Fungi

Germinating Spores and Mycelium

  • Germinating Spores: Necessary for the reproduction and propagation of fungi.

  • Mycelium: A network of filamentous structures that forms the vegetative part of a fungus, essential for nutrient absorption.

  • Cross Section of Gill: Structures within mushrooms that house reproductive cells.

  • Basidia: Club-shaped structures where spores are produced in certain fungi.

  • Button Stage: The initial stage of mushroom development before it matures into the mature basidiocarp.

  • Mature Basidiocarp: The fully developed fruiting body of a fungus, which is formed to produce and release spores.

Fungi Overview

  • Fungi are more closely related to animals than plants and are primarily heterotrophic.

  • They play essential roles in ecosystems as decomposers.

Geologic Time Scale

  • Definition: Divides Earth's history into a sequence of geologic eons and eras.

  • Major geological or biological events defined the eons, including occurrences like mass extinctions.

Precambrian SuperEon

  • Extent: Accounts for 88% of Earth's history.

  • Oldest Fossils: Likely represent the beginnings of life.

    • 3.5 Billion Years Ago: Introduction of Archaean Eon.

    • First life forms: Bacteria and Archaea.

    • Oldest known fossils: Stromatolites.

    • 4.6 Billion Years Ago: Hadean Eon.

    • Event: Formation of Earth.

Prokaryotes: Bacteria and Archaea

  • Characteristics:

    • Lack a nucleus; DNA is located in a region called the nucleoid.

    • No membrane-bound organelles are present.

    • Typically unicellular.

    • Possess a small cell size, leading to a high surface area to volume ratio.

    • Reproduce rapidly through binary fission.

    • Exhibit horizontal gene transfer.

  • Differences From Eukaryotes: Prokaryotes differ in cellular organization but are not inferior in evolutionary success.

Horizontal Gene Transfer

  • Importance: Highlights the complexity of defining species in prokaryotes.

  • Mechanisms:

    • Transformation: Uptake of DNA fragments from the environment by individual cells.

    • Conjugation: Direct transfer of genes between two cells.

    • Transduction: Gene transfer facilitated by viruses.

Bacteria vs. Archaea

  • Bacteria:

    • Contain peptidoglycan cell walls, which form a mesh-like layer surrounding the cytoplasmic membrane.

    • Display enormous metabolic diversity and include cyanobacteria known for oxygenic photosynthesis.

    • Include many pathogens affecting humans, agriculture, and wildlife.

  • Archaea:

    • Lack peptidoglycan, possess unique membrane lipids, and are often extremophiles but not exclusively.

    • Molecularly, Archaea are more closely related to eukaryotes than bacteria.

Prokaryotes and Planetary Chemistry

  • Impact on Nutrient Cycles:

    • Regulate global cycles of carbon, nitrogen, and sulfur.

    • Cyanobacteria carry out oxygenic photosynthesis.

    • Nitrogen fixation occurs converting N₂ into NH₃.

    • Processes include nitrification and denitrification.

    • Archaeal methanogenesis is significant in carbon cycling.

    • Other contributions include sulfur and iron metabolism, and decomposition.

Evolutionary Catalysts

  • Key Concepts:

    • Endosymbiosis leads to the origin of mitochondria and chloroplasts in eukaryotic cells.

    • Microbiomes are essential in both animals and plants.

    • Rhizobia and nitrogen-fixing symbiotic relationships are critical for ecosystems.

    • Endorsed the Great Oxygenation Event, which dramatically changed Earth’s atmosphere.

Pathogenic Bacteria

  • Overview: A minority of bacterial species are pathogenic; they have affected various sectors significantly.

  • Human History: Examples include the plague caused by Yersinia pestis which shaped demographics and societies.

  • Agricultural Impact: The fireblight pathogen, Erwinia, alters agricultural practices.

  • Wildlife Effects: Caused population declines, such as Leptospirosis.

  • Broader Impacts:

    • Challenge public health systems.

    • Regulate populations and restructure communities.

Forces of Selection

  • Pathogens act as agents of natural selection, influencing evolutionary and ecological dynamics.

  • Selection Pressures:

    • Host–parasite coevolution leading to the Red Queen Hypothesis.

    • Rapid microbial evolution, such as antibiotic resistance exemplified by Mycobacterium tuberculosis.

    • Changes in ecological structures.

Precambrian SuperEon Continued

  • 2.5 Billion Years Ago: Proterozoic Eon, significant due to the first eukaryotes and multicellular organisms.

  • 2.5 to 2 Billion Years Ago: Notable Great Oxidation Event.

  • 635 Million Years Ago: Ediacaran Period, marking the emergence of the oldest animal fossils like sponge-like Otavia and Archaeaspinus.

Paleozoic Era

  • Comprises 6% of Earth's History. (“Paleo” = ancient, “zoic” = of animals)

  • 542 Million Years Ago: Cambrian explosion:

    • Emergence of sponges, worms, jellies, and trilobites.

    • Ancestors of all modern animals appear.

  • 488 Million Years Ago: Ordovician Period characterized by algae, jawless fishes, and the first land plants.

  • 443 Million Years Ago: Silurian Period seeing the advent of jawed fishes and the appearance of insects.

Continued Paleozoic Era

  • 417 Million Years Ago: Devonian Period saw the rise of:

    • First seed plants.

    • Bony fishes and amphibians.

  • 359 Million Years Ago: Carboniferous Period marked by:

    • Emergence of reptiles and abundant ferns.

    • Flighted insects arise for the first time.

  • 290 Million Years Ago: Permian Period served as the stage for conifers, more reptiles, and the formation of Pangaea as amphibians decline.

  • Specific examples: Elkinsia polymorpha and Mazothairos.

Mesozoic Era

  • 4% of Earth's History. (“Meso” = middle, “zoic” = of animals)

  • 251 Million Years Ago: Noteworthy extinction event, the Permian extinction.

  • 248 Million Years Ago: Triassic Period emergence:

    • First dinosaurs and mammals.

    • Conifer and cycad forests flourish.

    • Appearance of Pterosaurs.

  • 206 Million Years Ago: Jurassic Period reveals:

    • Introduction of first birds.

    • Dominance of large reptiles in land and water conditions.

    • First flowering plants evolve, exemplified by Eotephradactylus mcintireae.

Continued Mesozoic Era

  • 144 Million Years Ago: Cretaceous Period characterized by:

    • Dinosaurs widespread.

    • Diversification of Angiosperms.

    • Present-day continents reflected.

  • 65 Million Years Ago: K-T Extinction event marks a significant extinction epoch.

Cenozoic Era

  • Less than 2% of Earth's History. (“Ceno” = new, “zoic” = of animals)

  • 65 Million Years Ago: Paleogene Period emergence:

    • Paleocene: The rise of first primates; diversification of pollinating insects.

    • Eocene: Rapid diversification of mammals and angiosperms; first whales appear.

    • Oligocene: Presence of elephants, horses, and grasses.

    • Examples: Plesiadapis and Pakicetus.

Continued Cenozoic Era

  • 23.8 Million Years Ago: Neogene Period highlights:

    • Miocene brings about first great apes, continued diversification of Mammals, and expansion of grasslands.

    • Pliocene sees early humans (e.g., Australopithecus) and modern whales evolve.

  • 1.8 Million Years Ago: Quaternary Period holds:

    • Pleistocene: Presence of Homo sapiens alongside large mammals, concluding with the Ice Age.

    • Recent events correspond with human civilization, alongside the potential for a sixth mass extinction event.

Notable Precambrian Structures

  1. Precambrian SuperEon

  2. Proterozoic Eon

  3. Archean Eon

  4. Hadean Eon

  • Geological Categories:

    • Eon

    • Era

    • Period

    • Epoch

Organizing the Timeline of Life

  • New Ways of Understanding:

    • Names associated with significant developments in organisms, starting from the Cambrian explosion 543 MYA to the emergence of modern Homo sapiens 0.01 MYA.

    • Life Evolution Factors: Documented series of milestones including notable species developments.

Fungi Classifications: Opisthokonta and Amoebozoa

  • Description: Most fungi are multicellular eukaryotes.

    • More closely related to animals than plants.

  • Heterotrophic Nutrition: Achieved through external digestion via enzymes; nutrients are absorbed across cell walls.

  • Cell Walls: Comprise chitin, a substance also found in arthropods.

  • Diversity: More than 100,000 described species exist.

  • Lifecycle: Primarily haploid during the life cycle.

Mycelium Structure and Function

  • Mycelium: Comprises a feeding network crucial for nutrient absorption.

    • Hyphae: Filamentous cells that release digestive enzymes.

  • Mushrooms: Reproductive structures (fruiting bodies) that produce haploid spores for dissemination.

Fungal Life Cycle (Dikarya Model)

  1. Hyphae Formation: Creates a haploid mycelium.

  2. Mating Types: Engage in

    • Plasmogamy: Fusion of cytoplasm where nuclei remain separate, leading to Dikaryotic stage (n + n).

    • Karyogamy: Fusion of nuclei resulting in a diploid zygote (2n), which undergoes meiosis to produce haploid spores.

  3. Dispersal and Germination: Spores disperse and germinate into new haploid mycelium.

Major Clades of Fungi

  1. Chytridiomycota: Early-diverging lineage; aquatic fungi with flagellated spores; includes pathogen impacting amphibians.

  2. Zygomycota: Now encompassing multiple lineages such as:

    • Mucoromycota: Filamentous and saprotrophic; includes bread molds like Rhizopus.

    • Zoopagomycota: Predominantly endo- or ectoparasitic fungi.

  3. Glomeromycota: Arbuscular mycorrhizal fungi, known for ancient symbiotic relationships with plants aiding land colonization.

  4. Dikarya: Featured by septate hyphae, divided into:

    • Ascomycota: Known as sac fungi.

    • Basidiomycota: Includes “club fungi” for spore production via basidia.

Fungi as Ecosystem Engineers

  • Decomposition Role: They engage in ecosystem respiration and nutrient cycling.

  • Digestive Capability: Fungi uniquely digest lignin, critical for breaking down dead plant biomass, preventing accumulation, and enabling carbon cycling.

  • Carbon Sequestration: Their activity significantly influences atmospheric CO₂ levels.

Mycorrhizal Networks

  • Plant Associations: 80–90% of plant species establish mycorrhizal relationships with fungi.

  • Carbon Flow Dynamics: Carbon flows from plants to fungi and vice versa for nutrients, notably phosphorus, demonstrating complex nutrient exchange.

  • Ecological Connectivity: Networks can connect multiple plants, thus redistributing vital resources across ecosystems.

Fungal Nutrient Limitation

  • Nutrient Accessibility: Nitrogen and phosphorus are common limiting factors in ecosystems.

  • Enzymatic Role: Fungal enzymes break down organic nutrient reservoirs, affecting plant community dynamics and succession lifecycle patterns.

Fungal Pathogens as Selective Forces

  • Ecological Disruption: Serve as parasites and ecological agents influencing natural selection, examples include:

    • Powdery mildew: Drives plant evolution.

    • Dutch elm disease: Restructures forest ecosystems.

    • White-nose syndrome: Causes cascading ecosystem effects.

    • Cordyceps: Manipulates host behavior.

Symbiotic Relationships in Fungi

  1. Lichens: Formed by a mutualistic association between fungi and algae/cyanobacteria, serve as primary colonizers of bare rocks, contribute to soil formation through nitrogen fixation if cyanobacteria are present.

  2. Mycorrhizae: Mycorrhizal fungi colonize plant roots to enhance water and mineral absorption capability, while plants provide sugars to fungi, showcasing coevolution and a critical role in early terrestrial ecosystems.

Ecological Roles of Fungi

  • Decomposers: Play a vital role in recycling nutrients within ecosystems.

  • Parasites: Cause diseases in plants and animals.

  • Mutualists: Participate in symbiotic relationships with plants (mycorrhizae) and organisms (lichens).

  • Commercial Importance: Fungi have significance in food production, fermentation processes, and medical applications.