Slime Molds, Fungi, and Multicellularity Vocabulary

Amoebozoans: Overview

• Two main forms:
  • Classic amoebas.
  • Slime molds: Divided into cellular and plasmodial types.

Slime Molds: Nutrient Availability and Morphology

• Nutrient-rich conditions:
  • Cellular slime molds: Exist as typical, small, microscopic cells with a nucleus.
  • Plasmodial slime molds: Exist in a coenocytic state (a large mass with multiple nuclei).
• Nutrient-limited conditions:
  • Both cellular and plasmodial slime molds undergo dramatic shifts in behavior and physical appearance.

Plasmodial Slime Molds: Visual Characteristics

• Coenocytic State: The plasmodial slime mold exists as a large mass with numerous nuclei when nutrients are abundant.

Cellular Slime Molds: Myxamoebas and Slug Formation

• Myxamoebas:
  • Solitary, haploid cells.
  • Actively feed and move around when nutrients are plentiful.
• Nutrient Limitation:
  • Triggers aggregation of myxamoebas to form a slug.
• Slug (Pseudoplasmodium):
  • Migrates and settles down before reproduction.
  • Differentiates into:
    • Base cells.
    • Stalk cells.
    • Tip cells that form spores.
  • Only spores survive to propagate the next generation.

The Altruism Problem

• Only the spore cells survive and reproduce.
• Other cells (base and stalk) die without reproducing.
• Evolutionarily, all cells should want to become spores (selfish behavior).
• However, survival requires differentiation into base, stalk, and spore cells.
• If all cells try to become spores, the entire group dies.

Multicellularity and Cell Differentiation

• Analogy to multicellular organisms like humans:
  • Only germ cells (egg or sperm) pass on genetic material.
  • Somatic cells (all other body cells) die.
• In true multicellular organisms, cells must be subservient to a developmental plan for the organism to survive.

Cheater Cells and Cancer

• Cheater Cells:
  • Cells that deviate from the developmental plan for individual reproduction.
  • In slime molds, these would be cells that abandon their assigned roles (e.g., base) to become spores.
• Cancer Cells:
  • Analogous to cheater cells in multicellular organisms.
  • Mutate and disregard developmental constraints, focusing solely on their own reproduction.

Complex Multicellularity: Key Aspects

• True Differentiation of Cell Types:
  • Cells are not identical and have distinct roles.
  • Example: Base, stalk, and spore cells in slime molds.
• Interdependence of Cell Types:
  • Survival requires the presence and function of all cell types.
• Alignment of Fitness and Export of Fitness:
  • Cells must adhere to a developmental plan and allow a subset of cells to propagate the organism.
• Unicellular Bottleneck:
  • Reconstitution of the organism in the next generation occurs through a single cell type (e.g., spore or gamete).

Cellular vs. Plasmodial Slime Molds: Terminology

• Pseudoplasmodium:
  • The slug formed in cellular slime molds.
  • Represents a truly multicellular entity.
• Plasmodium:
  • The multinucleate mass in plasmodial slime molds.
  • Represents a coenocytic state rather than true multicellularity.

Opisthokonts: Introduction

• Three main groups:
  • Fungi.
  • Animals.
  • Choanoflagellates.

Fungi: Unicellular and Multicellular Forms

• Unicellular Fungi:
  • Yeasts (e.g., baker's yeast).
• Multicellular Fungi:
  • Form mycelium: A branched network of cells.
    • A branched network of cells that may or may not be individual cells, that are all sharing information with each other.
• Mycelium:
  • A network of branched cells.
  • May be individual cells or a coenocytic structure.
  • Facilitates communication between cells.
  • Shape-shifting organism growing through the environment and assuming that shape of the space that they are entering into.

Fungi: Heterotrophic Nature and Absorption

• All fungi are heterotrophs.
• Engage in absorptive heterotrophy:
  • Secrete digestive enzymes into the environment.
  • Absorb digested nutrients directly.
• Requires a high surface area to volume ratio for efficient absorption across their membrane(s).
• Excel at absorbing nutrients (e.g., water, phosphorus).

Fungi: Environmental Sensitivity and Habitat

• Susceptible to dehydration due to their absorptive nature.
• Typically found in damp environments (e.g., basements, laundry hampers).

Fungi: Fruiting Bodies and Spores

• The visible part of multicellular fungi is often the fruiting body (e.g., mushroom).
• Fruiting body: Structure that disperses reproductive cells (spores).
• In basidiomycota (a group of fungi), spores are produced on gills.

Fungi: Diversity and Terrestrial Dominance

• High species richness: Over 100,000 described species.
  • Described: Characterized physical properties and published in peer review.
  • Museum collections are a big part of this as well.
• Most characterized monophyletic groups inhabit terrestrial environments.

Chytrids: Aquatic Fungi and Amphibian Decline

• Chytrids are aquatic fungi.
• May be a polyphyletic grouping.
• Implicated in the global decline of amphibian species.
• Colonize amphibian skin, impairing gas exchange and weakening the animals.

Fungi: Tolerance to Hypotonic Environments

• Many fungi can tolerate hypotonic environments with high nutrient levels.
• This allows them to grow in foods like jam and jelly, where most bacteria cannot survive.
• Mold growth on jam and bread is typically harmless.

Fungi: Life Cycles

• Diverse life cycles, including:
  • Alternation of generations.
  • Gametic life cycle.
  • Zygotic life cycle.
• Some fungi exhibit an n + n state where cells fuse, but nuclei remain separate until certain conditions are met.

Fungi: Ecological Roles

• Essential for nutrient cycling and ecosystem function.
• Decomposers capable of breaking down lignin (found in wood).
• Lignin degradation is crucial for the carbon cycle.
• Mycorrhizal associations: Fungi form symbiotic relationships with plant roots, enhancing nutrient and water absorption.
• The mycelium of the fungus acts like a larger set of access points to water and other nutrients for the plant.

Fungi: Practical Uses and Dangers

• Practical Uses:
  • Food (e.g., mushrooms).
  • Food production (e.g., bread, beer, kimchi).
  • Antibiotics (e.g., penicillin).
  • Biological control agents.
• Dangers:
  • Poisoning from misidentified wild mushrooms.
  • Pathogenic fungi: Can cause nuisance infections (e.g., athlete's foot, ringworm) or severe infections in immunocompromised individuals.
• Fungal infections are often difficult to treat due to the close evolutionary relationship between fungi and animals.
• Drugs are toxic to both fungus and humans.

Choanoflagellates: Filter Feeders and Animal Relatives

• Sister taxa to animals.
• Filter-feeding organisms.
• Can exist as unicellular or multicellular colonies.
• Multicellularity is triggered by nutrient limitation.
• Striking morphological similarity to choanocytes (cells in sponges that pump water through the sponge's body).
• Suggests a shared ancestor between choanoflagellates and animals.

Animals: Multicellular Heterotrophs

• Animal ancestor: Multicellular and heterotrophic.
• Key characteristics:
  • Cell adhesion.
  • Cell communication.

Recap: Multicellularity and Life Cycle Evolution

• Multicellularity has evolved independently multiple times.
• Each instance has unique mechanisms for cell attachment and communication.
• Unicellularity has likely evolved from a unicellular state, but there may be multiple ancestors of animals, no. Looks, like there is one Leca.
• Fungi - There is a lot of diversity within life cycles.

Exam Review

• Two Domains or Three Domains of Life:
  • Three Domains: Bacteria, Archaea, and Eukaryotes
  • Two Domains: Prokaryotes (Archaea and Bacteria), and Eukaryotes
• Bicorns and Unicorns Review