Research & Innovation 2015-16 - Page 118

How plants dupe dung beetles
into burying their seeds
A Cape restio (Ceratocaryum argenteum) produces large, hard nuts that
smell and look remarkably like dung. They are often buried by dung beetles,
though they provide no food for the dung beetles or their larvae – a classic
example of biological deception, and possibly one of the best examples of
faecal mimicry for seed dispersal anywhere in the world. They were recently
described by biologists in a paper in Nature Plants.
Deception is a very interesting biological phenomenon,
as it involves a co-evolutionary arms race between one
species (the deceiver, or mimic) that benefits from
resembling another species (the dupe, or model), with no
advantages for – and sometimes even to the evolutionary
disadvantage of – the latter. Some of the most striking
examples of deception in plants are those that deceive
insects into pollinating flowers without any reward.
Some orchids, for example, produce colourful flowers
that contain no nectar to reward pollinating insects.
These plants rely on sensory exploitation (insects are
attracted to colour in general), and in some extreme
cases, mimic other rewarding plants that occur in the
same place, thereby duping insects into pollinating their
nectarless flowers.
Deception for seed dispersal, however, is far less
common. Some plants produce hard red or black
seeds (such as the so-called ‘lucky beans’) that look
like berries; but these do not seem to fool birds, and
are hardly ever eaten or dispersed. Also, such seeds
are often poisonous, and their bright colours act more
as warning colouration than as an attraction to fruiteating birds. Dung beetles being duped into dispersing
‘dung-like’ Ceratocaryum nuts may therefore be the best
example globally of faecal mimicry for seed dispersal.
The scent of Ceratocaryum nuts is very strong. “I have
nine-month-old seeds in a paper bag in my office
that are still very pungent,” says Jeremy Midgley, a
professor in the Department of Biological Sciences, who
discovered the deception. Steve Johnson, a professor

Nature Plants

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