Final answer:
Mate discrimination in tiger swallowtail butterflies is revisited as an example of purifying sexual selection, illustrating that sexual selection can favor traits that increase fitness by reducing genetic variance for size in the population.
Step-by-step explanation:
The discussion of mate discrimination among male tiger swallowtail butterflies by female members of the species is an intriguing example of purifying selection, which is a form of sexual selection. In this case, the females preferentially select smaller males over larger ones, and this preference can lead to a reduction in the genetic variance for size within the population, as larger males are less likely to reproduce. This example is revisited because it provides a compelling contrast to other forms of selection that might result in increased variance, like negative frequency-dependent selection, or other forms of sexual dimorphism where traits can be exaggerated rather than minimized.
Understanding how sexual selection can lead to purifying selection is important because it demonstrates that sexual selection doesn't always lead to the development of larger or more elaborate traits, such as the peacock's tail. Instead, sexual selection can also favor more 'practical' traits that improve the fitness of the species. This concept is vital for grasping the complexity of evolutionary pressures and the subtle nuances of animal behavior and reproduction.