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  #1  
Old 04-26-2003, 01:59 PM
Helix1047 Helix1047 is offline
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Are there any organisms with multiple sexes, if so which ones

I recently asked my ecology prof, during a lecture on the evolution of mating
systems, If there exists any animals with more than 2 sexes. I vaguely recall
reading something about it, (in a book called "what if you could
unscramble an egg.") And one other fellow also seemed somewhat familiar
with the topic... But All we we got were alot of laughs.

Im not talking about Hermaphroditism, spontaneous sex change, or the existance
in a population of a non breeding group, (ex. worker Bees and worker ants.)

What I wanna know is, is there Genuinely a population of organism that has more
than 2 sexes, in which all sexes are involved, and each has a disntinctly
different role in reproduction.

If there is I would also like to know how this would work, and Under what
conditions would this prove to be selectively advantageous.

Ive tried looking this up on the internet with very little success, and entering
the words "Multiple sexes animals" only led me to an unwanted
awareness of the exsistance of various rather unsavory subcultures.
Ewww...

Any help on this matter would be greatly appreciated... Thanks in advance.
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  #2  
Old 04-26-2003, 02:12 PM
Dr. Lao Dr. Lao is offline
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I suppose you could consider social insects as having three sexes. Female queens lay eggs and which were fertilized by male drones. Sterile workers provide all the labor required to make the eggs hatch.

If you're talking about a species where three separate genders all contribute genetic material to the next generation, I've never heard of any outside of science fiction.
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Old 04-26-2003, 02:15 PM
Helix1047 Helix1047 is offline
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Dr. Lao.. Please read my question carefully...

I stated that "Im not talking about Hermaphroditism, spontaneous sex change, or the existance
in a population of a non breeding group, (ex. worker Bees and worker ants.)
"

In terms of your answer,.. I am referring to the latter... a species whith more than 2 sexes in which all contribute genetic material.

I have read that this applies to slime molds, but Im not sure if that's true... any higher animals..
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Old 04-26-2003, 02:20 PM
Polycarp Polycarp is offline
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I recall some "science popularization" material I read years ago in which prokaryotes were noted as "coming in six sexes" in that each contributes different material to a conjugation -- the only form of "sexual reproduction" (as opposed to fission or budding) that they do. I'd welcome some better data from a microbiologist on whether this is true or misrepresentative of the reality.
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Old 04-26-2003, 04:08 PM
Angel Fish Angel Fish is offline
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Both bacteria and fungi are capable of both sexual and asexual reproduction, and in the case of sexual reproduction they have, technically, more than two sexes.

Unlike every other living organism (pretty much, bar a few exceptions the OP has already ruled out) they have more than two 'sexes' although, when we refer to the 'sex' of a fungi, we are actually referring to genetic markers, rather than clear sexual characteristics or reproductive strategies.

The genetic markers essentially say "I am different", and prevent self fertilisation (under certain circumstances) amongst other things. Behavourally, however, they are identical.

So if you're asking "in the most simplistic way possible, are there more than two sexes in any species" the answer is yes - fungi and bacteria, but if you're asking "are there more than two types of reproductive strategy" the answer is...still yes!

Several species, most notably fish, have three or more reproductive behaviours - the most common being a sort of IIRC (and I'm callign up lecture material from quite a while ago now) guppy, which has three forms, alpha-male, beta-male and female. The alpha male corrals females in a harem, and protects them, and the beta male, which is coloured like a female, and much smaller than the alpha, pretends to be a female, and gets into the harem in disguise.

Equally, there are some crusteaceans (barnacles, possibly) who also exhibit several reproductive 'strategies' - also called alpha, beta and gamma.

IIRC, these reproductive behaviours are genetically programmed, and do not switch over a guppies' life time - on the other hand, the mechanism of fertilisation, the gametes involved, are identical, whether it's an alpha or beta male and a female involved.

So if you're asking "are there more than two sexes with distinct reproductive strategies AND differently marked gametes?" the answer is no.

If you google for "sexual dimorphism" and skip all the socio-biological sites,you should find some useful links.
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  #6  
Old 04-26-2003, 04:38 PM
Mangetout Mangetout is offline
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Primroses (primula vulgaris) have flowers that bear both male and female organs, but within the species there are also two different types of plant, known as pin-flowered (where the stigma(female organ) protrudes from the flower tube and the anthers(male organs) are hidden inside) and thrum-flowered where the arrangement is reversed.
AFAIK These aren't subspecies or varieties any more than you could say male and female humans are different subspecies.

The result of this is that a thrum-flowered plant deposits pollen on the head of a visiting insect - where it can only really be picked up by a pin-flowered plant. A pin-flowered plant deposits pollen on the proboscis of a visiting insect, where it can only really be picked up by a thrum-flowered plant.

Not exactly what you were looking for, I know, but it is an interesting example of a scenario where clearly defined criteria apply beyond the simple interaction of male and female.
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  #7  
Old 04-26-2003, 04:43 PM
astro astro is offline
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This thing has several sexual stages and is still not completely understood by science and has possibly the most complex life cycle of any creature. It is a completely new life form and a new phylum unknown before it was discovered in 1995.

A Lobster's Microscopic Friend - Symbion pandora - a new life form and a new phylum
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  #8  
Old 04-26-2003, 04:57 PM
Achernar Achernar is offline
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Quote:
Originally posted by Angel Fish
Both bacteria and fungi are capable of both sexual and asexual reproduction, and in the case of sexual reproduction they have, technically, more than two sexes.... So if you're asking "in the most simplistic way possible, are there more than two sexes in any species" the answer is yes - fungi and bacteria,
What can I search for to learn more about this?
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  #9  
Old 04-26-2003, 05:17 PM
Maastricht Maastricht is offline
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What Angelfish said.
This link is full of Latin polysyllables that can be used to start a Google search.
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  #10  
Old 04-26-2003, 06:39 PM
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Yes, there is an animal with 12 sexes. Was that a fungi? Someone already asked this question on the board & I forgot which animal I listed as 12, it was part of one of those boring lectures we have at the aquarium...

I'd look it up but my search engine isn't....searching
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  #11  
Old 04-26-2003, 07:47 PM
Helix1047 Helix1047 is offline
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Thank for the replies,.. but with the fish, crustaceans and primroses examples.....

Males are males, Females are females. Males regardless if they are Alpha or Beta, or the fact that they may once be females, produce Sperm, Females produce eggs, or ovules in the case of flowers.

Is there a species with at least one sex beyond male or female, (not hermaphrodite or sterile) that has a distinct role in reproduction that differs from both the male and female

If there is, Under what conditions would this evolve and prove to be an atvantage over other matiung stratgies...

I m sure Ive heard of one, i wanna know more about the fungi example too..

Thank you...
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  #12  
Old 04-26-2003, 11:50 PM
MMI MMI is offline
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The following information comes from Red Queen: Sex and the Evolution of Human Nature, by Matt Ridley

According to Ridley in 1991 Laurence Hurst of Oxford found a species of slime-mold with thirteen genders. But only two have to have sex to have offspring. Gender 13 is always contributes organnelles as well as other genetic information. Gender 12 contributes organelles unless the other partner is gender 13. Gender 11 contributes organelles unless the other partner is of genders 12 or 13 and so on down the line to gender 1. How the gender of the offspring is determined I have no idea.


Saying more than two genders but no hermaphrodites may not make sense, as there are plants with male, female, and hermaphrodite parts. Although apparently there does tend to be pressure towards having only two genders.

I am not sure there are any species in which genetic material from more than two genders are required. (I guess that is the question)
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  #13  
Old 04-27-2003, 01:19 AM
Rusalka Rusalka is offline
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Since every living thing on the planet has one thing in common (DNA) it is physically impossible for there to be three genders required for sexual reproduction. The reason is simple: sexual reproduction is defined as a situation where both parents contribute genetic material to the offspring. DNA is made up of those base pairs not triplets. (the "double" helix)

So the answer to the original OP is "no".
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Old 04-27-2003, 01:42 AM
Marley23 Marley23 is offline
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Three sexes would, it seems to me, be even more complicated than two, which sounds like a major strike against it. In some respects, one is preferable from the standpoint of passing on genetic material.
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Old 04-27-2003, 01:46 AM
Marley23 Marley23 is offline
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Of course, I'm fine with the present system.

To humanity's credit, we've managed to wring quite a lot of complication out of the bicameral gender thing.
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  #16  
Old 04-27-2003, 02:14 AM
Sapphire Wolf Sapphire Wolf is offline
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Related to the OP, but off on a tangent:

I once read a weird SF book (I think it was called Warbirds) which featured an alien society with, IIRC, five social classes.

True males
True females
Neuter males
Neuter females
True neuters

The true males and females were the only ones capable of reproducing - and they produced true neuters.

Neuter males and neuter females had the parts, but were sterile.

As I recall, the neuters moved up as need demanded - if there weren't enough true males, neuter males had physiological changes that made them true males. I don't recall what the explanation was for how that worked (if there was one).

I'd recommend that book on the society alone. The rest of it just plain sucked.
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  #17  
Old 04-27-2003, 08:28 AM
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Well yes, you have the human heterosexual male & human female and the gay male & gay female. The hetrosexuals mate and reproduce and the gay's adopt. Of course there are variations.
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  #18  
Old 04-29-2003, 11:31 AM
ZenBeam ZenBeam is offline
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Since every living thing on the planet has one thing in common (DNA) it is physically impossible for there to be three genders required for sexual reproduction. The reason is simple: sexual reproduction is defined as a situation where both parents contribute genetic material to the offspring. DNA is made up of those base pairs not triplets. (the "double" helix)
It's not the case that one of the base pairs is from the mother and the other is from the father. You have one complete set of base pairs from each parent. There's no physical reason you couldn't have three copies of each chromosome, one from each of your three parents.
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  #19  
Old 04-29-2003, 12:11 PM
CalMeacham CalMeacham is offline
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The idea shows up in science fiction every now and then. Isaac Asimov's The Gods Themselves involves tri-sexual aliens. There was a story about multi-sexual (seven sexes?) aliens in Playboy 15 or so years ago, and National Lampoon ran a comic in which something like ten sexes were required for the sex act. Reading the strip, you quickly realized why this kind of thing didn't happen in real life -- too hard to assemble the necessary participants.

If some race really did require more than two sexes, it would probably be more like the TV series Alien Nation, where onlt two of them had to get together at a time -- easier to arrange (just as two-body interactions rather than three-body ones dominate chemistry).
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  #20  
Old 04-29-2003, 12:50 PM
Gary T Gary T is offline
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I remember it being mentioned in one of my college biology courses that there was some organism with multiple sexes. Possibly it was what Polycarp, handy, or MMI referred to. I believe the course was Invertebrates, but I wouldn't swear to it.

What I remember is that there were 6 or 8 sexes, and reproduction could occur by mating with any different sex. In other words, a sex A could mate with a sex B, or a sex C, or a sex D, etc., but could not mate with another sex A.

Sorry I don't have anything more than that. It was brought up once briefly in class, 30 years ago.
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  #21  
Old 04-29-2003, 01:04 PM
Quercus Quercus is offline
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I think what you're asking is (to try and put it precisely): are there organisms where three different individuals contribute genetic material to a single offspring?

I do not believe that there are any known. I don't think it's very likely either; there's relatively little gain for adding more genetic variation, once you've gotten to two parents, and an exponentially harder time finding suitable mates (I mean, it's hard enough to get a date with one person at a time; what if you had to find a third person? How would you ever pick a movie you all liked?)

As others have said, there are organisms (such as many fungi) with more than two genetically determined mating strains, but each mating is only between two individuals.

And there are instances of more than two individuals with distinctly different roles contributing resources to an offspring, (but not all contributing genetic material directly). Examples include social insects and, in mammals and birds, maiden aunts and bachelor uncles helping to raise their neices/nephews.
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  #22  
Old 04-29-2003, 05:19 PM
Chronos Chronos is offline
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If we're looking at science fiction hypotheticals, the Puppeteers in Larry Niven's stories had only two distinct sexes, but three individuals were required for reproduction (I don't know if they all contributed genetic material). Two "males" would both mate with a single "female". However, the "females" were unintelligent and held as property, so "arrangements", so to speak, still only needed to be made between two partners.

And Rusalka, the two sides of the double helix can't come from different sources, because they're matched to each other. If you know the sequence of one leg of the "ladder", you automatically know the sequence of the other leg. While this is important for the method in which DNA strands are replicated, it is unconnected to the way that different chromosones come from different parents.
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  #23  
Old 04-29-2003, 06:12 PM
AndrewL AndrewL is offline
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If I recall correctly, the "female" Puppeteer wasn't even technically the same species as the "males" - the "females" has their own reproductive scheme, and were essentially hosts to parasitic Puppeteer larvae.

I have heard of other aliens in Sci-Fi where multiple sexes are needed to reproduce, but only two actually donate the genetic material. Which might make for an interesting story, but would never evolve - there's nothing in it, evolutionarily, for the non-gene-contributing sexes.
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  #24  
Old 04-29-2003, 06:33 PM
Sengkelat Sengkelat is offline
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I think slime molds are the champs -- the slime mold Physarum polycephalum has over 500 sexes.

Of course, each slime mold is up to eight sexes at once. This is accomplished as follows: Each slime mold has three genes, matA, matB, and matC. MatA and B come in 13 different types, matC in 3. Each slime mold has two copies of each gene. So an individual slime mold can make 8 different "genders" of sex cells, and the total potential for the species is 13 x 13 x 3, for 507 different genders altogether.

(Note: I'd hazard a guess that this is the same slime mold MMI is referring to)

But, in response to the OP, I don't think there are any organisms that need more than two participants to conceive. As previous posters have noted, there are obvious selection pressures against it; finding two appropriate partners is harder than finding just one.

I highly recommend the book "Dr. Tatiana's Sex Advice to All Creation." It's very funny and readable while at the same time being very informative about the evolutionary biology of sex. It's by Olivia Judson.
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  #25  
Old 04-29-2003, 06:55 PM
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IIRC there were two sorts of male puppeteers - egg donating and sperm donating. So it must have been less different than we suppose.

In Iain Banks's The Player of Games there was a culture with three sexes - males, females and 'apexes.' Apexes were dominant and tended to own the others. Apexes did leadership, males did soldiering and females did housework. Apexes had a reversible organ, which accepted sperm from a male, combined it with an egg, then implanted the zygote in a female to be reared.

In one or both of these cases the female added some genetic information by juggling what was donated by the other two somehow.

Probably not evolutionarily feasible for the reasons mentioned above. Though Banks's have the advantage that you don't need three at once - an Apex has to find a male and a female, but can afford to wait, storing the zygote.
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  #26  
Old 04-29-2003, 06:55 PM
Blake Blake is offline
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Quote:
What I wanna know is, is there Genuinely a population of organism that has more than 2 sexes, in which all sexes are involved, and each has a distinctly
different role in reproduction.
If that’s the question then the answer is yes, and the example is pretty much all plants as well as a lot of algae and fungi. Perhaps the best example would be the heterosporous water ferns. The adult plant is fairly similar to most ferns and produces spores. These germinate into a completely independant type of moss-like plant (the gametophyte) with a haploid genetic pool. These plants then produce the fern equivalent to sperm and eggs (and yes, the sperm can swim). These fertilise one another and the resulting embryo grows into a diploid adult fern. The gametophyte is essentially equivalent to having independant testicles and ovaries running around our cities. They have no dependence on the parent plants at all. So we have a situation with male gametophytes, female gameophytes and the larger, diploid sporophytes, each with a distinct role in reproduction and each with a different genetic makeup.

All plants utilise a similar process, although in some groups the gametophytes are bisexual and the gametophytes may be ‘parasitic’ upon the sporophyte, or vice versa. However with the heterosporous ferns there are genuinely 3 independent ‘genders’.
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  #27  
Old 04-29-2003, 07:03 PM
Blake Blake is offline
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Quote:
But, in response to the OP, I don't think there are any organisms that need more than two participants to conceive.
Is that what the OP was asking? I’m confused. Are we looking for

A) A critter that needs to arrange for three willing partners to be present at once, or
B) One in which 3 different types of organisms are needed to produce the next generation?

If A then I’m with the majority opinion. It’s difficult and it’s pointless since it doesn’t increase the genetic variability of the offspring to any great degree. I also can’t see how such a setup could ever evolve. Since there needs to be reproductively viable male and female or hermaphroditic individuals around already the third gender wouldn’t be avoiding self fertilisation in any way, while at the same time it would be dependant ion the other two sexes while they remain independent. I could only see this existing as some form of parasitism.
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  #28  
Old 04-30-2003, 01:57 AM
eburacum45 eburacum45 is offline
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Try this fun fungus -
http://botit.botany.wisc.edu/toms_fungi/feb2000.html
it has 28,000 different mating types, which means it can mate with all but one of the other 28,000 different sexes (all of which are morphologically identical...

but the requirement for three (or more) genetic parents is a little more difficult to fulfill-
- it doesn't happen yet, but perhaps it could happen at some time in the future...

*Keymales*
First developed by the GeneTEK megacorp in the Jovian League golden age, approx.2500 A.D., the Cryptokey geneline was additional to the male and female genome involved in ordinary sexual reproduction.

Without the additional cryptokey chromosomes, (which disappear by autolysis during the development of the embryo but before birth) the copyrighted organism would not be viable, and so even if a breeding pair were acquired by a rival corporation or nationstate the geneline could not reproduce.

This mechanism was refined by the Genen (thousands of years later) into a third sex, the Keymale or Kemale, which contributed only the 'key' chromosomes but were otherwise sterile.
copyright Orion's Arm 2003


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  #29  
Old 05-02-2003, 02:16 PM
Rusalka Rusalka is offline
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Quote:
Originally posted by ZenBeam
It's not the case that one of the base pairs is from the mother and the other is from the father. You have one complete set of base pairs from each parent.
You are quite right of course, I answered without thinking.

There are no animals which have contributed genetic material from three parents. Sometimes an animal has an extra chrosome from one of the parents when they are only supposed to have two, but usually (not always) such a defect makes the offspring unviable or sick.
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  #30  
Old 05-25-2013, 07:01 AM
Destriarch Destriarch is offline
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Yes, in a way

I see many wise responses here, but I believe I still have something to add to this. Some species of stick insect have three genders, these being male, female and parthenogenetic. Only two of these technically contribute to the sexual act. However, the offspring is parthenogenetic; it lays unfertilised eggs which then develop into fully sexual young that must reproduce sexually.

In a way, therefore, there are three 'genders' in this reproductive cycle since the species has evolved to the point where its survival depends upon all three for continuity.
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  #31  
Old 05-25-2013, 07:58 AM
AndrewL AndrewL is offline
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Do zombies count as a third gender?
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  #32  
Old 05-25-2013, 08:21 AM
DSeid DSeid is offline
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Originally Posted by Rusalka View Post
Since every living thing on the planet has one thing in common (DNA) it is physically impossible for there to be three genders required for sexual reproduction. The reason is simple: sexual reproduction is defined as a situation where both parents contribute genetic material to the offspring. DNA is made up of those base pairs not triplets. (the "double" helix)

So the answer to the original OP is "no".
I read more than halfway through before realizing this was zombie, and no regrets as some of the information here was pretty dang interesting, but this called for some correction and comment.

1) There are RNA organisms.

2) We have created circumstances in which three human individuals contribute genetic information - nuclear DNA from Mom; nuclear DNA from Dad; and mitochondrial DNA from an egg donor. Imagining a circumstance in which one gender only contributes a DNA containing organelle is not so difficult and certainy not impossible. It seems improbable however that there could be much advantage to that added complexity.

3) There is increasing acceptance of the concept of considering ourselves not just creaures of human DNA but as conglomerate of human DNA origin cells and a large number of bacteria existing as one superorganism. To the degree we accept that those bacterial cells are both part of each of us and yet not us then there is indeed more than a pair of individuals passing on genomes and involved over time.

4) Obligate zombie comment: a zombie scenerio would meet the requirement - male/female human produce individual who then gets zombie virus DNA from a zombie bite creating a complete zombie, which only exists with that third genetic contribution. So yes, zombies count as a third gender.
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  #33  
Old 05-25-2013, 11:51 AM
Exapno Mapcase Exapno Mapcase is offline
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Quote:
Originally Posted by Dr. Lao View Post
I suppose you could consider social insects as having three sexes. Female queens lay eggs and which were fertilized by male drones. Sterile workers provide all the labor required to make the eggs hatch.
Quote:
Originally Posted by Destriarch View Post
I see many wise responses here, but I believe I still have something to add to this. Some species of stick insect have three genders, these being male, female and parthenogenetic. Only two of these technically contribute to the sexual act. However, the offspring is parthenogenetic; it lays unfertilised eggs which then develop into fully sexual young that must reproduce sexually.
Could you please explain what exactly you added?
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  #34  
Old 05-25-2013, 01:03 PM
Chronos Chronos is offline
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He added a situation where an animal species has alternation of generations. Although that's the norm among plants, as Blake pointed out, this is the first I've heard of any animal that does it. Certainly nobody else in this thread pointed it out.
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  #35  
Old 05-25-2013, 06:34 PM
Blake Blake is offline
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Quote:
Originally Posted by Chronos View Post
He added a situation where an animal species has alternation of generations.
He didn't, as far as I can decipher his posts. Alternation of generations is a process where the organism has to pass through different life forms in order to reproduce sexually. What occurs in stick insects is simply asexual and sexual reproduction options being employed by a single species.

All stick insects can produce sexually, regardless of whether they were themselves produced sexually or asexually. The asexual generations are not needed for sexual reproduction. Its no different to what happens with most plants. Your lawn grass can reproduce asexually via runners, or it can produce sexually via seeds. And any individual plant can do either. It's not as though only runners can produce seeds, and only seedlings can produce runners. Any seedling can produce seeds as well as runners.

And it's the same with parthenogenic animals. Any animal can reproduce sexually at any time. It's not as though sexually produced animals can only reproduce parthenogenically, and parthenogenic animals can only reproduce sexually.

If there's any alternation of generations going on amongst insects, I've never heard of it.
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  #36  
Old 05-25-2013, 07:54 PM
Asympotically fat Asympotically fat is offline
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Obviously this is a zombie, but interestingly (though excluded by the OP) there is a species of shrimp with two sexes where the sexual divide rather than male-female is male-hermaphrodite (though members of the hermaphrodite sex cannot breed with each other as they are restricted to fertilizing their own eggs).
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  #37  
Old 05-26-2013, 06:59 AM
Dunkelheit Dunkelheit is offline
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In searching for an answer to this question I came across this article which models whether a three-sex reproductive system might work or be an advantage. This end of the biology spectrum isn't my forte, I'm much more a "big picture" biologist at the ecology end of the spectrum rather than the "building blocks" and cell biology end, but inasmuch as I understand what it's saying, it's an interesting look at the subject.

THE DYNAMICS OF THE EVOLUTION OF SEX: WHY THE SEXES ARE, IN FACT, ALWAYS TWO?/

"...The fact that evolutionary dynamics is irreversible and that asexuality is an evolutionary stable strategy is acknowledged by Margulis and Sagan (1986) who wrote '(It) is not because sexual species are better equipped to handle the contingencies of a dynamically changing environment but because of a series of historical accidents (that sex exist)'. Many ecological, physiological and biodynamical reasons why sex should not exist have been put forward (Mulcahy, 1975; Stearns, 1987; Greenwood and Adams, 1987; Maynard-Smith, 1978; Judson and Normak, 1996; for example). A convincing argument for the existence of sex was put forward by Hamilton et al. (1990) based on the advantage of sexual organisms to adapt faster than their parasites. My results confirm that biodynamically, sex is difficult to justify if evolution is viewed as a three-step process. The five-step model suggests that the main evolutionary advantage of sex is that it allows for mate choice. Appropriate mate choice in turn provides a mechanism that can direct the future genetic variability of a population by selecting highly adaptive phenotypes (and thus indirectly genotypes) even if natural selection acts discontinuously, which allows sexual organisms, among other things, to escape their parasites. This restriction of random variation through sexual selection has at least two advantages: it may select organisms with the right genotype to challenge future natural selection pressures, and it provides a kind of direction to the evolutionary process by selecting organisms based on sexual selection criteria which may provide adaptive potentials not easily selected for by short term natural selection processes. Appropriate sexual selection criteria, thus, may accelerate evolution enormously by providing a new dimension to the evolutionary process, giving a definite advantage to sexual organisms over asexual ones. Although sex with random mating may have evolved under very exceptional conditions, it was probably only when by chance, the first efficient mate selection criteria evolved, that plurisexuality could be fixed by evolution. Because asexuality is evolutionary stable, the emergence of sex can be explained only if we assume a strong irreversible dynamics in evolution.

Last edited by samclem; 05-26-2013 at 08:19 AM.. Reason: removed much of the text as a copyright violation
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Old 05-26-2013, 07:25 AM
Lemur866 Lemur866 is offline
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There are some advantages to sexual reproduction, and some for asexual reproduction. Lots of species switch back and forth between the two. So it seems that the optimum number of sexes is less than two.

Since with two sexes you already have the full benefit of sexual reproduction, adding an obligate third just makes things harder. So yes there are plenty of species that have more than two mating types.

But in cases where there are multiple mating types the purpose is to make mating easier, not harder. So in a fungal species with, say, 6 mating types, they don't need all six to mate. Instead an A needs any type that's not an A, a B needs any type that isn't a B, a C needs any type that isn't a C, and so on. In each mating there are only two gametes needed.

So while there are plenty of species that have more than two types of mating forms, there aren't any species on Earth where three gametes fuse.
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Old 05-27-2013, 01:56 AM
Dunkelheit Dunkelheit is offline
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Last edited by samclem; Yesterday at 02:19 PM. Reason: removed much of the text as a copyright violation

Hi Samclem, thanks for the edit if I overstepped the bounds of fair use, but the part you removed included the part that actually addressed the issue of tri-sexual reproductive strategies and why they're unlikely to work. You can go back and delete the remaining paragraph if adding this one exceeds fair use:

THE DYNAMICS OF THE EVOLUTION OF SEX: WHY THE SEXES ARE, IN FACT, ALWAYS TWO?

"Some of the sexual reproductive systems simulated by the model, such as trisexuals, do not occur in nature. I think to have provided a rationale for this: too much plurisexuality or gene mixing makes mate selection difficult to achieve. Trisexual-triploids or species with "more than two sexes", in which sex A, B and C have to fuse are not known and its existence is not likely as this system does not add on genetic variability but becomes very viscous to adaptation. That is, the existence of putative trisexual population will not be likely because of the viscous behavior towards selection of such populations, due to the decreased probability of three mates meeting compared to two, and because mate selection in trisexual populations is inefficient. Other alternatives, such as a system in which A can mate with B and C, B with A, etc., do exist and are in the end similar to a bisexual situation. Hurst and Hamilton (1992) studied such a situation, in which sex was defined according to the control of the inheritance of cytoplasmic genes, and found that true multiple sex in such a situation were either non-existent or binary. But "more than two sexes" may mean polyploid organisms or multiple-mating organisms, which do occur in nature. Maintaining a healthy genetic variability is important for biological species. This can be achieved more efficiently through multiple mating with a bisexual-diploid system rather than through a trisexual-triploid reproductive system. The results suggest that polyploid-trisexual organisms are unlikely to exist, providing a tentative answer to Fishers's original question stated above."

Last edited by Dunkelheit; 05-27-2013 at 01:58 AM.. Reason: include link to article
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