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.

中文翻译：

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Anchialine 虾的红色：类胡萝卜素、遗传变异和候选基因

红色是动物中广泛分布的表型，但在相对较少的分类群中描述了这种表型的色素和遗传基础。在这里，我们展示了夏威夷特有的 Anchialine 虾 Halocaridina rubra 由于虾青素的积累而呈红色。H. rubra 系统发育不同谱系的实验室菌落具有菌落特定量的虾青素，这些虾青素在发育上并且可能在遗传上是固定的。类胡萝卜素补充和限制实验未能改变菌落内基线水平的虾青素含量，这表明饮食限制不是导致颜色差异的主要因素。一种可能的候选基因产物被预测为负责在幽门螺杆菌中产生虾青素。rubra 和其他甲壳类动物与真菌中发现的双功能细胞色素 P450 家族 3 酶 CrtS 密切相关。然而，没有发现被认为催化鸟类和海龟酮化反应的酶 CYP2J19 的同源物。这项工作是将 H. rubra 红色着色的表型变异与基因型变异联系起来的第一步。未来的工作应该集中在 (1) 确定在膳食类胡萝卜素生物转化为虾青素中起作用的基因，(2) 检查哪些基因组变异可能会驱动离散谱系之间的颜色变化，以及 (3) 更明确地测试条件依赖性类胡萝卜素甲壳类动物的着色。这项工作是将 H. rubra 红色着色的表型变异与基因型变异联系起来的第一步。未来的工作应该集中在 (1) 确定在膳食类胡萝卜素生物转化为虾青素中起作用的基因，(2) 检查哪些基因组变异可能会驱动离散谱系之间的颜色变化，以及 (3) 更明确地测试条件依赖性类胡萝卜素甲壳类动物的着色。这项工作是将 H. rubra 红色着色的表型变异与基因型变异联系起来的第一步。未来的工作应该集中在 (1) 确定在膳食类胡萝卜素生物转化为虾青素中起作用的基因，(2) 检查哪些基因组变异可能会驱动离散谱系之间的颜色变化，以及 (3) 更明确地测试条件依赖性类胡萝卜素甲壳类动物的着色。