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What is internal consistency and why is it important for parasites? What is the result of this interaction?
- The host's interior environment is often consistent in a given area (temperature, pH, osmotic concentration, etc).
- This is required for the host body to function, and can be exploited by the parasites for survival. (parasites "prey" on the homeostatic mechanisms of hosts)
- Parasites have evolved characteristic habitats, and are typically highly specific to these areas.
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Give an analogy for host-to-host transmission. Is it easy?
- Host-to-host transmission is like swimming from island to island- VERY risky.
- Why risk your own survival if you can exploit the resources of the island you're on?
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Where are most endoparasites found?
- The digestive system of vertebrates, but they can be found in all parts of the body.
- *NOTE- different species are found preferentially within different regions of the gut due to drastically different conditions being present
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Describe the various stages in the life cycle of the Ascaris worm and where each resides.
Eggs swallowed -> hatch as larvae in small intestine -> penetrate mucosa to enter bloodstream -> liver -> lungs -> trachea -> esophagus -> small intestine (reside as adults)
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Define coelozoic, histozoic. Give examples
- Coelozoic: parasites within lumen of intestine or hollow organs
- eg. flukes, tapeworms
- Histozoic: parasites that live within tissue
- eg. some protozoans, nematodes
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Describe r and k selection with regards to parasties. What conditions influence each?
- R selection: high fecundity, high mortality, short lifespan, effective dispersal, varying population sizes over time (usually below carrying capacity)
- R selection prevails when selective forces on organisms are variable
- *NOTE- most parasites are r-strategists
- K selection: low fecundity, low mortality, longer life-span, relatively stable population sizes over time (usually below carrying capacity)
- K selection prevails when selective forces on organisms are constant
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Describe the two types of competition that effect the population dynamics of a parasites
- Single host can be infected with multiple parasites
- Exploitation: joint exploitation of a limiting resource within a host species by 2+ parasites (coexist)
- Interference: hostile mechanisms are used by one species to reduce survival of another to displace it. Typically via toxin production.
- *NOTE- these interactions can be intraspecific OR interspecific
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Define prevalence, intensity, mean intensity, incidence, density/abundance, infrapopulation, suprapopulation, site/location
- Prevalence: Number of hosts infected with 1 parasite divided by total number of hosts examined
- Intensity: Number of parasites in a single infected host (reported as a range)
- Mean intensity: average number of parasites in infected hosts
- Incidence: Number of new cases of infection appearing in a population within a given period of time divided by initial number of uninfected individuals
- Density (abundance): Number of individuals of a particular parasite per unit area, volume, or weight of the infected host tissue/organ
- Infrapopulation: all of the parasites of a particular species in the body of a single host
- Suprapopulation: all individuals of a species of parasite in all stages of development within all hosts in an ecosystem
- Site/Location: The tissue, organ, or part of the host in which a parasite is found
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Define epidemiology. What factors influence the epidemiology of parasites?
- Epidemoiology: study of factors responsible for the transmission and distribution of diseases
- Factors include age, sex, social/economic status, diet, distribution and presence of vectors and reservoirs, host specificity, and densities of host and/or parasite
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Define vector
Vector: means of transmission of parasite from one host to another (biotic or abiotic)
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Who is is responsible for monitoring epidemiology in the US? In the world?
- CDC (Centers for Disease Control and Prevention) in the US
- WHO (World Health Organization) and TDR (Tropical Disease Research Program) worldwide
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Describe the most-likely evolution patterns of modern parasites. What challenges were likely encountered? What will inevitably happen through coevolution?
- ectoparasites: likely evolved from non-parasitic omnivores, predators, or secretion-drinking animals
- endoparasites: likely survived after passage through the alimentary canal via cyst wall or thick cuticle and persisted
- Challenges would've included high osmotic pressure, temperature, oxygen supply, immunological response, and prevention of excretion (method of attachment)
- Being subjected to the same evolutionary forces (coevolution) parasites will inevitably become so well adapted to hosts that they cannot mature or survive in any other host (absolute specificity)
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What is the ultimate source of genetic variation? How is this important to parasitic evolution?
- Mutation is the ultimate source of genetic variation
- Parasites must adapt to their niches through changes in their genetic makeup (if a parasite cannot adapt to host mutation they will likely perish)
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What are the 3 factors causing evolution with a brief description of each? Describe the founder effect.
- Mutation: permanent change in the DNA molecule
- will initially affect only individiuals
- Natural selection: some individuals will more successfully reproduce than others (fitness)
- operates at the population level
- Genetic drift: isolated populations change genetically by chance
- operates in small populations
- Founder effect- if a select few individuals colonize an environment their gene pool (small, unvaried) will comprise the entire gene pool without the variation present in the entire population.
- *NOTE- founder effect is very important in parasite evolution (very small colonizing populations)
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Define taxonomy
Taxonomy: the study of naming and classifying organisms/the study of scientific classification
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