Coevolution of mast seeding in trees and extended diapause of seed predators

Abstract

Many trees in forests show synchronized and intermittent reproduction, which is called “masting” or mast seeding. According to recent theoretical studies, the evolution of masting is promoted both by recruitment through the seedling bank and by seed predators. An important class of specialist seed predators (e.g., weevils and some moths) are parasitoids that oviposit on or in fruits from which the next generation emerges over the following several years. This staggered emergence is called “extended diapause”. In this paper, we study the simultaneous evolution of tree masting and extended diapause of seed predators. If a fixed fraction of diapausing larvae matures every year, the evolution of trees results in masting (intermittent reproduction with a large fluctuation in reproductive activity) or non-masting (trees reproduce every year). The transition occurs discontinuously, showing evolutionary jumping. The range of seedling survivorship for which masting evolves is broader when the ovipositing efficiency and larval survivorship of the seed predators are large. Interestingly, the conditions for the evolution of masting are broadest for an intermediate fraction of extended diapause of seed predators. When both tree masting and the extended diapause of seed predators evolve simultaneously, the evolutionary end point of the fraction of extended diapause is clearly greater than the value that most favors masting evolution. The stochasticity caused by the finiteness of the number of trees tends to promote masting evolution.