The Fly Sensitizing Pigment Enhances UV Spectral Sensitivity While Preventing Polarization-Induced Artifacts

Area of Science:

• Animal behavior
• Sensory neuroscience
• Vision research

Background:

• Microvillar photoreceptors detect polarized light, offering invertebrates an extra sensory channel.
• Polarization sensitivity (PS) can cause false color and intensity perception, leading to adaptations for minimal PS in insects.
• Flies possess twisted rhabdomeres and UV-absorbing pigments to reduce PS.

Purpose of the Study:

• To investigate the spectral dependence of PS in Drosophila photoreceptors R1-6.
• To model the impact of a sensitizing pigment on UV polarization sensitivity.
• To assess the suitability of photoreceptors for polarization vision under natural illumination.

Main Methods:

• Voltage recordings from Drosophila photoreceptors R1-6.
• Measurement of the spectral dependence of PS.
• Modeling of PS in the presence and absence of a sensitizing pigment.
• Polarimetric imaging of natural environments.

Main Results:

• PS in UV was negligible in R1-6, but substantial above 400 nm.
• Modeling showed UV PS would be higher without the sensitizing pigment (1.2-1.8x).
• Outdoor polarization is highest in the short-wavelength spectrum.

Conclusions:

• The sensitizing pigment in R1-6 makes these cells unsuitable for polarization vision under natural light.
• R1-6 likely serves as an unpolarized reference channel.
• Fly ventral polarization vision may be mediated solely by R7 photoreceptors.