Data from: Genetic basis of stage-specific melanism: a putative role for a cysteine sulfinic acid decarboxylase in insect pigmentation

Melanism, the overall darkening of the body, is a widespread form of animal adaptation to particular environments, and includes bookcase examples of evolution by natural selection, such as industrial melanism in the peppered moth. The major components of the melanin biosynthesis pathway have been characterized in model insects, but little is known about the genetic basis of life-stage specific melanism such as cases described in some lepidopteran species. Here, we investigate two melanic mutations of Bicyclus anynana butterflies, called Chocolate and melanine, that exclusively affect pigmentation of the larval and adult stages, respectively. Our analysis of Mendelian segregation patterns reveals that the larval and adult melanic phenotypes are due to alleles at different, independently segregating loci. Our linkage mapping analysis excludes the pigmentation candidate gene black as the melanine locus, and implicates the gene encoding a putative PLP-dependant cysteine sulfinic acid decarboxylase as the Chocolate locus. We show variation in coding sequence and in expression levels for this candidate larval melanism locus. This is the first study that suggests a biological function for this gene in insects. Our findings open up exciting opportunities to study the role of this locus in the evolution of adaptive variation in pigmentation, and the uncoupling of regulation of pigment biosynthesis across developmental stages with different ecologies and pressures on body coloration.

黑化现象（melanism），即生物体整体体色加深，是动物适应特定环境的一类广泛存在的适应性演化形式，包含了自然选择（natural selection）驱动演化的教科书式范例，如斑点蛾的工业黑化现象。模式昆虫（model insects）中黑色素生物合成通路（melanin biosynthesis pathway）的核心组分已被解析，但针对如部分鳞翅目物种（lepidopteran species）中所报道的发育阶段特异性黑化现象的遗传基础，目前我们仍知之甚少。本研究针对安凡矍眼蝶（Bicyclus anynana）的两种黑化突变体——Chocolate与melanine——展开探究，二者仅分别特异性影响幼虫与成虫阶段的色素沉着过程。我们对孟德尔分离模式（Mendelian segregation patterns）的分析结果显示，幼虫与成虫的黑化表型分别由位于不同且独立分离的基因座（loci）上的等位基因（alleles）所致。连锁定位（linkage mapping）分析排除了色素沉着候选基因black作为melanine基因座的可能性，并暗示编码推定的吡哆醛磷酸（PLP）依赖型半胱氨酸亚磺酸脱羧酶（PLP-dependant cysteine sulfinic acid decarboxylase）的基因为Chocolate基因座。我们发现该候选幼虫黑化基因座在编码序列（coding sequence）与表达水平（expression levels）上均存在变异。本研究首次揭示了该基因在昆虫中的生物学功能。我们的研究结果为探究该基因座在适应性体色变异演化中的作用，以及解析不同生态环境与体色选择压力下各发育阶段色素生物合成调控的解偶联机制提供了全新的研究契机。