Variation in the density of p + OC ommatidia over the retina. A. Representative retinal mosaic maps of one female eye for each of four surveyed strains. Red dots indicate p + OC ommatidia, yellow dots y ommatidia, black dots DRA and grey dots ommatidia of unknown type. Black horizontal stripes indicate the observed equator in the center of the retina, grey horizontal strips the equator extrapolated towards the periphery. Vertical grey dashed lines indicate the center-most dorsal ventral row. B. Kernel smoothed density estimates of p + OC ommatidia, and conversely of y ommatidia, in retinal mosaic maps representing both sexes of three Drosophila species. Scale bar density values are arbitrary (see Methods) but linear, indicating a seven-fold difference in p + OC density between either end of the scale. Numbers in both A and B refer to the ID of individual retinas. Retinas 25, 27, 28 and 48 are depicted in both A and B.