Notes on Unikonta Lineages of Domain Eukarya and Fungi

TOPIC 8: UNIKONTA LINEAGES OF DOMAIN EUKARYA

ANNOUNCEMENTS

  • Exam #2: Scheduled for Wednesday

    • Bring a pencil

    • Arrive early to pick up bubble sheet

  • Lab this week (due before lab begins):

    • Prelab #7

    • Postlab #6

    • Bacterial Diversity Discussion Sections

  • No Class: On Tuesday, November 11

DOMAIN EUKARYA

  • Major Clades:

    • BIKONTA

    • UNIKONTA

      • Subgroups:

      • STRAMENOPILA

      • ALVEOLATA

      • RHIZARIA

      • PLANTAE

      • EXCAVATA

      • OPISTHOKONTA

      • AMOEBOZOA

MAJOR LINEAGES OF EUKARYA: AMOEBOZOA

  • Characteristics:

    • Lack cell walls.

    • Take in food by engulfing it.

    • Move via amoeboid motion and produce large, lobe-like pseudopodia.

  • Habitat:

    • Abundant in freshwater habitats and wet soils.

    • Some are parasites of humans and other animals.

  • Examples:

    • Includes the genus Amoeba and slime molds.

SLIME MOLDS

Cellular Slime Molds

  • Mostly live as unicellular amoeba, but can form multicellular "slugs" when conditions are adverse.

Plasmodial Slime Molds

  • Composed of multinucleated super cells.

MAJOR LINEAGES OF EUKARYA: OPISTHOKONTA

  • Etymology: "Opisthokonta" means "behind flagella".

  • Includes:

    • Choanoflagellates

    • Plus fungi and animals.

  • Mitochondrial Characteristics:

    • Mitochondria in this lineage have flat cristae (internal membranes).

    • Other lineages have tube-shaped cristae.

COMPARISONS

Rhizarians and Amoebas

  • Comparison:

    • Both groups have amoeboid body forms and move via pseudopodia and cytoplasmic streaming.

  • Clades Grouping Mystery:

    • Differences in grouping arise from the presence or absence of cell walls and the type of flagella present.

    • For instance, Amoeba may have one flagella while rhizarians might have two.

TOPIC 9: FUNGI

FUNGI CLADE

  • Subtopics:

    • Introduction to Fungi

    • Phylogeny

    • Reproduction

    • Symbioses with Other Organisms

    • Importance of Fungi

OPISTHOKONTA CLADE

Relationships

  • Fungi are closely related to animals, supported by:

    • DNA sequence data.

    • Both groups synthesize chitin, a long-chain polymer derived from glucose.

    • Flagella in chytrid spores and gametes are structurally and functionally similar to animal flagella.

    • Both groups store glucose as glycogen, a polysaccharide.

FUNGAL CELL WALLS

  • Composition:

    • Made of chitin, which is a polymer of N-acetylglucosamine (a derivative of glucose).

  • Digestibility:

    • Most animals cannot digest chitin without the aid of bacterial symbionts.

EXTRACELLULAR DIGESTION

  • Process:

    • Digestion occurs outside the organism.

    • Fungi secrete enzymes that break down food sources, after which the nutrients are absorbed by the fungus.

  • Comparison with Animals:

    • In most animals, digestion is also extracellular but occurs within a digestive tract.

FUNGAL MORPHOLOGY

  • Growth Forms:

    • Single-celled forms: Yeasts

    • Multicellular, filamentous forms: Mycelia (singular: mycelium).

    • Some fungal species can adapt to both forms under different conditions.

HYPHAE AND MYCELIA

  • Hyphae:

    • Long, narrow, frequently branching filaments.

  • Mycelium:

    • A mass of hyphae.

    • Each filament has cross-walls called septa with pores that allow for nutrient movement.

DYNAMIC NATURE OF MYCELIA

  • Growth Pattern:

    • Constantly grows towards food sources while dying back in nutrient-scarce areas.

    • The body shape of a fungus can continuously change throughout its life cycle.

THINK-PAIR-SHARE: BENEFITS AND COSTS OF MYCELIA

  • Benefits:

    • High surface-area-to-volume ratio, making nutrient and water absorption highly efficient.

  • Costs:

    • Prone to desiccation; most abundant in moist environments.

    • Reproductive spores have adaptations for surviving dry periods and can germinate when conditions become favorable.

FUNGAL PHYLOGENY

  • Grouping Basis:

    • Groups are defined by reproductive characteristics.

    • Genetic analysis has revealed that not all reproductive characters define monophyletic groups.

    • Phylogenetic relationships have changed significantly in recent years.

FUNGAL ANCESTORS WERE AQUATIC

  • Ancestral Reproductive Character:

    • Swimming spores and gametes present in modern chytridiomycota, and some blastocladiomycota and cryptomycota.

CHYTRIDIOMYCOTA

  • Characteristics:

    • Spores and gametes are motile via flagella and require moist environments for survival.

    • Many chytridiomycota are capable of digesting cellulose, playing a crucial role in decomposing plant materials and parasitizing marine diatoms, as well as being parasites affecting amphibians.

TERRESTRIAL FUNGI AND REPRODUCTIVE STRUCTURES

ZOOPAGOMYCOTA & MUCOROMYCOTA

  • Collectively referred to as "Zygomycetes"; produce a unique and resilient zygosporangium during sexual reproduction.

GLOMEROMYCOTA

  • Defined as a monophyletic group that forms mutualistic associations with plant roots.

  • Examples:

    • Arbuscular Mycorrhizal Fungi which produce large, robust spores.

BASTDIOMYCOTA

  • Defined as a monophyletic group that produces sexual spores on club-shaped sporangia called basidia.

  • Characteristics of Basidia:

    • Four spores form on the exterior surface.

ASCOMYCOTA

  • Monophyletic group that produces sexual spores in sac-like structures called asci.

  • Characteristics of Asci:

    • Eight spores formed within each ascus.

COMPARISONS: BASIDIOMYCOTA VS. ASCOMYCOTA

Feature

Basidiomycota

Ascomycota

Fruiting Body

Basidium

Ascus

Spores

Basidiospores

Ascospores

Spore Location

Outside Ascus

Inside Ascus

Spore Number

Four

Eight

Fungal Cell Structure and Feeding Strategies

  • All fungi have cell walls made of chitin and employ absorptive feeding mechanisms.

  • Different reproductive structures such as zygosporangium, basidia, and asci are characteristic of their respective groups.

FUNGAL REPRODUCTION

  • The reproductive stage, or fungal fruiting body (e.g. mushrooms), produces spores resistant to desiccation that remain dormant until favorable conditions arise.

FRUITING BODIES AND MYCELIA

  • Both structures are composed of hyphae, with reproductive structures being densely packed hyphae compared to more spaced hyphae in the mycelial mass.

FUNGAL LIFE CYCLE

  • Two Types of Reproductive Stages:

    • Asexual Reproduction: Involves the haploid mycelium producing spores.

    • Sexual Reproduction: Involves plasmogamy (fusion of cytoplasm) and karyogamy (fusion of nuclei), producing a diploid zygote.

SYMBIOTIC RELATIONSHIPS

  • Types of Symbioses:

    • Mutualism: Both species benefit.

    • Parasitism: One species benefits at the expense of the other.

MUTUALISTIC SYMBIOSES: MYCORRHIZAE

  • Fungi establish associations with plant roots, crucial for nutrient absorption in early land plant evolution.

  • Statistics: Approximately 90% of land plants today are in contact with mycorrhizal fungi.

  • Benefits: Fungi receive carbon, while plants gain soil nutrients.

TYPES OF MYCORRHIZAL FUNGI

  • Ectomycorrhizal Fungi (EMF): Form a fungal sheath around roots.

  • Endomycorrhizal Fungi or Arbuscular Mycorrhizal (AMF): Penetrate root cells and often form arbuscules with vesicles for nutrient exchange.

LICHENS

  • Composition: Formed from an Ascomycete and a photosynthesis partner (cyanobacteria or algae).

  • Note:* Sometimes includes basidiomycete yeasts.

TYPES OF LICHENS

  • Crustose Lichens: Directly contact the substrate, forming a crust.

  • Foliose Lichens: Leafy, not always in contact with the substrate.

  • Fruticose Lichens: Delicate and shrubby, possess a holdfast.

FUNGAL PARASITES

Chytridiomycosis in Amphibians

  • Caused by a parasitic chytrid, leads to thickening of skin resulting in inability to absorb nutrients, breathe, etc.

White Nose Syndrome in Bats

  • Caused by Pseudogymnoascus destructans, leading bats to awaken from hibernation and expend fat reserves.

  • Statistics: Approximately over 5 million bats affected with a mortality rate exceeding 95%.

SAPROTROPHIC FUNGI AND THE CARBON CYCLE

  • Definitions: Saprotrophs are organisms that digest dead organic material.

  • Significance: Essential for carbon cycling; breaking down deceased organisms prevents accumulation of carbon.

IMPACT OF FUNGI ON HUMAN HEALTH

  • Approximately 300 species of parasitic fungi can cause illness in humans.

  • Common Fungal Skin Diseases: Predominantly caused by ascomycetes; may include diaper rash and toenail fungus.

Serious Fungal Disease Examples

  • Valley Fever: Inhaled ascomycete with 60% of cases showing no symptoms; severe cases can lead to meningitis and death (3-5% mortality).

  • Deadly Fungi: Amanita phalloides (Death Cap Mushroom) has high toxicity and resembles edible mushrooms; half a mushroom can be lethal.

RECOGNIZING DEADLY FUNGI

  • Death Cap Characteristics:

    • Pale yellowish-olive green cap.

    • White stalk with a volva that is not visible until maturity.

    • Produces white spores.