How the pufferfish got its beak

May 07, 2012
A male pufferfish guards his eggs. The 'beak' of pufferfishes is a unique dental structure and Natural History Museum scientists have helped uncover how it is formed.

The origin of the unusual beak of pufferfishes has been discovered, giving new clues about how such unique structures can evolve, scientists report today.

Pufferfishes belong to a group that includes the triggerfishes, boxfishes and ocean sunfishes. They have some of the most unusual you're ever likely to see underwater.

Perhaps the most bizarre, however, is the 'beak' of pufferfishes. It's made of beak-shaped toothplates and it uses them to crush and slice

But exactly how is it formed? Scientists have found the answers.

A team led by Gareth Fraser of the University of Sheffield, including Natural History Museum scientists Ralf Britz, Zerina Johanson and Andie Hall, and Moya Smith of London’s King’s College, report their findings in the journal Proceedings of the National Academy of Sciences (PNAS).

Pufferfish larvae have normal conical teeth.

The team investigated how the teeth develop and the genes responsible.

They studied pufferfish young, or larvae, which begin life with normal conical teeth, taking hundreds of snapshots of the fishes developing. They identified the different stages of tooth development, staining tooth structures red so that they could easily see the changes. 

They found that the beak is formed by a strange modification of just the 4 front teeth. 

How the pufferfish got its beak
Pufferfish skull showing the unique beak-shaped toothplates.

Normal teeth at start

In the first stage, the individual teeth grew at exactly the same time and in the same positions as in other bony fishes. 

These are called the first generation teeth and they disappear through wear.

This developmental pattern has been conserved for over 400 million years, since the last common ancestor of the pufferfish and other fish like lungfish.

Stages of tooth development (stained red) showing the change from teeth, to bands, to the beginnings of a pufferfish 'beak'.

How the pufferfish got its beak
Stages of tooth development (stained red) showing the change from teeth, to bands, to the beginnings of a pufferfish 'beak'.

4 front teeth

The next stage involves the 4 teeth at the front. Replacement teeth develop underneath that have a very different shape, forming bands that extend along the length of the jaw. The first band develops when the larva is around 5mm long. 

More bands form underneath and make a stack that eventually replaces the first generation teeth once they are worn away. This becomes the beak structure.

Gene tinkering

The team thought this change may be due to a new gene network (a set of genes interacting in a new or undiscovered way). 

In fact, this change is initiated by a small change during the normal process of , following the existing genetic blueprint or template, originating at least 400 million years ago.

The only difference is that the genes are expressed along the whole length of the jaw, rather than restricted to one small area.

"So, what seems like a major evolutionary leap turns out to be a series of tiny steps in development," says Britz, fish researcher (ichthyologist) at the Museum. 

"Our study shows how evolution can produce highly modified morphological structures by just tinkering slightly with developmental programs.

"Our results are nicely summarized in the Latin sentence "Natura non facit saltus", Nature does not make jumps."

Explore further: 'Little janitor' merits attention in Florida springs' health debate, research shows

More information: PNAS paper: Replacing the first generation dentition in pufferfish with a unique beak

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User comments : 8

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okyesno
1 / 5 (14) May 07, 2012
So pufferfish have been around for hundreds of millions of years, and always with the said beak. No evidence for any evolution or gradual change through sucessive freaks of nature. What more evidence does it require for these scientists to see that they are chasing a fairy tale?
Infinite Fractal Consciousness
3 / 5 (6) May 07, 2012
okyesno, my spirituality developed as I learned about science. I am no longer atheist, but my spiritual conclusions are founded on what science has discovered about the universe, and I look forward to discoveries.

Your religion requires that you frequently deny reality.

I think you're doing it wrong.
okyesno
1 / 5 (11) May 07, 2012
Infinite,

Your religious conclusion is wrong. Science has disproved the idea that the universe has existed forever. If you really took science as a starting point for truth, you would gravitate towards the Bible and not new age beliefs for which no objective criteria exist.
Anorion
4.3 / 5 (6) May 07, 2012
oky you really make me post to you same thing on different treads
your bible is a fairy tale, just like lord of the rings and qur'an and other stuff like that.
if your not interested in science, and just love your bible, stop coming here and post religious bullshit. hell i don't go on religious sites post about evolution and geology and stuff. stop forcing your faith in fairy tales to everyone else
Dug
5 / 5 (2) May 07, 2012
Why wasn't the parrot fish beak studied? it's more obvious with broader specification for variations of development.
antialias_physorg
4.6 / 5 (5) May 07, 2012
No evidence for any evolution or gradual change through sucessive freaks of nature

Evolution works when there is pressure (selection) going on. Some species are so successful that there is hardly any selection pressure on a certain trait (e.g. crocodiles, but also many species of bacteria/fungi/viruses). So OF COURSE they don't need to change. Not every species is in the same tight race for survival. Some just don't have many competitors.

You're always seeing these things WAY too simplistic. Life is complex. Open your eyes once in a while and you'll notice it.
Peteri
5 / 5 (1) May 08, 2012
@Okyesno

You appear to be yet another religious attention seeker - one who has no interest in science whatsoever and yet who repeatedly posts anti-science nonsense on a science forum in order to provoke some kind of response from others, which sadly is the attention you seem to crave.

Additionally, your repeated posts seem to be a way for you to puff up your chest and proudly announce to the rest of us what a devout and faithful follower of your given brand of religion you are. I suppose you do it here because your small voice would simply be lost in any forum focussed exclusively on your own religion!

You may, in some child-like way, think you are being clever, or are making some valiant attempt to convert us to your ill-informed and distorted way of viewing the universe. In fact, all you are doing is repeatedly hijacking and distorting what would otherwise be interesting discussions by open-minded people interested in science.
antialias_physorg
5 / 5 (2) May 08, 2012
In fact, all you are doing is repeatedly hijacking and distorting what would otherwise be interesting discussions by open-minded people interested in science.

that#s probably the point. He's so afraid of science that he thinks by waging 'guerilla warfare' on science on forums he can somehow disrupt it or sow the seeds of discord.

But all he achieves is to make himself and his ilk target of closer scrutiny by science.
He's just another source of data. And when enough data is in we may well have the irrefutable evidence that religion is a mental illness. So it's not all bad.