Protist diversity I

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Protist diversity I

• Level 1 Biological Diversity
• Jim Provan

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Diversity of protists

• In Whittakers five-kingdom system, eukaryotes
  were divided into four of the five kingdoms
• Animalia
• Fungi
• Plantae
• Protista
• Kingdom Protista originally contained all
  eukaryotes that did not fit into one of the other
  three kingdoms
• Mostly microscopic, single-celled organisms
• Extremely diverse
• Paraphyletic

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Protist diversity
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Paraphyly of protists
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Protist diversity

• Nutrition
• Mostly aerobic and use mitochondria
• May be photoautotrophic, heterotrophic or
  mixotrophic
• Different modes scattered throughout different
  lineages
• Motility
• Life cycles
• Asexual, sexual and syngamous
• Can form cysts
• Habitat
• Mostly aquatic plankton and phytoplankton
• Symbionts

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The chloroplast

• Carries out photosynthesis
• Contains own genome
• Believed to be of endosymbiotic origin
• Phylogenetically related to cyanobacteria

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The mitochondrion

• Primary site of oxidative phosphorylation
• Contains own genome
• Gene sequences suggest closest relationship with
  ?-proteobacteria
• Believed to be of endosymbiotic origin

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Compartmentalisation of the eukaryotic cell
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Serial endosymbiosis

• Explains evolution of mitochondria and plastids
• Theory proposes ancestral endosymbiosis (one cell
  living inside another)
• Mitochondria derived from a-proteobacteria
• Chloroplasts derived from cyanobacteria
• Either undigested prey or internal parasites
• Some eukaryotes lack chloroplasts but most have
  mitochondria suggests that mitochondria evolved
  first

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Evidence for the theory of serial endosymbiosis

• Other endosmbiotic relationships are successful!
• Morphological similarity appropriate size
• Membranes contain similar enzymes
• Replicate by binary fission
• Single, circular genome
• Bacteria-like ribosomes and tRNAs
• DNA evidence (?)

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Secondary endosymbiosis

• Several taxonomic groups have plastids
• Plants
• Chlorophytes s.s. (Chlamydomonas)
• Rhodophytes s.s. (Porphyra)
• Glaucocystophytes (Cyanophora)
• Chlorarachniophytes (Chlorarchnion)
• Euglenids (Euglena)
• Cryptomonads (Guillardia)
• Haptophytes (Emiliana)
• Heterokonts (Laminaria, Phytophthora)
• Dinoflagellates (Amphidinium)
• Apicomplaxans (Plasmodium)
• Ciliates (Paramecium)

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Algal lineages
Primary (Double membrane) Secondary (Thre
e or more membranes)
Cryptophytes Heterokonts Haptophytes
Dinoflagellates Apicomplexans
Euglenoids Chlorarachniophytes
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Eukaryotes and the big picture of evolution
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Eukaryote phylogeny