The metabolic cost of seeing at night and during the day
Light carries information that the photoreceptors in eyes transmit to the brain in the form of electrical signals called light responses. While generating light responses photoreceptors consume metabolic energy. The balance between the cost and benefit of producing light responses is generally thought to have been optimised during evolution.
Animals have evolved in diverse visual environments that impose radically differing demands on their visual systems. These demands are particularly great for nocturnal animals that need to see well in near darkness, at light intensities that can be more than 100 million times lower than during the day. Due to the scarcity of light, reliable vision at night requires a specially adapted visual system. During the day there is abundant visual information available for the visual system, but coding the information into light responses consumes energy.
What kind of neural mechanisms are required for efficient day or night vision? How much energy do they consume? Is nocturnal vision more expensive than vision during the day? We will seek answers to these questions by studying visual processing in three closely-related species of dung beetles from the single genus Onitis: O. aygyulus (strictly nocturnal), O. alexis (dusk/dawn active) and O. belial (diurnal). The visual systems of these species have evolved for very different light intensities. The beetles are also endothermic and maintain an elevated body temperature during their flights. While the main function of the endothermic behaviour is to accelerate flight muscle kinetics, a higher temperature would speed up all physiological processes, including vision.
We are examining the photoreceptors of Onitis dung beetles using in vivo electrophysiological recordings and computer simulations based on the electrical properties of the photoreceptors, as well as on thermal imaging of the beetles’ endothermic behavior, to answer the following questions
- What is the metabolic cost of visual information during different times of the day?
- What are the cellular and molecular mechanisms that allow diurnal or nocturnal vision?
- Can endothermic behaviour affect the performance of the visual system?