Abstract
Butterflies have evolved different colour patterns on their dorsal and ventral wing surfaces to serve different signalling functions, yet the developmental mechanisms controlling surface-specific patterning are still unknown. Here, we mutate both copies of the transcription factor apterous in Bicyclus anynana butterflies using CRISPR/Cas9 and show that apterous A, expressed dorsally, functions both as a repressor and modifier of ventral wing colour patterns, as well as a promoter of dorsal sexual ornaments in males. We propose that the surface-specific diversification of wing patterns in butterflies proceeded via the co-option of apterous A or its downstream effectors into various gene regulatory networks involved in the differentiation of discrete wing traits. Further, interactions between apterous and sex-specific factors such as doublesex may have contributed to the origin of sexually dimorphic surface-specific patterns. Finally, we discuss the evolution of eyespot number diversity in the family Nymphalidae within the context of developmental constraints due to apterous regulation.
Highlights
Butterflies are a group of organisms well known for their diverse and colourful wing patterns
Owing to the dual role these patterns play in survival and mate selection, many butterflies have evolved a signal partitioning strategy where colour patterns appearing on the hidden dorsal surfaces tend to be bright and prominent, generally functioning in sexual signalling, whereas patterns on the exposed ventral surfaces tend to be cryptically coloured and most commonly serve to ward off predators [1,2]
The molecular mechanisms that lead to striking variations in the development of dorsal versus ventral surface-specific colour patterns remain unknown
Summary
Butterflies are a group of organisms well known for their diverse and colourful wing patterns. The molecular mechanisms that lead to striking variations in the development of dorsal versus ventral surface-specific colour patterns remain unknown Elucidating this process will help us understand the mechanism of diversification and specialization of wing patterns within the butterfly lineage. The candidate targets were manually designed by searching for a GGN18NGG sequence on the sense or antisense strand of apA and apB, preferably targeting the LIM and homeobox domains of the transcription factor (electronic supplementary material, table S1). They were blasted against the B. anynana genome on LepBase.org to check for off-target effects. Sequences from individuals with disruptions at the targeted regions were cloned into a PGEM-T Easy vector (Promega) and sequenced
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