Molecular Evolution and Developmental Expression of Melanin Pathway Genes in Lepidoptera

Muktai Kuwalekar, Riddhi Deshmukh, Ajay Padvi, Krushnamegh Kunte

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Pigmentation is involved in a wide array of biological functions across insect orders, including body patterning, thermoregulation, and immunity. The melanin pathway, in particular, has been characterized in several species. However, molecular evolution of the genes involved in this pathway is poorly explored. We traced the molecular evolution of six melanin pathway genes in 53 species of Lepidoptera covering butterflies and moths, and representing over 100 million years of diversification. We compared the rates of synonymous and non-synonymous substitutions within and between these genes to study the signatures of selection at the level of individual sites, genes, and branches of the gene tree. We found that molecular evolution of all six genes was governed by strong purifying selection. Yet, a number of sites showed signs of being under positive selection, including in the highly conserved domain regions of three genes. Further, we traced the expression of these genes across developmental stages, tissues, and sexes in the Papilio polytes butterfly using a developmental transcriptome dataset. We observed that the expression patterns of the genes in P. polytes largely reflected their known tissue-specific function in other species. The expression of sequentially acting genes in the melanin pathway was correlated. Interestingly, melanin pathway genes also showed a sexually dimorphic pattern of developmental heterochrony, i.e., females showed prominent upregulation of melanin pathway genes in pre-pupal stage compared to males, while males showed prominent upregulation in 9-day pupal wings compared to females. Our evolutionary and developmental analyses suggest that the vast diversity of wing patterning and pigmentation in Lepidoptera may have evolved despite largely constrained sequence evolution, with potential contribution from differential developmental expression of genes in a highly conserved pathway.

Original languageEnglish
Article number226
JournalFrontiers in Ecology and Evolution
Publication statusPublished - 14 Jul 2020
MoE publication typeA1 Journal article-refereed

Bibliographical note

Funding Information:
We thank Atharva Khotpal, Bhavanarayeni R., Sai Guha, and Sarvesh Menon for assistance in downloading and analyzing genome sequences, Saurav Baral and Vinod Shankar for help with molecular evolution analysis, Sergei L. Kosakovsky Pond for valuable inputs on HyPhy, NCBS Sequencing Facility for transcriptome sequencing, and NCBS Greenhouse Facility for butterfly breeding facilities. Funding. This work was partially funded by an NCBS Research Grant to KK, support of the Department of Atomic Energy, Government of India, under project nos. 12-R&D-TFR-5.04-0800 and 12-R&D-TFR-5.04-0900, and a CSIR Shyama Prasad Mukherjee Fellowship to RD.

Publisher Copyright:
© Copyright © 2020 Kuwalekar, Deshmukh, Padvi and Kunte.

Fields of Science

  • butterfly wing coloration
  • developmental heterochrony
  • melanization
  • pigmentation
  • wing patterns

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