Readers ask about shrinking toads, defining distance in an expanding universe and more


Toad talk

Guttural toads on islands in the Indian Ocean have shrunken limbs and bodies that may be evidence that “island dwarfism” can evolve quickly, Jake Buehler reported in “Toads on two islands are shrinking fast” (SN: 12/19/20 & 1/2/21, p. 13).

“I thought that island dwarfism usually happens to quite large animals … and that small animals … tend to evolve to larger sizes on islands,” reader Tim Cliffe wrote. “If small animals do tend to grow larger, do the authors talk about why these small toads would instead be taking the dwarfism route?”

Generally speaking, yes, large animals become smaller when they colonize islands, and small animals get bigger, Buehler says. “This ‘island rule’ isn’t absolute, and whether or not an animal moves toward dwarfism or gigantism may depend on the benefits normally afforded to them by their body size, and food constraints on the island,” he says. The researchers noted that a relatively large body size may protect guttural toads against predators. On the islands, the toads may have become smaller since there are fewer hungry predators to dissuade, Buehler says.

Or perhaps the island toads have a spread-out mating schedule, which could explain why the amphibians are shrinking. “On the mainland, guttural toads mate once a year, and females that grow to large sizes very quickly produce a lot of eggs,” Buehler says. But the island toads may be mating year-round, which would deflate the importance of getting large and producing a ton of eggs. “Figuring out exactly why island life is making these toads smaller is the next step in this project,” he says.

Defining distance

A collision of two black holes 17 billion light-years from Earth snagged records for the farthest, most energetic and most massive black hole merger, Erika Engelhaupt wrote in “Superlative science” (SN: 12/19/20 & 1/2/21, p. 34).

Some readers wondered how the black hole merger could have occurred 17 billion light-years from Earth if the Big Bang occurred 13.8 billion years ago.

“Distance is actually quite complicated to define for a universe that is expanding and in which spacetime is not static,” says Science News physics writer Emily Conover. “The gravitational waves produced by the merger took 7 billion years to reach us. That’s what’s called ‘lookback time,’ ” she says. “But that’s not the same thing as the distance of the source from us. Because the universe has expanded in the time it took those waves to reach us, the source is indeed 17 billion light-years away, according to one standard method of defining distance. That’s also why that distance doesn’t conflict with the age of the universe,” she says.

Room to improve

A compound in hallucinogenic mushrooms eased depression symptoms in 13 people in a small study, but larger studies are needed, Laura Sanders reported in “Psilocybin may help treat depression” (SN: 12/19/20 & 1/2/21, p. 6).

“The article spoke of concern that most participants were white and that a broader diversity would be more helpful” to determine how effective the compound is, reader Robert Walty wrote. “This is quite true and as a 75-year-old man, I am also concerned about depression in the elderly,” he wrote, noting that depression is common among older adults. “I look forward to larger studies with a truly broad diversity of participants.”

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