Biol 208: Lecture 23 - Mutualism - Parasitism

Symbiosis - define

• Mutualism

• Commensalism

• Exploitation

Symbiosis = INTRICATE + LONG TERM living of 2 organisms

• mutualism = +/+

• Commensalism = +/o

• Exploitation (parasitism) = +/-

Interactions can be mutualistic, commensal or parasitic depending on the context

Facultative vs. Obligate symbiosis

Facultative = occurring OPTIONALLY

Obligate = NECESSAIRY

• high dependence on partner → likely to go extinct if partner goes extinct

Whale + Barnacle - What type of interaction?

• Who is benefiting + who is not

• is this Obligate or Facultative

MOSTLY commensal → context dependent (location of barnacles)

• Barnacles on find = like brass Knuckles for fighting

• Too many = creates drag + skin conditions

Barnacle (+)

• benefit from substrate + dispersal provided by whale

• Only found on whales = OBLIGATE (some can be facultative)

Whale (o)

• No benefit or harm = FACULTATIVE relationship

Ticks + Host - What kind of Interaction

• Who is benefiting + who is not

• is this Obligate or Facultative

PARASITISM

Ticks (+) = OBLIGATE symbiosis

• feed on host blood + receives benefit (must have blood to grow + reprod)

Host (-)

• Harmed through loss of blood + disease risk

(not sure how important) Other examples of parasitic relationships

1. Mistletoe - Hemi parasitic plant (takes carbs from host But can also photosynthesize)

2. Tape worm

3. Tongue eating crustacean

Herbivore vs. Plant parasite

• What is the difference?

Parasites = intricate + long term relationship with a host

Herbivores + Predators do not = one time interaction

Give an example of Parasites ALTERING THE BEHAVIOUR of their hosts for their benefit

European starling, isopods + thorny head worm (parasite)

• Isopod = Intermediate host (parasite grows here but does not reach maturity)

• European starling = definite/ primary host (parasite reaches maturity)

What is the RED QUEEN HYPOTHESIS?

CO-EVOLUTION in host-parasite interactions = Perpetual co-evolution between the 2 is like an ARMS RACE

• species must evolve to keep up with the evolutions of their parasites + vice versa

“It takes all the running you can do to keep in the same place” - Lewis Carroll, through the looking glass

Plants + Mycorrhizae - What kind of Interaction

• Who is benefiting + who is not

• is this Obligate or Facultative

MUTUALISM BUT mycorrhizae can also be parasitic

Plant (+)

• benefit from mycorrhizae through INCREASED NUTRIENT UPTAKE in soil

Mycorrhizae (+)

• Benefit from plants through consumption of their root exudates (CARBS)

What are the 2 types of Mycorrhizal Fungi (MF)?

• Differentiate between the 2

• Which associates with more types of species?

1. Arbuscular (AMF)

   • PENETRATE the cortical cells (store E + Nutrients) of plant roots

   • in 80% of plants species

2. Ectomycorrhizal (EMF)

   • Does NOT penetrate

   • 2% of plant species (conifers, blueberries etc.)

Some plants don’t have mycorrhizae

Info dump on the experiment: Does Fertilizing soil select for less mutualistic mycorrhizal fungi?

• Methods

• Prediction

• Results

Method:

• Grew grass with AMF that either was from Unfertilized soil or Fertilized soil + one control with no AMF

Prediction:

• Nutrient poor soil = more carb exudates to the roots (Optimal foraging in plants = allocate E to the most limiting factor)

• Nutrient rich soil = Less carbs exudates to roots

Mycorrhiza colonizing HIGH nutrient soil will be AGRESSIVE in their carb acquisition at the express of the host b/c there is Low-release of exudates

Results:

• AMF are MORE mutualistic when grown in Nutrient POOR soil (like predicted) - plant growth was not as restricted

  • Like predicted

Mycorrhizae: Mutualism-parasitism continuum

• Experiment

• Results

• What does this mean?

Plants were grown with and without AMF + calculated the percentage change of Biomass

Results show that Plant-AMF relationships form a CONTINUUM from mutualistic to parasitic interactions

Parasitic vs. mutualistic depends on:

• Conditions of Soil

• Species of plant

Other examples of Mutualistic interactions

1. Coral + zooxanthellae

2. Lichen: Fungi + algae

3. Legumes + Rhizobia bacteria (fix nitrogen)

Info dump on Coral Bleaching

• causes

• What is occuring

Causes:

• temp change

• Runoff + pollution

• Overexposure to sunlight

• Extreme low tide

Healthy coral = mutualistic interaction with zooxanthellae (FOOD SOURCE) = give coral color

STRESS = expel zooxanthellae —> bleached color

Coral dies because no mutualistic effect with zooxanthellae

Info dump on Lichen

Fungal BIOFILM creates a shelter + keeps a humid environment for algae

Algae = photosynthesize —> Nutrients for Fungus

NON-SYMBIOTIC Mutualism?

• what is the difference from Mutualism (symbiotic)

• Give some examples

Not all mutualistic interactions are Intricate + Long term

• Symbiotic = Life LONG

• NON = SHORT term + then go separate ways

Examples:

• Pollination

• Frugivores

• Cleaning parasites off other animals

“Reciprocal Parasitism”?

Mutualism is kinda like reciprocal parasitism - beneficial actions towards the other are only because the interaction increases own fitness

Attracting pollinators

• Butterflies'

• Bees

• Nocturnal Moths

Butterflies = attracted to BRIGHT COLOURS

Bees = red blind = attracted to YELLOW or BLUE

Nocturnal moths = attracted to HEAVY SCENTS released during night

Nectar guide (image)

3 kinds of rewards for pollinators?

1. Pollen

2. Nectar

3. Prospect of mating with a female (orchid shaped like female + wasp)

   • Not very common in nature but this exists in this scenario b/c the interaction is not too costly for the wasp

Info dump: Bees as Commercial pollinators + Commercial pollinator Decline

• amount of global food prod due to pollination

• CCD

• Wild pollinators why are they declining?

1/3 of global food prod

CCD = COLONY COLLAPSE DISORDER

• phenomenon where worker bees would disappear or vanish from the hive despite enough food storage, leaving behind the queen, brood + a few nursing bees

Possible explanations:

• Parasites, pesticides, stress (multi factoral)

Decline in wild pollinators as well

Why? - Habitat, simplifying ecosystem

• eg. plant all canola, once harvested no more food for bees

Measures to counter pollinator loss

Setting up flower strips + increasing landscape heterogeneity