Wasps commit reproductive suicide to help this beautiful fig
Ficus erecta is part of a 'species complex' (a group of species difficult to discriminate or distinguish from one another, often interpreted differently by different authors, resulting in more or less species depending upon evidence available, philosophical approach and inclination) of about 30 species called subsection Frutescentiae (there are about 750 fig species in total). There are sometimes varieties recognised within what is called Ficus erecta but these are not widely used.
Apart from its striking leaves (just appearing in this botanic garden specimen in early spring - it is deciduous), the reproductive strategy of this species is worth some attention.
As with most fig trees, fertilisation is complicated. Like Australian native orchids, each fig species has a specific wasp species required for successful pollination. This relationship is thought to have existed for 65 million years, back to when dinosaurs may have snacked on fig fruits.
Figs typically produce three kinds of flowers - male, females with a long receptive stalk (style) and females with short receptive stalks. The latter are sometimes called gall flowers.
In a 'monoecious' species (with male and female flowers on the one plant) these three flowers are found within what looks like an immature fruit. A female wasp enters this chamber and lays eggs on the gall flowers (the short-styled females), while incidentally pollinating the other female flowers (long-styled) with pollen collected from previously from male flowers.
The males and females within a single chamber do not mature at the same time, to avoid self-pollination (self-pollination reduces genetic diversity, and therefore adaptability, in the resulting seed).
Male wasps emerge first and inseminate the females as they emerge. The male was then burrows out of the fig, leaving an escape route for the females.
As the females emerge they gather up pollen from the male flowers inside their nursery chamber and fly to another chamber with females ready for egg-laying (short-styled) and fertilisation (long-styled).
Some species, like Ficus erecta, have separate male and female plants (and flower chambers). I'm not expert enough to diagnose the sex of the specimen photographed here but we call this arrangement 'dioecy', and it prevents self pollination. Things are more complicated for the wasp though. The eggs can only be laid in 'male figs'. The 'female figs' have only long-styled flowers, the ones not suitable for egg-laying.
Yet the female wasps still visit the female figs, which is good for the fig (pollination) but a waste of time for the female wasp (they then have to search out a male fig to successfully lay eggs). It was discovered recently that the female flowers mimic the scent of male flowers, tricking the wasps into their pollinating visit.
There is more to this evolutionary tango, with some changes to wasp anatomy linked to the change in fig pollination strategy, but overall it relies on there being a bit of inbreeding in the wasps allowing for what is described as reproductive suicide for some lineages.
For you and I, we can enjoy the bold, erect leaves of Ficus erecta and get our fig fruits from the usual source - our domestic fig tree or the local market or shop. I saw and photographed this species in Chenshan Botanical Garden in Shanghai, China, one of the replacement plantings in this now nine-year old botanic garden where most of the top soil had to be replaced after the first unsuccessful plantings of the first few years.
It is fast becoming one of the great Chinese botanic gardens, and soon, I expect, one of the great world botanic gardens. And not just because of this fig.
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