FIGS & SEXUALITY: Of the c. 150 Bornean fig species 47 species are monoecious (both sexes in one tree) and 103 species are dioecious (each plant is either male or female). From DNA studies it is known that all figs were originally dioecious and monoecious figs were a later development in fig history.
WORLDWIDE the proportion of monoecious to dioecious fig species is around 50:50. Dioecy is best developed and most common in the wet evergreen rainforests of Borneo.
THE DISADVANTAGES OF DIOECY: In Borneo dioecious figs are usually locally common shrubs and lianas of the sub-canopy whilst monoecious figs are relatively scarce tall trees or stranglers which produce fig fruits (and fig wasps) at canopy level. Research has shown that these canopy level fig wasps are dispersed long distances by wind currents. However dioecious fig wasps are rarely found in canopy level insect traps and are assumed to fly from one fig tree to another in the forest understorey, where wind is almost non-existent.
EXTERNAL CLUES to the sexuality of dioecious figs are most obvious with Sections Sycidium and Eriosycea (all members of which are dioecious). Male figs are nearly always larger and paler than female figs. The fact that certain dioecious male and female figs could be separated in the field was first pointed out by Hill (1967) working in Hong Kong.
Frank Lambert (1992) was the first to describe sexual differences in Malesian figs.
“A comparison of the figs from three male Ficus species F. heteropleura, F. obscura and F. parietalis at Kuala Lompat, West Malaysia showed that there were distinctive, consistent differences in colour, texture and morphology between figs on male and female plants. Male figs are always paler in coloration than female figs and do not exhibit the colour changes associated with ripening. The male figs of F. parietalis are pale orange at all stages whilst female trees produced orange seed figs which ripen dark red.”
Adapted from Fig Dimorphism in Bird-Dispersed Gynodioecious Ficus Lambert (1992)