Limits to Fruit Production in a Monoecious Fig: Consequences of an Obligate Mutualism

Abstract

Fruit maturation patterns of a Costa Rican fig tree, Ficus pertusa, were studied. Like other figs, F. pertusa is pollinated by a species—specific wasp (Agaonidae) whose female offspring transfer pollen between trees. Pollination success (the proportion of inflorescences pollinated) ranged from 1 to 100% among 21 F. pertusa crops studied over 2 yr and averaged only 65%. Resource availability evidently was limiting to fruit set as well: every crop abscised many inflorescences at a predictable point during growth. This abscission period usually preceded the brief but variably timed period of pollinator arrivals; in most cases every pollinated, undamaged inflorescence set fruit. In contrast, many resource—limited species reduce crop sizes after pollination. Numerous advantages of fruit abortion have been proposed. However, fruit abortion would not be expected in plants that evolved under conditions of pollen limitation; although pollinators have been thought to be overabundant in highly coevolved pollination mutualism, figs' unique flowering phenology may in fact make pollen limitation common. The fact that future pollen carriers as well as seeds mature within fruits may also help explain these unusual fruit maturation patterns.