Tadpoles screaming underwater show unsuspected sentience
From ANIMAL PEOPLE, May 2010:
BUENOS AIRES–The ethical significance of the discovery that
tadpoles scream when threatened may take some time to occur to
scientists, ethicists, and animal advocates. A breakthrough in
scientific recognition of animal sentience, the finding took more
than three years just to win widespread notice after formal
publication in a leading journal.
Tadpoles might have been audibly screaming when threatened
for more than 200 million years before Guillermo Natale, Ph.D. of
the National University of La Plata in Buenos Aires, Argentina heard
the multi-note metallic sound emitted by tadpoles of the horned frog
Natale published a brief article about it in 2007 in Acta
Zoologica, produced since 1920 by the Royal Danish Academy of
Sciences & Letters. Then three years passed before Matt Walker,
editor of the BBC publication Earth News, noticed Natale’s article
and shared the news of the screaming tadpoles with the world on April
13, 2010. Within a month Walker’s write-up was amplified by more
than 6,200 other broadcast, print, and web media.
Yet few if any of tens of thousands of online commentators
appeared to consider the ethical implications of a finding mostly
reported as news of the weird.
“The discovery could have far-reaching implications for our
understanding of the behaviour and ecology of amphibians,” wrote
Walker. But that was as far as discussion of the meaning of Natale’s
finding appeared to go.
“That tadpoles communicate somehow is simply amazing,” said
Natale. “They possess the structures to do so within three days of
life,” Natale told Walker.
“It is the first time any vertebrate larva has been found to
use sound to communicate underwater,” Walker wrote. “The discovery
that frog tadpoles can make sounds raises the possibility that a host
of aquatic larvae communicate in a similar way.”
The finding demonstrates sentience in vertebrates at an
earlier stage than has ever before been scientifically established.
The tadpole scream is usually not a response to a direct physical
stimulus, Natale found. Most often it is anticipatory, meaning
that the tadpole must recognize a threat and perceive an advantage in
communicating, rather than just trying to escape, evade notice, or
The discovery of the tadpole scream may challenge the idea,
sometimes advanced as part of a “reduction, refinement,
replacement” strategy, that animal experiments might be made less
inhumane by using animals at earlier stages of development.
“We have definitely underestimated their abilities,” said Natale.
Natale was originally studying the mating calls of adult
Ceratophrys ornata. Native to Argentina, Uruguay, and Brazil,
Ceratophrys ornata are sometimes sold in pet shops as the so-called
Ceratophrys ornata “is now endangered as it gains popularity
among pet owners,” according to University of Ottawa biologist Vance
Trudeau. Seeking a way to breed Ceratophrys ornata in captivity,
Natale netted a Ceratophrys ornata tadpole and “heard a brief,
clear, very audible metallic sound,” he told the BBC.
Successful captive breeding enabled Natale to study
Ceratophrys ornata in his lab. Natale discovered that Ceratophrys
ornata tadpoles are “naturally aggressive and carnivorous, often
eating the tadpoles of other frog species,” Walker recounted.
Yet, “Much to our astonishment, they do not eat each other,”
“Producing distress calls is likely to help prevent the
tadpoles from cannibalising each other,” summarized Walker. “They
continue to emit distress calls underwater both as tadpoles and after
they have begun metamorphosis, when they become froglets. The
tadpoles also produce the sounds when removed from the water.”
Some insect larvae are known to communicate with sounds, but
many insects spend most of their lives in a larval stage.
Vertebrates by contrast tend to evolve rapidly out of the larval
stage, undergoing most of their development later.