Effectiveness of Selection

The results give very little indication that selection increased the efficiency of ovipositional choice. If selection had been successful there should have been an increase in correct laying relative to the total number of eggs laid. The results contain no indication of such a trend.

Perhaps the enormous variability of results has masked any trend that may have been present. Day to day fluctuations were large as Fig. 1 clearly shows. Furthermore a higher total number of eggs was laid by both strains in Generation 1 than in any other generation, with a very large amount of variance between the totals for the four generations (S₂ = 41,977,318.66). The percentages of eggs laid correctly by each strain each day were still fluctuating as markedly in Generation 4 as in any other generation. As shown in Fig. 2 there is no detectable daily or generational relationship between the percentages laid in either strain.

In the parental selection generation one would expect that approximately equal amounts of eggs would be deposited in all ten phials, and thus the one phial selected for in each population would contain approximately 10% of the eggs laid. This was not observed. The average percentage of eggs laid correctly in the amyl alcohol population in the first generation of selection (23.46%) was more than double the expected 10%, while the average percentage of eggs laid correctly in the ammonium carbonate population (4.67%) was only half that expected. By the fourth generation of selection the percentage of amyl alcohol population eggs laid correctly was actually less than in the first generation, dropping to 19.59%. At the same time the percentage of eggs laid correctly in the ammonium carbonate population rose to 42.96% in Generation 4. The overall results do not suggest that selection for correct ovipositional choice was successful in either strain.

If no variation in preference occurred the number of eggs laid correctly should tend to correlate with the total number laid, as in Generations 2 and 4 of the ammonium carbonate strain, and Generations 3 and 4 of the amyl alcohol strain. However, correlation coefficients for correctly laid, as compared with total numbers of eggs, all showed no significant relationship between the two except for Generation 4 of the ammonium carbonate strain, where r = 0. 9083, being highly significant at the 0.1% level. While there is no significant correlation for Generation 4 of the amyl alcohol strain, the correlation coefficient (r = 0. 4184) approaches significance more closely than those for any other generation of either strain. This tends to suggest that by Generation 4 there is beginning to be a stabilisation between total numbers and correct numbers of eggs laid.