By Michael
Irving
March 08, 2021
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The head and
body of a sacoglossan sea slug, one day after they separated. We hear it was an
amicable split photo credit: Sayaka Mitoh
VIEW 2 IMAGES
It’s not hard to see the value in
the ability to quickly drop your tail to evade a predator, or just ditch an
injured limb and grow a new one. Worms, newts, lizards,
and axolotls have
already figured this out, and even animals as large as alligators have
recently been found to have regenerative superpowers.
But it seems they have nothing on
the humble sea slug. In a new study, researchers from Nara Women’s University in
Japan discovered that two species of sacoglossan sea slug can casually drop
their heads and then regenerate their entire body from it – complete with a new
heart and other vital organs.
The incredible discovery caught
the researchers by surprise. They were raising the slugs in the lab to study
their biology, when they one day spotted the strange sight of a disembodied head
crawling around on its own. It seemed to be the result of autotomy – the process
of dropping a body part on command – although normally the discarded bit withers
and dies.
"We were surprised to see the
head moving just after autotomy," says Sayaka Mitoh, lead author of the study.
"We thought that it would die soon without a heart and other important organs,
but we were surprised again to find that it regenerated the whole body.”
The disembodied head of a
sacoglossan sea slug, crawling around on its own immediately after leaving its
body behind Sayaka Mitoh
The team turned their focus to
studying this bizarre behavior. They found that both the head and body moved
around independently after being separated, and within a few days the wound at
the back of the head closed up, as the head continued to feed on algae. Within a
week, the head regenerated a new heart, and it took about three weeks for the
slugs to grow their whole new body.
The headless bodies didn’t grow a
new head, but they did still move around and respond to touch for up to a few
months. Age appeared to be a factor in how well the process worked – younger
slugs could lose their heads just fine, but when older animals tried, the head
didn’t feed and died in 10 days or so.
There are still plenty of
unanswered questions surrounding the discovery. The researchers aren’t sure how
the slugs pull it off (literally and figuratively), but they suspect they are
packing stem cells or something similar in their necks.
They’re also unsure how the heads
can survive so long, but they have a fascinating hypothesis. It’s tied to
another unique ability the slugs have – they can actually fuel themselves
through photosynthesis like plants, by incorporating chloroplasts from the algae
they eat. This, the team says, could keep the head alive long enough to grow a
new body.
There’s also the important
question of why they do this in the first place, and what cues might trigger the
process. The researchers plan to investigate these areas in continued study of
the slugs.
The research was published in the
journal Current
Biology.
Source: Nara
Women’s University via Scimex