Meet the Protists 1 Protists: Molds Lecture 3 Spring 2014 Domain Eukarya What unites them as a group? The Origin of Eukaryotic Cells Evolution of the endomembrane system Which organelles are included in the endomembrane system? 2 Endosymbiosis Mitochondria Plastids Mitochondria evolved before plastids 3 Fig. 27.7 See Fig. 25.9 Endosymbiosis Evidence Mitochondria & chloroplasts: Similar size to bacteria Have own ribosomes, similar to bacterial ribosomes Inner membranes have enzymes and transport systems homologous to living prokaryotes Reproduction - binary fission Circular DNA with few or no proteins Mitochondrial DNA sequencing and ribosomal RNA sequencing from chloroplasts support the structural and molecular evidence 4 Origin of Multicellular Organisms Earliest multicellular fossil ~1.2 bya Multicellularity evolved several times independently among eukaryotes 5 1
Protist Phylogeny Supergroups Clades A group of species that includes an ancestral species and all of its descendents Paraphyletic 6 Protist Metabolism & Nutrition Most nutritionally diverse of all eukaryotes Photoautotrophs Chemoheterotrophs Mixotrophs combine both 7 Fig. 28.3 Protist Metabolism & Nutrition Group by nutritional mode, not by phylogeny 8 Protist Phylogeny 9 1. Absorptive protists (fungi-like) 2. Ingestive protists protozoans, etc. (animallike) 3. Photosynthetic protists algae (plant-like) These are all paraphyletic groupings Fig. 28.3 Oomycetes and Slime Molds Were classified as fungi previously Nutritional mode Superficially similar structures or lifecycles 10 Phylum Oomycota: the Oomycetes supergoup Chromalveolata clade Stramenopila Key traits of clade 2 flagellum Photosynthetic & non-photosynthetic oomycetes 11 Fig. 28.12 2
Oomycetes Oomycetes = egg fungus Why were the oomycetes considered part of the fungi? Nutritional mode (absorption) Multinucleated filaments (hyphae) Convergent evolution What advantage does this shape (long thin, intertwined) give to absorptive protists (and fungi)? 12 Convergent Evolution What is convergent evolution? 13 Fungal hyphae Oomycete hyphae Oomycetes vs. Fungi 14 Oomycetes: Metabolism & Nutrition 15 Review: Diploid vs. haploid? Oomycetes Fungi Cell Wall Cellulose Chitin Flagella Present (most) Absent (most) Lifecycle Most time as diploid Most time as haploid Absorption Digest food outside their body exoenzymes Decomposers (saprobes) Nutrients from nonliving organisms Water molds (e.g., Saprolegnia spp.) Parasites Nutrients from living organisms (cells of host) White rusts, downy molds Oomycete (water mold) hyphae surrounding dead fly in water Oomycetes: Ecological Roles 16 Asexual Reproduction 17 Plant pathogens Phytophthora What is a spore? Germinating zoospore Zoosporagium Fig. 28.17 3
Sexual Reproduction 18 Phylum Myxogastrida & Phylum Dictyostelida: Slime Molds 19 antheridium oospores Supergroup Unikonta Clade Amoebozoa Key trait Lobe-shaped pseudopodia Cellular extension used in moving and feeding Slime Molds 20 Slime Molds 21 Why were the slime molds considered part of the fungi? Produce fruiting bodies for spore dispersal Convergent evolution Two groups Plasmodial Slime Molds (Myxogastrida) Cellular Slime Molds (Dictyostelida ) Similar feeding modes Phagocytosis Differ in reproductive lifecycle Fungus fruiting body Plasmodial slime mold fruiting body Cellular slime mold fruiting body Plasmodial Slime Molds Phylum Myxogastrida Key traits Unicellular, multinucleate plasmodium 22 Primarily diploid Plasmodial Slime Molds Feeding stage Multinucleate (coenocytic) plasmodium Cytoplasmic streaming Function? 23 Fig, 28.24 4
Response to environment 24 Response to environment 25 Environmental cue No water Low temperature Dormant stage Sclerotia (sclerotium) Environmental cues No food Sexual reproduction stage Spores dispersed by wind Plasmodial Slime Molds: Ecological Roles Decomposers Agricultural pests E.g., cabbage clubroot disease, caused by Plasmodiophora brassicae 26 Phylum Dictyostelida Key traits Cellular Slime Molds 27 Unicellular, with an aggregate stage Primarily haploid No flagellated stage Cellular Slime Molds Feeding stage solitary cells (amoebas) Environmental cue No food Aggregate stage pseudoplasmodium Migration Spore production 28 Cellular Slime Molds: Ecological Roles Decomposer Found in forest soils and leaf litter Cheaters?? 29 5