Spectral patterns of the iridescence in the males of Sapphirina (Copepoda: Poecilostomatoida)

Abstract

Spectral reflectivity and transmission of the iridescent cuticle of six species of male Sapphirina (Poecilostomatoida: Copepoda) were measured by microspectrophotometry. Sapphirina angusta and S. opalina showed two spectral peaks of reflection, one at about 420 nm and the other at wavelengths longer than 750 nm. Sapphirina auronitens and S. gastrica had dominant peaks at wavelengths longer than 500 nm. Sapphirina ovatolanceolata had peaks between 430 and 600 nm, while S. metallina had various peaks along a wide range of wavelengths. The peaks at the longer wavelength in S. angusta and S. opalina may be related to the red pigments in the subcuticular layer of the species, or a result of a second-order effect of the multilayer system. The spectra of transmitted light were complementary to those of reflected light, indicating that the iridescence is caused by the interference of light by the integumental multilayer structure. The present results are also consistent with the hypothesis that the iridescence has a role in increasing the contrast of males against the ambient light conditions in the daytime distributional depth of the species.