Extractable Age Pigment-Like Autofluorescence and Its Relationship to Growth and Age in the Water-Flea Daphnia-Carinata King (Crustacea, Cladocera)

Abstract

Autofluorescent materials in the tissues of laboratory-reared Daphnia carinata were examined with the aim of elucidating possible age-dependent accumulations of the type suggested in previous literature. A diverse array of fluorophores was revealed with live animal and tissue section fluorescence microscopy and spectrofluorimetry of solvent extracts. Chloroform-soluble fluorescence with chemical and spectral properties similar to those of extractable age pigments was found. From proton magnetic resonance and FAB mass spectra of chromatographic fractions, this fluorescence appeared to be derived from phospholipid material. The effects of metal chelation and pH on this fluorescence were consistent with the presence of Schiff-base fluorophores as found in age pigments, but tissue fluorescence levels were growth-dependent rather than age-dependent. Absolute fluorescence intensity was most strongly correlated with body weight, the latter being closely associated with the reproductive status of the animal rather than its age. Weight-specific fluorescence covaried inversely with age and body weight. A substantial proportion of this fluorescence was derived from the frequently shed cuticle. The levels of this extractable fluorescence in crustacean tissue cannot be assumed to reflect age as has been suggested in previous literature. Implications for crustacean age pigment studies are discussed.