Leaves and figs of a male
Ficus leptogramma fig tree from the Crocker Range. Two thirds of Borneo’s figs including F. leptogramma are dioecious which means separate male and female trees. Unusually for male figs all stages of development from immature to ripe figs were present on the same tree indicating that this single tree (probably) produces fig wasps continuously.
Male Ficus leptogramma tree at 1,000m on the western slopes of the Crocker Range
In this photo you can see all stages of fig development from small immature fruit through to “ripe fruit” where the fig wasps have left rotting on the forest floor.
A young male fig in the receptive phase but not yet pollinated.
Note the few male flowers (stamens) near the ostiole on the left The rest of the tiny flowers in this fig are short styled “gall” flowers which are waiting for female fig wasps to enter this fig via the ostiole on the left -hand side and lay their eggs, one in each gall flower.
After the female wasps have laid their eggs in the flowers, the fig wasps start to grow inside the gall flowers as shown in this photograph. The round dark objects inside each flower ovary is a developing fig wasp.
This is the final phase. The fig wasps have hatched from the flowers and left the fig via the ostiole, which is on the lower right in this photo.
Each flower acted as a womb for a single fig wasp. Once the wasps have left the empty fig is of no value and drops off the tree to rot on the ground.
Close up of a empty flower once the fig wasps have left.
At the present time only two Bornean fig species are known which can produce fig wasps continuously from single trees, F. leptogramma as shown above and F. cereicarpa another Borneo endemic. Although the intervals vary , a typical individual male fig such as F. rosulata will produce fig wasps only four times a year. Individual female F. rosulata figs will only be receptive for the equivalent of four separate weeks a year i.e. roughly 10% of the time. This means that the absolute minimum viable population (figgery) of a group of Ficus rosulata fig trees for pollination to be successful is at least 20 trees (10 male and 10 female trees). In theory the minimum size “figgery” for F. leptogramma is only two trees (one male+one female), assuming that female F. leptogramma trees always have receptive figs on them. Data from Harrison (2013) Ecology of a fig ant plant (at Lambir).