Protists: Molds Lecture 3 Spring 2014
Meet the Protists 1 Domain Eukarya What unites them as a group?
The Origin of Eukaryotic Cells 2 Evolution of the endomembrane system Which organelles are included in the endomembrane system? Fig. 27.7 See Fig. 25.9
Endosymbiosis 3 Mitochondria Plastids Mitochondria evolved before plastids
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 5 Earliest multicellular fossil ~1.2 bya Multicellularity evolved several times independently among eukaryotes
6 Protist Phylogeny Supergroups Clades A group of species that includes an ancestral species and all of its descendents Paraphyletic Fig. 28.3
Protist Metabolism & Nutrition 7 Most nutritionally diverse of all eukaryotes Photoautotrophs Chemoheterotrophs Mixotrophs combine both
Protist Metabolism & Nutrition 8 Group by nutritional mode, not by phylogeny 1. Absorptive protists (fungi-like) 2. Ingestive protists protozoans, etc. (animallike) 3. Photosynthetic protists algae (plant-like) These are all paraphyletic groupings
9 Protist Phylogeny Fig. 28.3
Oomycetes and Slime Molds 10 Were classified as fungi previously Nutritional mode Superficially similar structures or lifecycles
Phylum Oomycota: the Oomycetes 11 supergoup Chromalveolata clade Stramenopila Key traits of clade 2 flagellum Photosynthetic & non-photosynthetic oomycetes Fig. 28.12
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 Fungal hyphae Oomycete hyphae
13 Convergent Evolution What is convergent evolution?
Oomycetes vs. Fungi 14 Review: Diploid vs. haploid? Oomycetes Fungi Cell Wall Cellulose Chitin Flagella Present (most) Absent (most) Lifecycle Most time as diploid Most time as haploid
Oomycetes: Metabolism & Nutrition 15 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 Plant pathogens Phytophthora
Asexual Reproduction 17 What is a spore? Germinating zoospore Zoosporagium Fig. 28.17
Sexual Reproduction 18 antheridium oospores
Phylum Myxogastrida & Phylum Dictyostelida: Slime Molds 19 Supergroup Unikonta Clade Amoebozoa Key trait Lobe-shaped pseudopodia Cellular extension used in moving and feeding
Slime Molds 20 Why were the slime molds considered part of the fungi? Produce fruiting bodies for spore dispersal Convergent evolution Fungus fruiting body Plasmodial slime mold fruiting body Cellular slime mold fruiting body
Slime Molds 21 Two groups Plasmodial Slime Molds (Myxogastrida) Cellular Slime Molds (Dictyostelida ) Similar feeding modes Phagocytosis Differ in reproductive lifecycle
Plasmodial Slime Molds Phylum Myxogastrida Key traits Unicellular, multinucleate plasmodium 22 Primarily diploid
Plasmodial Slime Molds 23 Feeding stage Multinucleate (coenocytic) plasmodium Cytoplasmic streaming Function? Fig, 28.24
Response to environment 24 Environmental cue No water Low temperature Dormant stage Sclerotia (sclerotium)
Response to environment 25 Environmental cues No food Sexual reproduction stage Spores dispersed by wind
Plasmodial Slime Molds: Ecological Roles 26 Decomposers Agricultural pests E.g., cabbage clubroot disease, caused by Plasmodiophora brassicae
Cellular Slime Molds 27 Phylum Dictyostelida Key traits Unicellular, with an aggregate stage Primarily haploid No flagellated stage
Cellular Slime Molds 28 Feeding stage solitary cells (amoebas) Environmental cue No food Aggregate stage pseudoplasmodium Migration Spore production
Cellular Slime Molds: Ecological Roles 29 Decomposer Found in forest soils and leaf litter Cheaters??