Development, plasticity and evolution of butterfly eyespot patterns.

The developmental and genetic bases for the formation, plasticity and diversity of eyespot patterns in butterflies are examined. Eyespot pattern mutants, regulatory gene expression, and transplants of the eyespot developmental organizer demonstrate that eyespot position, number, size and colour are determined progressively in a developmental pathway largely uncoupled from those regulating other wing-pattern elements and body structures. Species comparisons and selection experiments suggest that the evolution of eyespot patterns can occur rapidly through modulation of different stages of this pathway, and requires only single, or very few, changes in regulatory genes.

Brakefield PM ，Gates J ，Keys D ，Kesbeke F ，Wijngaarden PJ ，Monteiro A ，French V ，Carroll SB ... -  《NATURE》

Focus on butterfly eyespot development.

The beautiful eyespot patterns on the wings of butterflies help them to evade predators, but they also present biologists with a unique opportunity to investigate the reciprocal interactions of development and evolution.

Nijhout HF 《NATURE》

Wingless and aristaless2 define a developmental ground plan for moth and butterfly wing pattern evolution.

Butterfly wing patterns have long been a favorite system for studying the evolutionary radiation of complex morphologies. One of the key characteristics of the system is that wing patterns are based on a highly conserved ground plan of pattern homologies. In fact, the evolution of lepidopteran wing patterns is proposed to have occurred through the repeated gain, loss, and modification of only a handful of serially repeated elements. In this study, we examine the evolution and development of stripe wing pattern elements. We show that expression of the developmental morphogen wingless (wg) is associated with early determination of the major basal (B), discal (DI and DII), and marginal (EI) stripe patterns in a broad sampling of Lepidoptera, suggesting homology of these pattern elements across moths and butterflies. We describe for the first time a novel Lepidoptera-specific homeobox gene, aristaless2 (al2), which precedes wg expression during the early determination of DII stripe patterns. We show that al2 was derived from a tandem duplication of the aristaless gene, whereupon it underwent a rapid coding and cis-regulatory divergence relative to its more conserved paralog aristaless1 (al1), which retained an ancestral expression pattern. The al2 stripe expression domain evolutionarily preceded the appearance of the DII pattern elements in multiple lineages, leading us to speculate that al2 represented preexisting positional information that may have facilitated DII evolution via a developmental drive mechanism. In contrast to butterfly eyespot patterns, which are often cited as a key example of developmental co-option of preexisting developmental genes, this study provides an example where the origin of a major color pattern element is associated with the evolution of a novel lepidopteran homeobox gene.

Martin A ，Reed RD 《-》

optix drives the repeated convergent evolution of butterfly wing pattern mimicry.

Mimicry--whereby warning signals in different species evolve to look similar--has long served as a paradigm of convergent evolution. Little is known, however, about the genes that underlie the evolution of mimetic phenotypes or to what extent the same or different genes drive such convergence. Here, we characterize one of the major genes responsible for mimetic wing pattern evolution in Heliconius butterflies. Mapping, gene expression, and population genetic work all identify a single gene, optix, that controls extreme red wing pattern variation across multiple species of Heliconius. Our results show that the cis-regulatory evolution of a single transcription factor can repeatedly drive the convergent evolution of complex color patterns in distantly related species, thus blurring the distinction between convergence and homology.

Reed RD ，Papa R ，Martin A ，Hines HM ，Counterman BA ，Pardo-Diaz C ，Jiggins CD ，Chamberlain NL ，Kronforst MR ，Chen R ，Halder G ，Nijhout HF ，McMillan WO ... -  《-》

Distal-less regulates eyespot patterns and melanization in Bicyclus butterflies.

Butterfly eyespots represent novel complex traits that display substantial diversity in number and size within and across species. Correlative gene expression studies have implicated a large suite of transcription factors, including Distal-less (Dll), Engrailed (En), and Spalt (Sal), in eyespot development in butterflies, but direct evidence testing the function of any of these proteins is still missing. Here we show that the characteristic two-eyespot pattern of wildtype Bicyclus anynana forewings is correlated with dynamic progression of Dll, En, and Sal expression in larval wings from four spots to two spots, whereas no such decline in gene expression ensues in a four-eyespot mutant. We then conduct transgenic experiments testing whether over-expression of any of these genes in a wild-type genetic background is sufficient to induce eyespot differentiation in these pre-patterned wing compartments. We also produce a Dll-RNAi transgenic line to test how Dll down-regulation affects eyespot development. Finally we test how ectopic expression of these genes during the pupal stages of development alters adults color patters. We show that over-expressing Dll in larvae is sufficient to induce the differentiation of additional eyespots and increase the size of eyespots, whereas down-regulating Dll leads to a decrease in eyespot size. Furthermore, ectopic expression of Dll in the early pupal wing led to the appearance of ectopic patches of black scales. We conclude that Dll is a positive regulator of focal differentiation and eyespot signaling and that this gene is also a possible selector gene for scale melanization in butterflies.

Monteiro A ，Chen B ，Ramos DM ，Oliver JC ，Tong X ，Guo M ，Wang WK ，Fazzino L ，Kamal F ... -  《-》