A Novel Molecular Solution for Ultraviolet Light Detection in Caenorhabditis elegans
Figure 5
The C. elegans Light Response may be a Photophobic Response to the UV Light in Direct Sunlight
(A) Worms actively avoid blue-violet light. Field-of-view clearing assays on crowded plates of N2 (wild type) in green versus blue-violet light. Each plate contained 4,500 young adult animals at a density of 1.6 animals/mm2. Error bars are the standard errors from ten trials.
(B) The UV light in direct sunlight is sufficient to cause a locomotory response. Shown are the mean locomotion rates of wild type in ultraviolet, blue-violet, and blue light of powers found in direct sunlight. Note that the UV power measured by the light detector at the culture plate surface is restricted to wavelengths in the 350–375-nm range due to adsorption of lower wavelengths by glass in the microscope objective. Therefore, the power reading of 19.5 μW/mm2, taken at the culture plate surface, was biased toward longer wavelengths of the DAPI filter (350–375 nm). Sunlight passing through the DAPI filter directly onto the detector contains all wavelengths from 325–375 nm (because it does not go through glass), so the sunlight power reading of 19.5 μW/mm2 reflects both short and long wavelengths of UV. It is likely that the shorter wavelengths of UV light in sunlight, including wavelengths shorter that those passed by the DAPI filter, are required to maximize the locomotion response. Indeed, sunlight UV wavelengths down to 291 nm reach Earth's surface [7], and this is well below the range of the DAPI filter. The asterisk indicates statistical significance, with a p-value of 0.015 using the unpaired t-test with the Welch correction. Error bars are the standard errors in populations of ten animals.