Transcriptome analysis reveals wingless regulates neural development and signaling genes in the region of wing pigmentation of a polka-dotted fruit fly

Thermal plasticity of wing size and wing spot size in Drosophila guttifera

Thermal plasticity of melanin pigmentation patterns in Drosophila species has been studied as a model to investigate developmental mechanisms of phenotypic plasticity. The developmental process of melanin pigmentation patterns on wings of Drosophila is divided into two parts, prepattern specification during the pupal period and wing vein-dependent transportation of melanin precursors after eclosion. Which part can be affected by thermal changes? To address this question, we used polka-dotted melanin spots on wings of Drosophila guttifera, whose spot areas are specified by wingless morphogen. In this research, we reared D. guttifera at different temperatures to test whether wing spots show thermal plasticity. We found that wing size becomes larger at lower temperature and that different spots have different reaction norms. Furthermore, we changed the rearing temperature in the middle of the pupal period and found that the most sensitive developmental periods for wing size and spot size are different. The results suggest that the size control mechanisms for the thermal plasticity of wing size and spot size are independent. We also found that the most sensitive stage for spot size was part of the pupal period including stages at which wingless is expressed in the polka-dotted pattern. Therefore, it is suggested that temperature change might affect the prepattern specification process and might not affect transportation through wing veins.

The Genetic Mechanisms Underlying the Concerted Expression of the yellow and tan Genes in Complex Patterns on the Abdomen and Wings of Drosophila guttifera

How complex morphological patterns form is an intriguing question in developmental biology. However, the mechanisms that generate complex patterns remain largely unknown. Here, we sought to identify the genetic mechanisms that regulate the tan (t) gene in a multi-spotted pigmentation pattern on the abdomen and wings of Drosophila guttifera. Previously, we showed that yellow (y) gene expression completely prefigures the abdominal and wing pigment patterns of this species. In the current study, we demonstrate that the t gene is co-expressed with the y gene in nearly identical patterns, both transcripts foreshadowing the adult abdominal and wing melanin spot patterns. We identified cis-regulatory modules (CRMs) of t, one of which drives reporter expression in six longitudinal rows of spots on the developing pupal abdomen, while the second CRM activates the reporter gene in a spotted wing pattern. Comparing the abdominal spot CRMs of y and t, we found a similar composition of putative transcription factor binding sites that are thought to regulate the complex expression patterns of both terminal pigmentation genes y and t. In contrast, the y and t wing spots appear to be regulated by distinct upstream factors. Our results suggest that the D. guttifera abdominal and wing melanin spot patterns have been established through the co-regulation of y and t, shedding light on how complex morphological traits may be regulated through the parallel coordination of downstream target genes.

From Aedes to Zeugodacus: a review of dipteran body coloration studies regarding evolutionary developmental biology, pest control, and species discovery

Over the past two decades, evo-devo (evolution of development) studies have elucidated genetic mechanisms underlying novel dipteran body color patterns. Here we review the most recent developments, which show some departure from the model organism Drosophila melanogaster, leading the field into the investigation of more complex color patterns. We also discuss how the robust application of transgenic techniques has facilitated the study of many non-model pest species. Furthermore, we see that subtle pigmentation differences guide the discovery and description of new dipterans. Therefore, we argue that the existence of new field guides and the prevalence of pigmentation studies in non-model flies will enable scientists to adopt uninvestigated species into the lab, allowing them to study novel morphologies.

The color pattern inducing gene wingless is expressed in specific cell types of campaniform sensilla of a polka-dotted fruit fly, Drosophila guttifera

A polka-dotted fruit fly, Drosophila guttifera, has a unique pigmentation pattern on its wings and is used as a model for evo-devo studies exploring the mechanism of evolutionary gain of novel traits. In this species, a morphogen-encoding gene, wingless, is expressed in species-specific positions and induces a unique pigmentation pattern. To produce some of the pigmentation spots on wing veins, wingless is thought to be expressed in developing campaniform sensillum cells, but it was unknown which of the four cell types there express(es) wingless. Here we show that two of the cell types, dome cells and socket cells, express wingless, as indicated by in situ hybridization together with immunohistochemistry. This is a unique case in which non-neuronal SOP (sensory organ precursor) progeny cells produce Wingless as an inducer of pigmentation pattern formation. Our finding opens a path to clarifying the mechanism of evolutionary gain of a unique wingless expression pattern by analyzing gene regulation in dome cells and socket cells.

The modular expression patterns of three pigmentation genes prefigure unique abdominal morphologies seen among three Drosophila species

To understand how novel animal body colorations emerged, one needs to ask how the development of color patterns differs among closely related species. Here we examine three species of fruit flies - Drosophila guttifera (D. guttifera), D. palustris, and D. subpalustris - displaying a varying number of abdominal spot rows. Through in situ hybridization experiments, we examine the mRNA expression patterns for the pigmentation genes Dopa decarboxylase (Ddc), tan (t), and yellow (y) during pupal development. Our results show that Ddc, t, and y are co-expressed in modular, identical patterns, each foreshadowing the adult abdominal spots in D. guttifera, D. palustris, and D. subpalustris. We suggest that differences in the expression patterns of these three genes partially underlie the morphological diversity of the quinaria species group.

Evolution of wing pigmentation in Drosophila: Diversity, physiological regulation, and cis-regulatory evolution

Fruit flies (Drosophila and its close relatives, or “drosophilids”) are a group that includes an important model organism, Drosophila melanogaster, and also very diverse species distributed worldwide. Many of these species have black or brown pigmentation patterns on their wings, and have been used as material for evo‐devo research. Pigmentation patterns are thought to have evolved rapidly compared with body plans or body shapes; hence they are advantageous model systems for studying evolutionary gains of traits and parallel evolution. Various groups of drosophilids, including genus Idiomyia (Hawaiian Drosophila), have a variety of pigmentations, ranging from simple black pigmentations around crossveins to a single antero‐distal spot and a more complex mottled pattern. Pigmentation patterns are sometimes obviously used for sexual displays; however, in some cases they may have other functions. The process of wing formation in Drosophila, the general mechanism of pigmentation formation, and the transport of substances necessary for pigmentation, including melanin precursors, through wing veins are summarized here. Lastly, the evolution of the expression of genes regulating pigmentation patterns, the role of cis‐regulatory regions, and the conditions required for the evolutionary emergence of pigmentation patterns are discussed. Future prospects for research on the evolution of wing pigmentation pattern formation in drosophilids are presented, particularly from the point of view of how they compare with other studies of the evolution of new traits.