Continuation of a Field Natural Selection Experiment

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Algal consuming crustaceans living in freshwater lakes and ponds have a variety of adaptations to avoid being consumed by fish and other predators. One of these adaptations is to be active during Winter when fish feed very little, and to produce dormant stages in Spring and Summer when fish feeding activity is high. Dormant eggs of the copepod, Diaptomus sanguineus, are deposited on lake sediments where plankton-feeding fish cannot find them. The eggs hatch in Autumn after fish have again become quiescent. A recent study showed that after fish were removed from a small lake, the timing of the production of dormant eggs shifted to later in the spring than had been the case when fish were present. To test if this shift represents a genetic response to fish removal, the small lake was divided into quarters with a solid vinyl barrier. Fish were introduced to 2 of the quarters and were excluded from the other 2. This research will continue the necessary monitoring of the timing of production of dormant eggs in all quarters to see if it differs in the presence and absence of fish. Laboratory experiments will be carried out to test if any differences observed are genetically based.