Evolution Of Mimicry Research Articles

Sensory Discrimination and Its Role in the Evolution of Batesian Mimicry

The conditions of Batesian mimicry have been simulated in a laboratory experiment in which chickens represented the predators and green-coloured drinking solutions their prey. The darkest solution represented the model and when it was taken a shock was administered to the bird. Two groups of birds and two levels of shock were used. No shock was given when any of the paler solutions (the mimics) were drunk. The results are in accord with our previous predictions, derived from a study of the properties of sensory systems. The number of times any solution was drunk was dependent on the shock level always received by the bird when it drank the darkest solution, and was less at the higher shock level. At both shock levels the solutions which were more like solution 10 were taken less frequently. The curvature of the resulting regressions differ at the two shock levels, showing that solutions close to number 10 were less readily distinguished at the high-level shock. Thus, the relative selective advantage gained by a mimic is dependent on the penalty which accrues to the predator when it mistakenly takes the distasteful model which is being mimicked. When the consequences are severe, there is minimal selective advantage in improving mimicry beyond a certain point; however, if the consequences are mild, selective advantage continues to operate until a perfect resemblance is produced.

Studies in Warning Coloration and Mimicry. III. Evolution of Mullerian Mimicry

Studies in Warning Coloration and Mimicry. III. Evolution of Mullerian Mimicry

The evolution of mimicry: a problem in ecology and genetics.

One of the early successes of the theory of natural selection concerned the phenomenon of mimicry. Bates (1862) noticed that in South America there are a number of simple and conspicuous color-patterns common to several distantly related species of Lepidoptera living together in the same habitat. He argued that in each of these assemblages there was at least one species (the model) which was distasteful to the predators of butterflies, and had a conspicuous color pattern which in general resembled that of other members of its genus. The other species (the mimics), he thought, were relatively edible and had evolved an appearance similar to that of the model as the result of natural selection; any slight variation causing the predators to mistake an insect for the model and therefore not to attack it, would confer an advantage on its possessor and therefore be favored.

Behavioural evidence on the evolution of batesian mimicry

1.1. Four White Leghorn chicks were trained to avoid a drawing of a butterfly (the model) and than presented with various other butterfly drawings (the mimics).2.2. Some mimics resembling the model only slightly were avoided.3.3. Some of the literature indicating that animals usually respond to only a portion of the visual environment that they are capable of seeing is summarised.4.4. On the basis of the experiment and the literature, it is concluded that behavioural studies provide no evidence for and considerable evidence against the Saltation theory and tend to support the Neo-Darwinian theory of the origin of mimicry.5.5. Some possible explanations for the complexity of a model warning coloration and the completeness of a mimetic resemblance are discussed.6.6. It is suggested that the original resemblance acquired by an incipient mimic is a simple, generalised conspicuousness such as a large area of red or black. This would then be improved by selection of further mutations. The evolution of a more-or-less complete resemblance from the original generalised one may take place very rapidly.7.7. The possible importance of preadaptation in the origin of mimicry is suggested.8.8. The possibility that in some cases the new incipient resemblance may interfere with releasers involved in breeding behaviour is briefly discussed.

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.