Extinction mystery solved by computers mounted on critters

This particular species of snail is implicated in the extinctions of as many as 134 snail species worldwide. People introduced the carnivorous rosy wolf snail to Tahiti decades ago, and the predatory species left few survivors. But one Tahitian species managed to survive in dozens of valleys on the island: the tiny yogurt-coloured snail Partula hyalina.

“There must be something special about them,” said Cindy Bick, a researcher at the University of Michigan. Now, with solar data collected from some of the world’s tiniest computers attached to the shell of the rosy wolf and the leafy habitat of P. hyalina, Dr. Bick and her colleagues have illuminated how P. hyalina’s pale shell enabled the species to skirt extinction.

Their results were published in June in Communications Biology. In 2012, when Dr. Bick was still a graduate student, she began investigating the mystery of P. hyalina’s survival along with Diarmaid O Foighil, a professor of ecology and evolutionary biology and curator at the university’s Museum of Zoology. Together, they published a 2014 paper suggesting the species’ more bountiful clutch of offspring helped it survive better than other species. But even this was not enough to explain P. hyalina’s rare success.

“It’s doing more than surviving,” Dr. O Foighil said. Most land snails prefer the shade. The darkshelled rosy wolf snail, like many species, would dry out like jerky if left in the sun. But Dr. Bick read while doing research in the field journals of an early 20th-century malacologist that P. hyalina were often found on forest edges, where trees thin out in sunlight. Dr. Bick and Dr. O Foighil started thinking: If P. hyalina’s milky shell can reflect back and tolerate more sunlight, sunny forest fringes might offer a safe haven free from the rosy wolf.

They just needed a way to measure how much sunlight each species received each day. As the two zoologists were pondering snails, across campus, David Blaauw’s engineering lab had created the world’s smallest computer that has a battery: a 2-by-5-by-2 mm sensor slightly bigger than an aphid. The sensors receive data with visible light and transmit it through a radio.

Several years later, Dr. Blaauw’s team received a request that stood out: to attach the tiny computers to carnivorous snails in Tahiti. Dr. Bick’s proposal seemed perfect — a chance to test the sensors in the real world with collaborators close by and assist in a project that could advance wildlife conservation. The data revealed the sensors on P. hyalina’s habitat received, on average, 10 times as much sunlight as the rosy wolf snails did.

That confirmed the researchers’ hypothesis that the bright conditions protected the pale snails from the rosy predators. The rosy wolf snail was introduced to the Society Islands in the 1970s with the goal of controlling another invader, the giant African land snail. But the rosy wolf’s reign of terror drove many species of tree snails in the islands to extinction.

“I grew up around these environments and listened to the myths and stories featuring animals and plants that have now either gone extinct or are on the way to extinction if we do not act fast to conserve them,” said Dr. Bick, who is Pacific Islander. She added that she hoped this research supported efforts to maintain P. hyalina’s solar refuge habitats in the Society Islands. “Most of the time, we talk about things that are dead and dying,” Dr. Bick said. “This is a story of resiliency.”