アゲハチョウ(Papilio xuthus L.)の蛹色の保護色的意義

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In the Swallowtail butterfly, Papilio xuthus L., two types of pupae, viz., green type and brown (including 'Orange' of Ishizaki and Kato) type, are distinguishable. When larvae pupate on green twigs of plants they become pupae of the green type. But if the pupation takes place on dead branches, stone, cardboard etc. pupae of the brown type are usually produced. This pupal dichromism is thought to have a protective significance in the natural habitat although the function has not yet been demonstrated experimentally. The present authors carried out a series of experiments in order to clarifly whether or not the pupal dichromism in Papilio xuthus L. has any protective value. Just before the beginning of experiments, a pair of fowls (race: To-ten-ko) which had been starved for 24 hours were fed with P. xuthus pupae. At first they tended to prefer brown pupae to green one but soon they became to peck the both types of pupae without choice. In the first experiment performed in summer of 1958, pupae were arranged on the green lawn in 5 rows. Each row contatined 2 green and 2 brown pupae alternately placed about 40cm. apart from each other. The distance between two adjacent rows was also about 40cm., and two neighboring pupae were never of the same color. The pupae were placed the head end down among the leaves of lawngrass, so that the abdominal halves were visible from the outside. The fowls were then allowed to wander about on the lawn. Soon they came to the experimental area, pecked and swallowed the pupae they found. The color of the pupae thus pecked was recorded. After 5 minutes, the fowls were removed from the area, and all the remaining pupae were gathered and their color examined (Method A). During this experiment, 7 out of 10 brown pupae were eaten by the predators, while only 3 out of 10 green pupae were pecked. The experiment was repeated once more, and similar result was obtained (brown: 10 eaten, 0 remained; green: 1 eaten, 9 remained). In the next experiment, 4 pupae (2 green and 2 brown) were set to form a square with a side of about 10cm. on the green lawn, and the color of the pupa which was first pecked by the fowls was noted (Method B). After 10 repetitions of such experiments, it was found that, out of 10 firstpecked pupae, 7 were of the brown type and only 3 of the green type. In November, when the lawn turned grey, similar experiments performed again. Experiment by the Method A yielded no clearcut results, possibly because the fowl (in this case, 1 female only) had attained skill by learning in finding pupae. But in the experiment by the Method B, out of 10 first-pecked pupae, 7 were of the green type and 3 of the brown. Although further experiments must be done before drawing a definite conclusion, these results seem to indicate that the green pupae are more effectively protected on green grass than the brown ones, and vice versa on dead grass, at least from the attack of fowls. The pupal dichromism of Papilio xuthus L. appears, therefore, to have a protective significance. Of the two test-methods employed here, the Method B seems to be more reliable than the Method A, since by the former method the effect of learning may be avoidable.
1959-06-15

アゲハチョウ(Papilio xuthus L.)の蛹色の保護色的意義

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