OCR Text |
Show 1895.] COLOUR-VARIATIONS OP A BEETLE. 851 the surface. Several other species of Spartium grow in the south of Spain, but I did not find G. variabilis on any of them. Nevertheless, living specimens brought home to England ate the shoots of S. juncifolium, with which they were provided from the Cambridge Botanic Garden. It was at Granada, on March 28, 1894, that I first saw G. variabilis and was at once struck by the great variety of appearance presented by different individuals. In a few minutes I came upon most of the chief kinds, including what will be described as the red form with black spots, the greenish-grey form with black stripes, a totally black form, &c. As may be seen from the figures (Plate XLVII.) these different varieties are strikingly unlike in general appearance, and not having previously heard of this beetle I at first doubted whether all were one species. Then, finding specimens of dissimilar colours coupled together, I concluded that they did all belong to the same species, and as all intermediate forms were afterwards found, there can be no doubt on this point. Subsequently Dr. D. Sharp, to w h o m I am indebted for much help in examining these specimens, gave m e the name of the beetle and told m e that it was known to undergo great variation in colour1. I may add further that no difference could be seen in examination of the sedeagus of the several forms. It appeared that the case was worth further investigation with the object of determining with what frequency the various colours occur, and to what extent specimens collected at random could be grouped round special type-varieties to the exclusion of intermediate forms, thus manifesting the phenomenon known as organic stability in respect of those varieties. As so many specimens were found in cop. it seemed further that by recording the colours of specimens so coupled it might be possible to get an indication whether there existed any operative sexual selection as to colour. The next few days were spent in gathering a sufficient sample, and I then returned to Gibraltar to follow other work. Very soon, however, I found that the colours had so faded that the collection already made was useless for m y purpose. In fact, in dried specimens the red and the green both usually fade to an indifferent brown. I therefore went back to Granada and gathered a fresh sample of about 1500. These I put into a large wooden box and brought alive to England. In the following year (1895) I returned to Granada and collected, on March 24-28, about 2500 more, recording all the colours at the time. It at once appeared that the colour is to a great extent dependent upon sex, the males being generally of the red form with spots like fig. 1, while the females are generally o : the greenish form with stripes like fig. 23, though every colour is sometimes found in each sex. For this reason, before sorting the specimens for the purpose of determining the frequency of each 1 Several varieties have been briefly described by Weise (Deut. ent. Zeitschr. 1891, p. 160), but I infer that the colours were given from dried specimens. |