In 2017, a rosy wolf slug crawled along a sunlit path in Tahiti with an unexpected passenger: a bespoke computer the size of an aphid that was screwed delicately onto its case like a cylinder.
This particular snail species is involved in the extinction of up to 134 snail species worldwide. Humans brought the carnivorous rosy wolf slug to Tahiti decades ago, and the predatory species left few survivors.
But one Tahitian species has managed to survive in dozens of valleys on the island: the tiny yogurt-colored snail Partula hyalina. “They have to be special,” says Cindy Bick, a researcher at the University of Michigan.
Using solar data collected by some of the world’s smallest computers attached to the rose wolf’s shell and the leafy P. hyalina habitat, Dr. Bick and her colleagues now shed light on how P. hyalina’s pale shell enabled the species to circumvent extinction. Their results were published in Communications Biology in June.
In 2012, when Dr. Bick was still a PhD student, she began to investigate the secret of the survival of P. hyalina with Diarmaid Ó Foighil, professor of ecology and evolutionary biology and curator at the university’s Zoological Museum. Together they published a 2014 paper suggesting that the species’ more abundant progeny help it survive better than other species. But even that was not enough to explain the rare success of P. hyalina. “It does more than just survive,” said Dr. Ó Foighil.
Most land snails prefer the shade. The dark-shelled rosy wolf snail, like many other species, would dry out like a jerk if left in the sun. But dr. During his research, Bick read in the field diaries of an early 20th century malacologist that P. hyalina was often found at forest edges where trees thin out in sunlight.
Dr. Bick and Dr. Ó Foighil began to think: If the milky peel of P. hyalina reflects back and can handle more sunlight, sunny forest edges could provide a safe haven without the rose wolf. All they needed was a way to measure how much sunlight each species received each day.
While the two zoologists were thinking about snails on campus, David Blaauw’s engineering laboratory had developed the smallest computer in the world with a battery: a 2 by 5 by 2 millimeter sensor that is slightly larger than an aphid. The sensors receive data with visible light and send it over a radio.
A few years later, Dr. Blaauw made a remarkable request: to attach the tiny computers to carnivorous snails in Tahiti. Dr. Nick’s suggestion seemed perfect – a chance to test the sensors in the real world with staff nearby and help with a project that could advance wildlife conservation.
To prepare the sensors for the snails, Dr. Blaauw’s laboratory added a tiny energy harvester with solar cells so that the sensor could charge its battery in the sun. They encased the system in epoxy to make the sensor waterproof, protect it from strong light, and cushion it from the harsh life of an average snail.
You had a problem. They had to give the tiny computers the power to measure light, but keep the system free of large batteries that would flatten a snail. Inhee Lee, now Assistant Professor of Electrical and Computer Engineering at the University of Pittsburgh and then a researcher in Dr. Blaauw’s lab, helped solve the puzzle. Dr. Lee and Dr. Blaauw just reused the combine and measured the speed of its solar charge as a substitute for sunlight.
Using some invasive snails found in a Michigan garden, the researchers first tried using magnets and Velcro to attach the computers to the shells until they figured out how to glue a metal nut to the surface and screw the sensor into the nut . Then the snails and their tiny passengers were ready to withstand the simulated elements (water buckets).
In August 2017, Dr. Bick and Dr. Lee arrives in Tahiti with 55 sensors. They hopped from valley to valley, led by Trevor Coote, a writer for the newspaper and a specialist in these land snails who was based in Tahiti. (Dr. Coote died of Covid-19 in February 2021.)
Each day, the researchers chased the slugs for hours to make sure they couldn’t escape. Occasionally it rained on them. They didn’t have permission to attach computers to the endangered P. hyalina, so they taped cameras right next to the snails, on the leaves they slept on during the day, and essentially tracked how much sunlight the sessile snails received. But the computer-laden rosy wolf slugs presented a trickier challenge as the mollusks moved slowly but were determined to forage for food (one snail escaped with a sensor for a few days).
The data showed that the sensors in the P. hyalina habitat received an average of 10 times as much sunlight as the rosy wolf slugs. This confirmed the researchers’ hypothesis that the bright conditions protected the pale snails from the rosy predators.
The rosy wolf slug was introduced to the Society Islands in the 1970s to control another invader, the giant African land snail. But the reign of terror of the rosy wolf has caused many tree snail species on the islands to become extinct.
“I grew up in this environment listening to the myths and stories about animals and plants that are either extinct or are on the way to extinction if we don’t act quickly to preserve them,” said Dr. Bick, Pacific Islander. She added that she hoped this research supports efforts to conserve P. hyalina solar refuge habitats in the Society Islands.
“Most of the time we talk about things that are dead and dying,” said Dr. Bick. “This is a story of resilience.”
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