Biology Reference
In-Depth Information
of a symbol to indicate the room. This area of research is still in its infancy. It remains to
be seen how such experiments can be scaled up to more complex language and more
natural settings, or whether different selective factors can lead to different forms of
communication.
Dishonest signals
In the examples so far, we have focused on asking when and why signals would be
honest. However, nature is also full of examples of dishonest or coercive signalling. A
classic example of this is the lure that an anglerfish uses to attract other fish, which it
can then prey on (Fig. 14.18). The anglerfish (sender) clearly benefits from the
behavioural response to the lure by attracting prey, whereas the fish that respond to the
prey (receiver) pays the cost of being eaten. In Chapter 4 we discussed another example
of dishonesty, termed Batesian mimicry, where palatable species mimic the appearance
of unpalatable species. For example, potential predators avoid hoverflies because they
look like wasps.
Why don't receivers just ignore dishonest signals?
Presumably the answer is that the response is, on average, a
beneficial thing to do. So, for example, fish need to eat, and
worm-like things are usually worms, not the lures of
anglerfish, so it pays to try to head towards them. Similarly,
wasp-like things are usually wasps not hoverflies, so it pays
to avoid them. This suggests that dishonest signalling will
only be evolutionarily stable when it occurs at a relatively
low frequency.
Leena Lindström and colleagues (1997) tested how the
benefit of dishonest signalling varies with its frequency,
by experimentally mimicking an unpalatable prey and a
palatable Batesian mimic. They allowed great tits to feed
on mealworms, some of which were made unpalatable by
dipping in a chloroquinine solution. They attached small
blue cake decorations to these dipped mealworms, as a
signal of unpalatability, but also attached these
decorations to a variable proportion of the undipped
mealworms, to make a Batesian mimic. When the great
tits were allowed to feed on the mealworms, it was found
that they were more likely to eat the decorated mealworms
when a higher proportion of them were mimics. Hence,
the fitness of those deceptive mimics decreased as they
became more common.
This example raises a number of hard questions that we
will examine with a couple of more specific examples. Firstly,
when we observe deception, are we looking at a stable
equilibrium of honest and dishonest signalling, or are we
looking at signalling system that is breaking down and on
A signal is
dishonest when
the sender does
something that
manipulates the
behaviour of
the receiver to
the benefit of the
sender and the
detriment of
the receiver
Fig. 14.18
Photograph of an anglerfish.
Photo © David Shale/naturepl.com.
