UC biologists unlock secrets of beetle’s amazing vision

Now researchers at the University of Cincinnati have found that the beetles also need water to develop and maintain their sharp vision. And understanding the foundations of this mechanism could shed light on our own vision deficits.

True to its name, the stunning black and yellow beetles dive below the surface of ponds, carrying a bubble of air under their wings while foraging. Adults lay eggs near water because the larvae are aquatic — and hungry.

“They’re voracious,” said UC doctoral student and lead author Shubham Rathore in UC’s College of Arts and Sciences.

And their favorite prey is aquatic mosquito larvae.

“One little diving beetle must eat 700 mosquito larvae to make it to adulthood,” said senior author Elke Buschbeck, a professor of biological sciences at UC. “They are incredibly efficient predators.”

Their sharp vision allows them to stalk prey hiding in the water. The insects’ eyes have cylindrical tubes with a lens that projects an image onto their retina similar to our own. Like a finely tuned camera, the focal length between the lens and the eye must be precise or the little predator runs the risk of being nearsighted or farsighted.

UC researchers discovered that cellular osmosis — the diffusion of water — helps them achieve this perfect harmony in the rapid growth of their eye tubes shortly after molting.

The study was published in the journal Current Biology.

Osmotic pressure is a passive system that relies on simple physics as water flows from an area of high pressure to one of low. In experiments, researchers found that molting larvae placed in saltwater can’t absorb the water they need for proper eye development. As a result, they become farsighted or hyperopic.

The farsighted beetle larvae are clumsy hunters, taking longer to locate prey. And once they do, they are less likely to go in for the kill than larvae with normal vision, researchers said.

The findings could help us understand how similar developmental processes affect our own vision. Proper eye pressure is also important for our own vision. Myopia, or nearsightedness, is a growing concern around the world, according to the National Institutes of Health.

“It is predicted that by 2050, half of the Earth’s population will be nearsighted,” Buschbeck said.

“Biology is always nature and nurture. There is a genetic component. But there are also pretty substantial environmental components.”

Buschbeck has been studying animal vision for most of her career — even designing a custom ophthalmoscope for the purpose.

“Needing reading glasses makes me understand how important it is to be able to focus your eyes,” she said. “A lot of people can relate.”

Student Rathore, too, said he began to experience visual deficits when he started graduate school.

“As an undergraduate, I spent a lot of time outside hiking. But as a master’s student, I spent a lot more time reading online. And suddenly I needed glasses. It was a very stark change,” he said.

The beetle study was labor intensive. Rathore and classmate and co-author Amartya Mitra had to single out larvae in the aquarium just as they were molting to place them in a harmless saltwater solution. A custom computer program used a camera to detect when the larvae’s skin began to darken, signaling they were about to molt. The early-warning system would send a text alert to researchers, but it wasn’t foolproof. Rathore and Mitra spent countless hours in the lab monitoring the beetles.

“They tended to molt at night, so I ended up sleeping on the couch in the office a lot,” Rathore said.

Next, researchers are hoping to learn more about the genes responsible for regulating the water pressure in the beetles’ eyes.

Mitra said the project has obvious relevance to our own vision deficits. Insect models have helped scientists understand human health in a myriad of ways.

“We’re living in the middle of a nearsightedness epidemic,” Mitra said. “We don’t have concrete answers about why so we cast a wide net across species.”

A similar study published in the journal BMC Genomics also led by Rathore and Bushbeck has begun to unravel the vision genes responsible for regulating the water pressure in the beetles’ eyes.

The research was supported by grants from the National Institutes of Health and the National Science Foundation.

Featured image at top: UC biology Professor Elke Buschbeck studies the vision of insects and spiders in her lab. Photo/Andrew Higley/UC Marketing + Brand