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Fungi, those exotic "creatures" with which we have a love and hate relationship, may seem primitive to most people, but the truth is that they have one of the most uncanny mating systems out there. In order to digest this post as smoothly as possible, a disclaimer is a must. You need to give all your prior knowledge pertaining to gender a rest, because what you are about to witness defy all kinds of conventional conceptions about mating. With that warning out of way, we can now finally talk about sex among fungi.

From a reproduction perspective, sex is an act that involves two genders, a male and a female. At least, that is how humans define the reproductive art. To create a baby, a male has to use his member to drop the seeds in the bucket. Of course, the bucket is none other than the vajayjay. Since this fact is picked up simply by being alive for most people, there is no need to elaborate on it any further. However, if you are still holding tight to your usual gender conceptions, now is the time to put them on hold!

For us, the idea of reproduction through two opposite sexes seems so ingrained in our biology that we don't even give it a second thought. On the other hand, this concept might appear absurd, and even outdated for fungi. Yes, those folks have their own views on gender identity. For starters, fungi can mate with almost any other individual of their species. If this wasn't enough for you to dismiss your gender notions, you may need to take a look at a particular species of fungus scientifically known as Schizophyllum commune. Before you let your imagination run loose, the term Schizophyllum has actually nothing to do with schizophrenia as it simply means split leaves, hence the species' common name "split-gill". The fungi are so widely distributed they can be found on all continents, except Antarctica. While these properties might make the split-gill look like an average common fungus, the fact of the matter is that these seemingly modest fungi possess more than 20,000 sexes. For the sake of simplicity, let's refer to these sexes as mating types. So an individual split-gill fungus with a given mating type can virtually mate with any other member of its species that doesn't possess the same mating type, which means it can mate with all the other 19,999 sexes, assuming the total number of genders is 20,000.

But how these "primitive" animals managed to achieve this huge gender diversity? You might have noticed that we referred to fungi as animals. Well, that is because they are genetically closer to animals than plants. Now, let that sink in for a bit. Back to the original question, Schizophyllum commune fungi follow a tetrapolar mating system, meaning they have four or more mating types. Much like our genders are controlled by genes, the spill-gill's mating types are also controlled by a set of two genes. Those genes occur on two different locations on the chromosomes, and they are responsible for defining the fungus' mating type. Sounds complicated? It is and it isn't. Basically, it boils down to combinations. For example, suppose a fungus named Fungo happens to have the A1 mating type allele at location A, and the B2 mating type allele at location B. If we combine these two abbreviations, that would make our precious Fungo an A1B2 type. In order for Fungo to mate successfully, he has to find a fungus that has a different combination on both loci (e.g., A2B1). See? It was't that complicated at all!

In reality, this mating system is a little bit more complicated than the previous example, as each combination can, in turn, have multiple variants. So by calculating the total number of all possible combinations, scientists determined that the split-gill species possesses up to 28,000 sexes in some estimates. Right now, you might be thinking: Why does such a commonplace fungus go to extreme lengths to define its genders? The answer lies in sexual diversity. By increasing the number of possible sex variations, these fungi ensure they will always mate with a genetically different individual. In other words, fungi don't have to worry about the male-to-female ratio in their population, as they will always find a sexually compatible partner. At the end of the day, a so-called primitive existence turned out to be quite clever than we think!

Inspired by: Popsci & Cornell mycology
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