Have you ever tried to walk around in the fields or a forest at night, without any artificial light, just relying on your eyes? Then you might know that we humans are rather poor in seeing at very low light intensities.
Nevertheless, many animals have mastered a nocturnal lifestyle, using vision to navigate and forage, even with more than one million times less light available than on a sunny day. The main problem is that when only few photons are available vision becomes uncertain, or noisy. Photon arrival in general is a statistical process: at any given time the rate of photons arriving at the eye varies slightly – and this variation is higher, the lower light levels are. Moreover, photoreceptors themselves have a certain level of intrinsic noise that reduces visual reliability further – this does not affect vision much during the day since the incoming signal is many times stronger than the noise. At night however, with only few photons available per photoreceptor, the intrinsic noise together with the photon arrival uncertainty can decrease photoreceptor performance drastically.
The solution seems easy: increase the number of photons an eye captures. Which is exactly what the eyes of nocturnal animals do: they have larger lenses or larger photoreceptors, to increase photon capture. However, adaptations of the eye can only partly explain the astonishing sensitivity of nocturnal insects. We therefore assume that there are also adaptations at higher levels of visual processing in the insect brain.
This project aims at describing and localizing adaptations for nocturnal vision in the brain of hovering hawkmoths. In particular we hypothesize that visual signals are summed both in space and time. To both identify the nature and the location of this summation both anatomy and physiology of visual brain areas in different species of hawkmoths with different lifestyles are compared: nocturnal (Deilephila elpenor), crepuscular (Manduca sexta) and diurnal (Macroglossum stellaratum). The techniques used include the Golgi method, immunohistochemistry and intracellular electrophysiology.
For more information about the problem of vision in dim light: