How do animals have sex underwater?

07 February 2017

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Cheeky dolphin

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Question

Eleanor - How do animals have sex underwater?

Answer

Chris Smith put Eleanor's question to marine biologist Danni Green.

Danni - Well, there’s a huge variety of ways that they do this and I’ll tell you a couple of my favourites…

Barnacles, for example, because they’re stuck on a rock - they’re hermaphrodites as well but they’re not going to be able to guarantee they’ll be able to reach a partner to have sex. So they’ve overcome this by having an extremely long and extendable penis. Barnacles actually have the longest penis to body size ratio of any animal in the world.

Chris - How long are we talking?

Danni - I’m talking about 40 times the body length of the barnacle the penis can extend.

Chris - That’s quite long.

Danni - Yeah. You sort of wiggle that over and bob's your uncle, and your aunt because they're hermaphrodites.

Chris - Actually that’s true isn’t it?

Danni - Yeah. And it depends, the morphology of the penis changes depending on the wave energy too. So if it’s a really exposed, wavy place they’ll have to be a bit thicker, have to have a bit more heff to it. If it’s quite a sheltered shore then they can be long and thin.

Chris - Is that a reflection on the species or subspecies of barnacle or is it that the barnacle is adapting to the environment?

Danni - It’s adapting to the environment, yeah. They can change with the same species but just different wave exposures
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Chris - Okay, so that’s barnacles.

Danni - That’s barnacles. My favourite one is actually the green spoon worm, bonellia viridis. These things when they’re larvae and they settle on the seafloor they’re sexless; they have no sex assigned. And if they settle in a place that has no other of their conspecifics (the same species) nearby they’ll turn into females. They grow about 15 centimetres long and they’re quite an interesting looking thing.

But if they land near one of the same species, it’ll be a female and it touches them with this pigment called bonella, and that actually turns that larvae into a male. Then what they do is they have this kind of spoon shaped proboscis. They vacuum them up and store the male inside their genital sack. They keep them in their and they’re just little dwarf males and they never get any bigger than a few millimeters.

Chris - So how many males will the female have in her harem then?

Danni - As many as she wants. She’ll just store them in there. There job is just to produce sperm and they become like a pair of testicles, just reduced down. And she feeds them - it’s amazing.

Chris - How does she feed them then? Do they live off things secreted inside the female?

Danni - Exactly, yeah. It’s an amazing system.

Chris - What happens if the female dies? Do the males then perish with her or can they change their sex?

Danni - Yeah. They go down with the sinking ship if she dies. They can’t change after that.

Chris - Once they’ve determined their sex, that’s then locked in for life?

Danni - That’s locked in yeah.

Chris - Imagine that.

Danni - It’s quite cool.

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