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We would like to show you a description here but the site won’t allow us. In Acraea butterflies, male-killing Wolbachia can exert such selection pressure upon a species that the endosymbionts can cause sex-role reversal. Selection pressure can lead in some species to rapid suppression of the male-killing effect, while other species are unable to respond to the male-killing effect.
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The skunk as an example of warning coloration—Warning colours among insects—Butterflies—Caterpillars—Mimicry—How mimicry has been produced—Heliconidae—Perfection of the imitation—Other cases of mimicry among Lepidoptera—Mimicry among protected groups—Its explanation—Extension of the principle—Mimicry in other orders of insects—Mimicry among the vertebrata—Snakes—The rattlesnake and the cobra—Mimicry among birds—Objections to the theory of mimicry—Concluding remarks on warning colours and mimicry. We have now to deal with a class of colours which are the very opposite of those we have hitherto considered, since, instead of serving to conceal the animals that possess them or as recognition marks to their associates, they are developed for the express purpose of rendering the species conspicuous. The reason of this is that the animals in question are either the possessors of some deadly weapons, as stings or poison fangs, or they are uneatable, and are thus so disagreeable to the usual enemies of their kind that they are never attacked when their peculiar powers or properties are known. It is, therefore, important that they should not be mistaken for defenceless or eatable species of the same class or order, since in that case they might suffer injury, or even death, before their enemies discovered the danger or the uselessness of the attack. They require some signal or danger-flag which shall serve as a warning to would-be enemies not to attack them, and they have usually obtained this in the form of conspicuous or brilliant coloration, very distinct from the protective tints of the defenceless animals allied to them. The Skunk as illustrating Warning Coloration. While staying a few days, in July 1887, at the Summit Hotel on the Central Pacific Railway, I strolled out one evening after dinner, and on the road, not fifty yards from the house, I saw a pretty little white and black animal with a bushy tail coming towards me.
As it came on at a slow pace and without any fear, although it evidently saw me, I thought at first that it must be some tame creature, when it suddenly occurred to me that it was a skunk. It came on till within five or six yards of me, then quietly climbed over a dwarf wall and disappeared under a small outhouse, in search of chickens, as the landlord afterwards told me. This animal possesses, as is well known, a most offensive secretion, which it has the power of ejecting over its enemies, and which effectually protects it from attack. The odour of this substance is so penetrating that it taints, and renders useless, everything it touches, or in its vicinity. Provisions near it become uneatable, and clothes saturated with it will retain the smell for several weeks, even though they are repeatedly washed and dried. A drop of the liquid in the eyes will cause blindness, and Indians are said not unfrequently to lose their sight from this cause. Owing to this remarkable power of offence the skunk is rarely attacked by other animals, and its black and white fur, and the bushy white tail carried erect when disturbed, form the danger-signals by which it is easily distinguished in the twilight or moonlight from unprotected animals.
Its consciousness that it needs only to be seen to be avoided gives it that slowness of motion and fearlessness of aspect which are, as we shall see, characteristic of most creatures so protected. This term has been given to a form of protective resemblance, in which one species so closely resembles another in external form and colouring as to be mistaken for it, although the two may not be really allied and often belong to distinct families or orders. One creature seems disguised in order to be made like another; hence the terms 'mimic' and mimicry, which imply no voluntary action on the part of the imitator.
It has long been known that such resemblances do occur, as, for example, the clear-winged moths of the families Sesiidae and Aegeriidae, many of which resemble bees, wasps, ichneumons, or saw-flies, and have received names expressive of the resemblance; and the parasitic flies (Volucella) which closely resemble bees, on whose larvae the larvae of the flies feed. The great bulk of such cases remained, however, unnoticed, and the subject was looked upon as one of the inexplicable curiosities of nature, till Mr. Bates studied the phenomenon among the butterflies of the Amazon, and, on his return home, gave the first rational explanation of it.
The facts are, briefly, these. Everywhere in that fertile region for the entomologist the brilliantly coloured Heliconidae abound, with all the characteristics which I have already referred to when describing them as illustrative of 'warning coloration.'
But along with them other butterflies were occasionally captured, which, though often mistaken for them, on account of their close resemblance in form, colour, and mode of flight, were found on examination to belong to a very distinct family, the Pieridae. Bates notices fifteen distinct species of Pieridae, belonging to the genera Leptalis and Enterpe, each of which closely imitates some one species of Heliconidae, inhabiting the same region and frequenting the same localities. It must be remembered that the two families are altogether distinct in structure. The larvae of the Heliconidae are tubercled or spined, the pupae suspended head downwards, and the imago has imperfect forelegs in the male; while the larvae of the Pieridae are smooth, the pupae are suspended with a brace to keep the head erect, and the forefeet are fully developed in both sexes. These differences are as large and as important as those between pigs and sheep, or between swallows and sparrows; while English entomologists will best understand the case by supposing that a species of Pieris in this country was coloured and shaped like a small tortoise-shell, while another species on the Continent was equally like a Camberwell beauty—so like in both cases as to be mistaken when on the wing, and the difference only to be detected by close examination.
As an example of the resemblance, woodcuts are given of one pair in which the colours are simple, being olive, yellow, and black, while the very distinct neuration of the wings and form of the head and body can be easily seen. Black Ops Annihilation Map Pack Ps3 Download. Mimicry in other Orders of Insects. A very brief sketch of these phenomena will be given, chiefly to show that the same principle prevails throughout nature, and that, wherever a rather extensive group is protected, either by distastefulness or offensive weapons, there are usually some species of edible and inoffensive groups that gain protection by imitating them.
It has been already stated that the Telephoridae, Lampyridae, and other families of soft-winged beetles, are distasteful; and as they abound in all parts of the world, and especially in the tropics, it is not surprising that insects of many other groups should imitate them. This is especially the case with the longicorn beetles, which are much persecuted by insectivorous birds; and everywhere in tropical regions some of these are to be found so completely disguised as to be mistaken for species of the protected groups. Numbers of these imitations have been already recorded by Mr.
Bates and myself, but I will here refer to a few others. In the recently published volumes on the Longicorn and Malacoderm beetles of Central America there are numbers of beautifully coloured figures of the new species; and on looking over them we are struck by the curious resemblance of some of the Longicorns to species of the Malacoderm group. In some cases we discover perfect mimics, and on turning to the descriptions we always find these pairs to come from the same locality. Thus the Otheostethus melanurus, one of the Prionidae, imitates the malacoderm, Lucidota discolor, in form, peculiar coloration, and size, and both are found at Chontales in Nicaragua, the species mimicked having, however, as is usual, a wider range. The curious and very rare little longicorn, Tethlimmena aliena, quite unlike its nearest allies in the same country, is an exact copy on a somewhat smaller scale of a malacoderm, Lygistopterus amabilis, both found at Chontales. The pretty longicorn, Callia albicornis, closely resembles two species of malacoderms (Silis chalybeipennis and Colyphus signaticollis), all being small beetles with red head and thorax and bright blue elytra, and all three have been found at Panama. Many other species of Callia also resemble other malacoderms; and the longicorn genus Lycidola has been named from its resemblance to various species of the Lycidae, one of the species here figured (Lycidola belti) being a good mimic of Calopteron corrugatum and of several other allied species, all being of about the same size and found at Chontales.
In these cases, and in most others, the longicorn beetles have lost the general form and aspect of their allies to take on the appearance of a distinct tribe. Some other groups of beetles, as the Elateridae and Eucnemidae, also deceptively mimic malacoderms. Wasps and bees are often closely imitated by insects of other orders. Many longicorn beetles in the tropics exactly mimic wasps, bees, or ants. In Borneo a large black wasp, whose wings have a broad white patch near the apex (Mygnimia aviculus), is closely imitated by a heteromerous beetle (Coloborhombus fasciatipennis), which, contrary to the general habit of beetles, keeps its wings expanded in order to show the white patch on their apex, the wing-coverts being reduced to small oval scales, as shown in the figure.
This is a most remarkable instance of mimicry, because the beetle has had to acquire so many characters which are unknown among its allies (except in another species from Java)—the expanded wings, the white band on them, and the oval scale-like elytra. Another remarkable case has been noted by Mr. Neville Goodman, in Egypt, where a common hornet (Vespa orientalis) is exactly imitated in colour, size, shape, attitude when at rest, and mode of flight, by a beetle of the genus Laphria.
The tiger-beetles (Cicindelidae) are also the subjects of mimicry by more harmless insects. In the Malay Islands I found a heteromerous beetle which exactly resembled a Therates, both being found running on the trunks of trees. A longicorn (Collyrodes Lacordairei) mimics Collyris, another genus of the same family; while in the Philippine Islands there is a cricket (Condylodeira tricondyloides), which so closely resembles a tiger-beetle of the genus Tricondyla that the experienced entomologist, Professor Westwood, at first placed it in his cabinet among those beetles. In South America, the genus Heilipus is one of these hard groups, and both Mr.
Roelofs, a Belgian entomologist, have noticed that species of other genera exactly mimic them. So, in the Philippines, there is a group of Curculionidae, forming the genus Pachyrhynchus, in which all the species are adorned with the most brilliant metallic colours, banded and spotted in a curious manner, and are very smooth and hard. Other genera of Curculionidae (Desmidophorus, Alcides), which are usually very differently coloured, have species in the Philippines which mimic the Pachyrhynchi; and there are also several longicorn beetles (Aprophata, Doliops, Acronia, and Agnia), which also mimic them. Besides these, there are some longicorns and cetonias which reproduce the same colours and markings; and there is even a cricket (Scepastus pachyrhynchoides), which has taken on the form and peculiar coloration of these beetles in order to escape from enemies, which then avoid them as uneatable.
The figures on the opposite page exhibit several other examples of these mimicking insects. Innumerable other cases of mimicry occur among tropical insects; but we must now pass on to consider a few of the very remarkable, but much rarer instances, that are found among the higher animals. Mimicry among the Vertebrata. Perhaps the most remarkable cases yet known are those of certain harmless snakes which mimic poisonous species. The genus Elaps, in tropical America, consists of poisonous snakes which do not belong to the viper family (in which are included the rattlesnakes and most of those which are poisonous), and which do not possess the broad triangular head which characterises the latter.
They have a peculiar style of coloration, consisting of alternate rings of red and black, or red, black, and yellow, of different widths and grouped in various ways in the different species; and it is a style of coloration which does not occur in any other group of snakes in the world. But in the same regions are found three genera of harmless snakes, belonging to other families, some few species of which mimic the poisonous Elaps, often so exactly that it is with difficulty one can be distinguished from the other.
Thus Elaps fulvius in Guatemala is imitated by the harmless Pliocerus equalis; Elaps corallinus in Mexico is mimicked by the harmless Homalocranium semicinctum; and Elaps lemniscatus in Brazil is copied by Oxyrhopus trigeminus; while in other parts of South America similar cases of mimicry occur, sometimes two harmless species imitating the same poisonous snake. A few other instances of mimicry in this group have been recorded.
There is in South Africa an egg-eating snake (Dasypeltis scaber), which has neither fangs nor teeth, yet it is very like the Berg adder (Clothos atropos), and when alarmed renders itself still more like by flattening out its head and darting forward with a hiss as if to strike a foe. Meyer has also discovered that, while some species of the genus Callophis (belonging to the same family as the American Elaps) have large poison fangs, other species of the same genus have none; and that one of the latter (C.
Gracilis) resembles a poisonous species (C. Intestinalis) so closely, that only an exact comparison will discover the difference of colour and marking. A similar kind of resemblance is said to exist between another harmless snake, Megaerophis flaviceps, and the poisonous Callophis bivirgatus; and in both these cases the harmless snake is less abundant than the poisonous one, as occurs in all examples of true mimicry. In the genus Elaps, above referred to, the very peculiar style of colour and marking is evidently a 'warning colour' for the purpose of indicating to snake-eating birds and mammals that these species are poisonous; and this throws light on the long-disputed question of the use of the rattle of the rattlesnake. This reptile is really both sluggish and timid, and is very easily captured by those who know its habits.
If gently tapped on the head with a stick, it will coil itself up and lie still, only raising its tail and rattling. It may then be easily caught.
This shows that the rattle is a warning to its enemies that it is dangerous to proceed to extremities; and the creature has probably acquired this structure and habit because it frequents open or rocky districts where protective colour is needful to save it from being pounced upon by buzzards or other snake-eaters. Quite parallel in function is the expanded hood of the Indian cobra, a poisonous snake which belongs also to the Elapidae. This is, no doubt, a warning to its foes, not an attempt to terrify its prey; and the hood has been acquired, as in the case of the rattlesnake, because, protective coloration being on the whole useful, some mark was required to distinguish it from other protectively coloured, but harmless, snakes. Both these species feed on active creatures capable of escaping if their enemy were visible at a moderate distance.
Mimicry among Birds. The varied forms and habits of birds do not favour the production among them of the phenomena of warning colours or of mimicry; and the extreme development of their instincts and reasoning powers, as well as their activity and their power of flight, usually afford them other means of evading their enemies. Yet there are a few imperfect, and one or two very perfect cases of true mimicry to be found among them.
The less perfect examples are those presented by several species of cuckoos, an exceedingly weak and defenceless group of birds. Our own cuckoo is, in colour and markings, very like a sparrow-hawk. In the East, several of the small black cuckoos closely resemble the aggressive drongo-shrikes of the same country, and the small metallic cuckoos are like glossy starlings; while a large ground-cuckoo of Borneo (Carpococcyx radiatus) resembles one of the fine pheasants (Euplocamus) of the same country, both in form and in its rich metallic colours. More perfect cases of mimicry occur between some of the dull-coloured orioles in the Malay Archipelago and a genus of large honey-suckers—the Tropidorhynchi or 'Friar-birds.' These latter are powerful and noisy birds which go in small flocks.
They have long, curved, and sharp beaks, and powerful grasping claws; and they are quite able to defend themselves, often driving away crows and hawks which venture to approach them too nearly. The orioles, on the other hand, are weak and timid birds, and trust chiefly to concealment and to their retiring habits to escape persecution. In each of the great islands of the Austro-Malayan region there is a distinct species of Tropidorhynchus, and there is always along with it an oriole that exactly mimics it. All the Tropidorhynchi have a patch of bare black skin round the eyes, and a ruff of curious pale recurved feathers on the nape, whence their name of Friar-birds, the ruff being supposed to resemble the cowl of a friar.
These peculiarities are imitated in the orioles by patches of feathers of corresponding colours; while the different tints of the two species in each island are exactly the same. Thus in Bouru both are earthy brown; in Ceram they are both washed with yellow ochre; in Timor the under surface is pale and the throat nearly white, and Mr. Forbes has recently discovered another pair in the island of Timor Laut. The close resemblance of these several pairs of birds, of widely different families, is quite comparable with that of many of the insects already described. It is so close that the preserved specimens have even deceived naturalists; for, in the great French work, Voyage de l'Astrolabe, the oriole of Bouru is actually described and figured as a honey-sucker; and Mr. Forbes tells us that, when his birds were submitted to Dr.
Sclater for description, the oriole and the honey-sucker were, previous to close examination, considered to be the same species. Objections to the Theory of Mimicry. To set forth adequately the varied and surprising facts of mimicry would need a large and copiously illustrated volume; and no more interesting subject could be taken up by a naturalist who has access to our great collections and can devote the necessary time to search out the many examples of mimicry that lie hidden in our museums. The brief sketch of the subject that has been here given will, however, serve to indicate its nature, and to show the weakness of the objections that were at first made to it. It was urged that the action of 'like conditions,' with 'accidental resemblances' and 'reversion to ancestral types,' would account for the facts. If, however, we consider the actual phenomena as here set forth, and the very constant conditions under which they occur, we shall see how utterly inadequate are these causes, either singly or combined. These constant conditions are— 1.
That the imitative species occur in the same area and occupy the very same station as the imitated. That the imitators are always the more defenceless. That the imitators are always less numerous in individuals.
That the imitators differ from the bulk of their allies. That the imitation, however minute, is external and visible only, never extending to internal characters or to such as do not affect the external appearance. These five characteristic features of mimicry show us that it is really an exceptional form of protective resemblance. Different species in the same group of organisms may obtain protection in different ways: some by a general resemblance to their environment; some by more exactly imitating the objects that surround them—bark, or leaf, or flower; while others again gain an equal protection by resembling some species which, from whatever cause, is almost as free from attack as if it were a leaf or a flower. This immunity may depend on its being uneatable, or dangerous, or merely strong; and it is the resemblance to such creatures for the purpose of sharing in their safety that constitutes mimicry.