![]() However, they lack antehumeral stripes on the thorax and the small black spur on the side of the thorax of the two Red-eyed species. The immature female has an unmistakeable bright orange ( aurantiaca) phase.The American epic science-fiction film “Avatar” (directed, written, co-produced, and co-edited by James Cameron) takes place on a lush habitable moon named Pandora, which has a variety of fluorescent species. Actually, the Earth can be likened to the fictional Pandora, because it also has a large number of fluorescent species, including plants, animals and trees 1, 2. One common example is the firefly however, the fluorescence of the fireflies is categorized as a type of bioluminescence (BL) that is different from photoluminescence (PL). BL is a kind of visible-light emission generated by the chemical reactions of luciferase and oxygen 3, 4, 5, 6, while PL is a low-intensity visible-light emission excited by high-energy incident photons, such as ultraviolet (UV) light. ![]() Many fluorescent species found in nature (e.g., the damselflies examined in this study) give off PL emissions, but they are difficult to see both in the daytime and nighttime. This is because the sun light is too strong in the daytime, and there is no excited light present in the nighttime. If it is hard to see the PL, why do they (in this case damselflies) need these PL emissions. Why did they develop this capability during the course of evolution? In fact, PL emissions can be seen in the daytime, and make the color different. For example, the white paper and shirts always are added with fluorescent whitening agents, which can produce PL emissions to make them look whiter under lights. Hence, PL emissions must offer some advantage in the natural habitat of damselflies. Here we examine the PL emissions from the various colored-body portions of the male damselfly Ischnura senegalensis (Rambur, 1842), such as the compound eyes and the eighth abdominal segment of the tail, because the males exhibit a color mono-morphism 7. Ischnura senegalensis (Rambur, 1842), also known as the common bluetail, is a common type of damselfly that is widespread in Africa, the Middle East, and throughout southern and eastern Asia. They usually inhabit clean shallow water, and are easily found in running water and ponds. ![]() Unlike the monomorphic males, the female damselfly Ischnura senegalensis (Rambur, 1842) exhibit color dimorphism (namely, andromorph and gynomorph, as shown in Fig. The andromorph helps to reduce intrasexual and male harassment and allows them to gain mature mating (as shown in Fig. The andromorphic colors may be used as signals to improve sexual selection 8, because they provide good visual contrast for conspecific identity in the ambient light of a varying environmental background. The capability of assuming conspecific identity provides not only a better chance for sexual selection, but also an advantage in territorial defense 9, 10, 11, 12. In this study, the PL emissions from the cuticles of various colored-body portions of the male damselfly were observed and verified in PL spectromicroscopy, and confocal fluorescence microscopy.
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