Scientists Figured Out How Eels Reproduce (2022) | Hacker News Reader

Scientists Figured Out How Eels Reproduce (2022)

intelligentliving.co

127 pointsthunderbong22 comments

I remember being fascinated by animals as a kid and the mystery of where eels went was one of the big unsolved puzzles I remember hearing about.

Much more recently I heard on QI about how medieval people, not knowing about migration, believed, through a lot of leaps, that it was ok to eat barnacle geese at lent. Worth investigating if you are curious :)

I find it very hard to believe that people in the middle ages (or before or after) looked at birds and actually thought that they really spawned from trees or barnacles. After all, birds can fly, you observe large flocks of birds in the sky right before they vanish, you know that there are warmer regions in the south, so it's not a big stretch to imagine that birds could perhaps migrate southwards. You cannot prove it, but it's a good enough guess.

I think illustrations or stories from the middle ages are to be taken as symbolic or allegorical rather than factual like a biology book would be today. They wrote down a story not because they necessarily believed it be factually true, but because it taught a different kind of truth. For example, no one has ever believed that Red Riding Hood actually happened or that you can cut open a wolf's stomach to pull out a living person.

It took until the 1800s for us to finally understand where the hell birds go in the winter, we had all kinds of crazy theories before then. We finally realized birds migrate to Africa, with proof, when a stork arrived in Germany after surviving being shot by an arrow in Africa.

https://en.wikipedia.org/wiki/Pfeilstorch

> You cannot prove it, but it's a good enough guess.

You can guess that now in the 21st century, but we're talking about illiterate peasants who never traveled past their nearest market center. It's naive to assume we can even possibly empathize with their epistemological outlook.

For example, just look at the medieval sources about barnacle geese from the 13th century (from the educated class):

> Barliates, as Aristotle says, grow from wood, and are birds which the common people call 'barnesques', having a similar nature. [1] (I chose a short quote to make a point but please read the rest of the source, it's hardly an allegorical text)

They didn't have the concept of falsifiability or anything even remotely resembling the scientific process (or critical thinking, for the most part). The literate were obsessed with the classics and just took Aristotles and Ptolemy's word for everything, until Copernicus and Kepler had their way. Anything resembling scientific knowledge filtered down to the peasants or came from old wives tails entirely.

Even now with almost universal literacy we have a significant fraction (if not majority) of the population believing in ridiculously stupid nonsense like astrology. I don't find it hard to believe that people thought that geese's life cycle included barnacles.

[1] https://www.medievalbestiary.bestiary.ca/beasts/beastsource1...

> old wives tails

Please, can I have that for my typo collection?

> it was ok to eat barnacle geese at lent.

I think that was just a way to ethically cheat the fast...In southern Germany they got around it by wrapping the meat in a dumpling (Maultaschen), so that god wouldn't notice: "The Swabian German nickname for the dish, Herrgottsbescheißerle, means "small God-cheaters""

https://en.wikipedia.org/wiki/Maultasche#History

EDIT: just remembered another similar cheat, where beavers were defined as fish, allowed to be eaten at lent.

> Much more recently I heard on QI about how medieval people, not knowing about migration, believed, through a lot of leaps, that it was ok to eat barnacle geese at lent.

There’s a similar story about how rabbits in Japanese use the classifier 羽 (-wa, “wing”) normally utilized for birds, instead of the 匹 (-hiki) you’d expect for small animals, because Buddhist monks really wanted to eat them and thus declared their ears to be wings. I don’t know how historically accurate that is. (I’m also assuming this has to come from Chinese and thus likely also has a counterpart in Korean, but can’t prove that with a cursory look through Wiktionary.)

In Portuguese we use the term rabbit wings to distinguish the forelegs from the hind legs at the butcher.

This is a good video on that medieval belief:

Medieval Science was Baffled by Birds - CuriousCabinet123

https://youtu.be/vgFj-MMTqIc

Fascinating how certain animals have evolved with complex migration patterns to breeding grounds. And unfortunate that 95% of the population has already collapsed.

Makes me wonder what the world was like before this last great extinction.

tl;dr Eels have a long lifecycle with several stages. They do not develop sexual organs until late in their life, when they migrate back to the Saragossa Sea. This meant earlier autopsies of eels revealed no sexual organs, even though scientists could provoke them with hormone therapy. So, a team lead by Jose Azevedo tagged female eels in the Azores in 2018, and tracked them via satellite [0].

[0] https://www.nature.com/articles/s41598-022-19248-8

I sometimes think about the selection pressures that lead to complex life cycles, like fig wasps. I find myself thinking about it naively, like one existed and the other grew into the niche. But, realistically, everything is changing (slowly) all the time. I just notice it for, say, influenza because their cycle time is so short.

The important part of the story is that it took so long. People actively searched for an answer for thousands of years.

The answer itself is interesting, but more remarkable to me is how doggedly people pursued it for so long. It seems so basic that they must reproduce the way other vertebrates do, and yet the lack of apparent organs was baffling.

"figured out how" seems a little strong, when:

> questions remain about the timing and navigation of the eels across thousands of kilometers of open water

The click bait version adds “and it’s electrifying”.

everyone here is talking about eels but i prefer icktok

I'm just glad that somebody solved this very slippery problem.

In the satellite tracking experiment, I wonder how they sexed the eels to determine they were female before tagging, given the lack of primary sex organs at that time. Are there obvious secondary characteristics like size?

> The researchers behind this recent discovery used satellite tags to follow 21 female European eels as they navigated the final phase of their incredible journey southwest from the Azores, the volcanic archipelago of the North Atlantic Ocean west of Portugal.

They swabbed them and sequenced their DNA.

Thank you, I forgot that's cheap enough these days.

That just moves the question to how they figured out the genetic sex determination system of eels, or even how they figured out that sex is genetically determined in eels (and is it? many vertebrates don't have genetically determined sex).

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