This is just an educated guess. As the purple pigment, caused by anthocyanins, are on the bottom side of the plant, their purpose could probably be to direct the light.
Specifically, a purple pigment on the bottom of the plant would absorb certain wavelengths near the purple spectrum, and reflect other wavelengths back toward the portion of the plant with chlorophyll. In this way, light does not simply pass through the leaf, instead it is reflected back in towards the chlorophyll to maximize the amount of light being used for photosynthesis.
Answer:
Has more offspring that have the ability to survive and reproduce themselves.
Explanation:
Evolution fitness can be defined as a characteristic or quality possessed by living organisms and determines their adaptability, as well as level of success in terms of reproduction i.e giving birth to offsprings.
Hence, if you say that a ground squirrel has greater evolutionary fitness than another ground squirrel in the same population, you mean that the animal has more offspring that have the ability to survive and reproduce themselves.