Expression of a costly, plastic secondary sexual trait is correlated with age and condition in a damselfly with two male morphs

Males of the damselfly Mnais costalis Selys (Odonata: Calopterygidae) are m orphologically and behaviourally polymorphic, typically existing as clear-w inged non-territorial 'sneaks' and orange-winged territorial 'fighters'. Th e amount of orange pigment in the wing, as measured with a chromameter, var ied between individuals, and decreased as the reproductive season progresse d. Young individuals maintained in the laboratory on high or low nutrient d iets differed in the amount of pigment that developed in the wing. Males in the high nutrient group developed darker wings faster than those in the lo w nutrient group. Young adults of both sexes and morphs were fed C-14-radio labelled 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, indica ted that the orange pigment is at least partly constituted from melanin. Th ese data show that at least some pigment levels must be maintained continuo usly in the wings of orange males, and that maintenance is costly as it is compromised at low nutrient levels.