American Association for the Advancement of Science - Virginia Morell
Scientists have long worried whether animals can respond to the
planet’s changing climate.
Now, a new study reports that at least one
species of songbird—and likely many more—already knows how to prep its
chicks for a warming world.
They do so by emitting special calls to the
embryos inside their eggs, which can hear and learn external sounds.
This is the first time scientists have found animals using sound to
affect the growth, development, behavior, and reproductive success of
their offspring, and adds to a growing body of research revealing that birds can “doctor” their eggs.
“The study is novel, surprising, and fascinating, and is sure to lead
to much more work on parent-embryo communication,” says Robert Magrath,
a behavioral ecologist at the Australian National University in
Canberra who was not involved in the study.
The idea that the zebra finch (Taeniopygia guttata) parents
were “talking to their eggs” occurred to Mylene Mariette, a behavioral
ecologist at Deakin University in Waurn Ponds, Australia, while
recording the birds’ sounds at an outdoor aviary.
She noticed that
sometimes when a parent was alone, it would make a rapid, high-pitched
series of calls while sitting on the eggs.
Mariette and her co-author,
Katherine Buchanan, recorded the incubation calls of 61 female and 61
male finches inside the aviary.
They found that parents of both sexes
uttered these calls only during the end of the incubation period and
when the maximum daily temperature rose above 26°C (78.8°F).
To find out whether the calls somehow prepared the chicks for higher
temperatures, the scientists artificially incubated 166 eggs at a
standard temperature of 37.7°C (99.9°F).
During the last 5 days of
incubation, they exposed the eggs to either recorded incubation calls or
the parents’ normal contact calls.
When the chicks hatched, those that had listened to the incubation
calls were more vocal than the control nestlings.
What’s more, the
chicks that had been exposed to the incubation calls weighed less than the controls, they report online today in Science.
That could be an advantageous adaptation in a hot environment, the
scientists argue. “With a smaller body size, they’re better at losing
heat,” Mariette says.
She and Buchanan suggest that their lower body
mass might also reduce oxidative damage, the harmful buildup of unstable
molecules in proteins, fats, and DNA that can adversely affect
reproduction.
They clinched their results with data on the success of the chicks:
When kept in hot conditions, the lower weight chicks did indeed go on to
produce more fledglings in their first breeding season than did the
control birds.
But the control birds were more successful in cooler
conditions. And the incubation calls may have other lasting effects.
For
two breeding seasons, the males that heard these sounds preferred
nesting boxes that were hot, whereas the control males chose cooler
homes.
“It’s interesting and surprising that vocal communication at such an
early stage of development could have such persistent effects,” says
Renee Duckworth, an evolutionary ecologist at the University of Arizona
in Tucson.
Incubation calls were first found in superb fairy wrens (Malurus cyaneus),
another Australian songbird in a different family.
Unlike the finches,
the fairy wrens’ calls teach their embryos a special “password” to
elicit food from their parents after hatching.
Mariette and others now
suspect that the calls may be widespread and used in various ways to
program chicks for future challenges.
“This remarkable paper helps us understand how animals could adapt to
changing climate by showing that parental care alters nestling growth,”
says Sonia Kleindorfer, a behavioral ecologist at Flinders University
in Adelaide, Australia, who was not involved in the study. “It also
shows that … embryos can learn much more than we ever imagined.”
But
Kleindorfer, who studies fairy wrens, wonders whether the calls are
really sending a specific signal about the temperature, and are not just
a natural response to the heat.
She also wonders how often finches use
the incubation calls in the wild, because fairy wrens suffer increased
predation when they make these sounds.
Mariette thinks the finches’ ability to prepare their offspring for
their future environment makes sense because they live in arid habitats
and they breed whenever conditions are good—irrespective of the season.
She adds that these finches show that some animals, at least, aren’t
just sitting ducks when it comes to climate change—they may be much
better able to adapt to a warming world than we thought.
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