Final answer:
While variability and heritability of carotenoid concentrations in sugar maple leaves have been shown, without evidence of differential reproductive success, it cannot be concluded that natural selection is acting on this trait.
Step-by-step explanation:
To determine whether natural selection can operate on the variations in carotenoid concentration among different sugar maple trees, we must consider three main components: variability, heritability, and differential reproductive success. In this case, you have observed variability - different concentrations of carotenoids in leaves, and you have proven that there is heritability, with 50% of the variation being inherited. However, for natural selection to take place, the variations in carotenoids must also convey some differential reproductive success. This could mean that certain carotenoid concentrations could lead to a higher survival or reproduction rate among those trees due to various factors such as resistance to disease, ability to attract pollinators, or other environmental advantages. Without evidence of differential reproductive success attributed to the carotenoid concentration, we cannot conclude that all components of natural selection are present.
Genetic variance in a trait like carotenoid concentration is necessary for natural selection to act upon, as heritable traits can be passed from parent to offspring. If trees with a certain concentration of carotenoids reproduce more successfully, those traits become more common in the population, leading to evolution. However, if the variation in carotenoid concentration does not affect a tree's ability to survive or reproduce, it would not be subject to natural selection.
In conclusion, the inheritance of this trait has been demonstrated, but without evidence of a connection to reproductive success, the answer to whether all components of natural selection are present is B. no.