General Question

Seelix's avatar

Can someone explain to me (in simple terms) this aspect of animal reproduction [see details]?

Asked by Seelix (14879points) April 29th, 2011

What I’m confused about is animals who have sexual intercourse but lay eggs, like turtles and birds.

I know that fertilization takes place during intercourse, but how soon after that are eggs laid? Does the egg only develop a hard shell after fertilization?

And am I mistaken in thinking that some animals lay their eggs first, and then the male fertilizes them (frogs, maybe)?

I’m not a science person by any means, so links to sites full of technical language won’t help me.

Thanks in advance!

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13 Answers

Adirondackwannabe's avatar

You’re stretching my brain because it’s been awhile, but the female birds have intercourse and store the sperm temporarily and fertilize the eggs and then the shell forms. If you ever dissect a bird there are eggs in all forms of development within the bird. I don’t know about turtles. I’m rethinking the amphibians.

YoBob's avatar

It depends on the animal. There are some that lay eggs that are then fertilized. Many species of fish take this approach.

As for birds, I believe that the egg gets fertilized early in the process before the hard shell forms. However, I’m not quite sure of the facts on that one.

Adirondackwannabe's avatar

Rethought the amphibians. The frogs have intercourse and the eggs are fertilized and then laid. I think fish are the only ones that fertilize the eggs after they are laid, but I’m not certain that’s correct.

crisw's avatar

Yes, the shell forms after the eggs are fertilized. Amphibian eggs have no shell, reptile egg shells are leathery, and birds evolved the hard shell.

Technically, frogs have amplexus rather than intercourse- there is no penetration, the male just holds the female while he releases sperm. Generally, she releases eggs at the same time, so the fertilization is external.

Birds also usually just touch cloacas, although some (like ducks) do have an impressive penis.

YoBob's avatar

Yikes! That is impressive!

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crisw's avatar

@noelleptc And she has a fantastic accent.

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Seelix's avatar

Thanks so much! I really wish I hadn’t seen that gross duck penis, though! :S Ha ha!

I’ll have to check out this Green Porno later on.

Qingu's avatar

Eggs with a hard shell evolved with land vertebrates.

In the ocean, you can just lay eggs, a guy comes by and puts sperm on them, and they’re fertilized. No shell needed.

That’s what amphibians still do. They lay their eggs in the water.

Reptiles evolved to live far away from water. But that creates a problem for reproduction, because sperm doesn’t survive well in air. So sex needs to take place inside the body. But then there’s the question of what you do with the fertilized egg. Carrying it inside you is expensive (mammals later evolved this, but it takes a lot of energy). Developing a hard shell to protect the egg and provide it with a moist environment was reptiles’ solution to this problem.

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