By assuming that environmental stress affects the flies in the same way genetic stress would I compared the fecundity of females from all my treatment groups, early and late in life. By doing this I was able to test the effect of environmental stress at different ages. as such the control group served as a baseline for the fecundity to which the other groups was compared. There are several potential outcomes from the experiment. First of all, if the relative fecundity difference between the control group and the group that is exposed throughout life early in life, is larger than that difference between the control group and the group exposed late in life, this would indicate that mutations in general have a smaller effect late in life, supporting fisher’s model of adaptive evolution. For fisher’s model of adaptive evolution I found only weak proof that supports the idea. Looking at the Methanol treatment it seems to have a larger positive effect early in life than late in life. And even though I aimed for treatments to have a negative effect on the flies due to wanting to draw a parallel between stressful environments that reduce fecundity and deleterious mutation that reduces fecundity. The fact is that fisher’s model of adaptive evolution theory might not be applicable to positive mutations or rather according to them novel positive mutations should have less of an effect early in life due to individuals to be closer to their phenotypic maxima and thus be more likely to accumulate deleterious mutations which push them away from said maxima. All other treatments show no statistically significant proof for fisher’s model of adaptive evolution and would suggest that this would support that mutations in general, have a constant effect throughout life or a weaker effect early in life.
If, on the other hand, the effect of the induced mutation becomes larger with age, when comparing the control group and the group that is exposed throughout their life, there are two possible explanations. Either the effect of the deleterious mutation accumulates with age, or it becomes larger with age because it interacts with “true” aging mutations late in life.
These hypothesis can be separated by comparing the group that is only exposed late in life and the group exposed throughout their life. If the late life fecundity of the group exposed throughout their life is similar to the late in life fecundity of the group exposed late in life, then the results will point toward that the effect of deleterious mutation does not accumulate with age, and the larger effect late in life is attributed to interactions with true aging mutations. If the effect on fecundity late in life for the group exposed late in life is smaller than that in the group exposed throughout their life, this suggests accumulation of negative effects with prolonged activation of a deleterious mutation. And yet again to only treatment that shows significant accumulation of effect is Methanol the other treatments yet again showed no significant accumulation. The only interesting treatment is MSB which has the “late” treatment and “always” treatment converge very close to another, which could be a sign that the larger effect late in life is attributed to interactions with true aging mutations.
With regards to Positive Pleiotropy hypothesis about increasing rate of aging three treatments showed significant increases in rate of aging (Even if the effect of Methanol and MSB seems to have a positive effect on aging). Only constant exposure to MSB seems not to have an accelerating effect on the aging related effect.
There is also the question of if I was too lenient on the flies, when choosing treatments for the flies I always choose concentrations I thought would not cause excessive mortality. But since I have gotten results that points towards a positive effect of aging in the case of MSB, Methanol and to some degree when looking at early in life CuSO4. Maybe I should have chosen higher concentrations of the treatments to make sure that their toxic effects would manifest. Only heat shock seems to have an overall negative effect on the flies, and their results more closely resemble the expected result pattern.
If I were to repeat this experiment, I would choose higher concentrations of the toxins to be sure, that the environments they would experience were stressful and cause a negative effect on their fecundity to more closely resemble a deleterious mutation in effect.