Readers discuss tardigrades, poison dart frogs and more

A taste for toxins

Researchers have identified a protein that may help a poison dart frog collect toxins from food and transport them to the frog’s skin, Erin Garcia de Jesús reported in “How poison dart frogs hoard toxins in their skin” (SN: 2/10/24, p. 4).

Poison dart frogs eat toxic insects. Reader Robert Schier wondered about when frogs eat a nontoxic diet: “Do they not have poisons in their skin?”

In the wild, poison dart frogs chow down on insects that may pick up toxic alkaloid compounds from plants. In captivity, the frogs are fed nontoxic food, and they don’t have poisonous skin, Garcia de Jesús says. Researchers at the Smithsonian’s National Zoo and Conservation Biology Institute are exploring whether adding alkaloids to frog food can make captive frogs destined for reintroduction to the wild “spicy” again — to ensure the frogs return home with their defense mechanism against predators.

Tardigrade survival

Changes to an amino acid trigger hardy tardigrades to go into a state of suspended animation. In this dormant state, the microscopic animals curl up, turn their insides to glass and slow their metabolism to imperceptible levels, allowing them to be nearly invincible when times are tough, Tina Hesman Saey reported in “Here’s the key to tardigrade survival” (SN: 2/10/24, p. 10).

Reader Robert Schier was curious to learn more about this feat of survival. “If some metabolism is continuing, does that mean the animals will eventually starve or that waste products will continue to build up?”

Scientists debate whether tardigrades have metabolism in the dormant state at all. Comparative physiologist Hans Ramløv of Roskilde University in Denmark says tardigrades are essentially dead when their insides dry up and turn to glass. “How can they have metabolism? I mean, there’s no bloody water!” Tardigrades can go dormant when exposed to temperatures as low as absolute zero, where, by definition, there is no metabolism, he says. (At least, no organized metabolism; some random chemical reactions may still occur.) Evidence also suggests that a tardigrade’s biological clock stops during dormancy, an indicator that there’s no metabolism. 

Not every tardigrade can be revived after decades of dormancy. That may be because of extensive damage that the animals can’t repair quickly enough upon reawakening, Ramløv says.

Correlation vs. causation

Teenage brains may be especially susceptible to the harms of THC, the main psychoactive chemical in marijuana, potentially upping the risks of addiction, psychosis, depression and other mental health concerns, Aimee Cunningham reported in “Teen brains and THC don’t mix well” (SN: 2/10/24, p. 8).

Several readers said that the story seemed to imply that marijuana use caused teens’ mental health problems, but most of the evidence presented was correlational.

“The article clearly shows that depressed teens use marijuana more frequently [than nondepressed teens do] but doesn’t give evidence that the marijuana caused the depression,” reader Mark Sneeringer wrote. Reader Anne Barschall made a similar point: “How do we know whether teens who use cannabis are not just a self-selecting group who are already experiencing mental illness symptoms and therefore more likely to be diagnosed later?”

Science News appreciates the feedback and the reminder to be more explicit that an association is a link between two factors and does not mean that one factor caused the other. We recognize that being precise about correlation vs. causation is especially important in stories regarding health.

Correction

“Mapping U.S. earthquake risks” (SN: 3/9/24, p. 32) mistakenly identified southwestern Missouri instead of southeastern Missouri as a ground-shaking hot spot.