Single-Photon Sensitivity of Lamprey Rods with Cone-like Outer Segments

Photoreceptors in the sea lamprey exhibit single-photon sensitivity comparable to rods in other vertebrates.

• Most vertebrates possess duplex retinas with rods for dim light and cones for bright light and color vision.
• Lampreys have two types of photoreceptors, referred to as 'short' and 'long', which may correspond to rods and cones.
• The outer segments of both photoreceptor types in lampreys have a cone-like structure without a continuous plasma membrane.
• The findings suggest that the characteristics of rod phototransduction evolved before the divergence of jawed and jawless vertebrates.
• A rod-like outer segment with a membrane is not required for high-sensitivity light detection.

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