Specifically, the compensation mechanism in monarchs and locusts seems to be optimized for the difference in DRA architecture between both species, which dictates the region

of the sky observed by the DRA. We further propose that elevation compensation involves use of the circadian clock to track solar elevation changes over the course of the day. The use of a clock could explain how polarized and unpolarized light stimuli are properly integrated at the level of a single neuron, even though the stimuli are processed in separate pathways. For migrating monarchs to maintain a constant flight bearing over the day, they need a mechanism LY294002 price to compensate for the constantly changing sun position. We hypothesize that

this mechanism involves two distinct interaction sites between the circadian clock and MI-773 chemical structure the sun compass system. The first interaction ensures that all skylight information received by the sun compass system is consistent (elevation compensation), and the second interaction ensures that the animal flies in the correct direction, despite changing solar azimuth positions over the course of the day (azimuth compensation). Azimuthal compensation probably occurs on the output side of the sun compass, after integrating information from both eyes. Flight simulator experiments have shown that the antennae of the monarch are the location of the clock needed for azimuth compensation (Merlin et al., 2009) and defining a neural circuit from the antennae to the sun compass system is under investigation (Reppert et al., 2010). Elevation compensation, on the other hand, involves a clock interaction near the sensory periphery of the sun compass system, as this process is already apparent in the recorded TuLAL1 and TL neurons, which provide input to the sun compass. Thus, brain clock-derived, CRYPTOCHROME1-positive Vasopressin Receptor fibers in the monarch accessory

medulla may mediate this interaction, because of their close proximity to photoreceptor input from the DRA (Sauman et al., 2005). These two forms of compensation, though interrelated, are distinct, because migrating monarchs can use the solar azimuth alone, independent of E-vector tuning and solar elevation, for appropriately time-compensated directional flight ( Stalleicken et al., 2005). Further studies in the monarch will focus on the precise anatomical and functional interface of each of these two identified forms of clock-compass interactions. In a broader context, the complex integration of different skylight cues in insects is an example of how ambiguous aspects of the sensory environment are integrated into a coherent neuronal representation of the outside world. The fundamental problem of disambiguation occurs across all sensory modalities and across all species, including humans.