Download Comments on the nature of deception

Comments on the nature of deception
J. L. CLOUDSLEY-THOMPSON
Department of Zoology, Birkbeck College (University $London),
Malet Street, London, WClE 7HX
“Is the resemblance of a leaf-insect to a leaf an example of mimicry or crypsis?”
asks Vane-Wright ( 1980) in a thought-provoking article on the definition of
mimicry. It is easy to see that, from a distance, the insect may be generally cryptic
but, close up, mimics a leaf. I have long thought, however, that it might be better
to restrict the term ‘mimicry’ to cases in which one species of animal
resemblances another and to use the word ‘disguise’ for instances in which an
animal looks like a stick, lichen, bark, faeces, a stone or some other inanimate
object unattractive to potential predators. If so, are fulgorid bugs mimics of
alligators, or are they disguised as alligators? I addressed this query to VaneWright, who answered as follows.
“I’m afraid I stick to my contention that it is the ‘reference frame’ of the
operator that determines whether or not crypsis or mimicry should be
employed. Tiger stripes ‘are’ aggressive crypsis, leaf-insects are defensively
cryptic. But mantids which look like flowers (e.g. Idolomantis diabolicum) are
aggressive mimics, as their victims are (presumably) actively seeking out
flowers-and we imagine that most flowers have evolved their ‘flashy’
signals to attract pollinators. I don’t see how you could define such a
general word as disguise in an operational way different to mimicry and
crypsis as I have defined them, or as others have tried to do so.It might be
useful as a word for lumping both phenomena together.
In the case of what Miriam Rothschild called ‘dual signals’, where the signal
value apparently changes with distance, I see no reason why one cannot say
that fulgorids are cryptic at a distance, but possibly act as alligator mimics
when viewed close up. Harmless leaf-insects seem to me cryptic at any
distance! If you are looking for meat, leaves are of no interest.” (in litt., 22
April, 1980.)
Perhaps I have been unduly influenced by my friend and one-time supervisor,
Hugh Cott (19401, who classified as ‘cryptic’ all animals that resemble plants,
thereby restricting ‘mimicry’ to resemblance of one animal by another. Malcolm
Edmunds ( 19741, however, pointed out that resemblance to a stick or bark can be
very precise and, therefore, comparable in specialization to mimicry of another
animal; while Wickler (1968) defined mimicry in terms of a counterfeit signal
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J. L. CLOUDSLEY-THOMPSON
which deceives a ‘signal-receiver’ (or ‘operator’, to use Vane-Wright’s
terminology). “Cryptic organisms specialize in generating information of the
type not attended to or filtered out (reference frame) by the receivers, whereas
mimetic organisms specialize in producing information (signals) of the type
sought out by and of interest to a receiver.” (Vane-Wright, 1980.)
Natural phenomena can be classified in many different ways depending on the
criteria adopted. Using the reference frame of the operator, which is clearly the
most appropriate, I have to agree that the terms ‘mimicry’ and ‘disguise’ are
synonymous with regard to the relationship between fulgorid bugs and caimans.
At the same time, there does seem to be a fundamental difference between
mimicry of an ant by a spider and mimicry of an alligator by an insect. I find that
the resemblance of lycaenid pupae of the tribe Spalgini to anthropoid heads
never fails to rouse fervent dispute. Howard Hinton (1973, 1974) described
convincingly how size differences can be explained away in terms of hunting, in
insectivorous birds, by the method of ‘rapid peering’. If this argument is
accepted, no further problems should arise-apart from lingering doubts and
scepticisms! When the concept of frightening behaviour is introduced, however,
further dificulties appear.
.
Edmunds (1974) uses the term ‘deimatic’ to include all intimidating displays,
postures and frightening noises-pointing out that they ma occur in both
cryptic and aposematic animals. But is the hiss of a grass s n J e , for example,
deimatic behaviour, or is it mimicking the hiss of a poisonous snake-in
England, an adder? As Vane-Wright commented in his interesting letter already
referred to, “Perhaps mimicry is about species, or groups of species, not
generalised features of whole hyla-but that is not easy to write into a
definition!” He included examp es of related devices under the rubric “Decoys
and deflective marks” in his unified classification of mimetic resemblances
(Vane-Wright, 1976). Using the reference frame of the operator leads, in this
case, to the lumping together of phenomena as dissimilar as the hissing of
snakes,.lizards, hole-nesting birds such as tits and the wryneck, chameleons and
kittens and the squeaks of lepidopteran pupae; as well as false caterpillars and
pupation sites, dummy spiders on the stabilimenta of orb-webs and so
on-which have in common the function of discouraging predators through the
experience of wasted effort. This may be stretching classification beyond the
limits of usefulness.
Finally, I would like to comment on the absence of documented cases of scent
mimicry, in which a harmless species smells like a dangerous one. Aggressive
scent mimicry, on the other hand, is certainly known. Some of the lassoo or bolas
spiders are believed to emit the female pheromone to lure male moths closer and
orchids mimic the scent of hymenopteran females, thereby attracting s ecific
males for ‘pseudocopulation’pollination. Orchids and fungi that attract ies by
emitting a stink like decomposing meat are employing the same trick. Perhaps, as
Vane-Wright suggested in his letter, simple Batesian scent mimicry may be
improbable because production of an unpleasant odour would imply the ability
to secrete repugnatorial compounds, so that Miillerian scent mimicry would be
more likely to occur. On the other hand, a warning signal such as aposematic
coloration is not, in itself, necessarily unpleasant or distasteful. Where man is the
operator it may even be aesthetically attractive-such as the berries of deadly
nightshade or the colours of coral-snakes; and it is not inconceivable that
warning should be associated with otherwise innocuous scents.
P
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ON THE NATURE OF DECEPTION
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Figure I. Above, head of the alligator-bug (Fulgora) showing resemblance to a spectacled caiman
(Cnimzn), below. Not to scale. Drawn from photographs. (From the author's Tooth and Claw. Defensive
Strategies in the Animal Wmld, London:J . M . Dent, 1980.1
This would certainly appear to be a topic that might repay further investigation. In the case of insects and other terrestrial arthropods, which are all
relatively small animals, the operator can be an animal of a similar size range
(usually another arthropod), or a very much larger predatory enemy such as a
lizard or bird. Selection by different types of operator may produce divergent
effects which may not be easy to distinguish in the field. In this connection, it
should be remembered that the crab-spiders (Thomisidae) which match the
colours of the flowers on which they are resting, and therefore appear cryptic to
us, are conspicuous when photographed in ultra-violet light. It can only be
concluded, therefore, that such crypsis is defensive and related to predation by
birds and lizards: it is not, as has sometimes been assumed, aggressive. The
of Zdolomuntis (=Zdolium) diabolicum, referred to earlier, is likewise
proba ly deimatic and directed towards vertebrate predators*. Edmunds (1976)
considers it unlikely to have evolved as a lure to attract prey. There is much to be
said in favour of Vane-Wright's objective definition but there are many instances
of mimicry or disguise at the significance of which we can, as yet, do little more
than guess.
displai
"The resemblance to a Hower is, I think, primarily defensive (see Wickler, 1968, Fig. 32).
J. L. CLOUDSLEY-THOMPSON
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REFERENCES
COIT, H. B., 1940. Adclptiue Colmation in Animals. London: Methuen.
EDMUNDS, M.,1974. Dcfcnce in A n i d . A Suwq of Anti-Predalw Dcfmes. Harlow: Longman.
EDMUNDS, M., 1976. The defensive behaviour of Ghanaian praying mantids with a discussion of territoriality.
Zoological Journal ofthe Linnean Society, 58: 1-37.
HINTON, H. E., 1973. Natural deception. In R. L. Gregory & E. H. Gombrich (Eds),IUwion in Nature and Art:
96-159. London: Duckworth.
HINTON, H. E., 1974. Lycaenid pupae that mimic anthropoid h e a d s . J w d ofEn&mhgy,(A) 49: 65-69.
VANE-WRIGHT, R. I., 1976. A unified dassification of mimetic resemblances. Biological Journal ofthe Linnean
Society, 8: 25-56.
VANE-WRIGHT, R, I., 1980. On the definition of mimicry. Bio&gkdJwd ofthe Linnean Society, 13: 1-6.
WICKLER, W., 1968. Minricty in P h t s and A n i d . London: Weidenfeld & Nicolson.