Delayed greening in tropical leaves: an antiherbivore defense?

Many tropical species flush entire canopies of red, white, or light green young leaves. In these species, there is a delay of the normal greening process until after leaves have fully expanded and have begun to toughen. Delayed greening involves a delay in the input of chlorophyll, rubisco, nitrogen, and energy. Photosynthetic capacity is therefore lower than in species with normal greening. At full expansion, leaves begin to toughen quickly, and rates of herbivory drop by a factor of 4. We suggest that delayed greening has evolved as a mechanism for minimizing losses to herbivores by delaying input of valuable resources until after the leaf is fully expanded and better protected by toughness. These benefits outweigh the costs of forfeited photosynthesis in the shaded understory but not in the high light treefall gaps. This cost evaluation suggests that, in the face of herbivory, it is advantageous to have delayed greening in the shade and normal development in the sun. Data from 175 of the most common tree species on Barro Colorado Island confirm that delayed greening is extremely common in shade tolerant species and rare in gap specialists.