Biology 141 Lewis & Clark College

Lecture 18 Mutualisms

K.E. Clifton

Mutualistic interactions

Background and terms.

Both species benefit from a mutualistic interaction (+/+)

The relationship may be:

obligate: each of the two species needs the other to survive.

facultatative: each species can live independently but is more successful if the other species is present (like cleaner wrasses)

obligate for one partner and facultative for the other.

Many types of potential benefits, some examples:

failure of tree regeneration in an Oregon clearcut found to be due to missing mycorrhizae.

mycorrhizae = "fungus-root"; fungal hyphae live in close association with a plant's roots.

fungal hyphae break down complex organic molecules in soil, nutrients become available to roots.

fungus in return receives carbohydrates from plant roots.

provide great extension of root area. So mycorrhizae increase access to nutrients and water.

very common: 90% of plant species have associated mycorrhizae.

caution: DON'T confuse mycorrizae with nitrogen-fixing bacteria. Fungi are not bacteria, and mycorrhizal fungi do not fix nitrogen.

Reciprocal behaviors.

clown fish and sea anemones (even more here, since there is also symbiosis between algae in the anemones, called zooxanthellae, and the anemones... see below)

Acacia cornigera and ants.

providing protective environments, i.e. "farming".

humans' domestic crops.

leaf-cutter ants and fungi.

ants "milking" honeydew from aphids and caterpillars.

Naomi Pierce's experimental study of Glaucopsyche lygdamus, its ants, and its parasites showing benefit of ant attendants to caterpillars.

pollination, transfer of gametes in exchange for food.

gut inhabitants aid digestion in return for a protected environment and food.

algal symbionts:

single-celled algae live in sea anemones and corals.

fungi and algae living together form lichens.

 

Some videos of symbiotic relationships can be found here

Take me to the course moodle page