Sample Data

Data on a genetic bottleneck experiment were collected by Mr. Ben Davids at Morehouse College during the summer 2008.  A total of 24 independent trials were conducted that consisted of fourteen control populations, contained 25 randomly chosen males and females, and ten bottleneck populations, contained 5 randomly chosen males and females.  Both treatments were conducted in 150 x 25mm Petri dishes containing a single layer of dried mung beans.  Among the fourteen control populations, the average body mass of males at emergence was 3.82±0.36 mg (mean±SE) and the average body mass of females at emergence was 4.71±0.19 mg (Figure 1 shows a typical control population frequency distribution).

Among the ten bottleneck populations, six had mean male and female body masses larger than those observed in the control populations, two had average body masses smaller than those of the control populations, and two had mixed results with mean male mass smaller than in the controls but mean female mass larger than in the controls.  In the bottleneck experiments, male body mass remained smaller than that of females in every population, as was observed in the control populations.  A representative example of the adult mass frequency distribution produced from a bottleneck population in which the body mass for both males and females increased is shown below (Figure 2).

Among the six bottleneck treatment populations in which the mean male and female body masses were greater than those observed in the control populations, male body mass was 4.03±0.21mg (mean±SE) and female body mass was 5.07±0.21mg.  The body masses of both males and females from these bottleneck populations were significantly greater than those of males and females from control populations (Mann-Whitney U, N_a=14, N_b=6 two-tailed p=0.043 for males and p=0.004 for females).

Figure 1.  Frequency distribution of male and female body mass in a control population.  These data are for one control population that was started with 25 randomly chosen males and females from which 229 males and 250 females were produced. Mean body mass of males was 3.72±0.59 mg (mean±SD) and mean body mass of females was 4.68±0.69 mg in this population.

Figure 2. Frequency distribution of male and female body mass in a genetic bottleneck treatment population.  These data are for one bottleneck population that was started with 5 randomly chosen males and females from which 87 males and 77 females were produced. Mean body mass of males (mean±SD) was 3.97±0.50 mg and mean body mass of females was 5.35±0.60 mg in this population.