Eyes: Eye Type:
A Fly's Hairy Compound Eye
Insects in General:
Blue-spotted Hawker (Adversaeschna brevistyla)
Retired Professor of Anatomy, Ian Gibbins, has kindly shared his thoughts with us to help people learn:
"Despite extensive differences in size, shape, and functional organization, all insect compound eyes share common ancestry and consist of the same repetitive structure, the unit eye or ommatidium... The insect retina can be divided into large territories, zones, bands, or stripes with different morphological or functional properties... Very often, dorsal and ventral regions of the retina show important differences in morphology, physiology, and Rhodopsin (visual pigment) expression..." (Trends Genet. 2015 Jun; 31(6): 316-328.)
It turns out that in many insects, including dragonflies, crickets, butterflies, some bees and more, there are differences in the sensitivity of the upper and lower parts of the eyes: the upper parts are more sensitive to polarisation, which provides navigational info (the polarization of skylight follows the sun across the sky); upper parts often have yellow pigment in their lenses to filter out blue skylight => much higher contrast for moving objects agains a blue sky (like the filters you can use for black-and-white photography), and so on.
As I suspected, some of the genetic control of this differentiation is known, but not a lot. But one thing does seem pretty well established => the underlying pattern is highly conserved and all the variants we see really are variations on a theme, controlled by subtle yet powerful molecular genetic mechanisms :)