Rucete ✏ Campbell Biology In a Nutshell
Unit 5 THE EVOLUTIONARY HISTORY OF BIOLOGICAL DIVERSITY — Concept 31.4 Fungi Have Radiated into a Diverse Set of Lineages
Fungi have evolved into a wide range of ecological roles and morphological forms. Thanks to molecular studies and metagenomics, fungal phylogeny has been revised dramatically, with traditional groups like Zygomycota split up and newly recognized groups like Cryptomycota and Microsporidia now placed in basal positions of the fungal tree.
Cryptomycetes and Microsporidians
- Cryptomycetes (Phylum Cryptomycota)
- Unicellular fungi with flagellated spores
- Found in marine, freshwater, and soil habitats
- Often parasites of protists or other fungi
- Synthesizes chitin-rich cell walls
- Thought to be basal fungi, sister to microsporidians
- Microsporidians (Phylum Microsporidia)
- Unicellular parasites of animals and protists
- Lack flagella, but use harpoon-like organelles to infect hosts
- Have extremely small genomes (e.g., Encephalitozoon intestinalis)
- Some infect honeybees, possibly contributing to colony collapse disorder
Chytrids (Phylum Chytridiomycota)
- Found in lakes, soils, and hydrothermal vents
- Includes decomposers, parasites, mutualists
- Example: Anaerobic chytrids in cattle digestive tracts break down cellulose
- Produce flagellated spores called zoospores
- Retain ancestral traits like chitin cell walls and fungal enzymes
- Can be unicellular or form hyphal colonies
- Some species contribute to global amphibian declines
Zoopagomycetes (Phylum Zoopagomycota)
- Mostly parasites or commensals of animals, fungi, and protists
- Form nonflagellated spores and filamentous hyphae
- Some manipulate insect hosts for better spore dispersal
- Reproduce sexually via zygosporangia, which protect zygotes
Mucoromycetes (Phylum Mucoromycota)
- Includes food molds like Rhizopus stolonifer (black bread mold)
- Mainly decomposers and plant pathogens, but some form mycorrhizae
- Life cycle includes:
- Asexual phase: sporangia release many haploid spores
- Sexual phase: zygosporangia form and undergo karyogamy; survive tough conditions
- Species like Pilobolus use water jets to shoot spores toward light
Ascomycetes (Phylum Ascomycota)
- Known as sac fungi (~90,000 species)
- Produce spores in asci within ascocarps
- Include yeasts, morels, truffles
- Roles include decomposers, plant pathogens, lichen symbionts
- Asexual reproduction via conidia on conidiophores
- Neurospora crassa is used in genetic studies
- Dikaryotic stage allows prolonged genetic recombination
Basidiomycetes (Phylum Basidiomycota)
- Includes mushrooms, puffballs, shelf fungi, rusts, and smuts (~50,000 species)
- Named for the basidium where karyogamy and meiosis occur
- Fruiting bodies called basidiocarps (e.g., mushrooms)
- Best decomposers of lignin in wood
- Long-lived dikaryotic mycelium can form fairy rings
- Basidia in gills produce four haploid basidiospores dispersed by wind
- Important in nutrient cycling and plant symbiosis
In a Nutshell
Fungi have diversified into multiple lineages, from aquatic flagellated cryptomycetes to complex mushroom-forming basidiomycetes. Each group plays distinct ecological roles—decomposers, parasites, mutualists—and uses varied reproductive strategies. Molecular studies continue to reshape our understanding of fungal diversity and evolution.