Phylogenetic Concepts and Terminology

Key Terms in Phylogenetics

Understanding evolutionary relationships requires precise terminology. The following terms are foundational in constructing and interpreting phylogenetic trees.

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

• Synapomorphic: A derived trait shared by two or more lineages, indicating common ancestry.

• 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 of 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: Represents an extant 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 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 and Evolution

Developmental Cell Potency and Regulation

Developmental processes are regulated by genetic and environmental factors, influencing cell fate and organismal complexity.

• 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.

Morphogens and Genetic Regulatory Cascades

• Morphogens: Substances that establish positional information in developing tissues.

• Genetic Regulatory Cascades: Hierarchical gene regulation controlling development.

Evolution of Life Forms on Earth

Major Transitions and Metabolic Pathways

• 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.

Endosymbiosis and Eukaryotic Evolution

• Three Domain vs. Two Domain life phylogenies: Competing hypotheses about the major divisions of life (Bacteria, Archaea, Eukarya).

• Archaea cell membrane infolding: Hypothesized origin of the nucleus and endoplasmic reticulum.

• Endosymbiosis: Origin of mitochondria and chloroplasts via engulfment of prokaryotes.

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

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

Major Evolutionary Events

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

• Adaptive Radiation: Rapid diversification of lineages.

• Extinction effects: Mass extinctions shaping evolutionary history.

Major Eukaryotic Lineages and Life Cycles

Eukaryotic Synapomorphies and Supergroups

• TSAR and Excavata: Major eukaryotic supergroups with diverse 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 and diploid generations.

Archaeplastida and Plant Evolution

• Archaeplastida: Supergroup 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 Structure and Adaptations

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

• Floridean Starch, Viridiplantae Starch: Storage carbohydrates.

• Sporopollenin, Cuticle, Pores, Stomata: Adaptations for terrestrial life.

• Vascular tissue, cellulose, lignin, Tracheids, True Roots, Rhizoids, True leaves, Wood, Seeds: Key innovations in plant evolution.

• Flower anatomy, Fruits: Reproductive structures in angiosperms.

• Gametangia, Egg retention, Embryo retention: Features of plant reproduction.

Plant Life Cycles and Evolutionary Trends

• Haploid-dominated life cycles: Common in algae.

• Alternation of Generations: Alternation between multicellular haploid (gametophyte) and diploid (sporophyte) stages.

• Antheridia, Archegonia: Male and female gametangia, respectively.

• Gametophyte-dominated vs. Sporophyte-dominated life cycles: Evolutionary trend from gametophyte to sporophyte dominance.

• Heterospory: Production of two types of spores (microspores and megaspores).

• Pollen: Male gametophyte in seed plants.

• Fertilization evolutionary trends: Increasing independence from water for fertilization.

Fungi: Structure, Life Cycles, and Phylogeny

Fungal Structure and Nutrition

• Yeasts: Unicellular fungi.

• Mycelia (Mycelium): Networks of hyphae forming the main body of multicellular fungi.

• Heterotrophic: Obtain nutrients by absorbing organic matter.

• Detritivores: Decompose dead organic material.

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

• Hyphae: Filamentous structures making up the mycelium.

• Septa: Cross-walls dividing hyphae into cells.

• Coenocytic hyphae: Hyphae lacking septa, containing many nuclei.

Fungal Ecological Relationships

• Parasitism: Fungi obtain nutrients from living hosts, harming them.

• Commensalism: Fungi benefit without affecting the host.

• Mutualism: Both fungi and their partners benefit (e.g., mycorrhizae).

• Mycorrhizae: Symbiotic associations between fungi and plant roots.

Fungal Sexual Morphology and Life Cycles

• Flagellated gametes and spores: Ancestral trait, example of deep homology.

• Zygosporangia, Basidia, Asci: Sexual structures in different fungal groups.

Fungal Phylogeny and Major Groups

• Glomeromycetes, Ascomycota, Basidiomycota: Major fungal lineages.

Generalized Fungal Life Cycle

• Plasmogamy: Fusion of cytoplasm from two parent mycelia.

• Heterokaryotic stage: Cells contain two or more genetically distinct nuclei.

• Karyogamy: Fusion of nuclei to form a diploid zygote.

Specific Life Cycles

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

• Zygomycetes Life Cycle: Features 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

Primitive Holozoan Lineages

• Ichthyosporea, Filasterea, Choanoflagellates: Unicellular and colonial relatives of animals.

Metazoa (Animals)

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

Major Animal Groups and Phylogenetic Hypotheses

• Porifera, Ctenophora, Cnidaria, Placozoa: Basal animal lineages.

• Protosome, Deuterosome: Major divisions of bilaterian animals.

• Lophotrochozoa, Ecdysozoa: Subgroups of protostomes.

• Ambulacraria, Chordata: Subgroups of deuterostomes.

• Diploblastic: Animals with two embryonic tissue layers.

• Triploblastic: Animals with three embryonic tissue layers.

Developmental Genetics and Body Plan Evolution

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

• Genetic Regulatory Cascade: Hierarchical gene regulation during development.

• Regulatory Transcription factors, Enhancers: Control gene expression patterns.

• Hox Genes: Specify body segment identity.

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

Major Evolutionary Innovations

• Cambrian Explosion: Rapid diversification of animal body plans.

• Origin of Embryonic Tissue Layers: Key step in animal evolution.

• Origin of Contractile Tissue: Evolution of muscle and movement.

• Body Symmetry: Radial vs. bilateral symmetry.

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

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

• Body Cavities: Coelomate, pseudocoelomate, and acoelomate conditions.

Hox Genes and Morphological Traits

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

Table: Comparison of Major Plant Groups and Key Traits

Additional info:

• Polytomy in phylogenetic trees can indicate either rapid diversification or insufficient data to resolve relationships.

• Serial secondary and tertiary endosymbiosis refer to multiple rounds of plastid acquisition in eukaryotic evolution.

• Examples of convergent evolution include wings in bats and birds, and camera eyes in cephalopods and vertebrates.