UCT scientists have uncovered a fynbos plant that tricks dung beetles into thinking its seeds are antelope dung, duping the beetles into burying the seeds as they would do with dung.
This tricky piece of evolution enables the plant to ensure its seeds are underground and safe from being destroyed by fire – and ready for germination.
And the reason the beetles are fooled is that the seeds – or nuts, as the researchers call them – really do stink like dung.
This rare example of plant deception was discovered by Jeremy Midgley, from UCT’s Department of Biological Sciences, and the findings were published in the journal Nature Plants yesterday. This might be one of the best examples of faecal mimicry for seed dispersion anywhere in the world.
“It is a pretty amazing story,” Midgley said.
The discovery stemmed from Midgley’s project that looks at seed dispersal by rodents. At De Hoop Nature Reserve, he put some of the big seeds from the Cape restio ( Ceratocaryum argenteum) plant out and later saw that a few of them were buried. There are two rodents that, like squirrels, bury plant seeds to eat in the future, but neither of these rodents occurs at De Hoop, so he was puzzled.
The researchers’ camera turned up nothing. But they had tied fluorescent threads to the seeds and went looking for them at night. There the threads were, trailing from the buried seeds.
“The way we eventually found out was by pure fluke really. We were sitting watching the seeds when this dung beetle came up to the seed, rolled it away and pulled it down from underneath into the soil.”
Once dung beetles have buried their ball of dung, they either eat the dung or lay their eggs in the dung ball. Because the seed smells like dung, the beetle was fooled.
“We didn’t find any eggs. Presumably it tried to lay its eggs on the nut, but once it tried, it would realise it had been had. That is some pretty amazing deception.”
Tests on the seeds revealed that the chemical compounds given off by the seeds were similar to those emitted from eland and bontebok dung.
“They smell quite strong. I’ve had some here in my office for months and they still smell.”
Midgley said this burying action was “perfect” for the plant. “The seeds need to be buried to avoid being incinerated by fire, but not too deep or they won’t get the signal when a fire does come through.”
The fire is the signal for the plant to germinate.
De Hoop had two massive fires last month and Midgley plans to visit the area to see if the dung beetles seed stash has now begun to grow.
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