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.

黑色素沉着（melanism），即全身整体发黑的现象，是动物适应特定环境的一类普遍适应性特征，其中包含了自然选择演化的经典案例，比如桦尺蛾的工业黑化现象。尽管模式昆虫体内的黑色素合成通路的核心组分已得到充分解析，但针对特定生命阶段特异性黑色素沉着的遗传基础，目前仍所知甚少，例如部分鳞翅目物种中报道的相关案例。本研究以安纽矍眼蝶（Bicyclus anynana）的两种黑色素突变体Chocolate与melanine为研究对象，二者分别仅作用于幼虫与成虫阶段的色素沉着过程。我们对孟德尔分离模式的分析结果显示，幼虫与成虫的黑化表型分别由位于不同且独立分离位点上的等位基因所调控。连锁定位分析结果排除了色素沉着候选基因black作为melanine位点的可能性，并将编码假定依赖吡哆醛磷酸（PLP）的半胱氨酸亚磺酸脱羧酶的基因确定为Chocolate位点的候选基因。我们针对该幼虫黑色素沉着候选位点，检测到其编码序列与表达水平均存在变异。本研究是首个证实该基因在昆虫体内具备生物学功能的相关报道。本研究结果为探究该位点在色素沉着适应性演化变异中的作用，以及解析不同生态与体色选择压力下各发育阶段色素合成调控的解耦机制提供了全新的研究契机。