To provide consistent compass information, E-vector information from the relevant part of the sky (90° axis, 20°–90° elevation) has to

match AZD2281 the neuronal ΔΦmax values (absolute Φmax values normalized to the azimuth tuning). Importantly, polarized light information in this sky region changes with increasing solar elevation, as a result of the decreasing angular distance between the observed points and the sun ( Figure 1B; Figure S4). Because the DRA is exposed to a mixture of different E-vector angles at all times, we calculated the average perceived E-vector ( Figure 8C). Thereby, the contribution of individual E-vectors was weighted, based on the associated degree of polarization at the observed sky-point ( Figure S4). As the solar elevation changes predictably over the day, we calculated the mean perceived E-vector as a function of daytime for the date and location the migratory monarchs were captured (the last configuration of skylight cues they have experienced) ( Figure 8D). Indeed, the mean ΔΦmax value (29°) predicted with this function for the average recording time (ZT 5.4) closely matches the mean of the experimental data for monarchs (35°; p = 0.217) ( Figure 8A). Furthermore, the model predicts increasing ΔΦmax values at earlier and later times during the day. In fact, retrospective Selleck Talazoparib analysis of variation

in recording times around ZT 5 was consistent with time-dependent changes for E-vector tuning ( Figure S5). Overall, our data suggest that time-dependent adjustment of E-vector tunings provides a consistent representation of solar azimuth in the monarch sun compass over the course of the day. In the current studies, we have begun to unravel the anatomical and physiological properties of the essential sun compass system in migratory monarch butterflies. The results provide

a new synthesis of the navigational capabilities of migrating monarchs, which includes describing the structural similarity and functional equivalence between the locust and monarch sun compass network, defining how migrating monarchs integrate skylight cues for directional information, and proposing two distinct clock-compass interactions necessary for migration. We have shown that the central brain of the monarch butterfly contains all the brain regions associated with sun compass from navigation in other species (Homberg, 2004 and Sakura et al., 2008). These include the AOTu, the lateral triangle, the LAL, and all compartments of the CC. These homologies, particularly between the monarch butterfly and the desert locust, could be extended to the level of single neuronal cell types and subtypes (Table 1; Figure 3). Furthermore, the comparison of the distribution of pre- and postsynaptic endings within single cell types suggests highly similar patterns of connectivity, especially in specialized elements of the CC-polarization-vision network (TB1 and CL1 neurons; Heinze and Homberg, 2007 and Heinze and Homberg, 2009).