A comparative analysis of the photoprotection hypothesis for the evolution of autumn colors

The adaptive value of autumn colors – the seasonal production of red anthocyanins observed in many species of trees and shrubs – is still debated. According to the photoprotection hypothesis, anthocyanins protect leaves from photoinhibition and photooxidation at low temperatures, enabling the tree to reabsorb nutrients more efficiently before leaf fall. Hence, the hypothesis predicts that autumn colors are more likely to evolve in species growing in colder environments. We tested this prediction by comparing the climatic parameters of 237 North American tree species. We found that, while species with yellow autumn leaves grow under lower minimum temperatures than species with green leaves, there is no significant difference in temperaturebetween species with red autumn leaves and species with green or yellow autumn leaves. We conclude that, while reabsorbing chlorophyll in autumn, and the consequent unmasking of yellow carotenoids, may be an adaptation to cold temperatures, the production of red anthocyanins is not. Hence, our inter-specific comparative analysis does not support the photoprotection hypothesis as an explanation for the evolution of autumn colors.