Molecular Mechanisms of Larval Color Pattern Switch in the Swallowtail Butterfly

Abstract

In lepidopterans (butterflies and moths), larval body color pattern, which is an important mimicry trait involved in prey-predator interactions, presents a great diversity of pigmentation and patterning. Unlike wing patterns, larval body color patterns can switch during development with larval molting. For example, in the Asian swallowtail butterfly Papilio xuthus, a younger larva (first-fourth instar) has a white/black color pattern that mimics bird droppings, whereas the final instar (fifth) larva drastically changes to a greenish pattern that provides camouflage on plants. Insect mimicry has interested scientists and the public since Darwin's era. Broadly, mimicry is an antipredation strategy whereby one creature's color, shape, or behavior resembles another creature or object. In this review, I address basic knowledge about larval cuticular pigmentation and advanced understanding of its regulatory mechanism in P. xuthus; I also discuss larval body color patterns among members of the genus Papilio, followed by conclusions and prospects for further research.

Developmental Transcriptome Analysis of Red-Spotted Apollo Butterfly, Parnassius bremeri

“…The larvae appear dark colored because they have a pigmented cuticle. Cuticle development and pigmentation depend on several factors, including the involvement of phenoloxidases in the melanization pathway, and regulation by juvenile hormones and ecdysone hormones [ 37 ]. For instance, aldo-keto reductase AKR2E4, which is responsible for the reduction of 3-dehydroecdysone to ecdysone in the silkworm Bombyx mori L. [ 38 ], developmentally regulated arylphorin subunit [ 39 ], chorion peroxidase involved in the chorion cross-linking [ 40 ], members of juvenile hormone signaling pathway [ 41 ] and ecdysone signaling pathway [ 42 ], and most of them belong to the cuticle development.…”

Butterfly blues and greens caused by subtractive colour mixing of carotenoids and bile pigments

“…3A, #1; from Bois-Choussy and Barbier 1983), thus creating a blue-cyan colour. However, the bilins are in situ bound to proteins, which can modify the absorption spectrum (Huber et al 1987;Scheer and Kayser 1988;Iturraspe et al 1989;Jin and Fujiwara 2017). In the case of pterobilin, this may be of minor importance, but in the related pharcobilin and sarpedobilin, which are derived from pterobilin by cyclisation (Bois-Choussy 1977), protein binding can determine the conformation (Iturraspe et al 1989).…”

“…The green colouration may act as a contrasting signal when surrounded by a black frame, as in several Graphium species, but generally it will serve for camouflage against a background of green leaves, which are green due to carotenoid combined with chlorophyll. For insects, applying an optical method similar to that of leaves is clearly the preferred way to be green (Jin and Fujiwara 2017). However, for most butterfly species, realizing a green display with the method of structural colouration may offer too attractive of a possibility to avoid.…”

“…The green colouration clearly has a function in camouflage and crypsis (Jin and Fujiwara 2017). Indeed, the bile pigments (bilins) together with carotenoids notably colour the epidermis of lepidopteran larvae as well as pupae (Junge 1941;Ohtaki and Ohnishi 1967;Shirataki et al 2010;Jin et al 2019), but in the large majority of adult butterflies they are replaced by various other pigments, the papiliochromes, ommochromes, pterins and melanins, mentioned above.…”

“…The spectra of the various bilins derived from in situ spectrophotometry appeared to depend on the species, but the spectra reported by Bois-Choussy (1977) were somewhat confusing (Stavenga 2023). The latter may be due to the condition of the pigments, because extensive studies on larvae demonstrated that there both bilins and carotenoids are bound to proteins, which can substantially affect the pigments' absorption spectrum (Huber et al 1987;Scheer and Kayser 1988;Iturraspe et al 1989;Jin and Fujiwara 2017).…”