Ke Gao

The evolution of complex brains required the incorporation of newly evolved neurons into existing circuits, yet the genetic and developmental mechanisms enabling their integration remain poorly understood. Butterflies expanded their color vision by adding a second R7 photoreceptor per ommatidium, a rare departure from the conserved insect eye ground plan. Because each R7 makes an independent stochastic fate choice, this duplication increased the number of ommatidial types from two to three. We identified the genetic basis of this expansion and demonstrated how the brain accommodates the new input. R7 duplication was achieved by converting R3/4 cells to an R1/6 fate, triggering the R7 recruitment program on both sides of the ommatidium. By manipulating transcription factor expression in Drosophila , we engineered a “butterfly-fly” that recapitulates this ancient R7 duplication and three-type stochastic mosaic. In the fly brain, two R7 subtypes connect to specific types of Dm8 neurons, which are born in excess and undergo apoptosis if they fail to find synaptic partners. In our butterfly-fly model, these surplus Dm8s are immediately rescued and form subtype-appropriate connections. These findings suggest that population-level variation maintains a reservoir of potentially interacting neurons, providing a developmental substrate that allows the brain to immediately accommodate newly evolved neurons.

The evolution of complex brains required existing neurons and neural circuits to accommodate new inputs. The genetic and developmental mechanisms that enable such integration are largely unknown. Butterflies evolved more complex retinal mosaics through the addition of a second R7 color photoreceptor per ommatidium (unit eye). In Drosophila , the unique R7 makes a stochastic choice to express one of two opsin genes. In butterflies, the two R7s make independent stochastic cell fate choices in each ommatidium, producing three ommatidial types instead of two. Here, we investigate the developmental basis of this change and how the butterfly brain accommodates expanded sensory receptor input. We first identified the changes in gene expression that cause a second R7 cell to be specified. We then modified Drosophila retinas to have butterfly-like transcription factor expression, causing recruitment of an additional R7. The two R7s make independent stochastic choices, like butterflies, leading to three stochastically distributed ommatidial types. In Drosophila , the two R7 subtypes connect to their target neurons, either yDm8 or pDm8. Dm8 neurons of both types are born in excess and Dm8s that do not find connections with their cognate y or pR7s undergo apoptosis. In the presence of extra R7s in butterfly-like fly retinas, additional Dm8s are retained, leading to two Dm8s per medulla column that make appropriate connections with the matching R7 subtypes, facilitating the expansion of color vision. We propose that the presence of cells that would otherwise die provide developmental flexibility that can allow brains to accommodate newly evolved inputs.

A spectacular diversity of forms and features allow species to thrive in different environments, yet some structures remain relatively unchanged. Insect compound eyes are easily recognizable despite dramatic differences in visual abilities across species. It is unknown whether distant insect species use similar or different mechanisms to pattern their eyes or what types of genetic changes produce diversity of form and function. We find that flies, mosquitos, butterflies, moths, beetles, wasps, honeybees, and crickets use homologous developmental programs to pattern their retinas. Transcription factor expression can be used to establish homology of different photoreceptor (PR) types across the insects: Prospero (Pros) for R7, Spalt (Sal) for R7+R8, and Defective proventriculus (Dve) for R1-6. Using gene knockout (CRISPR/Cas9) in houseflies, butterflies, and crickets and gene knockdown (RNAi) in beetles, we found that like Drosophila , EGFR and Sevenless (Sev) signaling pathways are required to recruit motion and color vision PRs, though Drosophila have a decreased reliance on Sev signaling relative to other insects. Despite morphological and physiological variation across species, retina development passes through a highly conserved phylotypic stage when the unit eyes (ommatidia) are first patterned. This patterning process likely represents an “insect eye ground plan” that is established by an ancient developmental program. We identify three types of developmental patterning modifications (ground plan modification, nonstochastic patterns, and specialized regions) that allow for the diversification of insect eyes. We suggest that developmental divergence after the ground plan is established is responsible for the exceptional diversity observed across insect visual systems.

Given the limited availability of resources in nature, sexual attractiveness may trade off with immunocompetence, as the immunocompetence handicap hypothesis (ICHH) posits. In invertebrates, a direct link between trade‐offs through hormonal/molecular effectors in sexual signals and immunity has not been found so far. Here, we assessed how variation in sexual signals affected parasite infection in two sex pheromone selected lines of the moth Chloridea virescens: an attractive line with a low ratio of 16:Ald/Z11‐16:Ald and an unattractive line with a high ratio. When infecting these lines with an apicomplexan parasite, we found that the attractive Low line was significantly more susceptible to the parasite infection than the unattractive High line. Since the ratio difference between these two lines is determined by a delta‐11‐desturase, we hypothesized that this desaturase may have a dual role, i.e., in the quality of the sexual signal as well as an involvement in immune response, comparable to testosterone in vertebrates. However, when we used CRISPR/cas9 to knockout delta‐11‐desturase in the attractive Low line, we found that the pheromonal phenotype did change to that of the High line, but the infection susceptibility did not. Notably, when checking the genomic location of delta‐11‐desaturase in the C. virescens, we found that mucin is adjacent to delta‐11‐desaturase. When comparing the mucin sequences in both lines, we found four nonsynonymous SNPs in the coding sequence, as well as intronic variation between the two lines. These differences suggest that genetic hitchhiking may explain the variation in susceptibility to parasitic infection.

BACKGROUND: Geographic variation in male response to sex pheromone lures has been studied in the field in a number of moth species. However, only a few studies have investigated geographic variation in female calling and sex pheromone under field conditions. For an effective field implementation of sex pheromone lures, it is essential to know the local sex pheromone blend and local timing of sexual communication. We investigated the level and extent of geographic variation in the sexual communication of the important agricultural pest Helicoverpa armigera (Lepidoptera, Noctuidae) in three continents.RESULTS: We found there is no genetic variation in the calling behavior of H. armigera. In the female sex pheromone, we found more between‐population variation than within‐population variation. In male response experiments, we found geographic variation as well. Strikingly, when adding the antagonistic compound Z11‐16:OAc to the pheromone blend of H. armigera, significantly fewer males were caught in Australia and China, but not in Spain. This variation is likely not only due to local environmental conditions, such as photoperiod and temperature, but also to the presence of other closely related species with which communication interference may occur.Conclusion: Finding geographic variation in both the female sexual signal and the male response in this pest calls for region‐specific pheromone lures. Our study shows that the analysis of geographic variation in moth female sex pheromones as well as male responses is important for effectively monitoring pest species that occur around the globe. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The phylogenetic relationships of 16 species in 7 genera of butterflies belonging to the tribe Baorini in China were explored based on the partial sequences of three mitochondrial genes (Cytb, ND1 and 16S rDNA). Molecular phylogenetic trees were constructed using Maximum Likelihood (ML) and Bayesian Inference (BI) analyses. The monophyly of Baorini was confirmed with strong support. In addition, phylogenetic analyses suggest that Parnara, Baoris, Pelopidas and Caltoris are monophyletic. Baoris and Pelopidas are sister groups with strong support, whereas the relationships among Borbo, Pseudoborbo and Caltoris remain uncertain. A great differentiation was found between two subspecies of Parnara guttata, i.e., Pa. guttata guttata and Pa. guttata mangala in our molecular analysis results. Combined with their morphological differences, this leads us to suggest Pa. guttata mangala is an independent species.