Meeting Abstract
The male Chrysomya megacephala eye has dorsal ommatidia that are more than twice as large as the ventral ommatidia. Based on physical properties, the enlarged dorsal ommatidia are associated with increased light capture. Aside from that optical property and that such a sexually dimorphic trait often plays a role in reproductive behavior, the biological role of this eye is unknown. This study examined the effect of this specialized morphology on diurnal activity patterns by comparing males that differed in eye shape due to differences in body size. Males of differing body sizes were produced by manipulating larval nutrition. Body size and both total eye size and the ratio of dorsal to ventral ommatidium width were proportionally scaled. Larger males, however, had a greater number of dorsal ommatidia than is explained by body size alone. The finding that larger males have disproportionately more facets, coupled with proportionately larger facet width, led to the hypothesis that larger males would be more active at lower light levels than smaller males. To test this, flies were subjected to a simulated daily light cycle in a confined space and activity was recorded when a fly interrupted an infrared beam. We found that larger males move significantly earlier in the morning but not later in the afternoon compared to smaller males. As male blow flies often use carrion as a place to find potential mates, these results suggest that it is more important to be early to carrion than it is to be able to stay later.
