Freethought & Rationalism Archive

caravelair · 05-12-2003, 05:34 PM

as we all know, seahorse males are the ones that give birth. i'm just curious if anyone has done any theorizing about how/why they evolved this characteristic. how many species share this trait, and how closely related are they do species where the females give birth? i was just wondering about this.

caravelair · 05-12-2003, 05:37 PM

i would suspect that the closest common ancestor of female birthing and male birthing species would have to be one that fertilizes the eggs outside of the body. is that a reasonable assumption?

Undercurrent · 05-12-2003, 05:44 PM

It was my understanding that the male doesn't actually "give birth" so much as t has a pouch for the eggs, and holds them there until they hatch. It's a bit odd that the male does this, but it can be easily seen as an extension of the mechanism by which some frogs protect their eggs by carrying them on (or embedded in) their back.

RufusAtticus · 05-12-2003, 05:49 PM

In many fish species it is very common for the male to build a nest and guard it. Many relatives of seahorses take this one step further, and the males actually carry the eggs on the outside of their bodies. The internal pouch is just the next step.

lpetrich · 05-13-2003, 01:46 AM

Most bony fish perform external fertilization. The female lays eggs and then the male lays sperm.

Since it's the male who is second, it is often the male who ends up caring for the eggs, even to the point of carrying them in a pouch.

Blinn · 05-13-2003, 04:52 AM

To add a little bit to Rufus's comment, pipefish & seadragons (same family as seahorses- Sygnathidae) carry the eggs on the underside of the body, on a flat spot or sometimes a furrow, suggesting how a pouch may have evolved. Among pipefish species, it is usually the male that carries the eggs, but in some species it is the female.

cloudyphiz · 05-13-2003, 05:50 AM

dawkins uses the seahorse reproduction example in the selfish gene, he goes into quite a bit of detail about how things probably came to be the way they are (heady stuff though, and i don't remember it well enough to paraphrase from memory).

-gary

SULPHUR · 05-13-2003, 06:56 AM

Which male fish carries its young in its mouth. I don't know

MrDarwin · 05-13-2003, 07:41 AM

Quote:

Originally posted by Zetek
To add a little bit to Rufus's comment, pipefish & seadragons (same family as seahorses- Sygnathidae) carry the eggs on the underside of the body, on a flat spot or sometimes a furrow, suggesting how a pouch may have evolved. Among pipefish species, it is usually the male that carries the eggs, but in some species it is the female.

Just a little further away on the phylogenetic tree, males of the closely related family Gasterosteidae (sticklebacks) construct nests, coax the females in to lay eggs, and then care for the eggs until they hatch.

Blinn · 05-14-2003, 03:41 AM

Quote:

Originally posted by SULPHUR
Which male fish carries its young in its mouth. I don't know

Banggai cardinalfish for one, do.

05-12-2003, 05:34 PM	#1
caravelair Regular Member Join Date: Apr 2003 Location: toronto Posts: 420	seahorses as we all know, seahorse males are the ones that give birth. i'm just curious if anyone has done any theorizing about how/why they evolved this characteristic. how many species share this trait, and how closely related are they do species where the females give birth? i was just wondering about this.

05-13-2003, 06:56 AM	#8
SULPHUR Senior Member Join Date: Nov 2002 Location: hobart,tasmania Posts: 551	Fish Which male fish carries its young in its mouth. I don't know

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05-12-2003, 05:37 PM	#2
caravelair Regular Member Join Date: Apr 2003 Location: toronto Posts: 420	i would suspect that the closest common ancestor of female birthing and male birthing species would have to be one that fertilizes the eggs outside of the body. is that a reasonable assumption?

05-12-2003, 05:44 PM	#3
Undercurrent Veteran Member Join Date: Jan 2001 Location: Santa Fe, NM Posts: 2,362	It was my understanding that the male doesn't actually "give birth" so much as t has a pouch for the eggs, and holds them there until they hatch. It's a bit odd that the male does this, but it can be easily seen as an extension of the mechanism by which some frogs protect their eggs by carrying them on (or embedded in) their back.

05-12-2003, 05:49 PM	#4
RufusAtticus Veteran Member Join Date: Nov 2001 Location: NCSU Posts: 5,853	In many fish species it is very common for the male to build a nest and guard it. Many relatives of seahorses take this one step further, and the males actually carry the eggs on the outside of their bodies. The internal pouch is just the next step.

05-13-2003, 01:46 AM	#5
lpetrich Contributor Join Date: Jul 2000 Location: Lebanon, OR, USA Posts: 16,829	Most bony fish perform external fertilization. The female lays eggs and then the male lays sperm. Since it's the male who is second, it is often the male who ends up caring for the eggs, even to the point of carrying them in a pouch.

05-13-2003, 04:52 AM	#6
Blinn Veteran Member Join Date: Aug 2001 Location: Ohio, USA Posts: 1,162	To add a little bit to Rufus's comment, pipefish & seadragons (same family as seahorses- Sygnathidae) carry the eggs on the underside of the body, on a flat spot or sometimes a furrow, suggesting how a pouch may have evolved. Among pipefish species, it is usually the male that carries the eggs, but in some species it is the female.

05-13-2003, 05:50 AM	#7
cloudyphiz Senior Member Join Date: May 2001 Location: rochester, ny, usa Posts: 658	dawkins uses the seahorse reproduction example in the selfish gene, he goes into quite a bit of detail about how things probably came to be the way they are (heady stuff though, and i don't remember it well enough to paraphrase from memory). -gary

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