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An Evaluation of an Experimental Model for Sympatric Speciation

Other Differences Between the Two Populations

Other Differences Between the Two Populations

While selection was not successful in the desired direction, it was not without effect on the two populations of flies. The first generation in both cages tended to show a two day cycle of peak and trough in egg laying which was never repeated once selection began. Some physiological pattern in egg laying may have been interrupted by the artificially imposed selection.

Furthermore, some dissimilarities did arise between the two populations during the course of selection. The ammonium carbonate strain, for example, suffered a marked reduction in the number of eggs laid. Since the two strains experienced identical conditions at any one time, and the populations were of identical size, it can be assumed that the two populations should lay approximately equal numbers of eggs in any generation. This did not happen. In every generation the amyl alcohol strain laid more eggs than the ammonium carbonate strain, the difference becoming larger as the experiment progressed, with the exception of the last generation. In successive order of generations, amyl alcohol flies laid 1,216, 1,671, 3,175 and 2,519 more eggs than the ammonium carbonate flies. These differences are highly significant.