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.