18 | New Scientist | 7 November 2020
CORALS have an evolutionary
superpower. Adult corals can
pass on mutations they have
acquired during their lives to
their offspring, overturning
a long-standing belief that
no animals can hand down such
mutations – although most can’t.
“Juvenile corals inherited
mutations that were acquired
during the parents’ lifespan,”
says Iliana Baums at Pennsylvania
State University. “It has not been
observed before in animals, but
it has been observed in plants.”
Corals belong to one of the
oldest animal groups. They are
similar to plants in many ways,
such as spending most of their
lives fixed in one place, in their
case on reefs, says Baums. One
way that corals and their relatives
differ from mammals or birds is
in their germ line, the cells in their
bodies that form eggs or sperm.
In most animals, including
humans, the germ-line cells are
strictly separated from the rest of
the body. This limits which genetic
mutations can be passed on. For
example, a gene might mutate in
one cell of a person’s body and
change that cell’s behaviour –
perhaps turning it cancerous – but
the mutation won’t be passed to
their children. Only mutations in
germ-line cells can be inherited.
Biologists already knew that
coral germ lines aren’t like this.
Adult corals have groups of
primordial stem cells that can give
rise to both germ-line cells and
body cells. Body cells sometimes
change back into stem cells,
and then into germ-line cells.
This blurs the line between the
germ line and the rest of the body.
Baums and her colleagues
have now found evidence that
mutations that arise during
a coral’s lifespan can enter the
germ line and be passed on.
They studied elkhorn corals(Acropora palmata) from Florida
and Curaçao. These live in colonies
of genetically identical polyps
that divide asexually, allowing
the colony to grow. They also
release sperm and eggs into the
water that were thought to need
to encounter sperm or eggs from
another colony to develop.
The study began with a peculiar
observation: some eggs developed
into larvae without being fertilised.
To confirm this, the team collected
more larvae and compared their
genes with the parent colony.The larvae only contained genes
from the colony, albeit reshuffled.
“There was no input of foreign
sperm,” says Baums. The team still
isn’t quite sure what happened.
However, there was an even
bigger surprise lurking. The team
knew that individual polyps in the
colony weren’t quite genetically
identical. It has been there formany years, and some of the
polyps had acquired mutations
during their lives that weren’t
there in the founding individual.
The analysis revealed that some
of these mutations were present
in the larvae (bioRxiv, doi.org/fgf5).
The finding indicates that corals
can pass on new genetic variants,
and evolve, in a way that no other
animal is known to do so.
“They ran all thinkable
controls, therefore I think
technically it’s absolutely sound,”
says Thorsten Reusch at the
GEOMAR Helmholtz Centre for
Ocean Research Kiel in Germany.
Baums and Reusch both say it is
important not to misinterpret the
finding. One possible misreading
concerns the long-disproved
idea that acquired traits can be
inherited and that this explains
how new species evolve. For
example, the long necks of giraffes
were imagined to have arisen
because early giraffes stretched to
reach tall trees, making their necks
longer, and they passed this to their
offspring. The idea is sometimes
known as Lamarckism, afterbiologist Jean-Baptiste Lamarck.
However, in Lamarckism,
mutations are driven by an
animal’s actions, so the creature
has some control over which
genes it passes on. In reality,
mutations arise randomly and any
that benefit an animal may help it
survive and produce offspring –
and that seems to be just as true of
the corals. “It doesn’t reintroduce
Lamarck,” says Reusch.
But it means corals have a way
of creating genetic diversity even
when reproducing asexually. In
this, they again resemble plants.
Reusch and his colleagues
showed in a recent study that
colonies of seagrass can undergo
a similar process, in which clones
pass on acquired mutations.
Beneficial ones can spread to
dominate entire seagrass colonies.
Baums and her team have yet to
find evidence that any of the coral
mutations are beneficial, but they
plan to investigate this next. ❚“Corals have a way of
creating genetic diversity
even when reproducing
asexually, like plants”AL
EX
MUST
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A diver approaching a
large colony of Elkhorn
coral in the Caribbean SeaBiologyMichael MarshallCorals evolve in an unusual way
These are the first animals seen to pass on mutations found outside sex cells