Sex-specific Tyrian purple genesis: precursor and pigment distribution in the reproductive system of the marine mollusc Dicathais orbita

Exploitation of Tyrian purple from muricid molluscs, since antiquity, has prompted much interest in its chemical composition. Nevertheless, there remains a paucity of information on the biosynthetic routes leading to observed sexual differences in pigmentation. A liquid chromatography-mass spectrometry (LQ-MS) method was developed to simultaneously quantify dye pigments and precursors in male and female Dicathais orbita. The prochromogen, tyrindoxyl sulfate, was detected for the first time, by using this method in hypobranchial gland extracts of both sexes. Intermediates tyrindoxyl, tyrindoleninone, and tyriverdin were detected in female hypobranchial glands, along with 6,6′-dibromoindigo, while males contained 6-bromoisatin and 6,6′-dibromoindirubin. Multivariate analysis revealed statistically significant differences in the dye composition of male and female hypobranchial glands (ANOSIM, P = 0.002), thus providing evidence for sex-specific genesis of Tyrian purple in the Muricidae. Dye precursors were also present in male and female gonoduct extracts, establishing a mechanism for the incorporation of bioactive intermediates into muricid egg masses. These findings provide a model for investigating sex-specific chemical divergences in marine invertebrates and support the involvement of Tyrian purple genesis in muricid reproduction