doublesex regulates early embryonic sex differentiation in holometabolous insects, along with the development of species-, sex-, and morph-specific adaptations during pupal stages. How does a highly conserved gene with a critical developmental role also remain functionally dynamic enough to gain ecologically important adaptations that are divergent in sister species? We analyzed patterns of exon-level molecular evolution and protein structural homology of doublesex from 145 species of four insect orders representing 350 million years of divergence. This analysis revealed that evolution of doublesex was governed by a modular architecture: Functional domains and female-specific regions were highly conserved, whereas male-specific sequences and protein structures evolved up to thousand-fold faster, with sites under pervasive and/or episodic positive selection. This pattern of sex bias was reversed in Hymenoptera. Thus, highly conserved yet dynamic master regulators such as doublesex may partition specific conserved and novel functions in different genic modules at deep evolutionary time scales.

Butterfly wing patterns are key adaptations that are controlled by remarkable developmental and genetic mechanisms that facilitate rapid evolutionary change. With swift advancements in the fields of genomics and genetic manipulations, identifying the regulators of wing development and mimetic wing patterns has become feasible even in nonmodel organisms such as butterflies. Recent mapping and gene expression studies have identified single switch loci of major effects such as transcription factors and supergenes as the main drivers of adaptive evolution of mimetic and polymorphic butterfly wing patterns. We highlight several of these examples, with emphasis on doublesex, optix, WntA and other dynamic, yet essential, master regulators that control critical color variation and sex-specific traits. Co-option emerges as a predominant theme, where typically embryonic and other early-stage developmental genes and networks have been rewired to regulate polymorphic and sex-limited mimetic wing patterns in iconic butterfly adaptations. Drawing comparisons from our knowledge of wing development in Drosophila, we illustrate the functional space of genes that have been recruited to regulate butterfly wing patterns. We also propose a developmental pathway that potentially results in dorsoventral mismatch in butterfly wing patterns. Such dorsoventrally mismatched color patterns modulate signal components of butterfly wings that are used in intra-and inter-specific communication. Recent advances-fuelled by RNAi-mediated knockdowns and CRISPR/Cas9-based genomic edits-in the developmental genetics of butterfly wing patterns, and the underlying biological diversity and complexity of wing coloration, are pushing butterflies as an emerging model system in ecological genetics and evolutionary developmental biology. © 2017 Wiley Periodicals, Inc. How to cite this article:WIREs Dev Biol 2018, 7:e291. doi: 10.1002/wdev.291 MIMICRY IN BUTTERFLIES: A SINGULAR ADAPTATIONF ew adaptations in nature are as striking and widely appreciated as bright, diverse wing color patterns of butterflies. These color patterns have evolved to serve diverse and crucial functions in sexual selection, predator avoidance, and thermoregulation. Of these, aposematism and mimicry 1,2 (Box 1) are phylogenetically widespread and exhibit considerable diversification with respect to polymorphism 3 and sex-limitation 4,5 (Figure 1), whereby one or both sexes may have morphological variants that are strongly regulated by allelic variants. 7,8 This morphological diversity reflects diverse ecological regimes, intense selection pressures and molecular mechanisms that have shaped the evolutionary and genomic histories of butterflies. Density-and frequency-dependent Such rich biological detail and the diversity of butterfly wing color patterns themselves provide some unusual advantages as study systems in evolutionary biology and developmental genetics. Butterflies are at a golden point where, like birds, they are large and conspicuous enough to follow in the field to underst...

Gene duplication is a vital process for evolutionary innovation. Functional diversification of duplicated genes is best explored in multicopy gene families such as histones, hemoglobin, and opsins. Rhodopsins are photo-sensitive proteins that respond to different wavelengths of light and contribute to diverse visual adaptations across insects. While there are several instances of gene duplications in opsin lineages, the functional diversification of duplicated copies and their ecological significance is properly characterised only in a few insect groups. We examined molecular and structural evolution that underlies diversification and sub-functionalisation of four opsin genes and their duplicated copies across 132 species of the diverse insect order-Lepidoptera. Opsins have largely evolved under purifying selection with few residues showing signs of episodic and pervasive diversifying selection. Although these do not affect overall protein structures of opsins, substitutions in key amino acids in the chromophore-binding pocket of duplicated copies might cause spectral sensitivity shifts leading to sub-functionalisation or neofunctionalisation. Duplicated copies of opsins also exhibit developmental stage-specific expression in Papilio polytes, suggesting functional partitioning during development. Together, altered spectral sensitivities owing to key substitutions and differential expression of duplicated copies across developmental stages might enable enhanced colour perception and improved discrimination across wavelengths in this highly visual insect group.