Laboratory populations, genetic consequences

Many species of parasitic nematodes are maintained in the laboratory in host species in which they are not found in nature. This has the potential consequence that the laboratory population is, in some way, different from the natural population. Transfer and adaptation of a parasite from a natural host into a different species in the laboratory entails a process of selection. The selection will act on the trait ability to survive in a nonnatural host . Most of the parasite population may have had little, or indeed no, ability to survive in the non-natural host. Thus, at its most extreme form, this selection will have been for the very small proportion of the parasite population with the ability to survive in a non-natural host. A consequence of this is that the parasite population will have gone through a genetic bottleneck. 

The existence of multiple AChE isoenzymes has several consequences. First, it increases the chances of an insect having one that is, or by a minor genetic change can be rendered, insensitive. The molecular redundancy combined with a selection pressure in the form of persistent insecticide applications would facilitate target site resistance development. Second, it could be a factor in the frequent lack of target site cross resistance between OPs and carbamates, and even between different OPs. Third, it would facilitate the disappearance of the insensitive form(s) in the absence of a selection pressure. This would especially easily explain observed instability of resistance if the form(s) with decreased affinity for the inhibitors also have decreased affinity for the neurotransmitter. Insensitivity to the inhibitor may be accompanied by a reduced rate of neurotransmitter hydrolysis (56. 28), but this is not always the case. It seems that the reduced rate of neurotransmitter hydrolysis does not impair survival, at least in laboratory cultures of insects. It is unclear what impact such reduced rates have in field populations. 

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