Red Coloration in an Anchialine Shrimp: Carotenoids, Genetic Variation, and Candidate Genes

Abstract

Red coloration is a widely distributed phenotype among animals, yet the pigmentary and genetic bases for this phenotype have been described in relatively few taxa. Here we show that the Hawaiian endemic anchialine shrimp Halocaridina rubra is red because of the accumulation of astaxanthin. Laboratory colonies of phylogenetically distinct lineages of H. rubra have colony-specific amounts of astaxanthin that are developmentally, and likely genetically, fixed. Carotenoid supplementation and restriction experiments failed to change astaxanthin content from the within-colony baseline levels, suggesting that dietary limitation is not a major factor driving coloration differences. A possible candidate gene product predicted to be responsible for the production of astaxanthin in H. rubra and other crustaceans is closely related to the bifunctional cytochrome P450 family 3 enzyme CrtS found in fungi. However, homologs to the enzyme thought to catalyze ketolation reactions in birds and turtles, CYP2J19, were not found. This work is one of the first steps in linking phenotypic variation in red coloration of H. rubra to genotypic variation. Future work should focus on (1) pinpointing the genes that function in the bioconversion of dietary carotenoids to astaxanthin, (2) examining what genomic variants might drive variation in coloration among discrete lineages, and (3) testing more explicitly for condition-dependent carotenoid coloration in crustaceans.

Testosterone regulates CYP2J19 -linked carotenoid signal expression in male red-backed fairywrens ( Malurus melanocephalus )

“…Our results corroborate a growing number of studies suggesting the importance of CYP2J19 for red coloration in birds [23,24,82,83] and other animals [84,85]. The genetic basis of carotenoid-based coloration is not yet well resolved [3,32], but a handful of genes with large effects have been identified in recent years that are associated with carotenoid coloration (e.g.…”

“…Specifically, 1-year-olds are more likely to serve as helpers in their natal group and hence have lower levels of circulating testosterone, whereas most 2year-olds transition into a breeding role, even after having completed moult into unornamented plumage [63,81], which may explain this shift in carotenoid concentration between the two age groups. Future work with greater sampling will reveal how tightly linked age, testosterone and gene Our results corroborate a growing number of studies suggesting the importance of CYP2J19 for red coloration in birds [23,24,82,83] and other animals [84,85]. The genetic basis of carotenoid-based coloration is not yet well resolved [3,32], but a handful of genes with large effects have been identified in recent years that are associated with carotenoid coloration (e.g.…”

Stereochemistry of Astaxanthin Biosynthesis in the Marine Harpacticoid Copepod Tigriopus Californicus

“…Genetic studies in birds have contributed the most prominent advances in the study of astaxanthin biosynthesis in animals with the identification of the ketolase gene [ 15 , 16 ]. However, biochemical studies in zooplankton have also contributed to the knowledge of this pathway [ 17 , 18 , 19 , 20 ]. Along this line, Weaver et al recently proposed T. californicus as a model organism for the study of astaxanthin synthesis in animals [ 18 ].…”

Evidence for hybrid breakdown in production of red carotenoids in the marine invertebrate Tigriopus californicus

“…In this often-colorful group, red and blue pigmentation is frequently produced by the accumulation of the ketocarotenoid astaxanthin, along with other ketocarotenoids [ 13 ]. Notably, the precursors and products in ketocarotenoid pathways in many crustaceans are the same as those in birds, and the oxidizing enzymes involved in these crustacean pathways are predicted to be functionally similar to the enzymes employed by avian species [ 18 , 33 , 34 ]. One particular crustacean group, oceanic and lake-dwelling copepods, have frequently been utilized in carotenoid pigmentation studies due to their critical link in ecological food webs and their amenability to experimental manipulation [ 8 , 35 , 36 ].…”