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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.
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?
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
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)
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
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
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
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
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
Vector: means of transmission of parasite from one host to another (biotic or abiotic)
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
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)
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)
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)
Taxonomy: the study of naming and classifying organisms/the study of scientific classification
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