Title: On the bioconversion of dietary carotenoids to astaxanthin and its distribution in the 1 marine copepod, Tigriopus californicus

10 Red carotenoid-based coloration is widely distributed across marine and terrestrial animals and 11 has taken a prominent role in studies of how phenotypic traits evolve in response to natural and 12 sexual selection. Key to these studies is an understanding of the physiological mechanisms that 13 give rise to red coloration, yet an ideal model system for such work has not been identified. The 14 red marine copepod Tigriopus californicus is used as a model system for studies in 15 ecotoxicology, genetics, and physiology, but the mechanisms involved in its bright red coloration 16 have not been well studied. Like nearly all animals that display red carotenoid coloration, T. 17 californicus likely convert yellow carotenoids present in their algal diet to red carotenoids. We 18 conducted precursor/product feeding experiments to demonstrate that T. californicus bioconverts 19 dietary carotenoids to the red carotenoid, astaxanthin. In separate treatment groups, copepods 20 were fed carotenoids that are precursors to specific astaxanthin bioconversion pathways. We 21 . CC-BY-NC-ND 4.0 International license peer-reviewed) is the author/funder. It is made available under a The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/174300 doi: bioRxiv preprint first posted online Aug. 15, 2017;