The effects of target contrast on Drosophila courtship

Many animals use visual cues like object shape, color, and motion to detect and pursue conspecific mates. Contrast is another possibly informative visual cue, but has not been studied in great detail. In this study, we presented male Drosophila melanogaster with small, fly-sized, moving objects painted either black, white, or grey to test if they use contrast cues to identify mates. We found that males frequently chased grey objects and rarely chased white or black objects. Although males started chasing black objects as often as grey objects, the resulting chases were much shorter. To test whether the attraction to grey objects was mediated via contrast, we fabricated black and grey behavioral chambers. However, wildtype males almost never chased any objects in these darkly colored chambers. To circumvent this limitation, we increased baseline levels of chasing by thermogenetically activating P1 neurons to promote courtship. Males with thermogenetically activated P1 neurons maintained a similar preference for grey objects despite elevated levels of courtship behavior. When placed in a black chamber, males with activated P1 neurons switched their preference and chased black objects more than grey objects. We also tested whether males use contrast cues to orient to particular parts of the female body during courtship. When presented with moving objects painted two colors, males positioned themselves next to the grey half regardless of whether the other half was painted black or white. These results suggest that males can use contrast to recognize potential mates and to position themselves during courtship.