Rik asks
...what’s known and unknown about these unique eyes?
1. The color we see comes from a layered interference filter on the surface of each ommatidium. This has been imaged on sectioned eyes using electron microscopes in the ‘60s. The spacing between layers tunes the filter, changing the color.
2. Each ommatidium retina has 8
rhabdomes (light sensor’s)arranged in a grid pattern. Looking in from the cornea you can see 7. Rh8 is stacked below Rh7. And Rh7 and Rh8 are in the center position of the array. Rh7 and Rh8 are the color sensing cells, Rh1-6 are light/motion sensing, but not color. There are several types of sensor found in the color positions, each sensitive to a different spectral frequency range, blue, green and UV. The different Rh7-8 sensors scattered at different ommatidium in the compound eye provide color vision. This was studied in the 70’s through early 2000’s.
3. The eyes of lab fruit flies have less spectacular contrast between ommatidium filter colors and the colors are arranged stochastically (random). The color of the cornea filter is matched to the sensor type of the underlying Rh7-8 color sensor cells. Studied in early 2000’s. We humans also have stochastic patterning in our color vision cells.
4. The color sensing cells in doli are matched to the corneal filter. This was determined at NYU around 2013. In striped eye doli where the corneal array has ‘errors’ in the stripe pattern, the sensor cell array has matching errors.
5. Some doli genera have stochastic eye patterns, not all are striped.
6. Some doli genera have quasi-striped eyes. Stripes with so many errors that they nearly look stochastic. In Hawaii
Chrysosoma globiferum (accidental from Taiwan) and
Condylostylus longicornus (accidental from California) one with striped eyes and one with quasi striped eyes both frolic on the same landscaping and apparently flourish.
7. Some doli have the sensor stripes with little patterning observable in light photos.
Tachytrechus vorax, a doli that inhabits sandy beaches near the Great Lakes in the US has no visible stripes but striped sensor cells. A related fly
T. angustipennis has weakly visible stripes and striped patterning of the color sensors.
8. The striped eye Dolis inhabit a wide range of ecological nitches. I have watched adults feed along shallow puddles catching tiny worms and larvae. Others hang out on green leaves (like the hosta in my yard) eating aphids and springtails and catching small midges on the wing. They are visual hunters, and acrobatic flyers. They often have elaborate courtship with wing waving and flight displays. They hunt during the day. Some are most active in morning and evening, others during the mid day. They thrive in the tropics and in colder climates like I have in northern Illinois.
The advantage of striped patterning is not clear, but the filters no doubt tune the eyes to provide the contrast needed find mates and meals.
Hope this helps!
Keith
