FEEDBACKDECEMBER 19, 2020 & JANUARY 2, 2021Toad talk
Guttural toads on islands in the Indian
Ocean have shrunken limbs and bodies that
may be evidence that “island dwarfi sm”
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 dwarfi sm 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 dwarfi sm route?”
Generally speaking, yes, large
a nimals 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 dwarfi sm or
gigantism may depend on the benefi ts
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 preda-
tors. 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 m ating year-round,
which would defl ate 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
E ngelhaupt wrote in “Superlative science”
(SN: 12/19/20 & 1/2/21, p. 34).
Some readers wondered how the black
hole merger could have occurred17 b illion light-years from Earth if the
Big Bang occurred 13.8 billion years ago.
“Distance is actually quite compli-
cated to defi ne for a universe that is
expanding and in which spacetime is
not static,” says Science News physics
writer Emily Conover. “The gravita-
tional 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 defi ning distance. That’s also
why that distance doesn’t confl ict with
the age of the universe,” she says.Room to improve
A compound in h allucinogenic mushrooms
eased depression symptoms in 13 people
in a small study, but larger studies are
needed, Laura S anders reported in
“P silocybin 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 help-
ful” 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
c ommon among older adults. “I look
forward to larger studies with a truly
broad diversity of participants.”Join the conversation
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