BIOL1006 Lecture Notes - Lecture 20: Multicellular Organism, Natural Selection, Gastrointestinal Tract
9 Jun 2018
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Lecture 20: multicellular
- Cells can come together: colonial species
- Cells can stay together: true multicellularity
- A range of adaptations are required for multicellularity
- Complex life started with the evolution of eukaryotes
- Multicellularity evolved many times
- Multicellularity has two different origins
Origins of multicellularity
Multicellularity evolved:
- Once in animals
- Three times in fungi
- Six times in algae
- Multiple times in bacteria
What is required for multicellularity to evolve?
- Cells must adhere to other cells
- Cells must communicate with eachother
- Cells must cooperate with eachother
- They need to specialize, so that not all cells do the same thing
- Cells should not reject eachother
Whateer orks…
- Natural selection too cares only about what works
- Hence, irrespective of how cells come together, if the result is a functional unit, then
selection can act on this
- Thus, different roads that all lead to Rome
When it all began: Ediacaran (635mya)
- Until around 600M years ago, only single-celled organisms were found
- This changed with the arrival of the Ediacaran fauna
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Document Summary
A range of adaptations are required for multicellularity. Complex life started with the evolution of eukaryotes. They need to specialize, so that not all cells do the same thing. Natural selection too cares only about what works. Hence, irrespective of how cells come together, if the result is a functional unit, then selection can act on this. Thus, different roads that all lead to rome. Until around 600m years ago, only single-celled organisms were found. This changed with the arrival of the ediacaran fauna. Contains a number of animals that can be assigned to modern groups. Choanoflagellates: can be solitary or unicellular or stay together and be multicellular. Striking similarity between choanoflagellates and choanocytes- specialized feeding cells in sponges (suggests ac common ancestor) Snowflake yeast: single mutation results in multicellular yeast. Multicellular yeast is selected for whenever it is better to stick together. Colonial organisms were the first evolutionary step from single-celled to multicellular organism.
