The Origins Of Multicellularity Flashcards
True multicellularity means
- Having different types of cells
- usually some specialised germline cells for reproduction
- somatic cells for other functions
Unicellular
Only one cell
Lots of one type of cell
Colonial
Lots of different types of cell
Multicellular
For most of time, all life was
Single celled
How do we answer whether multicellularity evolved one, or multiple times?
By building an evolutionary tree
Did multicellularity evolve once, or multiple times?
Multiple times!
When did multicellularity evolve?
- in Plantae: green algae + land plants
- in Amoebozoa: mycetozoan slime moulds
- in Opisthokonta: animals and fungi (inc. microsporidia)
- in Chromalveolata: Stramenopiles
Why might it be better to be big?
- swim further
- harder to be eaten
- catch more food
Choanoflagellates
- Collared flagellates
- the closest thing to an animal without being an animal
How do choanoflagellates catch bacteria?
Setting up water currents
Why are choanoflagellates indicative of the advantages of multicellularity
More cells = more current = more bacteria
Why might it be better to be multicellular?
- big
- split functions
- flagellar retraction
- self-cannibalism
What are the advantages of split functions
splitting somatic from germline might help protect germline
Describe the self-cannibalism theory of multicellularity (Kerszberg and Wolpert 1998)
- With scarce food, a multicellular organism can autocannibalise
- when Environment recovers and more food is available, the cells can grow back
- seen in the flatworm, hibernating mammals
Describe choanoflagellates
- long flagellum surrounded by a collar
- protists
- microscopic
- closely related to animals
- marine and freshwater
- feed on bacteria
- quite diverse
What is the collar in choanoflagellates?
Actin-supported tentacles
Describe loricate choanoflagellates
Cell secreted a glass basket
What is the opposite of a loricate choanoflagellate
Naked choanoflagellates
Describe the evolution of animal gametes
- haploid sex cells of very different sizes
- different sizes = different investment of resources
- had a massive effect on subsequent evolution of animal behaviour
Describe epithelial cell sheets
- evolutionary innovation in animals
- watertight
- allow maintenance of ion concentrations
- tough
- fold to make complex shapes
The cell theory was a
Watershed moment
Why is it important to protect the germline?
mutations, predation and damage undesirable
How might the germline be protected?
- physical protection: hide em
- cellular mechanisms: molecular repair mechanisms
What do the choanoflagellates use to set up their currents?
Flagellum
What is the flagellum made of?
Tubulin
