The courtship tracking of Drosophila melanogaster

Abstract

The courtship of male Drosophila melanogaster, which occurs so far as is known exclusively on the ground, may be regarded as a tracking process upon which are superimposed specific elements of courtship behaviour. Two methods were utilised to study this process, both of which involved the use of a fixed female courtship stimulus. The male courted this female whilst 1. running on the moving floor of a revolving chamber (female stationary) and 2. tracking her as she was rotated on a radius in a stationary chamber. Behaviour in the first apparatus was recorded via an electronic eye watching the flies and a keyboard operated by the experimenter. Behaviour in the second apparatus was filmed and subsequently analysed frame by frame. The patterning of courtship around the female was shown to be limited by the velocity at which the male had to run in order to court the female. At lower velocities more excursions ("circling") to the side of the female were made. The mean distance of the male behind the female increased with velocity. The slope of this effect provides an estimate of the reciprocal feedback gain of the control system for tracking. Strain and velocity dependent differences in courtship variables were revealed. The proportion of wing extension emitted in tracking varied widely, the lowest value being shown by the strain which tracked the fastest (WT Kapelle). It is proposed that the relation between these two variables is of fundamental importance in determining the outcome of courtship. Using females moving sideways it was demonstrated that males orientate to the abdomen in close range of the female (<4 mm centre to centre), and more centrally at greater distance, where visual stimuli probably dominate as cues to orientation. Sinusoidal modulation of the female's velocity enabled a preliminary stimulus-response analysis of the linear aspects of courtship tracking. For males tracking females whose speed was modulated at a mean of 1.2 Hz a phase lag of 148±30ms was determined for the translatory component and 21±55ms for the rotatory component of the male's response. A strain difference between wild type Kapelle and Canton-S strains in tracking efficiency permits the conclusion that courtship tracking ability may provide a basis for selective mating in Drosophila.