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The plant that disguises itself as DUNG: Shrub fools beetles into burying its seeds by making them look and smell like animal droppings

The rush-like Ceratocaryum argenteum produces large, hard, smelly nuts
Scientists say they give off a pungent smell just like antelope dung
They found the nuts produce more volatile chemicals than fresh droppings
This appears to trick the beetles into rolling the seeds away to bury them

Published: 10:13 EST, 6 October 2015 | Updated: 12:31 EST, 6 October 2015

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Plants are well known for using powerful scents to attract animals in order to help them spread, but one ingenious shrub has taken this to a rather pungent extreme – by producing seeds that smell of dung.

The rush-like Cape Restio, also called Ceratocaryum argenteum, produces large, hard nuts that mimic antelope droppings to trick dung beetles into rolling them away to bury them.

Researchers studying the plant have described the deception as 'remarkable'.

Researchers have found that nuts produced by a plant called Ceratocaryum argenteum (label a, b and c) gives off strong smelling chemicals that mimic the pungent aroma of antelope droppings (label g). The smell gets more powerful with age and this appears to trick dung beetles (label f) into rolling them away

They found that dung beetles appear to be unable to distinguish between the strong smelling nuts and real dung balls, yet they are completely inedible to the insects and their larvae.

Speaking to the Mail Online, Professor Jeremy Midgley, a biologist at the University of Cape Town who led the study, said: 'The seeds are very pungent, humans can easily smell them.

'I have nine month old seeds in a paper bag in my office that are still very pungent.

DUNG BEETLES' HEAVENLY GPS

Scientists have previously found the beetles use stars to navigate, and have found that a nocturnal species uses moonlight as a form of compass to roll balls of excrement in a straight line.

By looking at the beetle’s brain cells, they found that ‘compass neurons’ respond to the position of the sun during the day, but switched to respond to polarised light during the night.

Scientists at Lund University in Sweden have shown that species of African dung beetles active during the daytime - diurnal - and night - nocturnal - use different celestial cues to roll dung along in a straight line.

All dung beetles roll animal faeces, which they eat, into a ball and roll it away to a safe place where it is unlikely to be stolen.

Once a beetle set its course, the researchers used mirrors to change its view of the sun or the moon so they could work out whether the beetle used the celesial objects to navigate.

They found that during the day, both species used the sun as a compass.

But at night, when the polarised light of the moon is at least a million-fold dimmer than that of the sun, the diurnal species used the moon itself as a navigational tool.

'At this stage only dung beetles seem to be attracted to the seeds.'

In a study published in Nature Plants, Professor Midgley and his colleagues report how the dark, hard nuts produce 300 times more volatile chemicals than other seeds of similar plants.

Intriguingly the older the seeds got the more volatile chemicals they produced.

They found the levels of volatile chemicals from fresh faeces left by bontebok – a small grass grazing antelope – were somewhere between the fresh Cape Restio seeds and old seeds.

Using motion sensitive cameras and fluorescent markers, the researchers were able to monitor how animals reacted to the seeds and were surprised to see dung beetles rolling them away.

After scattering 195 seeds at the De Hoop Nature Reserve in South Africa, they found that within 24 hours the dung beetles had rolled nearly half of them away.

They also found, however, that a small mammal – the striped field mouse Rhabdomys pumilio, - which normally consumes seeds, also avoided the Cape Restio nuts.

However, when the seeds were de-husked, they found the mouse consumed them veraciously.

Joseph White, another of the team working on the study, said: 'We used motion-sensing trail cameras to observe small mammal interactions with the nuts under field conditions, and it seemed that they were either disinterested or even repelled by the seeds.

'When they cracked open seeds it was clear small mammals were interested in the nutritious inner parts of the seeds. We suspect that the smell of the nuts repels small mammals.

The researchers set up motion sensitive cameras around the De Hoop Nature Reserve in South Africa to watch how animals reacted to the seeds of the Cape Restio and were surprised to see that half of the nuts were rolled away by dung beetles (pictured), which are unable to eat the hard nuts

Ceratocaryum argenteum (pictured) looks a little like reeds or bamboo, but produces large nuts that have a deeply unpleasant smell

'In future we will put an extract of these seeds on palatable seeds and see whether this causes small mammals to lose interest in these seeds.'

The researchers believe the smelly seeds may be part of an evolutionary arms race between plants and insects.

While many plants use strong scents to attract insects to help pollinate flowers, there are fewer examples of them using similar methods to disperse seeds.

Some plants produce hard seeds which look like berries, but these rarely seem to dupe birds, say the researchers.

Dung beetles feed almost exclusively on animal droppings, often gathering them into large balls that they roll away to use a food source, burying it to stop it being stolen or to use as a brooding chamber for their larvae.

Dung beetles feed almost exclusively on animal droppings (pictured), often gathering up fresh dung into large balls and burying them to avoid it from being stolen. They sometimes the insects also use the dung as a brooding chamber for their larvae

Mr White the Cape Restio may be one of the only examples in the world of 'faecal mimicry' and is one that requires a delicate balance.

He said: 'Too much dung and the nuts will not be buried because beetles have too much of a choice, too little dung and there will be a similar lack of burial owing to too few dung beetles – we still have much to learn about the dynamics of such faecal mimicry.'

Professor Steve Johnson at the University of KwaZulu-Natal in Durban, added that they now hoped to identify which volatile chemicals are responsible for attracting the beetles.