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3,916,000 Yen (FY 1998; 2,000,000 Yen)
Males of the damselfly Mnais costalis (Odonata: Calopterygidae) are morphologically and behaviourally polymorphic, typically existing as clear-winged nonterritorial 'sneaks' and orange-winged territorial 'fighters'. The amount of orange pigment in the wing, as measured with a chromameter, varied between individuals, and decreased as the reproductive season progressed. Individuals maintained in the laboratory on high and low nutrient diets differed in the amount of pigment in the wing. Males in the high nutrient group developed darker wings faster than those in the low nutrient group. Young adults of both sexes and morphs were fed 14C radiolabelled tryptophan or tyrosine (precursors of the pigments ommochrome and melanin respectively). Ommochrome was restricted to the pseudopterostigma of the males of both morphs and was not present in females. The presence of tyrosine in the wing cells of orange males but not of clear males indicated that the orange pigment is at least partly constituted from melanin. These data show that at least some pigment levels must be continuously maintained in the wings of orange males, and that maintainance is costly since it is compromised at low nutrient levels. The results suggest that any trade-off, which may operate between the strategy of each male morph, may do so via the immune system and the expression of secondary sexual characters. This is important in the context of conservation biology because it shows that the insect immune system is plastic and can be adjusted according to environmental conditions. It means that insects in stressed environments may divert resources from their immune-systems, so that the presence of insects in a given environment may not mean that the population is healthy.
Dimorphism; immune system; Odonata; reproductive success;Mnais costalis