Like Humans, Grasshoppers Grapple With Gravity’s Effects on Blood Pressure

When push comes to shove, we humans are just giant sacks of fluid. Weighed down by gravity, our internal liquids would simply slosh and pool in the parts of our anatomy closest to the ground, if not for the wonders of the circulatory system: an intricate network of vessels, wreathing a central, pumping heart that’s always around to balance the blood back out.

But grappling with gravity isn’t just a conundrum for us hefty mammals. Teeny, lithe insects with vastly different body plans must cope with these forces as well—and now, researchers are finally starting to understand how.

Reporting this week in the journal Proceedings of the National Academy of Sciences, a team of insect physiologists at Arizona State University has found that grasshoppers, too, use their bodies to fight the perils of gravity. That’s especially surprising because, unlike us, their lymph—basically, invertebrate blood—isn’t held in vessels that can contract and expand to regulate flow. Instead, grasshoppers appear to use an insect-specific combination of tricks to redistribute the liquid in their bodies.

“This study shows that grasshoppers have amazing control of their body pressure at different orientations,” David Hu, who studies the intersection of physics and biology in animals at Georgia Tech, but wasn’t involved in the study, tells James Gorman at the New York Times.

A team led by Jon Harrison first stumbled upon their discovery while examining grasshoppers in the linear accelerator at the Argonne National Laboratory in Illinois, a device that uses synchrotron X-rays to generate precise, high-quality images and video of its contents. While studying the insects' air sacs—which store, pump and exchange air like lungs—the researchers noticed that the structures ballooned or constricted in different patterns depending on what positions their owners took.

When the grasshoppers stood upright, less lymph made it into their heads, where the sacs filled with air, while gobs of fluid flooded shrunken air sacs in their abdomens. Just the opposite occurred when the bugs were flipped upside down: Fluid filled their noggins, while their abdomens puffed with air. The effect, the team realized, was similar to what went on in humans, with gravity tugging liquid down into the body’s lowest points.

But the lymph never completely drained from the most elevated regions of the grasshoppers’ bodies, hinting that they, too, were counteracting gravity’s effects.

“This is a dramatic example showing how similar animals are physiologically, despite how different they may appear,” Harrison says in a statement.

What’s behind the grasshopper’s weighty trick isn’t entirely clear, but at least three factors are likely at play. Two are heart rate and breathing rate, both of which can increase or decrease to change the amount of lymph and oxygen, respectively, getting to cells. The other is a valve system—that is, an anatomical flap somewhere in the body that, when shut, can keep lymph from flowing willy-nilly. (Notably, vertebrate versions of all these strategies exist in us, too. For example, when people do headstands, their heart rates slow to keep too much blood from building up in their brains.) The insects did, however, have to be conscious to keep the lymph moving. When the grasshoppers were anesthetized, gravity began to win out again.

As Harrison explains in the statement, there’s probably more going on in grasshoppers that “we don’t know about,” though he and his team are investigating further.

Katherine J. Wu | | READ MORE

Katherine J. Wu is a Boston-based science journalist and Story Collider senior producer whose work has appeared in National Geographic, Undark magazine, Popular Science and more. She holds a Ph.D. in Microbiology and Immunobiology from Harvard University, and was Smithsonian magazine's 2018 AAAS Mass Media Fellow.