Dorsoventral motion processing asymmetry in drosophilid vision (Diptera: Drosophilidae)

Stabilizing positional disturbances is critical to controlled flight. To be effective, responses must match disturbances, a process that requires an accurate estimation of their magnitude. However, it is unknown how flies accomplish this task in the wild or if the visual characteristics of the habitat play a role in this process. We tested the effect of one of those characteristics, the density of moving elements in optic flow, to find whether flies that evolved in different environments exhibit steering responses tuned to the visual conditions of their habitats. To this end, we compared stabilizing responses among three species of drosophilids, Drosophila melanogaster and Zaprionus indianus, both native to Afrotropical forests; and D. mojavensis, a desert-dwelling fly. Using a virtual arena, we presented the flies with sideslipping dot-fields emulating translational disturbances either above or below the fly. We found that the desert species inhibits its motor responses to dorsal stimuli, a trait that could be related to the absence of such visual cues in its habitat. In contrast, both forest species show similar and strong responses to motion above them with minor differences that could be tied to their natural histories. Finally, the three species show clear and similar responses to ground motion, as expected due to the clear dominance of translational vectors in this region of their visual field. We consider that our findings provide strong evidence that the physical characteristics of the habitat play a critical role in tuning the visually-guided stabilizing responses in flies.