Did you know that Clownfish have Thyroids?
Or, that in nature, Thyroid hormones are often responsible for metamorphosis and other morphological
changes?
Hi guys and girls, I’m ReefMan, and today we’re talking about a really neat paper
titled “Thyroid hormones regulate the formation and environmental plasticity of white bars
in clownfishes”.
It was published in the Proceedings of the National Academy of Sciences in May of 2021
- and as always you can find a link and the full info down below in the description.
I also wanted to say thank you to the researchers who sent me a lot of really nice footage from
their lab.
You’ll be seeing that throughout the video.
Additionally, clownfish have bars - not stripes… and they have thyroids too!
I guess I’ve never really considered the internal biology of fish, but they share that
in common with us at least!
The researchers noticed that Percula Clownfish spend time in two species of anemone - Heteractis
magnifica, which is extremely hard to keep alive long term in our reef tanks and is sometimes
called the Ritteri Anemone - and Stichodactyla gigantea, or the giant carpet anemone which
is also very hard to keep alive, but a little more common in reef tanks.
It turns out,clownfish that breed in S. gigantea get their bars a lot earlier in life than
those that breed in H. magnifica.
Why is this?
What might be different between these two groups of fish - they’re the same species
after all, you’d expect them to have similar life stages.
These Clownfish are not the only animals to have differing expressions of genes based
on the environment they live in.
This is called phenotypic variation, and we see this in some species of butterfly where
the patterns on their wings are totally different depending on the season that they change from
caterpillar to butterfly.
Daphnia can grow protective armor and even spikes in response to chemical cues given
off by predators.
Metamorphosis of all sorts tends to be regulated by thyroid hormones, and because Clownfish
bars start to show up as they metamorphosis from larvae to small fish, the team thought
that perhaps those same hormones could control the production of their famous orange and
white coloration.
They set up tanks in their facility to rear Clownfish in.
They actually used A. ocellaris instead of A. percula in the experiment, but the two
species are very similar as you all know.
Rearing them from eggs allowed the team to experiment with the levels of thyroid hormone
that the fish would have.
In some larvae, they outright blocked the hormone production, in others they added extra
hormone.
Blocking the production of thyroid hormones in the clownfish larvae delayed the formation
of white bars.
Excess thyroid hormone accelerated it.
But why would that happen in different species of anemone, or would it even happen at all?
To figure that out, the team tested wild caught A. percula clownfish collected from both H.
magnifica and S. gigantea anemones.
They found that the fish from the S. gigantea anemones - the fish that get their bars earlier
in life - also had increased levels of thyroid hormone.
Clownfish go through seven distinct stages of development from larvae to juvenile fish.
It’s not until stage 5 that their adult coloration begins to form, mid way through
their metamorphosis from larvae to fish.
The fish that the team reared with extra hormone had a higher chance of misshapen bars.
The cells that would normally be found primarily in the white bars - iridophores - were found
across their bodies instead.
The treated fish were also less orange.
Now before you get any ideas, I asked the team about our “designer” clownfish - like
those produced by ORA.
These clownfish are genetic mutants, not treated with hormones, but no one has yet studied
the real difference.
This may be a topic of upcoming research though, so we’ll have to watch these authors to
see if they figure out the real difference between a “designer” clownfish and their
wild counterparts.
The team was not able to figure out why clownfish reared in S. gigantea would have higher levels
of thyroid hormone.
S. gigantea is a much more aggressive anemone versus H. magnifica.
It has a stronger sting.
Perhaps this more dangerous environment has something to do with it.
More research is needed.
All in all, this was a fascinating paper.
Thank you again to the authors who provided the footage that you’ve seen.
Subscribe if you liked the video and would like to see more like it.
Leave a comment if you have questions, I’ll try to answer them as best I can, or maybe
the authors themselves can share more information.
Check out the paper if you want the full details.
Stay safe, have a fantastic day.
Bye!