By Erin Weeks
In 2000, a government building in Maryland had a bit of a springtail infestation on its grounds.
Whenever it rained during humid months, springtails swarmed the lawn. These damp-loving hexapods in the order Collembola are harmless to humans and are rarely even noticed, despite being one of the most abundant animals found in soil. Nobody might have noticed them at the building in Maryland, either — except that it housed a team of U.S. Department of Agriculture (USDA) scientists, several of whom saw the springtails as an opportunity rather than a problem. Fifteen years later, their curiosity has led to a discovery about what helps put the “spring” in springtails.
Springtails have an unusual appendage that juts out from the bottom of their abdomens — a tube-like structure called the collophore, which has puzzled scientists for centuries. Researchers have suggested it could be involved in the regulation of body fluids, in the mechanics of jumping on liquid surfaces, and for adhesion of some sort.
For many years, entomology textbooks and courses have treated the collophore as a wholly mysterious appendage, said Ron Ochoa, an entomologist with the USDA. Now, he thinks that should change.
Ochoa and several colleagues recently published an article in the Annals of the Entomological Society of America containing high-resolution images that suggest the collophore serves a sticky purpose — and is in fact an organ whose adhesive qualities may help orient springtails as they jump. Somewhat like fleas, springtails hop when disturbed. They use a different mechanism, however, relying on a long, tail-like appendage called the furcula to spring them from a surface. Springtails look erratic when they jump; sometimes they jump forward, and sometimes they perform back flips. Researchers have assumed that these discrepancies were, if anything, based on the length of a springtail’s furcula rather than the animal’s control.
Back in 2000, botanist and co-author Eric Erbe began showing Ochoa images of termites he’d taken through a low temperature scanning electron microscope. Ochoa, a mite expert, was impressed by the incredible detail captured in the images.
“With this technique, you are not on the desk, looking down at [specimens]; now you are with them, walking with them. You can look at them in a completely different way,” said Ochoa. “It is a giant door to start to see the micro world at the same level that humans see regular life.”
“I said, you know, arthropods would be a lot of fun to image,” Ochoa recalled. That’s where the locally sourced springtails came in. The team used liquid nitrogen to freeze hundreds of specimens on copper plates — the springtails were instantaneously frozen this way, captured in their last position like the victims at Pompeii. That meant some springtails were frozen at different stages of jumping. When the researchers compared them, they noticed something curious. In the springtails frozen pre-jump, the collophore remained firmly attached to the surface. But in specimens just a little closer to mid-jump, the collophore was detached, with the organ’s first segment retracted. Exactly how the collophore sticks to a surface remains to be seen — it could secrete a glue, the team suggests, or remain actively extended through a jump.
“What was the only thing touching the ground? I couldn’t believe it — it was just the furcula,” Ochoa said of the mid-jump images. Ochoa and Erbe knew this was significant but felt they lacked the expertise to publish a paper on the findings. So, for over a decade, nothing came of the springtail images.
“Suddenly, the hero showed up,” Ochoa said. Colin Favret, an entomology professor at the University of Montreal, took a look at the images and agreed that they needed to write it up for publication. In their recent Annals of the Entomology Society of America paper, they suggest that the collophore may serve to direct the springtail’s jumps and flips. Ochoa said he likens the process to someone on a bike applying their front brakes too hard, causing them to flip forward.
“The front tire brake is the collophore, and the furcula is the back tire,” he said. By coordinating the two appendages, springtails might have a little more control over their erratic springing. To conclusively confirm their findings, the authors suggest the use of high-speed, macro videography to look, in real time, at the frozen movements captured in their still photos. But Ochoa is already convinced of what such work would find.
“We need to stop saying that the collophore is a mystery organ,” Ochoa said. “Here, it is very clear what it does.”
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