Variation in a Mutualism: Phenology and the Maintenance of Gynodioecy in Two Indian Fig Species

11 studied phenological variation in the coevolved mutualism between gynodioecious figs (genus Ficus) and their species-specific pollinator wasps. The phenology of tropical gynodioecious figs is important to vertebrates relying on fig fruit as a resource, and to understanding the evolution of gynodioecy in Ficus. 2 Gynodioecious fig species have hermaphrodite trees with closed, urn-shaped inflorescences bearing male and female flowers, and female trees with inflorescences bearing female flowers. Pollinators entering receptive inflorescences on hermaphrodite trees pollinate, lay eggs in female flowers, and die; weeks later, offspring emerge, mate and carry pollen from hermaphrodite trees to other trees. Wasps entering inflorescences on female trees pollinate female flowers but cannot lay eggs, and die without leaving offspring. Hermaphrodite ('male') trees produce pollen and wasps, and no seeds; female trees produce only seeds. 3 During 1991 and 1992, I observed the phenology of two gynodioecious fig tree species, Ficus exasperata and F. hispida, in a dry and a wet site in Coorg District, south India. 4 Ficus exasperata trees displayed a synchronous phenology very similar to that predicted by one hypothesis relating the evolution of gynodioecy to phenology. Female trees of F. exasperata produced seeds synchronously during the monsoon season and 'male' trees produced pollinator wasps and pollen synchronously during the peak period of female receptivity. Crop production occurred more frequently in the dry than in the wet site. Female trees bore mature fruit for longer periods than 'male' trees. 5 In contrast, several phenological traits of F. hispida departed strongly from prediction. This species displayed an asynchronous phenology at the population level. Receptivity and wasp or seed production in F. hispida occurred year-round, female trees produced more crops than 'male' trees, and there was considerable overlap in timing of 'male' and female inflorescence production. Durations of phenological phases were longer on female than on 'male' trees at the wet site. 6 An asynchronous phenology appears to be more advantageous in aseasonal than in seasonal environments. If the two phenological types observed in this study are found to be widespread, then the possibility that functional dioecy in Ficus evolved via more than one pathway must be considered.