Protist diversity II

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Protist diversity II

• Level 1 Biological Diversity
• Jim Provan

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Phylogeny of eukaryotes
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Diplomonads and Parabasala

• Amitochondriate
• Originally believe to have diverged before
  acquisition of mitochondria
• Presence of nuclear gene homologues now suggests
  that mitochondria have been lost
• Diplomonads have multiple flagella and two
  separate nucleii
• Infectious

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Euglenozoa

• Contain flagella
• Two main groups
• Euglenoids
• Paramylon (glucose polymer) used as a storage
  molecule
• Anterior pocket with one or two flagella
• Kinetoplastids
• Contain a single large mitochondrion and a unique
  organelle (kinetoplast)
• Symbiotic / pathogenic

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Alveolata

• Encompasses
• Photosynthetic flagellates (dinoflagellates)
• Parasites (apicomplexans)
• Group that move by cilia (ciliates)
• Have small, membrane-bound cavities under cell
  surfaces (alveoli)

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Dinoflagellates

• Components of phytoplankton may cause red tides
• Most are unicellular, some are colonial
• Some are photosynthetic symbionts, some are
  non-photosynthetic parasites
• Plastids are brownish and contain chlorophylls a
  and c and a mix of carotenoids (including
  peridinin)
• Food stored as starch
• Chromosomes lack histones and are always
  condensed
• Have no mitotic stages

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Apicomplexans

• All parasites of animals
• Infectious cells called sporozites
• Apex of sporozites has organelles for penetrating
  host cells
• Life cycles have both sexual and asexual
  reproduction, often requiring more than one host
• Several species of Plasmodium cause malaria
• Anopheles mosquitoes serve as intermediate host
• New, resistant forms of Plasmodium are appearing
• Little success in developing a vaccine
• Plasmodium spends most of its life cycle in blood
  or liver cells
• Has the ability to alter its surface antigens

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Life history of Plasmodium
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Ciliates

• Species use cilia to move and feed
• Most solitary cells in fresh water
• Cilia are short and beat in synchrony
• Submembraneous system coordinates beating
• Some species move on leg-like cirri
• Others have rows of tightly packed cilia which
  act as locomoter membranelles
• Among most complex of cells

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Two types of ciliate nuclei

• Macronucleus
• Is large and has over 50 copies of the genome
• Genes packaged into units, each with hundreds of
  copies of just a few genes
• Controls everyday functions by synthesising RNA
• Necessary for asexual reproduction macronucleus
  elongates and splits instead of undergoing
  mitosis
• Micronucleus
• Small and present in 1-80 copies
• Does not function in growth, maintenance or
  asexual reproduction
• Functions in the sexual process of conjugation

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Conjugation and genetic recombination in
Paramecium
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Stramenopiles

• Includes several heterotrophic groups as well as
  a variety of photosynthetic protists (algae)
• Oomycota (water moulds etc.)
• Heterotrophic
• Ostensibly similar to fungi but have analogous
  hyphae, cellulose cell walls (as opposed to
  chitin), prevalent diploid stage and
  biflagellated cells (true fungi have no
  flagellated stages)
• Heterokont algae
• Diatoms have hydrated silica shells and generally
  reproduce asexually
• Chrysophytes (golden algae) have carotene and
  xanthophyll accessory pigments and are mostly
  unicellular
• Phaeophytes (brown algae) are all multicellular
  and mostly marine

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Seaweeds

• Have differentiated tissues and organs similar to
  plants
• Analogous
• Holdfast ? root
• Stipe ? stem
• Blade ? leaf
• Commercially important
• Food (Laminaria and Porphyra)
• Agar
• Thickeners
• Lubricants

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Alternation of generations in algae
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Rhodophyta (red algae)

• Have no flagellated stages
• Accessory pigment phycoerythrin
• Not always red dependent on depth
• Mostly multicellular
• Diverse life cycles but alternation of
  generations is common

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Chlorophyta (green algae)

• Two main groups
• Chlorophyceae
• Charophyceae
• Share a common ancestor with green plants
• Unicellular, colonial or multicellular
• Nearly all reproduce sexually by way of
  biflagellated gametes

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Life cycle of Chlamydomonas
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Rhizopods (amoebas)

• Simplest unicellular protists
• No flagellated stages
• Pseudopodia used in feeding and movement
• All reproduction is asexual
• Inhabit freshwater, marine and soil habitats
• Most are free living, although some are parasitic

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Actinopods

• Possess axopodia, slender form of pseudopodia
• Increase surface area which helps floating and
  feeding
• Some prey may stick to axopodia and be
  phagocytosed
• Two main groups
• Heliozoans (primarily freshwater)
• Radiolarians (primarily marine)

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Plasmodial slime moulds (Myxomycota)
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Cellular slime moulds (Acrasiomycota)