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Ficus ixoroides: Ecology

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ixoroides - 14

Ficus ixoroides  is a rare rheophytic fig only found along rivers in Sarawak and northern Kalimantan. The fig fruits ripen green/yellow and look similar to Ficus fistulosa  which suggests that the ripe female figs attract bats for  seed dispersal.

Secondary dispersal: However  the thick narrow leaves and rheophytic  riverine habit suggests that female fig fruit containing seeds  are also dispersed by water and fish. Rivers always flow downhill  so all river or stream dispersed plants also  require a secondary disperser  (in this case bats and possibly fish)  which can carry the seeds upstream and uphill.

Photos by Astrid Cruaud and Jean-Yves Rasplus.     Location: River bank between Pa Lungan to Pa Umor in the Bario Highlands of NE Sarawak.  Co-ordinates:   3.761009 115.526397

These are all male figs growing on a male plant. Prior to pollination male and female figs look similar and can only be told apart by  examining the interior of the fig.
Ficus ixoroides immature male fig. The pink objects at the top of the photo  are the male flowers  surrounding the hole (ostiole) at the base of each fig. The ostiole is  blocked with  “one way” interlocking bracts so that only pregnant female fig wasps ready to lay their eggs can force their way in  with their uniquely adapted  heads. Once inside  the female fig wasps lay a single egg in each tiny gall flower.
After about a month  the adult fig wasps emerge from their brood chambers in the gall flowers and the males and female fig wasps mate. The wingless males  then clear the ostiole of bracts allowing the winged females to escape from the fig  without damage to their wings. Enroute through the ostiole the females collect pollen from the anthers of the male flowers surrounding the ostiole. Once they reach the surface of the fig the female fig wasps fly off to search (by scent) for  receptive figs in which to lay their fertile eggs. The wingless  males hang around on the surface of the fig acting as decoys,  waiting to be eaten by predatory ants who might otherwise attack the pregnant females before they could escape.
The narrow tough leaves allow Ficus ixoroides to  survive  powerful  river currents during floods. There are at least four rheophytic (river or stream adapted figs)  found in Borneo, Ficus limosa, Ficus macrostyla and Ficus subsidens as well as F. ixoroides.

 

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