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.
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.
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.
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.
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.
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’.
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.
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*
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.
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.
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.
There are RNA organisms.
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.
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.
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.
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.
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.
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).
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 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.
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.
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:
“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.”