Evolution of Multicellularity

1
Evolution of Multicellularity

• Gamble - Bio
• Spring 2007

2
Single --gt Multi-Celled

• It is difficult to pinpoint precisely what
  mechanisms were tested and tried.
• Difficult to find fossil data at this level.
• Earliest colonies of bacteria dated to more
  than 3 billion years ago.
• Cyanobacteria known as
• --gt Stromatolites

3
Stromatolites

• Earliest known fossils.
• Also known as Blue-Green algae.
• Possible source of O2 in the Earths atmosphere.
• Photosynthetic

4
Before that

• Archaebacteria
• Chemosynthetic
• Hydrothermal Vents ???
• Hyperthermophiles
• Also live in other extremely harsh environments.

5
Multicellularity

• How did we get from single-celled to
  multi-celled?
• What is multicellularity?
• 4 main principles
• - specialization
• - cellular messaging
• - cooperation in forming self
• - cellular self-destruction

6
Three leading theories

• Symbiotic
• Cellularization
• Colonial

7
Symbiotic Theory

• Cooperation of different species of single-celled
  organisms.
• Over time become dependent on each other and
  their genomes fuse.
• Many questions remain.
• Believed to be the source of mitochondria and
  chloroplasts.

8
Cellularization Theory

• Single-celled organisms formed membranes around
  their organelles.
• Compartmentalization
• Believed to have happened in organisms with
  multiple nuclei.
• Hard to prove and not widely accepted.

9
Colonial Theory

• Symbiosis and cooperation between organisms of
  the SAME species.
• Has been observed many times in nature.
• Most accepted theory.

10
Green Algae

• Protists
• Can be single or multi-celled.
• Along with Cyanobacteria, filled early atmosphere
  with O2.
• Found in VERY diverse environments.

11
Some Characteristics

• Cell Wall - Surrounds and protects, similar to
  land plants.
• Chloroplasts - Where photosynthesis occurs.
• Flagella - Long, whip-like tail that helps them
  move propel themselves.
• Eyespot - light sensitive structures

12
Increasing Complexity

• Chlamydomonas --gt Gonium --gt Pandornia --gt Volvox
  --gt Spirogyra
• Chladophora
• Single-Celled --gt
• --gt Few-Celled Colonies --gt
• --gt larger colonies --gt
• --gt colonies with --gt true
  multicellularity
• division of labor

13
Energy Acquisition

• Bacteria vs. Green Algae
• Bacteria Chemosynthesis OR Photosynthesis
• Green Algae Photosynthesis
• Algae use structures to help in photosynthesis
• - Flagella to move to light source.
• - Eyespot to orient to light source.
• - Chloroplast to metabolize light energy.

14
Bacteria vs. Green Algae

• BOTH can be asexual.
• BOTH have short generation times and reproduce
  very quickly.
• Green Algae however can ALSO reproduce sexually
  by forming GAMETES while bacteria usually do not.

15
Costs and Benefits

• Are mates hard to find?
• Are the environmental conditions changing?

16
Diversity

• Bacteria and Algae may vary in
• - Modes of energy acquisition
• - Habitat
• - Size, shape, and organization
• - Reproductive strategy
• - Method of locomotion

17
Credits/Photos
Sources Photos

• http//www.answers.com/topic/evolution-of-multicel
  lularity
• http//www.nature.com/hdy/journal/v86/n1/full/6888
  080a.html
• http//www.sirinet.net/jgjohnso/monerans.html
• http//evolutionofcomputing.org/Multicellular/Evol
  utionOfMulticellularity.html
• http//web.mit.edu/mit-whoi/www/research/bo/figs/g
  reen_algae.jpg

• http//www.bbc.co.uk/science/horizon/2003/pics/lif
  eonmars.jpg
• http//www.lbl.gov/Science-Articles/Research-Revie
  w/Magazine/1999/images/blacksmoker.jpg
• http//www.wmnh.com/wmel0000.htm
• http//www.cbs.dtu.dk/staff/dave/roanoke/bio101ch0
  6.htm
• http//physics.ucr.edu/People/Home/Mills/assets/im
  ages/giardia_image1_400.gif