Pigmy sloths on dope

Panama: An entire species of three-toed sloths may spend its life high on a valium-like drug, researchers think.

Pigmy three-toed sloths, Bradypus variegatus, are the smallest of the six sloth species and likely evolved their dwarfism after they became marooned on their island home, Escudo, off the coast of Panama, nearly 9000 years ago. It seems they also developed a drug addiction, which until now had not been suspected in these extremely slow-moving mammals.

“It’s really quite wacky out there,” says Bryson Voirin, who studied the island’s sloths.

Bryson and his team at the Smithsonian Tropical Research Institute in Panama discovered the drug habit by accident while carrying out some rather cool brain wave studies comparing sleep patterns in the island sloths compared to mainland sloths. The scientists stuck small EEG devices on the heads of sloths – a non-invasive process that takes less than an hour before the animals are returned to their tree – to record their brains’ electrical activity.

Sloths slept for 9.6 hours a night, wherever they lived, and had very similar REM (active, dreaming) stages of sleep patterns. But when the researchers looked at the SWA (slow wave activity) sleep stage, which is described as the ‘quality sleep’, they found stark differences in the wave patterns.

“All mainland sloths had similar SWA patterns, but the pigmy sloths showed a big peak, corresponding to a lack of quality sleep,” Bryson says. Puzzled, Bryson showed his pigmy sloth sleep graph to sleep expert Niels Rattenborg, also at STRI. “Niels said it looked very much like the sleep pattern of a person addicted t0 Valium,” he says.

At first, the team ruled this out, although, “they are definitely the most laid-back of sloths, with a very gentle and calm behaviour,” Bryson says. But failing to come up with any other explanation, they decided to investigate the drug theory.

Unlike mainland sloths, which browse a range of more than 20 tree varieties, pigmy sloths live exclusively on red mangrove leaves. In fact, if the researchers put one of these sloths onto any other tree, they soon made a beeline for the red mangroves. Now, it seems they may be getting some prescription-only sedatives in their salad.

Bryson is testing his hunch that a fungus living on the mangroves may be drugging the dopey creatures. He is testing mangrove leaves and looking at the sloth poo and urine to see if he can find signs of the drug or its metabolites.

“It would certainly explain why they don’t leave the mangroves,” he says.

The little creature is only around 50cm high and is critically endangered because the remaining 300 individuals are easy prey for poachers and people who visit the island and chop down the mangroves.