REGULATION OF DOPA DECARBOXYLASE EXPRESSION DURING COLOR PATTERN-FORMATION IN WILD-TYPE AND MELANIC TIGER SWALLOWTAIL BUTTERFLIES

The eastern tiger swallowtail butterfly Papilio glaucus shows a striki ng example of Batesian mimicry. In this species, females are either wi ld type (yellow and black) or melanic (where most of the yellow colour is replaced by black). In order to understand how these different col our patterns are regulated, we examined the temporal order of wing pig ment synthesis via precursor incorporation studies, enzyme assays, and in situ hybridisation to mRNA encoding a key enzyme, dopa decarboxyla se, We show that dopa decarboxylase provides dopamine to both of the t wo major colour pigments, papiliochrome (yellow) and melanin (black), Interestingly, however, dopa decarboxylase activity is spatially and t emporally regulated, being utilised early in presumptive yellow tissue s and later in black. Further, in melanic females, both dopa decarboxy lase activity and early papiliochrome synthesis are suppressed in the central forewing and this normally yellow area is later melanised, The se results show that the regulation of enzyme synthesis observed in th e yellow/black pattern of a single wing, is similar to that involved i n melanism, We infer that dopa decarboxylase activity must be regulate d in concert with downstream enzymes of either the melanin and/or the papiliochrome specific pathways, forming part of a developmental switc h between yellow or black, This modification of multiple enzyme activi ties in concert is consistent with a model of melanisation involving c oordinate regulation of the underlying synthetic pathways by a single Y-linked (female) factor.