It is known that increased reproductions leads to reduced longevity for female fruitflies. Patridge and Farquhar (1981) studied whether the same phenomenon held for male fruitflies. The data are also discussed in Hanley and Shapiro (1994). The experiment set up five treatment groups, each consisting of 25 randomly assigned male fruitflies. The males in one treatment were housed with eight virgin females per day. In another treatment, the males were housed with one virgin female day. There were three control groups: males housed with eight newly impregnated females, housed with one newly impregnated female, and housed alone. (Newly inseminated females will not usually mate within two days).
The data are contained in the file fruitfly, with a row for each male in the following format:
Column 1: the number of females
Column 2: the type of female—0 denoting newly pregnant, 1 denoting virgin, and 9 when there were no females
Column 3: lifespan in days
Column 4: length of thorax (mm), which is fixed at birth
Column 5: percentage of time spent sleeping
a. Calculate summary statistics for lifespan in each group and compare. Display the data in parallel boxplots. Qualitatively, what do you conclude?
b. Do the same for percentage of time spent sleeping.
c. Make a scatterplot of lifespan versus thorax length. Is thorax length predictive of lifespan and did the randomization balance thorax length between the groups?
d. Use the F test to test for differences in longevity between the groups. Use both Tukey’s method and the Bonferroni method to compare all pairs of means. Summarize your conclusions.
e. Repeat the analysis using the Kruskal-Wallis test and the Bonferroni method.
f. How does the availability of virgin females affect the sleep of male fruitflies?
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