We humans are used to using the XX/XY chromosomes to determine which sex we belong to. If you have two X chromosomes, you are a female, while you are a male if you have one X chromosome and one Y chromosome. However, if you were a bird you would need two Z chromosomes to be a male, while a female bird will have one Z chromosome and one W chromosome. This is still straight forward, but once we get to mushrooms, things get a bit more complicated to say the least.
An image of the human sex chromosomes. X is the big one on the left, and the small one on the right is the Y. This means it is XY, so it is from a male. Image by National Human Genome Research Institute, posted as Public Domain.
You can find more than 4,000 sexes in mushrooms
In the phyla called Basidiomycota within fungi, we can find incredibly many types of sexes, known as mating types. A mushroom can create fertilized offspring with any another mating type, but not the same as the one it is. The reason as to why it cannot mate with its own type is to prevent selfing, an event where the mushroom would fertilize itself.
Basidiomycota is a phylum that consists of most of the mushrooms we pick when we are in the forest, with a few exceptions. The exceptions, such as true morels (Morchella ssp) all belong in the phylum Ascomycota, which do not have this high amount of mating types (in fact, they only have two, and are in a sense more relatable to animals).
One of the very many fungi that belongs to the Basidiomycota phylum. Most of the common mushrooms belong in this phulym. Image by Scott Darbey, posted with the Creative Commons Attribution 2.0 Generic license.
Why mushrooms has so many mating types
There is actually a somewhat simple explanation as to why the mushrooms can have so many different mating types, while most other organisms only have a few. As I said in the introduction, most organisms have their sex determined by their chromosomes. In Basidiomycota, it works on a very different level. The mating types are not decided by a whole chromosome, and instead by a few genes. There a known cases of four different genes that decide the mating type, with several different alleles for each gene.
In the phylum of Ascomycota there are only two mating types, but these are also determined by a single gene, not by several of them.
Trying to explain it a bit easier
What does this mean? An allele is one possible variation of a gene sitting on a locus in a chromosome. The higher amount of the alleles, the more variation will be found in the mushroom, which in this case will mean a higher amount of different possible mating types. If there are few alleles for a trait, there will be little variation of the things the alleles code for.
Try to think of it as hair color in humans. This is not decided by a whole chromosome, but instead by a combination of genes. If you have alleles to have blonde hair, this will be reflected in your phenotype (the physical appearance*), just like the mating type will be determined by the alleles in mushrooms.
The thing to take away from this post is that the sexes in Basidiomycota is determined by two, three or even four different genes, not by a whole chromosome. This opens up the opportunity to have many different sexes / mating types, because there are so many different gene combinations for these.
*Phenotype is used when we are talking about the physical appearance of an organism, but using the term physical appearance is not 100 % correct, since a few more features would be included in the phenotype. However, for non-biologist, think of phenotypes as the physical appearance of the organism.
Thanks for reading
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Understanding mating systems in mushrooms is pretty difficult, and it is a very complex system, so some of my information might be a little wrong, and it certainly does not explain all of it. However, I hope you enjoyed this little taste of how mating types functions in the Basidiomycota. Check the sources below if you are interested to learn more about the mating types in mushroom.
Sources
- Mate recognition in fungi, by L A Casselton, Heredity (2002) 88, 142–147. DOI: 10.1038/sj.hdy.6800035. This is a scientific paper written about mate recognition, which also includes some info about the mating types. This can be pretty difficult to understand for people who don’t really know a lot about fungi.
- The Wikipedia page on Mating in fungi also has lots of information, but this is also pretty complicated to read for people who are not familiar with fungi.
- Not used as a source, but check out the Wikipedia page on alleles to better understand them.
Mushroom-Monday
This post is part of a project I started, called #Mushroom-Monday. I plan to post about mushrooms every Monday, and I want as many people as possible to join me! Today I’m also giving away some STEEM to people who join me, so check out my post about Mushroom-Monday by clicking here.
Fascinating post! I've never spent time thinking about the sexes of plants or fungi so this was especially eye opening for me! Well written, clearly explained and excellently cited! Looking forward to your continued content!
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Thank you! I am happy to hear that the steemSTEM channel liked it :)
Great info. I definitely did not know about the 4,000 + sex types. You explained the geneological nature but I am wondering the evolutionary reason behind having so many different sexes. I know that mycelium network is very advanced because of it's decentralized and redundant nature. If one area of the network is broken by an animal then there are other paths. Maybe the same logic somehow applies with the sex types?
I guess I explained how the got so many mating types without even touching the reason why. And to be honest I have not really read anything about why they have this complex system. However, my first thought would be that they do not use the sex in a strict way like we do. For them it does not matter which mating type they create an offspring with, and that the mating types instead act as a regulator to prevent it from mating with the exact same type (so it will not fertilize another part of itself).
Ah ok like sex differentiation for the sake of variety and plurality amongst the species.
THis is one of those "facts about nature" that I have read, but it is still hard to work out - for me, at least. And the mushrooms, themselves, have different numbers of sexes. The closest I can get is to think of plant varieties. Some apples need pollen from other apples. But only the pollen from certain varieties will work, not all of them.
And in fungi, the spores are what mate. So how many different sexes might be present within a small area, like my yard? How far do those spores have to go to find another fungus of a different sex? So crazy!
I agree that it it definitely very difficult to grasp this fact ;) I also think the mating types function more like varieties than genuine sexes. One thing I completely forgot to include in the post is that the meting type only determines what other individuals the fungi can mate with, and does not affect other attributes (like we are used to in animals and even plants). So the mushroom will look exactly the same no matter which mating type it is.
Answering how many mating types present in your yard is impossible. With several thousand options in Basidiomycota, I don't think it is likely that any are the same mating type unless its a clone from one of the other fungi.
As I mentioned, the mating types is a mechanism to mainly prevent self-fertilization, so I don't think fungi really has a problem when it comes to finding available mates.
Now there's a math problem -- What densities and arrangements of spore distribution would require 40 sexes, 400, or 4000 to create a sufficient level of genetic mixing over the long run?
Does it mean that my yard is so full of fungus spores of all different kinds of fungi, that they have to be able to sort themselves out? I was amazed this fall to see a new mushroom in my yard, the Shaggy Parasol - in 4 widely-spaced locations across my 1.3 acres. Their spores must have been everywhere across the landscape at one time.
Well, I wonder how long would be a bachelor in gender studies, if they included mushrooms ... LOL. Very interesting, btw.
As a matter of fact, my girlfriend is currently working on her master's degree in gender studies, so we tend do have a lot of interesting conversations when it comes to these things. However, when discussing things like this, it is important to distinguish between sex (that is given biologically in your genes) and gender (which focuses of your own identify, social roles etc).
I got the point that genders aren't 1:1 with sex. Anyhow, you need sex to define a gender, in terms of logics. If you say , by example, transgender, you need to say that a transgender is someone which is not aligned with biological sex. In terms of logic, this is a proposition which requires biological sex to exist. The most common definition of "transgender" is "Transgender also an umbrella term: in addition to including people whose gender identity is the opposite of their assigned sex (trans men and trans women), it may include people who are not exclusively masculine or feminine" . But, to make this sentence consistent, you always need to define an "assigned sex" (at least two). Then , you are right when you say that gender and sex may differ. But still, gender is an assertion about sex, so that, if you have 4,000 sexes, you may have an unbelievable number of ways to be transgender . You have the number of possible choices of two into 4000, only if "transgender" means somebody between TWO assigned sex. If you assume that a transgender could be something in between 3 assigned sex, with 4000 possible sex, you are entering very, very big numbers.
Yep, you are right on the fact that gender is based on biological sex. However, I don't think there is much of an issue with gender identifications within the fungi species :) Or, at least not that we are aware of.
I will be following these MMs closely. I am fascinated by what I just learned.
I'm happy to hear that you liked the posts :)
I feel like humans have at least 4,000 gender pronouns now, lol
Heh, I'm now a bit more confused than before reading this, though maybe those two beers I drank earlier might have something to do with it. However, 4000+ sexes is weird.
I have a question though. We now know that mushrooms make symbiotic bonds with plants like trees, flora. But is there similar symbiosis between fungi and fauna? I think some yeasts might be able to live in the digestive tracts of animals, and also know of leaf cutter ants which farm a fungus, but is it really symbiosis in either case? And if not, can there be one?
I'm asking, because when I was younger I used to read a lot of science fiction, and in one of the books there was described a symbiosis between a mushroom and human. The mushroom could think, and forming a symbiotic bond with a human they'd form an ultimate mind of sorts. (I don't remember whose book it was, nor the title. But the book left me a strong impression anyhow.) I know those kinds of symbiosis are kind of far fetched, but it was definitely something that got me thinking; What if?
Thanks for a long and good comment! To answer this I first need to have some definition for the term symbiosis. The problem with this term is that there are lots of different definitions, but for my ecology studies we have always used something along the lines of "any persistent interaction between individuals of different species", which I think is pretty commonly used in ecology. This includes mutualistic interactions (positive for both species), commensalistic (positive for one species, and does not affect the other species), and parasitic (positive for one species, negative for the other). The interaction has to be over time, so a random encounter of two species does not count as symbiosis.
With this broad term we can definitely conclude that there is lots of symbiosis between fungi and animals. I'm not very familiar with these types of fungi, but there are for sure lots of fungi that uses humans and other animals as hosts. This is a parasitic symbiosis. There are also animals which use fungi to help digest their food, so this is a good example of mutualism.
The problem with using this broad term of symbiosis is that it is everywhere. With this definition even human-dog relationships are mutualistic symbiosis, where the human gains increased happiness / increased security or whatever you use your dog for, while the dog gains food and shelter. But with this definition, all the examples you made are a form of symbiosis.
Anyway, over to the sci-fi question you have. We don't really have any fungi that does what you described, but I suppose it could theoretically be possible. There are other parasites that can alter the behavior and personality of their hosts, but for this part we are talking about a parasitic symbiosis, not a mutualistic one. A good example is the protozoan Toxoplasma gondii, which uses cats at their main host. However, all other warm-blooded animals can be infected, and infected rodents will be altered into being more likely to be preyed upon by a cat. So in this example the parasite makes the host get killed to it can continue its life-cycle. Some scientists also think humans will have a personality change when they are infected this with parasite, and there is even a term for it: "Crazy cat-lady syndrome". Note that this is a protozoan and not a fungi, and I'm not even sure if fungi can do this, since I'm not all that familiar with infectious or single-celled fungi.
Great read on the article itself and your comment.
Thank you!
Very interesting! Thanks.
I'm glad you found it interesting! Thanks for reading :)