Fungi Diversity

Fungi Diversity

Today we are studying a group of organisms that evolved 0.8 and 0.6 billion years ago that are not plants or animals.

Introduction to Fungi

• Kingdom Fungi is a monophyletic clade within the Subgroup Opisthokonta in the Supergroup Unikonta.

• Fungi have cell walls made of chitin.

• Fungi rely on saprotrophic nutrition (external digestion).

  Saprotrophic nutrition: a process of chemoheterotrophic extracellular digestion involved in the processing of decayed organic matter

• Fungi can be unicellular or multicellular.

• Fungi may utilize both sexual and asexual reproduction within their life cycle.

• Fungi are soft bodied, and therefore little evidence of the structure of ancestral lineages is available.

• Fungi are thought to have arisen from an aquatic flagellated ancestor, with later lineages colonizing land.

• As environmental pressures changed through geologic time, different lineages evolved.

• One of the traits that helps us distinguish between fungal phyla is reproductive structures.

• Fungi have complex life cycles with haploid, diploid, and heterokaryotic stages.

• The different sexual and asexual reproductive structures are unique to each phylum of fungi.

Introduction to Fungi - Reproduction

Zygomycota Life Cycle

• Example: Rhizopus

• During asexual reproduction, some hyphae will develop sporangia.

  Sporangia: an enclosure in which spores are formed.

• Sporangia produce haploid spores that travel in the air and germinate once a suitable substrate is reached.

• During sexual reproduction, adjacent hyphae of different mating types produce gametangia.

  Gametangia: a specialized organ or cell in which gametes are formed in algae, ferns, and some fungi.

• Gametangia fuse and develop into a zygosporangium that then undergo meiosis to form haploid spores.

Ascomycetes Life Cycle

• Asexual reproduction can proceed with either spores or budding.

• Some hyphal cells differentiate into conidiophores producing conidiospores.

  Conidiophores: a type of asexual reproductive spore of fungi

• Budding occurs in single-cell yeasts.

• During sexual reproduction, adjacent hyphae of different mating types fuse.

• Dikaryotic hyphae grow into a hyphal mass forming the ascocarp.

  Ascocarp: the fruiting body (sporocarp) of an ascomycete fungus.

• Nuclei fuse to form a diploid nucleus in each ascus then undergo meiosis to form 4 haploid spores, which may undergo mitosis to form 8 haploid spores.

Basidiomycota Life Cycle

• Asexual reproduction does NOT occur in this group.

• Basidiocarps produce sexual spores called basidiospores through meiosis.

  Basidiocarps: the fruiting body of a basidiomycete

• Basidiospores disperse and germinate into different mating types.

• Hyphae of different mating types meet and fuse to form a dikaryotic mycelium.

  Dikaryotic mycelium: fungal hyphae in which each cell has two genetically distinct nuclei.

• Under appropriate conditions the fruiting body (basidiocarp) will emerge and begin the process over.

Classification Within the Basidiomycota

How do we characterize the different classes, orders, families, genera, and species within a single phylum?

We still rely heavily on reproductive structures, but take a narrower view.

Given that two specimens have gills and basidiospores, researchers investigate the shape, color, and structure of these features.

Other characteristics examined include:

• Cap color

• Cap shape

• Cap size

• Stem color

• Stem shape

• Stem size

• Gill attachment

• Gill spacing

• Gill color, among others

🤝 Fungal Symbioses

Fungi form symbioses with many other groups of organisms.

Lichens and mycorrhizae are excellent examples of predominantly mutual symbiosis.

Lichens

• Lichens are the result of a fungus and an alga living symbiotically.

• The alga may be eukaryotic or prokaryotic.

• 14,000 fungal species are known to form lichens.

• Lichens come in multiple forms:

  • Fruticose

  • Foliose

  • Crustose

Mycorrhizae

• Mycorrhizae are associated with the roots of plants.

  • Endotrophic

  • Ectotrophic

• These fungi provide a larger network to deliver water and nutrients to the plant under stressful conditions and receive sugars produced by the plant in return.

• In not so stressful conditions, the fungi can shift to act like parasites, taking sugars from the plants and not providing anything in return.

Fungal Parasites

Fungi are also known to parasitize plants and animals.

Some well-known fungal parasites:

• Ergot cereal crop disease that can poison humans (proposed to have played a role in the Salem witch trials)

• Ringworm presents as a red ring on the skin of an infected individual; may also cause hair/fur loss

• Dutch elm disease decimated much of the elm population in the eastern US

• Batrachochytrium dendrobatidis causes a fungal disease that is decimating amphibians worldwide

• Cordyceps- https://www.youtube.com/watch?v=vijGdWn5-h8

🌍 Fungal Ecology

• Inhabit nearly all habitats on earth including deep subsurface ocean sediments, tundras, human skin, dry sandy soil in SW US, and more!

• Play a critical role in returning nutrients from decaying organic matter to soils, sediments, & aquatic environments

• Decomposers, symbionts, food source

💸 Economic Importance of Fungi