LE 12: Parasitism, Mutualism, and Commensalism Flashcards
What is the spectrum of parasitism, mutualism, and commensalism?
Parasitism: -
Mutualism: +
Commensalism: 0
What is Parasitism?
one organism benefits and the other is harmed
- obligate relationship for parasites
What are the different types of parasites?
Endoparasites: affect organisms on they surface
Ectoparasites: affect organisms in the inside
What is the life cycle of parasites within a community?
Intermediate host: host that parasites use during development
Definitive host: host that parasites use to reach their adult stage and to reproduce
≠ necessarily kill all hosts/cause disease in all of their hosts
- need a host for at least part of their lifecycle
What is commensalism? Give examples.
when one species benefits and the other isn’t harmed much/benefits much
Example: cows walk through fields and stir up insects
- the cattle egrets are able to forage for insects
- ≠ really affect the cows and there ≠ any direct benefits
Example: deers get burs on them
- plants benefit because they get carried and reproduced
- deer ≠ get affected much
Parasites are commensal during other phases of their lifecycles; increases fitness
What is mutualism and the different types? Give examples.
When both species benefit from each other (win-win).
Types:
- Facultative/generalist: many pollinators and plants
- Obligate/specialist: one to one species
Example: yucca moths and yucca flowers have a specialist mutualism relationship
- yucca flowers will terminate if there are too many moth eggs; flowers ≠ reproduce and the eggs ≠ come to term
- results in selection on yucca moths that have moderate amounts of fecundity
What are some examples of grey areas in mutualistic relationships?
Leaf sheep eats algae that harbors a bacteria.
- bacteria has a toxin that protects the algae from herbivory
- leaf sheep is immune to the toxin and digests the algae for energy + uses chloroplast to make even more energy
How does Parasitism, Mutualism, and Commensalism affect population? Give examples
Acacia trees and ants have a mutualistic relationship.
- ants increase the survivorship of acacia trees by warding off other herbivorous insects
- herbivores have more food to eat
Hosts in parasitic relationships, can evolve to have defenses that reduce the virulence of a parasite.
- rabbits can get myxoma
- populations with more epidemics reduces the mortality of the population due to the evolution to have better defenses
What is coevolution and the Red Queen hypothesis? Give an example.
Coevolution: when two or more species affect each other’s evolution
Red Queen Hypothesis: Organisms are constantly evolving just to stay where they are/ to not go extinct
Example: wasps injects its eggs into caterpillars
- virus lives mutualistically in wasps to prevent caterpillars from evolving immune defenses to the eggs
- caterpillars have behavioral defenses to ward off the wasps
How does a change in ecological conditions affect such relationships? Give an example.
Honey Damselfish are groomed by cleaner fish to get rid of ectoparasites.
- less ectoparasites = cleaner fish eats more of the Honey Damselfish
- the relationship shifts more from mutualism to parasitism as the parasitic load decreases
What is virulence?
Ability of a pathogen or parasite to cause tissue effects.
- virulence factors are genetic an can have up/down regulation of genes/ transfer them to other bacteria
- can be a byproduct of the lifecycle of the parasite
How can virulence affect such relationships? Give an example.
Bats in North America are sick from a fungus and bats from Europe/China are not sick from them.
- bats in China/Europe ≠ get sick because they have evolved to build defenses to it after being affected for long periods of time
Constant coevolution allows for commensalism.
Isolation can lead to virulence, where organisms ≠ evolve but the disease evolves to become more novel/potent
How do parasites result in behavioral modifications in their hosts? Give an example.
Flies get affected by parasitic fungus, leading them to sit higher on leaves and on the bottom of them.
- Spores of the flies get shed onto the uninfected flies below them
Selective pressure on parasites results in the spread of their genes
- infected mouse is less fearful of predators/cats
