Phylogeny, Evolution, and Major Lineages: Study Notes

Phylogenetic Concepts and Terminology

Key Terms in Phylogenetics

• Autapomorphic: A derived trait unique to a single lineage or taxon.

• Synapomorphic: A derived trait shared by two or more taxa and their most recent common ancestor.

• Plesiomorphic: An ancestral trait present in the ancestor of a group.

• Symplesiomorphic: An ancestral trait shared by two or more taxa.

• Outgroup: A taxon outside the group of interest, used to infer ancestral states.

• Root: The most ancestral branch in a phylogenetic tree.

• Node: A branching point representing a common ancestor.

• Internal branch: Connects nodes, representing evolutionary lineages.

• Terminal branch: Leads to the tips (current taxa).

• Polytomy: A node with more than two descendant branches, indicating unresolved relationships.

• Tip: The endpoint of a branch, representing a current or extinct taxon.

Homology and Homoplasy

• Homology: Similarity due to shared ancestry.

• Genetic homology: Similarity in DNA sequences due to common ancestry.

• Deep homology: Conservation of genetic regulatory mechanisms across distant lineages.

• Developmental homology: Similarity in developmental processes due to shared ancestry.

• Structural homology: Similarity in anatomical structures due to common ancestry.

• Homoplasy: Similarity not due to shared ancestry (e.g., convergent evolution).

• Convergent Evolution: Independent evolution of similar traits in different lineages.

Developmental Biology: Cell Potency and Regulation

Developmental Cell Potency

• Transcription factors: Proteins that regulate gene expression by binding to DNA.

• Enhancer factors: DNA regions that increase transcription of associated genes.

• Cytoplasmic determinants: Molecules in the egg cytoplasm that influence cell fate.

• Induction cell signaling: Process where one cell influences the fate of another through signaling molecules.

Developmental Cell Processes

• Division control: Regulation of cell division during development.

• Interactions: Communication between cells guiding development.

• Differentiation: Process by which cells become specialized.

• Movement and shape modification: Morphogenetic changes during development.

• Apoptosis: Programmed cell death, essential for normal development.

Molecular Regulation

• Morphogens: Substances that establish gradients and pattern tissues.

• Genetic Regulatory Cascades: Hierarchical gene regulation controlling development.

Evolution of Life Forms on Earth

Major Events and Processes

• LUCA: Last Universal Common Ancestor of all life.

• Autotrophs: Organisms that produce their own food from inorganic sources.

• Chemoautotrophs: Use chemical energy to fix carbon.

• Photoautotrophs: Use light energy to fix carbon.

• Wood-Ljungdahl Pathway: Ancient pathway for carbon fixation in some bacteria and archaea.

• Anoxygenic photosynthesis: Photosynthesis that does not produce oxygen.

• Oxygenic photosynthesis: Photosynthesis that produces oxygen, leading to an oxygen-rich atmosphere.

Phylogenetic Models

• Three Domain vs. Two Domain life phylogenies: Competing models for the tree of life (Bacteria, Archaea, Eukarya vs. Bacteria and Archaea with Eukarya nested within Archaea).

Origin of Eukaryotes

• Archaea cell membrane infolding: Hypothesized to produce the nucleus and endoplasmic reticulum.

• Endosymbiosis: Origin of mitochondria (from aerobic heterotrophic prokaryote) and chloroplasts (from cyanobacteria).

• Development of cytoskeleton, mitosis, and meiosis: Key innovations in eukaryotes.

• Primary, Secondary, Serial Secondary, Tertiary endosymbiosis: Multiple rounds of endosymbiotic events leading to complex plastids.

Major Evolutionary Events

• Snowball Earth episodes: Periods of extensive global glaciation affecting evolution.

• Adaptive Radiation: Rapid diversification of lineages into new ecological niches.

• Extinction effects: Mass extinctions reshaping biodiversity.

Major Eukaryotic Lineages and Life Cycles

Eukaryotic Synapomorphies

• Features unique to eukaryotes, such as membrane-bound organelles, linear chromosomes, and complex life cycles.

TSAR and Excavata Life Cycles

• Haploid dominant: Life cycle where the haploid stage is predominant.

• Diploid dominant: Life cycle where the diploid stage is predominant.

• Sporophyte/Gametophyte Alternation: Alternation between multicellular haploid (gametophyte) and diploid (sporophyte) generations.

Archaeplastida and Related Groups

• Archaeplastida: Major group including red algae, green algae, and land plants.

• Viridiplantae: Green plants, including green algae and land plants.

• Embryophyta: Land plants.

• Tracheophyta: Vascular plants.

• Spermatophyta: Seed plants.

• Glaucophyta, Rhodophyta, Ulvophyceae, Zygnematophyceae: Major algal lineages.

Plant Evolutionary Innovations

• Chlorophyll a, Chlorophyll b, Beta-carotene, Phycobilins: Photosynthetic pigments.

• Floridean Starch, Viridiplantae Starch: Storage carbohydrates.

• Sporopollenin: Resistant polymer in spores and pollen.

• Cuticle, Pores, Stomata: Adaptations to terrestrial life.

• Vascular tissue, cellulose, lignin, tracheids: Support and transport structures.

• True roots, rhizoids, true leaves, wood, seeds, flowers, fruits: Key plant structures.

• Gametangia, egg retention, embryo retention: Reproductive adaptations.

Plant Life Cycles

• Haploid-dominated vs. Sporophyte-dominated life cycles.

• Alternation of Generations: Alternation between multicellular haploid and diploid stages.

• Antheridia: Male gametangia.

• Archegonia: Female gametangia.

• Heterospory: Production of microspores (male) and megaspores (female).

• Pollen: Male gametophyte in seed plants.

Fungi: Structure, Life Cycles, and Phylogeny

Fungal Structure and Nutrition

• Yeasts: Unicellular fungi.

• Mycelia (Mycelium): Multicellular, filamentous fungal body.

• Hyphae: Thread-like filaments making up mycelium.

• Septa: Cross-walls dividing hyphae into cells.

• Coenocytic hyphae: Hyphae lacking septa, multinucleate.

• Heterotrophic: Obtain nutrients by absorption.

• Detritivores: Decompose dead organic matter.

• Storage compounds: Glycogen, starch, mannitol, laminarin.

Fungal Ecological Relationships

• Parasitism: One organism benefits at the expense of another.

• Commensalism: One benefits, the other is unaffected.

• Mutualism: Both organisms benefit.

• Mycorrhizae: Symbiotic association between fungi and plant roots.

Fungal Sexual Morphology and Life Cycles

• Flagellated gametes and spores: Example of deep homology with other eukaryotes.

• Zygosporangia: Sexual structure in zygomycetes.

• Basidia: Spore-producing structure in basidiomycetes.

• Asci: Spore-producing structure in ascomycetes.

Fungal Phylogeny

• Glomeromycetes, Ascomycota, Basidiomycota: Major fungal groups.

General Fungal Life Cycle

• Plasmogamy: Fusion of cytoplasm from two parent mycelia.

• Heterokaryotic: Stage with two or more genetically distinct nuclei per cell.

• Karyogamy: Fusion of nuclei to form diploid zygote.

Specific Fungal Life Cycles

• Chytrid Life Cycle: Includes both sporophytic and gametophytic mycelium.

• Zygomycetes Life Cycle: Formation of zygosporangia and asexual sporangium.

• Basidiomycota Life Cycle: Diploid basidium produces four haploid spores.

• Ascomycota Life Cycle: Diploid ascus produces eight haploid spores.

Animal Evolution: Holozoa, Metazoa, and Body Plans

Holozoa and Primitive Lineages

• Holozoa: Clade including animals and their closest unicellular relatives.

• Ichthyosporea, Filasterea, Choanoflagellates: Primitive unicellular and colonial lineages.

Metazoa (Animals)

• Primitive lineages are multicellular and differentiated, with multiple cell types.

Major Animal Groups

• Porifera: Sponges.

• Ctenophora: Comb jellies.

• Cnidaria: Jellyfish, corals, etc.

• Placozoa: Simple, flat animals.

• Protostome vs. Deuterostome: Major divisions based on embryonic development.

• Lophotrochozoa, Ecdysozoa: Protostome subgroups.

• Ambulacraria, Chordata: Deuterostome subgroups.

Developmental Genetics and Body Plans

• Developmental Genetics Tool-kit: Genes controlling animal development.

• Genetic Regulatory Cascade: Hierarchical gene regulation.

• Regulatory Transcription factors, Enhancers: Control gene expression.

• Hox Genes: Specify body regions along the anterior-posterior axis.

• Homeotic Mutations: Mutations causing body parts to develop in the wrong place.

Major Evolutionary Events in Animals

• Cambrian Explosion: Rapid diversification of animal body plans.

• Origin of Embryonic Tissue Layers: Diploblastic (two layers) vs. triploblastic (three layers).

• Origin of Contractile Tissue: Evolution of muscle.

• Body Symmetry: Radial vs. bilateral symmetry.

• Cephalization and Nervous System: Evolution of a head and centralized nervous system.

Bilateria and Body Cavities

• Bilateria: Animals with bilateral symmetry and three tissue layers.

• Body Cavities: Coelomate, pseudocoelomate, acoelomate conditions.

Phylogenetic Hypotheses

• Scientists use morphological and molecular data to infer evolutionary relationships.

• Polytomy: May indicate rapid diversification or insufficient data.

Hox Genes and Morphological Traits

• Hox gene expression patterns correlate with body plan diversity (e.g., Serpentes example: loss of limbs).

Table: Comparison of Major Plant Groups and Key Traits

Group	Vascular Tissue	Seeds	Flowers	Dominant Generation
Non-vascular Embryophyta	No	No	No	Gametophyte
Vascular Embryophyta	Yes	No	No	Sporophyte
Gymnosperma	Yes	Yes	No	Sporophyte
Angiosperma	Yes	Yes	Yes	Sporophyte

Example: Alternation of Generations in Plants

• Sporophyte (2n) produces haploid spores by meiosis.

• Gametophyte (n) produces gametes by mitosis.

• Fertilization produces a diploid zygote, which grows into the sporophyte.

Example: Fungal Sexual Life Cycle (Ascomycota)

• Fusion of hyphae (plasmogamy) produces a heterokaryotic stage.

• Nuclear fusion (karyogamy) forms a diploid nucleus in the ascus.

• Meiosis produces eight haploid spores per ascus.

Additional info:

• Some terms (e.g., "Serial Secondary" and "Tertiary" endosymbiosis) refer to multiple rounds of plastid acquisition in eukaryotic evolution.

• "TSAR" refers to a major eukaryotic supergroup: Telonemia, Stramenopiles, Alveolates, and Rhizaria.

• "Serpentes example" refers to the evolutionary loss of limbs in snakes, associated with Hox gene changes.