Protective Mimicry Research Articles

How weird can mimicry get?

Classical mimicry theory distinguishes clearly between the mutualistic resemblance between two or more defended species (muellerian mimicry), and the parasitic resemblance of a palatable species to a defended species (batesian mimicry). Modelling the behaviour of predators, without initially taking ecological complications into account, is a good strategy for exploring whether this division is valid. Two such behavioural models are described: conditioning theory, which simulates changes in motivational attack levels according to the norms of current learning theory; and saturation theory, which considers how a predator may become saturated with a particular toxic compound, and then cease feeding on the prey species that delivers it. This effect is to be clearly distinguished from simple satiation. Most formulations of the conditioning model allow the direction of reinforcement produced by a particular prey to change according the predator's current state of motivation: this leads to the existence of quasi-batesian mimicry, a parasitic mimicry between two species that could both be described as defended. At high densities, two prey species that share a chemical defense will be ‘muellerian mutualists’, mutually protecting each other against predators that have been saturated with the defensive compound. This mutualism may be accompanied by true muellerian mimicry of the colour patterns, or the patterns may be completely different. This can therefore be regarded as a form of mimicry in a non-visual communication channel. Even an apparently palatable prey species may be effectively unavailable to predators if its density is such as to deliver a particular nutrient in excess of the predator's need for a balanced diet. Such a nutrient in effect becomes a toxin, and such an abundant prey species would be partly defended and potentially able to act as the model in a mimicry system. Thus there might be protective mimicry between ‘palatable’ species, and a ‘palatable’ species might even function as the model for a ‘defended’ mimic. These unorthodox kinds of mimicry probably exist transiently during fluctuations of prey populations. It is less likely that these conditions persist for long enough to induce the evolution of mimicry, and the relationships perhaps usually occur when mimicry already exists for other reasons. Mimicry rings may be mutually stabilised by a combination of toxic mutualism and the exchange of species between the rings. Colour polymorphism in a defended species is strictly neutral whenever the population is dense enough to saturate the predator. This, as well as quasi-batesian mimicry, may help to explain the minority of warningly coloured species that are polymorphic.

Shape change behavior by mesopelagic animals

In situ observations in Monterey Bay and elsewhere revealed a common behavior pattern among certain species living at mesopelagic depths between 200 and 800 m. When these animals were presented with threatening stimuli, they responded by curling their elongate bodies into circular shapes. They maintained this posture, hanging motionless in midwater, until the danger had passed. This behavior was strongly associated with dim light and occurrences were rare in well‐lit shallow depths, at depths beyond the penetration of sunlight, and at night. This behavior is interpreted as a case of protective mimicry, in which these animals change their appearance to resemble medusae as unpalatable models.

Mimicry of Vertebrates: Are the Rules Different?

Examples of mimicry among vertebrates are numerically fewer than examples involving insects. The relatively small number of species of vertebrates, compared with the number of species of insects, probably explains some of the apparent scarcity of mimicry. Possibly more important is a mismatch between the primarily visual sensory world of humans and the predominantly chemosensory, auditory, and tactile worlds of most other vertebrates, which has probably concealed many manifestations of mimicry. Systematic investigation of the information that vertebrates convey through these sensory modalities will probably reveal many additional examples of mimicry. Concrete homotypies-those cases in which the model can be identified as a particular species of animal-are widespread among fishes and amphibians and have been suggested for birds and mammals. Both Batesian and Mullerian protective mimicry systems have been described. Because vertebrates grow during their lifetimes without conspicuous changes in morphology, size limitation is manifested in some mimetic systems. Non-protective mimicry also occurs among vertebrates: mimicry of females is an alternative reproductive strategy for males, and many nest parasites mimic the eggs and young of their hosts. Abstract homotypies-cases in which the model cannot be identified as a particular species or group of species-are characteristic of mimicry of venomous snakes. Large body sizes, ontogenetic change in body size, and potentially lethal deterrents to attack by predators are the special characteristics of venomous snakes as models in mimicry systems. The risk for a dupe that mistakes a venomous snake for its mimic makes mimicry of venomous snakes a high-stakes game. The special characteristics of these mimicry systems (broad generalization of the characteristics of models, mimics that incorporate features of two or more models, and innate avoidance of models by predators) probably reflect that risk for a dupe. As such, these mimicry systems provide a new perspective on the mechanics of mimicry that may have parallels in some examples of mimicry of invertebrates.

Mimicry and crypsis - a behavioural approach to classification

Mimetic strategies are characterized by interference in information processes, whereby certain signalreceivers are deceived by a mimic. The function of mimetic behaviour as well as of other behavioural patterns which have evolved is to satisfy the needs of the environment. Therefore it would seem justified to classify the phenomena of mimicry and crypsis on the basis of the aims which mimics have. Furthermore, several ethological ideas and terms of the organism-environment-interrelationships (irrelevant and relevant environment; communicative and information environment) are investigated to find out whether they are suitable to characterize and define animal and plant imitations. There are at least three complexes of mimetic strategies: 1. 1. Imitations of signals in order to satisfy the protection needs of the mimic, including protective mimicry (Batesian, Müllerian mimicry and further examples of protective mimicry) and protective crypsis. 2. 2. Imitations of signals in order to satisfy the metabolic needs of the mimic, including aggressive mimicry and aggressive crypsis. 3. 3. Imitations to optimize reproduction of animals and plants, whereby we can classify with respect to the signal-receiver (species-specific or interspecific receiver) as well as with respect to the nature of the mimicked signal (communicative or non-communicative releaser). 4. 4. While imitations to satisfy protection and metabolic needs could be comprised in one mimicry complex because of the close co-evolution of the strategies of predators and preys, the imitations used for reproduction of animals and plants should be separated. In some examples (e.g. sporocyst of the parasitic worm Leucochloridium macrostomum ) this idea leads to new interpretations.

Linnaeus, animals and man*

Linnaeus is often undervalued as a zoologist. His importance lies not only in the introduction of binomial nomenclature and his Systema Naturae. As a systematist he divided the insects into the groups, Coleoptera, Hemiptera, Lepidoptera, Neuroptera, Hymenoptera, Diptera and Aptera. His programme, as expressed in his Methodus in Systema Naturae (1st ed.) is astounding in its biological manysidedness. He was before his time in many respects: he wrote and lectured upon bird migration, biological control of insects with their parasites or predators, protective mimicry, the struggle by all organisms for survival, contagious diseases as well as fermentation due to small living particles. He was the first to call attention to the close relationship between man and the anthropoid apes.

Coevolution: Heterotypic Schooling in Caribbean Reef Fishes

Coevolution: Heterotypic Schooling in Caribbean Reef Fishes

Protective Mimicry of the Chickadee

Protective Mimicry of the Chickadee

New Case of Protective Mimicry in a Caterpillar

New Case of Protective Mimicry in a Caterpillar

Protective Mimicry and Common Warning Colours

I HAVE just read with interest Sir George Hampson's criticism of certain supposed examples of protective mimicry. Such outspoken attacks are satisfactory in bringing out the truth one way or the other; and they contrast very favourably with vague expressions of opposition unaccompanied by reasons, and not stated in a manner or on an occasion which would permit reply.

Protective Mimicry of a Moth

Protective Mimicry of a Moth

Protective Mimicry of a Moth

Protective Mimicry of a Moth

A Case of Protective Mimicry

A Case of Protective Mimicry

A Case of Protective Mimicry

A Case of Protective Mimicry

Protective Mimicry

MR. BATESON'S letter on “Aggressive Mimicry” (NATURE, October 20) recalls to my mind a curious case of protective mimicry which came under my notice last August on Dartmoor. Large patches of the heath had been burnt, a common practice on the moorlands to ensure a fresh young growth for the sheep. The whole ground was alive with a common species of orthoptera (Locustina), the small green grasshopper with short antennæ. They leapt aside at every step in the short grass and scrubby heath; upon the burnt patches they were equally numerous, but with this difference—all, without exception, were coal black on abdomen, thorax, and head, whilst the wings were of an ashen hue. So much did the colour adaptation resemble the blackened turf and heath they hopped amongst it was almost impossible to follow them with the eye; we made many amusing attempts, but were nearly always defeated. I measured one of these burnt patches, and found it to be from thirty to forty yards square. A yard or two from this, on the untouched herbage all the Locustina were bright green. I found one specimen on the borderland in a transition state, not dull all over as I had expected, but in spots and patches of bright green and black. One enemy at least of these insects abounded on the moor, namely, the common lizard (Zootæa vivipara), for I have observed there is no food lizards will eat more greedily than grasshoppers. I have seen some that I have in captivity swallow twenty or thirty in two or three minutes, even after their usual meal of worms. They always became greatly excited, if one may apply so warm an expression to such cold-blooded animals, and rushed about the case when a collection of live grasshoppers were thrown to them. Certainly I was much struck by the rapid action of the power possessed by these Locustina on Dartmoor of assimilation to environment, and did not doubt but that this colour adaptation was for the purpose of protection, the eye producing by reflex action the change in the pigment cells.

On an interesting Example of Protective Mimicry discovered by Mr. W. L. Sclater in British Guiana.

On an interesting Example of Protective Mimicry discovered by Mr. W. L. Sclater in British Guiana.

Book Reviews

SOME time ago we had the pleasure of recommending an excellent little book by Mr. Worsley-Benison, called “Nature's Fairy-land,” consisting of a series of simple, pleasantly-written papers on some of those aspects of Nature which are most likely to excite the interest of children. The present volume has been planned on exactly the same lines, and is in every way worthy of its predecessor. In the opening essay the author describes the proceedings of two house-martins who did him the honour to select as the site for their nest a small wooden projection under the eaves of his roof. This paper has all the freshness and charm that spring from direct observation, and young people will read it with genuine pleasure. Among the subjects dealt with in other papers are wild roses, water scavengers, the dragon-fly's haunt, protective mimicry in insects, “fast asleep for months,” and the ministry of leaves.

Mimicry

SUCH remarkable instances of mimicry as that described by the Duke of Argyll in NATURE, vol. xxvii. p. 125, as occurring in a moth, make heavy demands upon the faith of the non-scientific reasoner, since it seems to him impossible that organic Nature in her “blind groping in the dark” could, under any imaginable combination of circumstances, have succeeded in taking the successive steps requisite to bring her to such a state of perfect adaptation to condition. But the proverbially keen sight of birds, as at present organised, is apt to lead to erroneous. inferences with regard to the evolution of protective mimicry in their insect prey, seeing that the high development of this faculty now attained by them renders nugatory any disguise that is not almost perfect. The theory of natural selection, however, requires the gradual perfecting of this, no less than of other structural and physiological acquirements; and there is no reason for supposing that the Ornithoscelidan ancestors of the feathered tribes possessed exceptional visual powers, but rather that the reverse was the case; so that it may be concluded that improvement in vision and in rapidity of flight proceeded pari passu. This being granted, the initiatory steps of mimicry in the Lepidoptera may have been tentative, and well within the competence of ordinary variability.

Natural Enemies of Butterflies

IT would be very interesting to ascertain what testimony can be brought forward to show that the Rhopalocera are commonly the prey of insect-eating birds. The return of a gentleman who has been collecting butterflies and studying their transformations for the last five years in Brazil, and who by my request has given especial attention to the matter, is the immediate occasion of my inquiry. Protective mimicry is a fact too well established to admit of its supporters feeling the question a delicate one. Admission into your paper will speedily settle the question.

MR. THOMAS BELT, F.G.S

THE scientific world will hear with regret the recent death of the well-known naturalist and geologist, Mr. Thomas Belt, F.G.S., which has just been telegraphed from Colorado. It is believed to have been caused by mountain fever. Elected a Fellow of the Geological Society in 1866, the geological world owes to him the division of the Lingula flags into Maentwrog, Ffestiniog, and Dolgelly flags, proposed in 1867. In 1874 appeared his well-known and deservedly popular “Naturalist in Nicaragua”, in which he showed how his professional avocations as an engineer had lent keenness to his observing faculties, and how an acute reasoner can utilise his observations. The work conveyed much information on protective mimicry, plant-fertilisation, sexual selection, and the other collateral issues of the theory of evolution. It contained the first sketch of those views on glacial geology which were the most prominent subject of the author's study for the rest of his life. These views were given in considerable detail in the Geological Magazine for April, 1874, and were well expounded by Mr. Henry Woodward, F.R.S., in his presidential address of that year to the Geologists' Association. Mr. Belt skilfully answered his opponents in NATURE, vol. x., his controversial speaking and writing being always marked by a candour and temper which, if it did not carry conviction, could not fail to elicit admiration from perfect strangers and mere spectators. In November, 1875, he read a paper to the Geological Society “On the Drift of Devon and Cornwall”(Quart, four. Geol. Sac., vol. xxxii.), and another “On the Steppes of Southern Russia” (Quart. Jour. Geol. Sac., vol xxxiii.), in June, 1877. He also contributed various papers to the Quarterly Journal of Science, amongst others one, “On the Loess of the Rhine and the Danube,” in January, 1877, and one “On the Glacial Period in the Southern Hemisphere,” in July, 1877.

Entomology at the Royal Aquarium

AN aquarium is put to its legitimate use when it is made the home of natural history exhibitions, and any attempt to rescue one from the too dominant sway of the showman deserves every support at the hands of science. The Entomological Exhibition, the opening of which at the Royal Aquarium we noticed last week, is also quite a novelty, though it is the outcome in a particular branch of the idea that led to the Loan Exhibition of Scientific Apparatus at South Kensington; as in that case the exhibitors are induced by no hope of prizes, but merely from the love of their science to lend their treasures. One learns from such an exhibition as this how much genuine love for natural history exists amongst men whose daily lives are devoted to manual labour, and that there are those who live within sound of Bow Bells, who make as good a use of their more limited opportunities as Edward in Banffshire. Here is a Mr. Machin, compositor by trade, whose long day's work has not prevented him from collecting and rearing a magnificent series of crepuscular and nocturnal moths, shown in twenty beautifully-arranged cases and accurately named; and the collections of some others are scarcely less noticeable in this respect. But apart from the interest attaching to some of the exhibitors, the material brought together affords an opportunity both to the entomologist proper and to the general naturalist not often to be met with. The greater portion of the whole exhibition is perhaps inevitably taken up with British lepidoptera, but these are not, as might be feared, an endless multitude of specimens of no special interest beyond their rarity and beauty, but are made to teach as well as please. Lord Walsingham, for example, shows the larvæ, pupæ, and imagines of nearly 370 species with the plants on which they occur—so that we have their complete life-history so far as it can possibly be represented to us. This, perhaps, from its scientific character and the beautiful means of preservation adopted, is the most interesting to the general naturalist, but there are others more limited, but scarcely less instructive—as those shown by the Messrs. Adams, in which the usual parasites are included in the series with each insect. Other instructive collections are those which illustrate the varieties of a single species; such is the set of specimens of Colias edusa, exhibited by Mr. Harper, a grand series showing insensible passages between perfectly distinct colourings. The influence of climate on colour is well illustrated in the melanic northern varieties of several species of moths, which are usually of a lighter colour in the south of England, the two varieties being placed side by side in the Yorkshire collections, and the results of selective breeding in the same direction in the photographs, unfortunately not specimens, of the common gooseberry moth, varying from nearly white to almost entirely dark. The moths and butterflies of the fen districts, which are now becoming so scarce, are represented by a very large collection by Mr. Earn. But one of the most interesting objects is a large white close-set web, in appearance like a cloth—some eight feet by four feet, spun by the larvae of a moth, Ephestia elutella, that feeds on chicory. It is a portion only of a larger web, six times the size, formed on the walls and ceiling of a chicory warehouse in York, by the incessant marching to and fro of the well-fed larvcæ. The threads composing it are less than 1/6000 inch in diameter, and as they are nearly contiguous and eight or ten deep; the portion exhibited represents about 4,000 miles of their wanderings. When twisted into a rope, it has been made to support a weightof 561bs. The foreign Lepidoptera also figure largely, and are naturally attractive from their beauty, and in General Ramsay's cases from Nepaul, for their rarity. This portion of the series, however, is chiefly valuable for the illustrations of protective mimicry which it affords. Admirable specimens of the leaf butterfly, Kallima inachis, with the varying tints of their under surfaces, are in Gen. Ramsay's collection, and Mr. Swanzy has a grand series specially arranged of Diademas and Papiliones mimicking—some in the females and some in both sexes—the nauseous smelling members of the Danaidæ and Acraidæ. Similar series are shown by Rev. J. A. Walker and Mr. Weir. The extraordinary differences between male and female in some butterflies is well illustrated by Mr. Briggs' collection of Lycænas.