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Some major episodes in the history of life Fungi 1. General characteristics of fungi 2. Ecological roles of fungi 3. The fungus life cycle 4. The four fungal phyla Figure 31.9 Phylogeny of fungi Traits of fungi: 1. Eukaryotic 2. Heterotrophic, with absorptive nutrition (exoenzymes) 3. Body made of hyphae—thin, long strands of cells -interwoven net of hyphae is called a mycelium -cell walls usually composed of chitin 4. Dispersal via asexual and/or sexual spores 5. Unique life cycle, including a heterokaryotic stage Septate hyphae (left) and nonseptate (or coenocytic) hyphae (right) Learn to match structures in these groups to the stages of the generalized fungus life cycle Figure 31.2 Fungal structure The mycelium: How is its structure related to the absorptive nutrition of the fungus? 1 Figure 31.3-31.4 Examples of fungal hyphae Mycelia • Highly branched, have very high surface area:volume ratio – 1 cm3 of soil may contain 1 km of hyphae • All parts of fungal body (except reproductive structures) in close contact with environment • Interior of any cell is in close contact with environment One ecological role of fungi: mycorrhizae Fungal ecology • Most fungi are decomposers • Many fungi are parasites, causing diseases in plants or animals • A very few fungi are predators - eat very small animals (nematodes) in the soil • Fungi are always heterotrophs, but… • Fungi are involved in important mutualisms with plants and algae “Mycorrhiza” = Fungus/root (plural: mycorrhizae) Plant Soil Nutrients Sugars Fungus • Some fungi attach to plant roots, forming a “mycorrhiza” • These fungi obtain nutrients from the soil and pass some of them along to the plant • In return, the fungus receives carbon (sugars) from the plant • One type of mycorrhiza, the ectomycorrhiza, is usually a basidiomycete fungus on the roots of conifers, oaks, eucalypts, and a few other trees • Many of the mushrooms you see in the forest are the basidiocarps or sexual fruiting bodies of mycorrhizal fungi Two main types of mycorrhizae • Ectomycorrhizae form sheaths over the outer surface of a root, and may grow into the extracellular spaces of the root cortex, but do not penetrate cell walls 2 main types: 1. Ectomycorrhizae (pictured here; mostly Basidio-, some Ascomycota) and 2. Arbuscular Mycorrhizae (formerly “endo-”, all are Glomeromycetes) 2 Figure 37.12 Ectomycorrhizae and endomycorrhizae. Two main types of mycorrhizae • Ectomycorrhizae form sheaths over the outer surface of a root, and may grow into the extracellular spaces of the root cortex, but do not penetrate cell walls • Endomycorrhizae (arbuscular mycorrhizae) extend into the interiors of root cells Figure 37.12 Ectomycorrhizae and endomycorrhizae. Figure 31.123 Lichens: a symbiosis between a fungus (usually an ascomycete) and a photosynthetic organism (alga or cyanobacterium). Usually presumed to be a mutualism. Grow very slowly, can live for a very long time. Figure 31.24 Anatomy of a lichen Figure 31.5 Generalized life cycle of fungi (Layer 3) **Notice the lack of a multicellular diploid stage 3 Figure 31.9 Phylogeny of fungi Fungi 1. General characteristics of fungi 2. Ecological roles of fungi Basidiocarps Flagellated zoospores Ascocarps Zygosporangia (sporangium) 3. The fungus life cycle 4. The four fungal phyla Learn to match structures in these groups to the stages of the generalized fungus life cycle Figure 31.11 Phylogeny of fungi Chytridiomycota • • • • Chytrids and Zygomycetes may be paraphyletic ‘early’ fungi: flagellated spores, zoospores Lakes, ponds, soil Some are saprobes, some parasitic Some single celled, most have coenocytic hyphae • A ‘link’ to animal evolution? 1.5 billion years animals and fungi diverged, but fossil evidence is sparse! Zygomycota Chytrid ecology • Mostly unicellular, some species form colonies with hyphae • Mostly saprobes (eat dead organisms), some parasites • Disease caused by a chytrid fungus appears responsible for many cases of amphibian decline • • • • • • • Form a zygospore: resistant structures during sexual reproduction About 1,000 species - variable life histories! Including molds, parasites and commensal symbionts Coenocytic hyphae, with septa only where reproductive cells are found Asexual phase: haploid spores develop in sporangia at the tips of upright hyphae When conditions get bad: sexual reproduction and the zygospore Zygosporangium is a resistant multinucleate structure where heterokaryotic nuclei fuse to form diploid nuclei that undergo meiosis When conditions improve: meiosis and the release of haploid spores 4 Figure 31.12 The life cycle of the zygomycete Rhizopus (black bread mold) Notice the lack of a heterokaryotic mycelial stage Glomeromycota: AMF • This is a ‘phylum?’ currently grouped with the zygomycota • They are classified as arbuscular Mycorrhizal Fungi (AMF) • All (?) are asexual • They are symbionts - over half of living fungi in soil are probably these! • Important commercially Figure 37.12 Glomeromycota are arbuscular mycorrhizae (endomycorrhizae). Ascomycota: sac fungi • • • • • • • Figure 31.16 Ascomycetes (sac fungi): Scarlet cup (top left), “true” truffles (bottom left), morel (right) 35,000 species! Marine, freshwater , terrestrial habitats Produce sexual spores in saclike asci Fruiting bodies: ascocarps Variety of morphologies and life histories from single celled yeasts to morels Many are plant pathogens, many are saprobes, many live with algae as lichens (about 40%) Produce conidia - naked spores on conidiophores (asexual reproduction) Extensive heterokaryotic stage Figure 31.17 The life cycle of an ascomycete 5 Figure 31.17 The life cycle of an ascomycete Figure 31.18 Basidiomycota (club fungi) •30,000 species •Long lived dikaryotic mycelia •Basidium: transient diploid stage •Important saprobes (can decompose lignin) •Fruiting bodies are basidiocarps •Asexual reproduction not as common Figure 31.20 The life cycle of a mushroom-forming basidiomycete aka fruiting body, basidioma Basidiomycete Gills, and their attached basidia and basidiospores. Basidiomycetes are named after their basidia. hymenial layer False truffles: spherical, underground, mammal-dispersed basidiomycete fruiting bodies evolved from mushroom ancestors Figure 31.19 A fairy ring 6 Table 31.1 Review of Fungal Phyla Not always! Always has microscopic basidia 7