On the bioconversion of dietary carotenoids to astaxanthin and its distribution in the marine copepod, Tigriopus californicus

Abstract Red carotenoid-based coloration is widely distributed across marine and terrestrial animals and has taken a prominent role in studies of how phenotypic traits evolve in response to natural and sexual selection. Key to these studies is an understanding of the physiological mechanisms that give rise to red coloration, yet an ideal model system for such work has not been identified. The red marine copepod Tigriopus californicus is used as a model system for studies in ecotoxicology, genetics, and physiology, but the mechanisms involved in its bright red coloration have not been well studied. Like nearly all animals that display red carotenoid coloration, T. californicus likely convert yellow carotenoids present in their algal diet to red carotenoids. We conducted precursor/product feeding experiments to demonstrate that T. californicus bioconverts dietary carotenoids to the red carotenoid, astaxanthin. In separate treatment groups, copepods were fed carotenoids that are precursors to specific astaxanthin bioconversion pathways. We found that copepods from each precursor pigment group produced astaxanthin, and that the amount produced depended on which carotenoid was supplemented. We also describe the distribution of astaxanthin in developing egg sacs and show that the red color of the naupliar eyespot is not due to astaxanthin. We briefly discuss the potential of Tigriopus californicus to serve as a model system for the study of carotenoid metabolism in animals.