Related Physiological Characteristics And Molecular Regulation Mechanism Of Melanopolymorphs In Harmonia Axyridis

Phenotypic polymorphism is one of the adaptively external characteristics of organisms to the environment,which can be obtained through many ways.In insects,it is mainly achieved through the blackening polymorphism.Melanization is a common phenomenon in insects and melanin synthesis is a conserved physiological process that occurs in epidermal cells.Moreover,a comprehensive understanding of the mechanisms of melanin synthesis influencing insect pigmentation are well-suited for investigating phenotype variation.The Asian multi-colored(Harlequin)ladybird beetle,Harmonia axyridis,exhibits intraspecific polymorphism based on relative levels of melanization.It is a model insect for studying phenotypic diversity,environmental adaptability,physiological mechanism and genetic evolution.However,the specific characteristics of melanin synthesis in H.axyridis remains elusive.In this study,the predatory behavior of adults of different color types of H.axyridis to different prey was studied in seasonal environmental conditions(temperature and photoperiod).The results showed that temperature,photoperiod,color type,gender and prey had significant effects on the predatory behavior of adult,and there was significant interaction between color type and other factors.In this study,we performed gene-silencing analysis of the pivotal inverting enzyme,tyrosine hydroxylase(TH),and DOPA decarboxylase(DDC)in the tyrosine metabolism pathway to investigate the molecular and regulatory mechniasm of melanin synthesis in H.axyridis.Using RNAi of TH and DDC genes in the third and fourth instar larvae,we demonstrated that the function of TH in H.axyridis is pleiotropic and dopamine melanin was the primary contributor to the overall body melanization of H.axyridis.Furthermore,our study provides the first conclusive evidence that dopamine serves as a melanin precursor for synthesis in the early pupal stage.We further demonstrated that suppression of pannier can significantly decrease the expression levels of Ha TH and Ha DDC.These results in their entirety allow for the conclusion that transcription factor pannier can regulate dopamine melanin synthesis in the dorsal elytral epidermis of H.axyridis.The results of this paper will provide theoretical basis for the study of genetic evolution and molecular mechanism of pleomorphic species.