Diversification and expression of vision-related genes in Lepidoptera

Diversification of lepidopteran (moth and butterfly) color vision is due to gene duplication, gene loss, and sequence variation of opsin genes. How other vision-related genes are evolving in this group is not well characterized. This dissertation aims to survey the evolution and expression of candidate genes involved in lepidopteran vision. In my first study, I tested whether vision-related genes varied in expression between sexes and seasonal forms of a phenotypically plastic butterfly, Bicyclus anynana. B. anynana displays plasticity and sexual dimorphism in eye size. I identified eye development genes differentially expressed between seasonal forms, making them candidates underlying eye size differences. I found that more genes were differentially expressed between seasonal forms than sexes, with rearing temperature having a larger effect on the expression of vision-related genes in females. One of the genes that was differentially expressed between seasonal forms was annotated to have a CRAL-TRIO domain. Members of this gene family have a role in chromophore transport in vertebrates and Drosophila (pinta). This gene family has been shown to be evolving by linage-specific duplications in insects and has an expansion in Lepidoptera. For my next study, I used phylogenetics and transcriptomics to assess the evolution and expression patterns of members of this gene family in the butterfly Heliconius melpomene. Results indicated that a family member non-orthologous to Drosophila pinta takes on the role of chromophore binding. This brought upon the question: which phototransduction genes are conserved between Lepidoptera and Drosophila? For the last study of my dissertation, I used phylogenetics and transcriptomics to explore more gene families in order to identify which phototransduction cascade genes were conserved between Drosophila and Lepidoptera, and within Lepidoptera. Results suggested that moth and butterfly phototransduction cascades involve similar genes that vary from Drosophila cascades in instances where Lepidopteran-specific paralogs have a potential role in vision. This dissertation explored the role of plasticity in vision-related gene expression (chapter 1), provided the first evidence of visual function for a CRAL-TRIO domain gene in butterflies (chapter 2), and offered insights into the Lepidopteran phototransduction cascade (chapter 3)