How a melanism mutant responds to thermal variation: a case study in ladybird beetle Harmonia axyridis demonstrating thermal phenotypic plasticity

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. Harmonia axyridis 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 (ml), discovered within our laboratory-reared colony (f. succinea 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 (wt). 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).