Fungi Reproduction - Video Tutorials & Practice Problems
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Fungi Reproduction - 1
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Hi. In this video we're gonna talk about how fungi reproduce. Now, fungi show sexual and asexual reproduction. Though, there are some fungi that only reproduce asexually, and we call those deuteromycetes. Now, it's worth noting that all fungi are gonna reproduce using spores, regardless of whether it's sexual reproduction, asexual reproduction, whatever. And the spore producing structures that fungi create, are usually called fruiting bodies, kind of an informal name for them. As you'll see there are more technical terms for types of fruiting bodies, and we'll cover those as we go on. Now fungi don't fall into the traditional male female dichotomy like many other organisms we've talked about do. Fungi do have mating types, but their different mating types don't actually appear morphologically different. So you're probably wondering, how do fungi know who to mate with? The answer is, they wait and see which bathroom they go in. No, I'm kidding. They use pheromones to communicate their mating type and these are secreted chemical signals that the fungi will secrete and other fungi will pick up on and say, hey, you're looking pretty good tonight. Now, if you're curious about learning a little bit more about, these, chemical signals and fungal mating, if you check out the, chemical signals chapter, you actually can learn a little bit about yeast mating. Now, before we move on, I do want to say that part of the reason, we don't use a simple male female dichotomy when talking about fungi mating types is because they have so many different mating types, within a single species. In fact, some species actually will have 1,000 of different mating types. So, that's why the little, the old male female break down just doesn't cut it. Anyhow, fertilization, will occur by hyphae fusing together, and then eventually their nuclei fusing together. And this is gonna be something, a trend you're gonna see in, all the types of fungi we're gonna talk about except the chytrids. They, actually do it a little different. We'll get to that later. But first, I just wanna give you, a general overview of what a fungal life cycle might look like. Right? This is not specific, this is just general. So the first stage of sexual reproduction, if you want to think of it in stages, is going to be the fusion of hyphae. You see that happening here. We call that plasmogamy. And essentially it's when the cytoplasm of 2 cells fuse. But the, nuclei don't fuse yet. We don't have fusion of nuclei. That actually has its own special name. So the resulting cell is going to be considered heterokaryotic. And that's because it's gonna have, 2, it can have 2 or more technically, but let's just say 2 for now, nuclei that are genetically different from one another. In the case of, our example of fungus, these are going to be 2, haploid nuclei that are genetically distinct. It can, it can be more than 2 nuclei, just to, be clear about that. Heterokeriodic, can refer to something that has 2 or more genetically distinct nuclei. And in our example, I'm just gonna, leave it at 2 nuclei to keep things simple. And so you'll often see this written as n plus n. Now remember n usually means haploid. But because our fungus is going to have 2 haploid nuclei together in a cell, we sometimes see it written as n+n. Now in our example, we're talking about a cell that is dikaryotic, meaning it contains 2 nuclei. Right? So, dikaryotic means has 2 nuclei. Heterokaryotic means it has 2 or more, genetically distinct nuclei. Right? Karyo is going to refer to the nucleus. And Hetero means different. Di means 2. That's where these terms come from. Now, the final stage of sexual reproduction is going to be when those 2 haploid nuclei fuse and form a zygote. And we call this karyogamy, and you can see that happening right here. Here we have our, technically, here we're actually seeing plasmogamy and karyogamy. So let me be clear about that. We have first plasmogamy. And then here, so this first portion is plasmogamy, and then this second portion is Karyogomy. And that is the fusion of the 2 nuclei into one new, now diploid, nucleus. And this is going to form the zygote. The zygote will form a spore producing structure. Right? Brooding body, if you will. And in most fungi, the zygote is actually the only diploid stage of the fungus. And, that's why we don't really have a good picture of it in this, nice little drawing of a fungal life cycle because it's really, often just, you know, a transient single celled structure. Now, this fruiting body that you see here, you might recognize as a mushroom. Yes. In fact, mushrooms are the fruiting bodies of various fungi. So when we talk about fungi, we're actually usually talking about the reproductive structures, not the main fungal body, the mycelium. So, this fruiting body develops. It's gonna give off its spores. Right here we have spores, and these spores are going to disperse and, what this image is trying to depict is being dispersed, through rain, through, insects, That's more in the realm of ecology. We'll talk about dispersal, in a different chapter. The main point is these spores are going to eventually germinate, form hyphae, that's what these are, these are hyphae, and then the process will repeat. 2 hyphae of different mating types. That's what these two colors are supposed to represent, mating types. So these 2 hyphae of different mating types will get together again. Fuse hyphae, plasmogamy, karyogamy, zygote leads to spore producing structure, which releases spores. Right? The fruiting body releases spores, those spores germinate, more hyphae, and on and on and on. Now, I did say there was an exception to this cycle and that comes in the form of the chytrids, which are actually the only fungi to exhibit alteration of generations. Remember, alteration of generations is, when you have a, multicellular sporophyte generation and gametophyte generation. Right? Similar to plants, and some protists for that matter. Now what distinguishes the chytrids are their flagellated spores and gametes. And we actually have a special term for these, flagellated spores, we call them zoospores. And these are, again, produced by chytrids, which are fungi that do not follow the model of reproduction that we just went through. Alright, with that, let's flip the page and take a look at some specific.
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Fungi Reproduction - 2
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Now zygomycetes are named for their distinctive reproductive structure, the zygospirangium, and this is what's formed after plasmogamy. So you'll notice, here we have our plasmogamy stage, 2 hypha are going to get together and they're going to fuse and form a zygote after karyogamy. Right? So, first, they'll fuse, cytoplasm, then the nuclei will fuse, will form a zygote at that point. And the zygote is gonna develop into the zygosporangia, which is the spore producing structure of a zygomycete that arises from the fusion of hyphane. And actually, very cool, it sits as kind of this blob. So here we have our zygosporangium. Right. Again, sporangium, that's gonna be the singular form of this word. So our zygosparangium, right here, this structure, and, essentially, this is going to sprout, sport producing structure that will you can see right here and the structure will rupture giving off the various spores. And those spores will then, eventually turn in germinate, turn into hyphae, and grow and, you know, get together and repeat the cycle. So this is the sexual zygomycetes but it's worth noting that they actually have an asexual form of reproduction where these sporangiophores form from, their hyphae and, basically their stalks with, sporangia at the tip. So a structure not unlike this one we saw here. Of course, these are going to release spores that, were created through asexual reproduction though, not sexual reproduction. And again, those asexual spore producing structures are called sporangiophores, not sporangiophores. Alright. Moving on, we have Basidiomycota and these are mushrooms that we're familiar with eating. Though actually, as you'll see, not all mushrooms that we eat are basidiomycota. Now, basidiomycota have reproductive structures that are made of gikaryotic hyphae, and, again, these are mushrooms. And these dikaryotic hyphae have what are called vesidia on their end. So looking at our diagram here, the fruiting body is also called the basidiocarp. You can see it right there. It kind of looks like a cross section, like if you cut a mushroom in half, but basically, basidiocarps are mushrooms that we're used to seeing. Like, if you were to draw a cartoon of a mushroom, you'd be drawing a basidiocarp. So these, basidiocarps are, again, made up of these dikaryotic hyphae and on their tips which, if we're looking at this mushroom here, basically hanging, in on the underside of the mushroom are these basidia or basidium, singular. And these are the spore producing cells in which karyogamy is gonna occur. And they're going to produce basidiospores, which go on to germinate, form hyphae. And, you know, those hyphae of different mating types will get together, plasmogamy. The dikaryotic hyphae will then form, mushroom, a bacilliocarp, and the process will repeat itself. And, it's these basidia, these spore producing structures, that give this group of fungi its name. Now let's turn the page and talk about the other type of mushroom we
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Fungi Reproduction - 3
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Ascomycota have reproductive structures that are made of dikaryotic hyphae, but unlike basidiomycota, they form asci on their ends, not decidia. Now, ascii are spore producing structures, and they specifically produce 8 haploid spores, called ascospores and these are contained, these ascae that is, are contained within an ascocarp, which is the fruiting body of ascomycota. And you might recall from the first video on fungi that we looked at a morel mushroom. Well, that's an example of an ascocarp. So, the basidiocarps and ascocarps are the mushrooms that we're normally eating when we eat mushrooms. And again, those are the reproductive structures of fungi, not the main fungal body, the mycelium. Now, looking at ascomycoder reproduction, we actually will form, the ascus. You can see the initial ascus there. We have the 2 cells, they'll fuse to form the zygote, and then we'll have a series of cell divisions. You don't really need to worry about the specifics of all of that, but through a series of cell divisions, we go from having a diploid zygote to 8 haploid spores. You can see those all here, and they are contained in the ascus sac. And the ascus itself really is kind of like a sac, and that's why these are sometimes called sac fungi. And what's kind of crazy about these ascous sacs is when the spores are ready to go, these ascosax, which unlike bassidia, remember bassidia hang down there, on the external surface of the bassidiacarp. These ascae are actually inside the ascocarp and these spores will be ejected, forcibly ejected from this sac. So they burst forth and are spread that way. And of course the ascospores will germinate, turn into hyphae. And these hyphae can actually also, reproduce asexually. And when they reproduce asexually they form spores called Conidia. And what's interesting is these conidia, as you can see happening here and here, these conidia can actually also be involved in sexual reproduction. So they can fertilize, another, fungus of, different mating type or, they can, germinate and turn to hyphae in an asexual reproductive process. Alright. That's all I have for fungal reproduction. I'll see you guys next time.