving forward, Colin and colleagues want to study a larger variety of marine organisms to determine the range of animal sizes that rely on suction thrust to propel through the water.

“That’s one of our main goals -- to get bigger, get smaller, and get a better survey of what animals are really relying on this suction thrust,” Colin says.

Colin’s MBL Whitman Center collaborators on this study include John Costello of Providence College and John O. Dabiri of California Institute of Technology. Previous research on lampreys was conducted in collaboration with MBL Senior Scientist Jennifer Morgan.

Citation: Colin, S.P., Costello, J.H., Sutherland, K.R., Gemmel, B.J., Dabiri, J.O. and Du Clos, K.T. (2020) The role of suction thrust in the metachronal paddles of swimming invertebrates. Scientific Reports, DOI: 10.1038/s41598-020-74745-y
 

Polychaete worm, Tomopteris, with setae moving on each side of the body in metachronal waves

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The Marine Biological Laboratory (MBL) is dedicated to scientific discovery – exploring fundamental biology, understanding marine biodiversity and the environment, and informing the human condition through research and education. Founded in Woods Hole, Massachusetts in 1888, the MBL is a private, nonprofit institution and an affiliate of the University of Chicago.

If you’ve ever stayed in the MBL’s Swope Center, you may not recognize the accommodations that greeted 12 University of Chicago students who arrived last month for the first-ever “Autumn Quarter at MBL.”

Each undergraduate’s home for eight weeks is a relatively luxurious, social-distancing spread: a double room with a single bed and a desk set, comfy armchair, refrigerator and microwave, and private bathroom. The students went into quarantine pending results of their first COVID-19 test, during which time customized meals were delivered to their rooms. And along with a bag of MBL swag, the students enrolled in “Imaging for Biological Research” found an interesting box on their Swope room desks: a kit with the parts to build a simple microscope, and two prepared samples for imaging.

“We had our first lab in our rooms, while we were in quarantine. It was great, though it was difficult to build the microscope over Zoom. A lot of times one of us would say, ‘Wait, wait! I put the wrong lens on!’” says Miranda McKibbin, a UChicago biology major. “It was a little sad because we couldn’t go outside and get samples of organisms to look at. But then a few days later, we could!”

Sorting through sea urchins and other marine organisms brought up by Gemma’s trawl. L-R, MBL Collector Bill Grossman and UChicago Autumn Quarter students Hannah Holmes and Kimberly ‘Charlie’ Wang. Credit: David Mark Welch

Bringing the first student group back to the MBL since March, when COVID-19 emptied the campus, took an enormous, all-hands effort to comply with a new normal. “We had to rethink all of our processes, from A to Z,” says Kerri Mills, MBL’s housing and conferences manager. Every MBL department, from Facilities to Human Resources, was deeply involved. But it was a joy to pitch in, by all accounts.

“We missed having students here!” says MBL Director of Education Linda Hyman. “Holding this course was a way to help out the University of Chicago, which had to prioritize in-person classes for new students. It was also a proof-of-concept for MBL to hold a small course while respecting public health standards. The proof in the pudding will be next year, when we scale up to many more students. But this was also an opportunity to get students back on campus, which we frankly couldn’t wait to do! Hands-on research courses are what we do best.”

“I think we’re ready for anything, now that we’ve been through this process,” says Ann Egan, MBL’s director of human resources. “The whole campus was involved, and the students are thrilled to be here. It’s been an amazing experience.”

Teaching in Quarter Time

The “Autumn Quarter at MBL” is a mix of new and returning courses, but none are business as usual at MBL. Pandemic aside, the students are juggling not only one or two lab courses in Woods Hole, but also online UChicago courses, tutoring gigs, remote jobs and internships. (One student, Aster Taylor, is doing quantitative image analysis for MBL Senior Scientist Roger Hanlon, a continuation of their Metcalf fellowship last summer.)

To accommodate the students’ packed schedules, the faculty had to move away from the familiar MBL course structure of daily, intensive training. While spread over more weeks, though, the course immersion remains: Students attend lectures but spend most of the time in the field and lab, learning how to use high-end equipment and conduct real-world research.

Autumn Quarter student Miranda McKibbin and MBL faculty member Elena L. Peredo holding cultures of desert-adapted green microalgae in the “Microbiomes Across Environments” course. Credit: Daniel Cojanu

On a recent afternoon in the “Microbiomes Across Environments” course, taught by MBL faculty David Mark Welch and Elena Peredo, nine students are buzzily engaged in lab activities, conversing through face masks and across 6-foot distances. They had been out on the MBL’s research vessel, the Gemma, where they collected sea urchins, starfish, and horseshoe crabs. Back in the lab, they used swabs to sample the microbiome from several organs of the animals, and talked about the research questions they might ask. Is the microbiome different between a male and female crab, and how? How do the mouth and anus microbiomes differ? How does the microbiome change after the animal has been in the lab for several days? “We are teaching them how microbial ecologists ask questions,” says Mark Welch.

“I was really excited about the field component of this course,” says Megan Garvery, a biology and visual arts major, “especially now when everything is online.” Miranda McKibbin agrees. “Interacting with the animals, doing the DNA swabs, was really unique. At another school, you might just get little tubes of samples. Here, you are a part of where the organisms actually came from.”

Today the students are purifying and amplifying short pieces of DNA from the microbial samples. These pieces will be sequenced in the MBL’s Bay Paul Center, and the students will get back computer files containing tens of thousands of unprocessed DNA sequences. They will then use bioinformatics to analyze the data, so they can answer the comparative questions they’ve chosen. After returning to Chicago for the Thanksgiving break, they will present their results in an online symposium.

“There’s been a real sea change in our understanding of what it means to be an organism,” Mark Welch says. “The microbiome is a critical part of an organism’s health and behavior, the way it develops, whether or not it can regenerate. All of the students, no matter what their major, will leave with that appreciation for the complexity of organisms.”

A Lot to See

Student Jonathan Tang prepares to insert a slide in the confocal microscope in the “Imaging for Biological Research” course. Credit: Daniel Cojanu

“Imaging for Biological Research” is a new course developed by MBL Director Nipam Patel and co-taught by Louis Kerr and Carsten Wolff of the MBL’s Central Microscopy Facility. Students learn the fundamentals of imaging, then quickly advance to using state-of-the-art microscopes to address biological questions.

Indeed, a few weeks into the course, students can sit comfortably at the controls of a $500,000 confocal microscope in Loeb Laboratory.

“We don’t usually get to use microscopes like this! Dissection microscopes are what you normally find in a lab,” says Jonathan Tang, a biology major, as he works intently to image a glowing fruit-fly embryo.

The four students are learning the careful work of identifying an embryo at a certain stage of development, mounting and orienting it correctly on a slide, and obtaining high-quality, beautiful images using the confocal. As Patel explains, each student is responsible for imaging two of the eight genes called Hox that are expressed along the head-tail axis of the embryo. “These genes have been known for a long time, but they are ideal for teaching students the fundamentals of developmental biology,” he says.

This composite by the Imaging course students shows the expression of 8 Hox genes in Drosophila embryos. Credit: Miranda McKibbin, Michelangelo Neff, Jonathan Tang, and Aster Taylor.

MBL Director Nipam Patel assisting student Michelangelo Neff in the Imaging course. Credit: Daniel Cojanu

 
Soon, they will move to imaging other organisms, including zebrafish, butterflies, crustaceans, and skates. And in the last three weeks, they will each have an independent project, guided by one of the faculty.

One student will work with Gayani Senevirathne, a postdoctoral course assistant from the University Chicago, to image the Hox genes in zebrafish. Kerr will help a student image butterfly wing scales using electron microscopy. Wolff and a student will look at live cell movements in early crustacean embryos.

And Patel will help the fourth student image all eight Hox genes in a single embryo, which has not been published before.

“It will be really fun to see, and it will also make a great textbook figure,” says Patel, who plans to submit it to a journal. “More importantly, it teaches the students all the methods they need to get a figure like that.”

Live from Woods Hole

The third course in the MBL Autumn Quarter bundle is “Neurons and Glia: A Cellular and Molecular Perspective,” taught by UChicago faculty Bill Green and Robert Carillo. While it is fully online with no lab at present, some of the participants, including Green, are in Woods Hole.

“We added it to the Autumn Quarter to get the ball rolling,” Green says, who hopes to expand MBL-based neuroscience offerings to UChicago students in the coming years. This year, MBL Senior Scientists Joshua Rosenthal and Jennifer Morgan gave special lectures in the course.

Miranda McKibbin uses a DNA purifier donated to the MBL by Promega Corp. Credit: Daniel Cojanu

Marine organisms collected on the Gemma for the Microbiomes course. Credit: David Mark Welch

Most of the Autumn Quarter students agree that, pandemic or not, Woods Hole is a very nice place to be. “It’s also been awesome to have so many cool researchers around and available to learn from, whether through Zoom guest lectures in class or from other online events. I can’t even imagine what the MBL must be like when there isn’t a pandemic,” says Kimberly “Charlie” Wang, a UChicago biology major. And while the students are busy academically, they have time to stay physically active on bikes provided by the MBL and enjoy a beautiful fall season in Woods Hole.

“Being here has given us a chance to meet new people, have places to explore and do so safely, because there is a nice, small group,” says Megan Garvey. “And we’re not just sitting at home on Zoom!”

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The Marine Biological Laboratory (MBL) is dedicated to scientific discovery – exploring fundamental biology, understanding marine biodiversity and the environment, and informing the human condition through research and education. Founded in Woods Hole, Massachusetts in 1888, the MBL is a private, nonprofit institution and an affiliate of the University of Chicago.

Contact: Diana Kenney
508-289-7139; dkenney@mbl.edu

Biomedical Fellow Olivia Willis of Australian Broadcasting Corp. training in microscopy and imaging. Credit: Maryn McKenna

 

Environmental Fellows Sarah Kaplan of The Washington Post and María Mónica Monsalve of El Espectador field sampling in Woods Hole. Credit: Craig LeMoult

 

The Fellows take a break from research to visit the Cape Cod National Seashore. Credit: Diana Kenney

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The Marine Biological Laboratory (MBL) is dedicated to scientific discovery – exploring fundamental biology, understanding marine biodiversity and the environment, and informing the human condition through research and education. Founded in Woods Hole, Massachusetts in 1888, the MBL is a private, nonprofit institution and an affiliate of the University of Chicago.

The Logan Science Journalism Program is sponsored by: George & Helen H.B. Logan; Friends and Alumni of the Science Journalism Program; Golden Family Foundation; Howard Hughes Medical Institute; Irving Weinstein Foundation, Inc.; Ross Foundation; and the Byron H. Waksman Fund for Excellence in Science Communication.