<b>How a melanism mutant responds to thermal variation:</b><b> a case study in ladybird</b><b><i> </i></b><b>beetle</b><b><i> Harmonia axyridis</i></b> <b>demonstrating</b> <b>thermal phenotypic plasticity</b>

The Thermal Melanism Hypothesis proposes that body colour darkness affects species´ thermoregulatory performance by adjusting heat absorption, and higher cuticular melanization benefits more under colder conditions. Melanism also represents the most common type of phenotypic variation under natural conditions, but little is known about the thermal melanism features of the body color mutants. <i>Harmonia axyridis</i> represents an exemplary insect exhibiting thermal phenotypic plasticity in both its dark spot pattern on dorsal pupa and elytra, but also varied among genotypes. A melanism mutant (<i>ml</i>), discovered within our laboratory-reared colony (f. <i>succinea</i> morph) and displaying elevated melanin level throughout all mobile stages, provides an ideal model for exploring whether a melanism mutant displayed similar thermal phenotypic plasticity as the wild type (<i>wt</i>). In addition, it would be valuable for detecting how changes in carotenoids deposition (yellow background) alongside the thermal plasticity in elytra melanin level (dark spots).热黑化假说（Thermal Melanism Hypothesis）提出，体色深浅可通过调节热量吸收影响物种的体温调节性能，且低温环境下体壁黑化程度更高的个体获益更多。黑化亦是自然条件下最常见的表型变异类型之一，但目前学界对体色突变体的热黑化特征尚知之甚少。异色瓢虫（Harmonia axyridis）是一类典型昆虫，其蛹背与鞘翅上的黑斑模式均表现出热表型可塑性，且不同基因型间也存在差异。本研究在实验室饲养的黄变型（succinea morph）异色瓢虫种群中发现了一种黑化突变体（ml），该突变体在所有活动阶段均表现出黑色素水平升高的特征，为探究黑化突变体是否会表现出与野生型（wt）相似的热表型可塑性提供了理想的研究模型。此外，该突变体还可用于解析鞘翅黑色素水平（黑斑）的热可塑性与类胡萝卜素沉积（黄色底色）变化之间的关联机制，具有重要研究价值。