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The Protista: Evolution’s 2nd Wave ν ν ν ν 100,000 living species, 35,000 fossilized members Ancestors to metazoans: plants, fungi, animals Low specialization, high complexity The origins of Eukaryotic complexity: Two trends allowed the eukarya to arise from the eubacteria υ Compartmentalized cell structure υ Increased genomic size The Evolution of Compartmental Organellar Structure: The Autogenesis Theory ν ν 1. Increased membrane surface area 2. Compartmentalization w/ regional specialization: Nuclear membrane, endoplasmic reticulum, Golgi apparatus, others Evidence for the Endosymbiotic Theory: ν ν ν ν ν ν 1. size 2. homology to prokaryotic plasma membranes 3. replication: binary fission, not de novo synthesis 4. DNA structure: circular loop and packing 5. complete “intracellular” intracellular” protein synthesizing machinery 6. ribosomal structure, sequence and Abx sensitivity Traditional hypothesis for how the three domains of life are related. Note how the Eukarya are monophyletic. monophyletic. The Origins of Eukaryotic Diversity: K. Protista ν I. Evolutionary Trends: Proks. Proks. to Euks. Euks. υ υ A. Comparmentalized Cell Structure Φ Autogenesis Theory Φ Serial Endosymbiotic Theory B. Genome Size and Sex Φ Archezoans: Diplomonads Φ 3 Life Cycles: Meiosis, sex and genetic variation Evolution of Compartmentalized Structure: Serial Endosymbiotic Theory - Lynn Margulis 1. Parasites or prey are internalized 2. Mutualistic relationship develops Serial Endosymbiosis: Primary and secondary endosymbiosis form the basis for the origin of algal diversity A hypothetical proposal toward the rapid evolution of complex eukaryotic structure and diversity: An alternative “polyphyletic” hypothesis for how the three domains of life are related ν ν ν ν Consider the concept of “horizontal evolution” evolution” - the wholesale incorporation of genomes Consider the evolutionary process brought about by SET: “Symbiogenesis” Symbiogenesis” - the origin or new organelles or life forms via symbiotic relationships b/w previously independent organisms (networking instead of competition) Margulis - Euks are better conceived as microbial communities rather than as individuals Margulis - Among early euks, euks, SET has greater importance than random mutations Protistans are NOT monophyletic Archaebacterium: provides cytoplasm Autogensies: expands mesosome to provide membranes Daptobacter or Bdellovibrio bacteria: provide O2respiring functions (mitochondria) Cyanobacteria: provide photosynthetic functions Protists w/ aerobic metabolism Fungi Chloroplast containing algae Animals Plants The Nuclear Lineage: Genomic Size, Mitosis, Meiosis and Sex Among bacteria: Is more DNA adaptive? Archezoans: Giardia a diplomonad What are the advantages of diploidy? diploidy? υ More genes and vegetative life style υ Ability to mask bad genes and test new genes υ Prerequisite for sexual reproduction 3 Patterns of cell division: υ Binary fission υ Mitosis υ Meiosis ν ν ν ν Note: These groups only represent a sample of protist diversity; many other lineages are not shown on the tree. A comparison of mitosis and meiosis: Identical duplication versus guaranteed variation through recombination and gametic fusion Eubacterium: spirochete provides undulopodium (flagellum) and eventually mitosis The Evolution of Sexual Reproduction: Life Cycles of Protists and Other Eukaryotes ν ν ν 1. The Gametic Cycle: diploid dominant υ protozoans, all animals, a few algae 2. The Zygotic Cycle: haploid dominant υ some fungal protists, fungi, some algae 3. The Sporic Cycle: Alternation of Generations υ algae and higher plants, 1n and 2n adult stages, shift in dominance 3 Patterns of Sexual Reproduction 2n adult meiosis mitosis GAMETIC n gametes 2n zygote 2n adult mitosis meiosis 2n zygote SPORIC n adult mitosis n gametes mitosis n spores ZYGOTIC meiosis n gametes 2n zygote mitosis n adult n spores mitosis