Colonization of Land and the Diversification of Eukaryotes

Protists

• So diverse they almost don’t fit into one category

• Early eukaryotes developed nuclei, organelles, and filled niches

Endosymbiotic Hypothesis

• Several million years ago, an early protist acquired a bacterium and rather than digesting it, incorporated it as a mitochondrion

• Later protists acquired other structures with became plastid elements

  • These became the chloroplasts

  • Other plastid elements were obtained

• This has happened several times so it is serial endosymbiosis

Origins of Multicellularity

• Occurred several times

• Chlamydomonas

  • Single celled alga - probably a precursor of volvox which is colonial

• Volvox

  • multicellularity may have arose over time

• Choanoflagellates

  • possible common ancestor of animals (collar cells of sponges)

Special Characteristics of Protists

• Mostly unicellular

• Eukaryotic

• Diverse habitats

• Motility

• Various modes of nutrition

  • Autotrophic

  • Heterotrophic

  • Mixotrophic

• Mostly reproduce asexually, but some have sexual reproduction stages

• Colonial

Life Cycles

• Most protists are free living, but some are parasites

Nutrition

• Photoautotrophic (producers)

  • carry out photosynthesis and are considered phytoplankton

• Many are symbionts

  • These along with a fungal partner carry out photosynthesis

  • Lichen

Algae

• General term for protists that carry out photosynthesis

• No plant tissues or vascular structures

• Red Algae

  • Rhodophyta (seaweed)

  • Used in agar, cosmetics, sushi

  • Red color due to photosynthetic pigments

• Brown Algae (also seaweed)

  • accessory pigment makes them brown: fucoxantjn

  • Carbohydrates stored as laminarin

  • Phaeophyta

• Yellow-Green Algae

  • Diatoms

  • Silica in shells: essentially sand

  • Major phytoplankton component

Locomotion in Protists

• Varied

• Cilia

• Pseudopodia - amoeboid movement

• Flagella - unlike bacteria, same as human sperm

Four Supergroups: Excavata

Later evolved from the early heterotrophic and photosynthetic eukaryotes.

Named for excavated feeding groove

• Excavata

  • Diplomonads - have mitosomes which are simplified mitochondria

    • Giardia intestinalis

  • Parabasalids - have simpler mitochondria called hydrogenosomes

    • Trichomonas vaginalis

  • Eugenozoans

    • crystalline rod in their flagellum and a kinetoplast

      • Trypanosomes, sleeping sickness

Four Supergroups: Archaeplastida

• Red algae - due to phycoerthretin, a photosynthetic pigment

• Charophytes - similar to plants (same chlorophyll), green algae

• Chlorophytes - also green algae

Four Supergroups: SAR

SAR

Include diatoms which are extremely important in photosynthesis (global impact)

• Stramenopiles

  • Brown algae are multicellular stramenopiles and have a holdfast, stripe, and blades (seaweed)

  • makes them resemble plants

• Alveolates - Plasmodium malaria

• Rhizarians - Amoeba

Four Supergroups: Unikonta

Other amoebas, later gave rise to fungi and animals

• Amoebozoans - tubulinids and slime molds

• Opisthokonts - animals, fungi, related protists

Parasites

Usually spread by insect vectors

• Giardia lamblia - diarrhea

• Trypanosoma bruci - Sleeping sickness with Tsetse flies

• Trypanosoma cruzi - Chaga’s disease spread by kissing bug

• Trichomomas vaginalis - STD

• Entamoeba histolytica - Amoebic dysentery, caused by fecal contamination in water

Plasmodial Slime Mold vs. Dictyostellum

PSM

• Giant multinucleated mass called a plasmodium

• Produce Spores

• Arose independently

Dictyostellum

• cellular slime mold

• autonomous amoeba join up to form a multinucleated entity (cellular slime mold)

• Produce spores

• Arose independently