Parasite-Host Population Systems and Genetic Stability

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Abstract
Parasite populations (houseflies) were exposed to and isolated with each of 6 simulated host-plant types with the following 6 chemicals as toxicants (resistant factors) in the plant types: citric acid, CuSO4, magnesium nitrate, NaCl, ammonium phosphate and KOH. When the fly population was exposed to a single host-toxicant type, the fly evolved rapidly (7-10 generations) to overcome the single host toxicant. When the fly population was exposed to all 6 simulated host-toxicant types in 1 multicell system, the fly population did not evolve and overcome any of the host-toxicant types. Relative to the genetic feedback mechanism, coevolution and stability among parasite and host, the evidence suggests that genetic stability (preventing the parasite from overcoming host resistance) is possible in parasite-host population systems with the appropriate combination of suitable genetic diversity (resistant characters) in the host population, ample gene flow between parasite colonies (if colonies occur in the parasite-host population system) and suitable selection coefficients on the parasite population resulting from its host population.