what is symbiosis? (lecture 1)

Question 1

What is the etymology of symbiosis?

Answer 1

modern Latin derivation from Greek sumbiōsis ‘a living together’

• from sumbioun ‘live together’
• from sumbios ‘companion’

Question 2

What is the historical use of the word symbiosis?

Answer 2

• originally coined to explain familial support within human society
• then used only for mutualism
• now mutualism, parasitism, commensalism

Question 3

What are mutualism, parasitism and commensalism?

Answer 3

mutualism:
- both partners in a symbiotic relationship derive fitness benefits

parasitism:
- one partner (parasite) derives fitness benefits at a cost to the other (host)

commensalism: one partner derives fitness benefit at no cost to the other

Question 4

What is flawed about assuming mutualism, parasitism and commensalism are separate branches of symbiosis?

e

Answer 4

• assumes symmetry
• e.g. that benefit to parasite is proportional to damage to host, that mutualisms benefit partners equally
• not always the case, e.g. parasitism inherently asymmetrical as needs living host, mutualisms not always equal
• doesn’t account for temporal dynamism
• organisms can form multiple symbiotic relationships through life cycle
• trophic shifts/symmetry changes through life cycle may result in different relationship dynamics through time
  e. g. orchids
• gives very rare commensalism equal weighting

Question 5

What is symbiosis considered to mean biologically?

Answer 5

• controversial & argued about but
• Anton de Bary: “the living together of unlike organisms”
• better though is the “intimate living together of unlike organisms”

Question 6

Why is a scale model to represent symbiotic relationships better

Answer 6

• accounts for asymmetry
• allows for temporal dynamism
• explains rarity of commensalism

Question 7

What is mycorrhizal symbiosis?

Answer 7

• association between fungus and roots of plants
• fungus access nutrients unavailable to roots (e.g. in chemical state, in soil pores too small for roots)
• fungus gets carbon (photosynthates) from plant

Question 8

What is some background information on orchids?

Answer 8

• 33,000 specoes
• release 100,000 minute seeds
• orchid seeds have no seed reerves, protected by tester

Question 9

How do orchids display temporally dynamic symbiosis?

Answer 9

• symbiotic germination = “mycoheterotrophy”
• fungus dependent germination
• seeds parasitic to fungus
• adult orchids are autotrophic
• allocate C to fungus
• life stage dependent trophic switch
• mutualistic
• must transition through commensalism at some point