CRISPR/Cas9 Deletions in a Conserved Exon of Distal-Less Generates Gains and Losses in a Recently Acquired Morphological Novelty in Flies

Abstract

Distal-less has been repeatedly co-opted for the development of many novel traits. Here, we document its curious role in the development of a novel abdominal appendage (''sternite brushes'') in sepsid flies. CRISPR/Cas9 deletions in the homeodomain result in losses of sternite brushes, demonstrating that Distal-less is necessary for their development. However, deletions in the upstream coding exon (Exon 2) produce losses or gains of brushes. A dissection of Exon 2 reveals that the likely mechanism for gains involves a deletion in an exon-splicing enhancer site that leads to exon skipping. Such contradictory phenotypes are also observed in butterflies, suggesting that mutations in the conserved upstream regions have the potential to generate phenotypic variability in insects that diverged 300 million years ago. Our results demonstrate the importance of Distal-less for the development of a novel abdominal appendage in insects and highlight how site-specific mutations in the same exon can produce contradictory phenotypes.

Demonstrating sexual selection by cryptic female choice on male genitalia: What is enough?

“…Male genitalia are used much more than female genitalia (e.g., Richards , Tuxen ; Scudder ; see also lists in Eberhard ), despite the fact that taxonomists routinely examine both males and females, and attempt to distinguish the species identities of both. The greater practical difficulty of observing female genitalia because some structures are internal does not explain their greater uniformity in the many others, in which species‐specific male genital structures contact sites on the female's external surface that are easily observed and are more uniform than the corresponding male structures (to cite a few: bumblebees—Richards ; many nematocerous flies—Wood ; sepsid flies—Eberhard , ; Rajaratman ; ladybird beetles—Eberhard ; roaches—Beier ; Scudder ; embiopterans—Ross ; and many leidopterans—Scudder ; Drummond ).…”

“…); five genera of sepsid flies (Eberhard , , , , ; Rajaratnam et al. ); a tiphiid wasp ( Aelurus ) (Eberhard ); the house mouse Mus musculus (Diamond ); and the cactus mouse Peromyscus eremicus (where it elicits physiological changes in the female that are associated with implantation of embryos in the uterus) (Dewsbury and Estep ). Genital stridulation or “singing” occurs in a tipulid fly (Eberhard and Gelhaus ) and (probably) a moth (Forbes ) (see also Eberhard for rhythmic genital movements during copulation in at least 67 of the 107 insect and spider species observed).…”

Temporal flexibility of gene regulatory network underlies a novel wing pattern in flies

“…Taken together, these results show that the Hedgehog circuit is flexible over time and emphasize the possibility that en is coopted partly independently from its wing disc network in S. leonensis to its novel expression pattern prefiguring the wing white spots. Examples of partial GRN recruitment are scarce, but such molecular events have been proposed to underlie the development of abdominal appendages in sepsid flies (72,73), the formation of eyespots in butterflies (74,75), and the origin of gin-trap in beetle pupae (76).…”

Distinguishing serial homologs from novel traits: Experimental limitations and ideas for improvements

“…Here, we have to address the origin of spider spinnerets, [ 34 ] abdominal appendages of lepidopterans, sawflies, or scorpion fly larvae, [ 35 ] and sepsid fly male abdominal appendages. [ 36 ] All these traits still need to be approached experimentally using novel powerful genetic technologies.…”