Lecture 12: Parasites and Disease Flashcards
Behavior Modification
increases its transmission by changing the behavior of its host
(ie - parasite infects snail; snail eaten by birds, birds poop, snails eat poop.
Estimates suggest that as many as ____________ are parasites!
-half of all species
Why are there so many parasites?
1) most free living species have parasites associated with them
2) Most parasites are specialists (they attack few or maybe just one species)
Evidence of Specialization
(Each) Species of parasite = one species of host
and Coevolution
Coevolution
- Genetic change in one species in response to change in another.
- Coevolution occurs in species that are closely interacting, (e.g., mutualists, parasites & hosts, pollinators and plants)
How do we detect coevolution of parasite and host?
Quantitative approach looking for Co-speciation
What is the Quantitative approach?
Quantitative approach: Evaluate branch patterns of both parasite and host phylogenies in parallel
Co-speciation
A kind of coevolution that occurs when one species (host) speciates and the other one (parasite) does too.
Most parasites must:
Most parasites must:
1) Find “SAFE” host versus a hostile environment
2) ESTABLISH on/in host (e.g., cross into skin, gut wall, etc.)
3) EVADE host immune system, or if ectoparasite, behavioral defense (grooming, swatting)
4) grow and REPRODUCE in host
5) DISPERSE from and find new host
*Adaptations for one species of host unlikely to be effective for another
ectoparasite
lives outside host (flea)
Parasites are grouped by
-size
1) Microparasites: unicellular (e.g., viruses, bacteria, protists, and single-celled fungi)
2) Macroparasites: multicellular (e.g., arthropods, nematodes, flatworms, and multicellular fungi)
Size influences…
-the way the host is used…
- Microparasites generally infect cells,
- Macroparasites are usually external or in the gut
Microparasites generally…
-infect cells
Macroparasites are usually…
-external or in the gut
Are parasites unicellular or multicellular?
- Microparasites: unicellular (e.g., viruses, bacteria, protists, and single-celled fungi)
- Macroparasites: multicellular (e.g., arthropods, nematodes, flatworms, and multicellular fungi)
How are parasites transmitted?
Directly or indirectly
Direct (parasite) transmission
-from one host to another of the same species
Indirect (parasite) transmission
-transmission via another species
Types of direct (parasite) transmission
vertical or horizontal
What is vertical transmission?
Vertical transmission is transmission from parent to offspring in early development, generally from mother to offspring.
- through infected gametes (most often eggs) - through birth process (mother –> offspring)
what is horizontal transmission?
-transfer via contact with infected individuals or contaminated products
Strictly vertically-transmitted parasites (i.e., no horizontal transmission) are…
unusual
Why are strictly vertically-transmitted parasites (i.e., no horizontal transmission) unusual?
- Dependent on their hosts, often evolve into mutualists, rarely make their hosts sick.
- But some manipulate the reproduction of their hosts to increase their own transmission
How is it possible for a parasite to cause a male to turn into a female?
-because they have a haplodiploid genetic system
Example: Wolbachia bacteria
-Wolbachia bacteria pass on from one generation to the next via infected eggs (i.e., from mother)
• Takes over reproductive system so host only produces females
