Experiments on sex recognition and the problem of sexual selection in Drosoophilia.

Abstract

Much has been written on the subject of sexual selection since Darwin first developed the theory, and many remarkable observations have been iecorded.There has, however, been very little experimental work in this field.Darwin and those who have followed him have obtained much of their evidence from the insects, and within this group some of the most striking cases of elaborate mating habits have been reported in the Diptera, and here too there is to be found a most remarkable array,, of secondary sexual characters.Perhaps the most extreme case is that of the Elaphomyia described by Wallace, in which the male has long, hornlike processes arising from his head, which are absent in the female.The families of Platypezidae, Dolichopodidae, and Empididae are especially rich in secondary sexual characters, which occur in the legs, wings, antennae, face, or other parts.In the two latter families some very curious observations on mating habits have been recorded (see especially Poulton's account ('13) of Hamm's work on Empididae). 1 Some of the best experimental evidence m favor of sexual selection is that obtained by Lutz (1911), who worked with an abnormal wing venation in Drosophila ampelophila which he found to be strongly selected against.To Dr. Lutz is due the suggestion that the mutants in this fly obtained by Morgan would form excellent material for the study of the problem.The method of some of the experiments was also suggested by Lutz.I took up the matter at the suggestion of Professor Morgan, to whom I am greatly indebted for most of the material and for his encouragement and criticisms.Several discussions of the matter with Dr. Lutz have also been very helpful.Some 1 1 have myself observed courtship in a few Dolichopodidae and in a number of other Diptera.These observations will be published in full later.