On the definition of mimicry
R. I. VANE-WRIGHT
Department of Entomology, British Museum (Natural History), London S W7 5 BD
Acrepled /Or publication August I 9 7 9
operational distinction between crypsis and mimicry i s made in terms of the cognitive and
perceptual systems of ‘signal-receivers’. Cryptic o r g a n i s m specialize i n generating information of the
type not attended to o r filtered out (reference frame) by the receivers, whereas mimetic o r g a n i s m
specialize in producing information (signals) of the type sought out by and of interest to a receiver.
Miniici?; is defined in terms of a system of three living organisms, model, mimic and operatoi(signal-recriver), in which the mimic gains in fitness by the operator identifying i t with the modrl.
Some advantages and applications of the definition are briefly discussed.
,411
KEY WORDS:- crypsis - mimicry - definition
cognition - identity.
- signals
- signal-receiver - operator - perception -
CONTENTS
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Iiitroducrion
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PI-ecisicinof resemblance
Signals, non-signals and n o signals
Exclusions. inclusions, and definition
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Applications
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Acknodedgernent
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Referrnres
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I NTRODUCTI 0 N
Is the resemblance of a leaf-insect to a leaf an example of mimicry o r crypsis?
The words crypsis and mimicry are often used as if they are interchangeable in
describing such phenomena. Although it is probably impossible to provide a
‘perfect’ definition h e . , mutually exclusive) for either term, inconsistency in usage
is largely unnecessary, and can lead to confusion. In most instances a clear
distinction can be made.
Edmunds (1976 : 3) describes various primary defensive adaptations amongst
mantids as examples of ‘stick mimicry, grass mimicry, leaf mimicry and bark
mimicry’. These special resemblances he contrasts with camouflage, o r crypsis,
where the insects show some generalized resemblance to the background. In
adopting this terminology, Edmunds notes that Cott (1940) classifies all such
examples as cryptic, on the grounds that resemblance to a plant implies crypsis,
whilst resemblanct to an animal implies mimicry. Edmunds rejects Cott’s
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R. I . VANE-WRIGHT
terminology on two counts: the observation that resemblance to a stick or leaf
can be very precise (and so comparable in morphological specialization to
mimicry of another animal); and Wickler’s (1965, 1968) definition of mimicry in
terms of a counterfeit signal which deceives a signal-receiver.
PRECISION OF RESEMBLANCE
The degree of morphological and behavioural specialization throughout both
cryptic and mimietic organisms, however defined, varies enormously. As it is
unlikely that any satisfactory method for ‘objectively’ measuring degree of
morphological specialization can be devised, such a criterion cannot be
employed in endeavouring to separate cryptic and mimetic phenomena in a
consistent fashion.
SIGNALS, N O N - S I G N A L S A N D N O SIGNALS
The second point is complex. Edmunds (1976: 3) goes on to state that ‘cryptic
animals rely for protection on producing few or no signals, hence they are not
easily found by predators. Mimetic animals, by contrast, are detected by predators . . .’. If mimics are detected by predators, and if palatable leaf-insects are
mimics, how do they survive?
The essence of the distinction which I wish to draw between the words crypsis
and mimicry relates to the cognitive and perceptual systems of the ‘signalreceiver’ (Wickler, 1965, 1968) or ‘operator’ (Vane-Wright, 1976). The various
sensory systems of any organism are bombarded from without by a deluge of
potential signals. The perceptual system has to reject not only ‘noise’ generated
from within, but also from without-a major task in perception is to filter, to
separate important information from the unimportant. This is intimately
connected with cognition, attention, and the ‘search-image’ or ‘model-in-thebrain’. Our own ability to respond only to traffic and vehicle lights when driving
in a big city at night, and not to all the other coloured lights, is a classic example
of this cognitive-perceptual filtering process. But this system is not perfect or
without risk-we may miss a traffic light placed unusually high or low, or
respond inappropriately when faced with an incorrectly coloured tail-lamp.
Some irrelevant stimuli may occasionally be responded to, and important
information may sometimes be ignored.
Silberglied (1977 : 3 6 4 ) has discussed aspects of communication by
Lepidoptera in similar terms, and suggests that ‘one may view crypsis as a form
of communication in which the prey animal has been selected to decrease, rather
than increase (as in aposematism), its signal-to-noise ratio’. Endler (1978)
discussess animal colour patterns as ‘a compromise between factors which favour
crypsis and those which favour conspicuous colour patterns’, and indicates that
crypsis involves background matching, whereas non-cryptic or aposematic
patterns must be non-matching. The difference between crypsis and mimicry, at
least in one regard, is then clear. A cryptic organism specializes in sending out
information normally considered uninteresting by the appropriate operator. By
producing information of the type filtered out or not attended to (‘non-signals’)
by the cognitive-perceptual system of the potential signal-receivers, i t avoids
detection. This often involves simulating the reference-frame of the operators it
DEFINITION OF MIMICRY
3
does not ‘wish’ to be detected by. A mantid achieves this by being green and sitting
on a similarly coloured green leaf, or by looking like a whole green leaf and
sitting amongst green leaves. (A mimetic species, on the other hand, produces
information of the type that interests the operator (‘signals’)-either attractive or
repellent, etc.) Most visually searching predators which might eat mantids are not
looking for leaves, sticks, grass o r bark-like objects to eat, they are looking for
insect-like objects, using some generalized cognitive ‘model’ of an insect as a
search-image. Therefore, I do not think it appropriate to include these examples
of resemblance by rnantids under the term mimicry, as suggested by Edmunds
(1976);they areexamples ofcrypsis, as dealtwith by Robinson (1969).
Edmunds (1974) uses the term ‘anachoresis’ to categorise those organisms
which, by burying, or complete concealment within or under some other object,
escape detection by sending out no information. This category can be used to
include the ‘no-signal’ animals of Edmunds’ ( 1976) discussion.
EXCLUSIONS, INCLUSIONS, A N D DEFINITION
Wiens ( 19 7 8 : 367) provides a definition of mimicry in which the model may be
animate o r inanimate, so as to include crypsis within mimicry. Wiens answers his
own question, what is the fundamental difference between whether an operator is
unable to discriminate one insect from another or from the physical
environment, with the assertion that the result in both cases is the same: ‘only the
models differ’. However, it is my contention that the differences between animate
and inanimate models, ‘non’ and ‘positive’ signalling, and various sorts of
operator search behaviour (as mediated by the physiological problems of
perception and cognition), all have important potential consequences for the
dynamics of such systems (Edmunds, 1974: 18-21; Vane-Wright, 1376: 49-54;
1978: 68) as, for example, the situation discussed by Endler (1978)with respect to
predator perception and crypsis.
Are all signals of interest to an operator to be regarded as mimetic? Surely not.
If mimicry were to be used as an antonym of crypsis solely with regard to signals,
without further definition, then the bell announcing food to one of Pavlov’s dogs
would be an example of dinner mimicry!
The second problem in the definition of mimicry concerns Wickler’s (1968)
insistence that the operator (or ‘dupe’ of Pasteur, 1972) must be deceived (i.e. put
at a relative disadvantage) by the existence of the mimic. Wickler was, however,
inconsistent in the application of his own definition, seeking to include examples
of synergic intraspecific systems (e.g. the Haplochromis egg-dummy system)
involving a mimetic signal within the phenomenon of mimicry, but to exclude
certain synergic interspecific systems (e.g., classical Mullerian mimicry; see VaneWright, 1976: 47-48). The difficulty of having to exclude ‘Mullerian mimicry’
from mimicry in general is avoided by defining mimicry in terms of mistaken
identity by the operator, as has been done, without special emphasis, by the great
majority of biologists interested in mimicry (e.g., Wallace, 1889: 42; Fisher,
1930: 164; Sheppard, 1975: 182). An insectivore which has learned to avoid viletasting lycid beetles by their black and yellow colour may also avoid similarly
coloured pompilid wasps, even on the first encounter. If so, it makes this
decision through identifying, on the basis of its similar black and yellow signal
pattern, the wasp for one of the beetles, and the resemblance of the two may be
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R I. VANL-WRIGHT
regarded as mimetic despite the fact that the predator has not been ‘deceived’
(on the grounds that the fiercely stinging wasps are potentially unnaccepatable
food, like the poisonous beetles). Wickler (1968) went on to suggest that there
was no difference between models and mimics in a Mullerian situation, whereas
Wiens ( 1 978 : 370) suggests that there are ‘only models and operators’. However,
Turner’s analysis (197 7 : 178-1 80) indicates that the evolution of Mullerian
convergence will generally proceed in a fashion similar to Batesian convergence,
a distasteful species (or complex) acting as a model which ‘captures’ other,
usually rather less noxious o r numerous aposematic species. And for any
particular, individual operator, a sampled aposematic species will be a functional
model, while unsampled aposemes will be the functional mimics.
Wiens (1978: 367-372) seeks to exclude Mullerian mimicry on similar grounds
to those proposed by Wickler, a n d , in addition, ‘weed mimicry’
(Wickler, 1968: 42-44; Vane-Wright, 1976: 381, on the basis that the
selective agents involved are machines, not organisms. Apart from the possible
objection that Wiens is prepared to accept inanimate models, but disbar nonliving operators, in this context machines are but tools used by man. If weed
mimicry causes a problem, man is the operator which may respond by altering
the characteristics of his harvesting equipment.
I would now like to repeat, in modified form, my previous definition of
mimicry (Vane-Wright, 1976: 50).
Mimicry involves an organism (the mimic) which simulates signal properties $a second
living organism (the model) which are perceived as signals of interest by a third living
organism (the operator), such that the mimic gains injtness as a result of the operator
identfiing it as an example of the model.
The explicit inclusion of fitness in the definition, which allows both for greater
precision and simpler wording, follows Wiens (1978: 367). This also underlines
the fact that mimicry is a special case of Darwin’s theory of evolution by natural
selection (Vane-Wright, 1979).
A PPLI CAT10N S
Insistence on such a definition and the differences between it and Wickler’s or
Wien’s definitions may appear to involve trivial hair-splitting. However, the use
of other definitions, coupled with the frequent confusion between the
phenomena of mimicry and individual mimics (Rothschild, in press), has
contributed to a recent debate over whether or not there is any difference
between Mullerian and Batesian mimicry (Huheey, 1976; Benson, 1977;
Sheppard 8c Turner, 1977). A definition of mimicry based on the concepts of
signals of interest and mistaken identity is consistent with the inclusion of such
phenomena as Mullerian resemblances under the rubric ‘mimicry’, the
theoretical differences between Batesian and Mullerian mimicry (cornerstones
of all mimicry theory), and also enables the terms mimicry and crypsis, in the
great majority of cases, to be applied usefully and unambiguously to different
individual phenomena.
Two interesting cases of organic resemblance which may pose some difficulties
of classification have recently been described. Barlow & Wiens (1977) discuss the
similarity in appearance of many Australian mistletoes to the foliage of their
hosts. They note that some herbivores, particularly possums, generally seem to
DEFINITION OF MIMICRY
5
prefer to eat the mistletoes rather than the host plants. The problem in classification is: are possums normally searching for discrete mistletoe plants against an
uninteresting background of tree foliage (crypsis), or are they actively avoiding
the foliage of most trees and so, identifying the mistletoes as parts of the trees,
avoiding the mistletoes too? I t seems most likely that, searching with the
expectation of finding mistletoe delicacies, the possums are perceptually treating
the tree foliage as the reference frame, the background of uninteresting
information. If so, this phenomenon can be placed as an example of protective
crypis, involving special resemblance, and is entirely similar to the leaf-insect
situation. If not, it is an example of Batesian mimicry (class VIA: Vane-Wright,
1976). Wiens (1978: 283) reviews further evidence that the principal operators in
this case may be ovipositing lycaenid and pierid butterflies, which must seek out
their mistletoe hosts, and may do so visually (as suggested by Gilbert, 1975, for
Heliconius butterflies searching for passion vines), but the argument concerning
classification of the situation remains the same.
Similar considerations apply to the concept of ‘predator mimicry’ recently put
forward by Zaret (197 71, who describes how predatory South American fluviatile
fishes such as Cichlu species are closely resembled by some of their potential prey
(e.g., Crenicichlu spp.) which swim with them. Is this crypsis or mimicry? Zaret
adduces evidence that the predatory Cichlas actively recognize each other, and so
avoid cannibalism, from which they refrain. If the similarity of fish such as
Crenicichlu to Cichlu species affords protection to the former through mistaken
identity by Cichlu individuals of Crenicichlu for other Cichlu conspecifics, then this
is genuinely a case of mimicry. Interestingly, it fits class VIB, ‘antergic defensive
bipolar ( S , + R) mimicry’, of which few good examples have previously been
recognized (Vane-Wright, 1976: 40-41).
Wiens (19781, in his most valuable review of mimicry and crypsis in plants,
introduces two new categories of mimicry (reproductive and dispersal) in his
‘functional classification’. Whilst I disagree, as indicated above, with his
inclusion of crypsis within and exclusion of Miillerian convergence from
‘mimicry’, his special classification is undoubtedly of considerable utility in
bringing together certain phenomena previously ignored or treated in isolation.
This is a primary function of all special classifications and definitions in biology.
ACKNOWLEDGEMENT
I would like to thank an anonymous referee for suggesting many corrections
and improvements to the draft originally submitted, a number of which I have
gratefully adopted.
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