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Summary statementThe genesvestigial, scallopedandwinglesscomprise a conserved regulatory module that was co-opted repeatedly for the evolution of flat structures, such as insect wings, and crustacean carapace, tergites and coxal plates.SummaryHow novelties arise is a key question in evolutionary developmental biology. The crustacean carapace is a novelty that evolved in the early Cambrian. In an extant crustacean,Daphnia magna, the carapace grows from the body wall as a double-layered sheet with a specialized margin. We show that the growing margin of this carapace expressesvestigial, scallopedandwingless, genes that are known to play key roles in regulating growth at the insect wing margin. RNAi-mediated knockdown ofscallopedandwinglessimpair carapace development, indicating that carapace and wing might share a common mechanism for margin outgrowth. However, carapace and wings arise in different parts of the body and their margins have different orientations, arguing that these structures have independent evolutionary origins. We show thatscallopedis also expressed at the margin of unrelated flat outgrowths (tergites and coxal plates) in the distantly related crustaceanParhyale hawaiensis. Based on these observations, we propose that thevestigial-scalloped-winglessgene module has a common role in the margin of diverse flat structures, originating before the divergence of major crustacean lineages and the emergence of insects. Repeated co-option of this module occurred independently in the carapace, wing and other flat outgrowths, underpinning the evolution of distinct novelties in different arthropod lineages. |
