Sex Ratios of Offspring
Some organisms, such as fig wasps, exhibit local mate competition, in which competition for
mates takes place in a limited area and only a few males are required to fertilize multiple
females. In the case of the fig wasp, when only one fertilized mother enters a fig flower, the only
males available to fertilize the daughters are the sons.
1. In the below simplified version of local mate competition, assume that only one male is
needed to fertilize all the females and that each female can produce six offspring. Complete the
table with the number of grandoffspring that would be produced for each offspring sex ratio.
Offspring sex ratio
0 female: 6 male
1 female: 5 male
2 female: 4 male
Number of grandoffspring
3 female: 3 male
4 female: 2 male
5 female: 1 male
6 female: 0 male
2. Given the results in the table, what offspring sex ratio is favored? What does this mean for the
overall sex ratio of the population?
3. Imagine that two fig wasps lay their eggs in the same flower, so that a mother's male offspring
can mate either with their sisters or with the daughters of the other mother. How would the
offspring sex ratios likely be different in this case?
