14 December, 2010

Scorpion fluorescence - a way to avoid moonlight?

Scorpions fluorescence under UV-light. This is a great phenomenon for scorpion scientists and enthusiasts wanting to find and study scorpions, but its function has not been known so far. Suggested functions have been uv-light detection, mate identification, species identification, luring of prey, light amplification and that the fluorescence has no fuction at all.

Carl Kloock has written several papers on scorpion fluorescence (previous blog post), and in his latest paper (authored together with Abraham Kubli and Ricco Reynolds) it is concluded that their experimental data support the hypothesis that scorpion fluorescence serves as a means for the detection of UV-light at very low levels. Further, it is suggested that the UV-light acts as a cue for moonlight avoidance (fluorescence is a way to detect the presence of uv-light which is correlated to a moonlit night and this cause the scorpions to stay hidden in their hidings).

This is the first experimental evidence for a potential function for scorpion fluorescence, but further studies are necessary before final conclusion can be made on this phenomenon.

The hypothesis that fluorescence in scorpions functions in the detection of ultraviolet light was tested. We reduced the fluorescence of scorpions by prolonged exposure to ultraviolet light on a 16:8 h light:dark cycle and compared their activity levels and light environment choices to unmodified scorpions in simple arenas that were half in shadow and half exposed to light. Three different lighting conditions were tested: infrared (IR) light only, IR + ultraviolet light and IR + white light. Treatments were illuminated by infrared light for videotaping. Activity level was measured by the number of transitions from the exposed to shadowed regions, and choice was measured by the percentage of time spent in the shadowed portion of the arena. Under IR + ultraviolet light, fluorescent scorpions reduced their activity levels and the variance in habitat choice increased, compared with reduced-fluorescence scorpions. There were no differences between fluorescent and non-fluorescent scorpions in the IR only condition or in the IR + white light condition. This is interpreted as evidence that fluorescence aids in the detection of and response to ultraviolet light, and possible implications of this result in natural habitats are discussed. This is the first experimental demonstration of a possible function for scorpion fluorescence.

Kloock CT, Kubli A, Reynolds R. Ultraviolet light detection: A function of scorpion fluorescence. Journal of Arachnology. 2010;38(3):441-5. [Subscription required for fulltext, but free fulltext after 12 months]

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