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Author Topic:   Sexual Evolution
ausar_maat
Member (Idle past 5498 days)
Posts: 136
From: Toronto
Joined: 10-04-2005


Message 1 of 9 (447649)
01-10-2008 10:30 AM


I have a question(s). How and at what point did sexual reproduction begin in species, especially mammals? In other words, how did mammals speciation into sexes come about? By what biological process? Any good books on the topic would be highly appreciated.
thank you

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AdminPhat
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Message 2 of 9 (447837)
01-11-2008 3:18 AM


Thread moved here from the Proposed New Topics forum.

  
Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


Message 3 of 9 (447848)
01-11-2008 4:41 AM
Reply to: Message 1 by ausar_maat
01-10-2008 10:30 AM


Things do not "speciate" into sexes; both sexes are the same species.
Mammals evolved from reptiles (via some now extinct intermediaries), reptiles already reproduced sexually, reptiles evolved from tetrapods that also reproduced sexually, they, in turn, reproduced from sexually reproducing fish. In fact, as far as I know, Pikaia, the earliest representative of the Chordates (the group that contains all creatures with backbones) appears to have been sexually reproducing. So, in fact, we don't know when sexual reproduction evolved, just that it happened prior to about 550 million years ago in the group that led to mammals.
Current thoughts on the matter is that it evolved roughly 1200 million years ago, in single celled organisms.

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Minnemooseus
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Posts: 3941
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001
Member Rating: 10.0


Message 4 of 9 (447853)
01-11-2008 5:54 AM


Foraminifera
As I recall from paleontology class, the same foram species might reproduce sexually or asexually.
quote:
The alternation of sexual and asexual generations is common in Foraminifera species. Asexual haploid generations form a large inner chamber known as the proloculus; these are termed megalospheric. The proloculus is smaller when produced by sexual diploid generations; these are termed microspheric. Reproductive cycles tend to be short.
Source: Foraminifera - microbewiki
Now, maybe a biologist can step in and expand on this.
Nothing to do with sex, but more on forams:
Foraminifera - Wikipedia
Introduction to the Foraminifera
(not a biologist) Moose

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Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


Message 5 of 9 (447860)
01-11-2008 6:39 AM
Reply to: Message 4 by Minnemooseus
01-11-2008 5:54 AM


Re: Foraminifera
Species that can reproduce both sexually and asexually are far from uncommon. Aphids are another example; in fact, they can be born pregnant.
Move into the plant world and there's even more examples.

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 Message 7 by Lithodid-Man, posted 01-11-2008 2:18 PM Dr Jack has replied

  
ausar_maat
Member (Idle past 5498 days)
Posts: 136
From: Toronto
Joined: 10-04-2005


Message 6 of 9 (447869)
01-11-2008 8:52 AM
Reply to: Message 5 by Dr Jack
01-11-2008 6:39 AM


Re: Foraminifera
Does that invalidate the Foraminifera origin of sexual reproduction?
Also, you alluded to there not being a consensus on this question, but is there a specific book(s) on this very topic of the origins of sexual reproduction from the Cambrian era to mammals?
I can't seem to find any author engaging the subject specifically. Any references anyone?
btw thank you Minne for the source you gave, it did begin to shed some light.
Edited by ausar_maat, : No reason given.

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Lithodid-Man
Member (Idle past 2930 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 7 of 9 (447965)
01-11-2008 2:18 PM
Reply to: Message 5 by Dr Jack
01-11-2008 6:39 AM


Re: Foraminifera
Mr. Jack-
Yes, there are many species that can reproduce sexually and asexually. Not to nit-pick but aphids are not one of them. Aphids like a number of sexually reproducing species use parthenogenesis. While parthenogenesis doesn't use sex and therefore seems like it is asexual, it is actually still sexual reproduction. In true asexual reproduction a haploid or diploid cell (depends on taxa) or group of cells can organize into a complete replica of the adult called a clone. In parthenogenesis a haploid egg of a diploid species either fuses with another egg from the same parent (just like it would in standard sexual reproduction) or undergoes mitosis becoming diploid then behaves like a fertilized egg. The key difference is that in asexual reproduction the daughter product is a clone of the adult. In parthenogenesis, even though a single parent is responsible, the normal shuffling (recombination) occurs so that embryo is similar but not a clone. In most animal species parthenogenesis is an accident, but several taxa (including insects like aphids) have it as a major reproductive tactic. Some groups of rotifers (bdellids) use parthenogenesis alone.
To further complicate things parthenogenesis is different from from selfing, sexual reproduction in a simultaneous hermaphrodite. In those species their sperm fertilize their eggs. The fact that most simultaneous hermaphrodites have distinct barriers to selfing suggests that this is not optimal. For example, some terrestrial gastropods (snails and slugs) will only self when in isolation for an extended period.
I look forward to this topic developing. I am going to be offline for the next 4 days but look foreward to seeing this thread develop. My MS work was on the evolution of sexual systems in crustaceans so hope I can contribute.

Doctor Bashir: "Of all the stories you told me, which were true and which weren't?"
Elim Garak: "My dear Doctor, they're all true"
Doctor Bashir: "Even the lies?"
Elim Garak: "Especially the lies"

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Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


Message 8 of 9 (448393)
01-13-2008 9:37 AM
Reply to: Message 7 by Lithodid-Man
01-11-2008 2:18 PM


Re: Foraminifera
I would have described parthenogenesis as a form of asexual reproduction, since it involves only a single parent.

This message is a reply to:
 Message 7 by Lithodid-Man, posted 01-11-2008 2:18 PM Lithodid-Man has not replied

  
Asgara
Member (Idle past 2302 days)
Posts: 1783
From: Wisconsin, USA
Joined: 05-10-2003


Message 9 of 9 (489460)
11-27-2008 10:18 AM


Bump for Heygabbagabba
again, a bump for Heygabbagabba's questions in pnt
Message 1

  
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