Higher Diptera Research Articles

Cyp6g2 is the major P450 epoxidase responsible for juvenile hormone biosynthesis in Drosophila melanogaster

BackgroundJuvenile hormones (JH) play crucial role in regulating development and reproduction in insects. The most common form of JH is JH III, derived from MF through epoxidation by CYP15 enzymes. However, in the higher dipterans, such as the fruitfly, Drosophila melanogaster, a bis-epoxide form of JHB3, accounted most of the JH detected. Moreover, these higher dipterans have lost the CYP15 gene from their genomes. As a result, the identity of the P450 epoxidase in the JH biosynthesis pathway in higher dipterans remains unknown.ResultsIn this study, we show that Cyp6g2 serves as the major JH epoxidase responsible for the biosynthesis of JHB3 and JH III in D. melanogaster. The Cyp6g2 is predominantly expressed in the corpus allatum (CA), concurring with the expression pattern of jhamt, another well-studied gene that is crucial in the last steps of JH biosynthesis. Mutation in Cyp6g2 leads to severe disruptions in larval-pupal metamorphosis and exhibits reproductive deficiencies, exceeding those seen in jhamt mutants. Notably, Cyp6g2−/−::jhamt2 double mutants all died at the pupal stage but could be rescued through the topical application of JH analogs. JH titer analyses revealed that both Cyp6g2−/− mutant and jhamt2 mutant lacking JHB3 and JH III, while overexpression of Cyp6g2 or jhamt caused a significant increase in JHB3 and JH III titer.ConclusionsThese findings collectively established that Cyp6g2 as the major JH epoxidase in the higher dipterans and laid the groundwork for the further understanding of JH biosynthesis. Moreover, these findings pave the way for developing specific Cyp6g2 inhibitors as insect growth regulators or insecticides.

Twenty-seven ZAD-ZNF genes of Drosophila melanogaster are orthologous to the embryo polarity determining mosquito gene cucoid.

The C2H2 zinc finger gene cucoid establishes anterior-posterior (AP) polarity in the early embryo of culicine mosquitoes. This gene is unrelated to genes that establish embryo polarity in other fly species (Diptera), such as the homeobox gene bicoid, which serves this function in the traditional model organism Drosophila melanogaster. The cucoid gene is a conserved single copy gene across lower dipterans but nothing is known about its function in other species, and its evolution in higher dipterans, including Drosophila, is unresolved. We found that cucoid is a member of the ZAD-containing C2H2 zinc finger (ZAD-ZNF) gene family and is orthologous to 27 of the 91 members of this family in D. melanogaster, including M1BP, ranshi, ouib, nom, zaf1, odj, Nnk, trem, Zif, and eighteen uncharacterized genes. Available knowledge of the functions of cucoid orthologs in Drosophila melanogaster suggest that the progenitor of this lineage specific expansion may have played a role in regulating chromatin. We also describe many aspects of the gene duplication history of cucoid in the brachyceran lineage of D. melanogaster, thereby providing a framework for predicting potential redundancies among these genes in D. melanogaster.

Transient opening of tricellular vertices controls paracellular transport through the follicle epithelium during Drosophila oogenesis.

Paracellular permeability is regulated to allow solute transport or cell migration across epithelial or endothelial barriers. However, how cell-cell junction dynamics controls paracellular permeability is poorly understood. Here, we describe patency, a developmentally regulated process in Drosophila oogenesis, during which cell vertices in the follicular epithelium open transiently to allow paracellular transport of yolk proteins for uptake by the oocyte. We show that the sequential removal of E-cadherin, N-cadherin, NCAM/Fasciclin 2, and Sidekick from vertices precedes their basal-to-apical opening, while the subsequent assembly of tricellular occluding junctions marks the termination of patency and seals the paracellular barrier. E-cadherin-based adhesion is required to limit paracellular channel size, whereas stabilized adherens junctions, prolonged NCAM/Fasciclin 2 expression, blocked endocytosis, or increased actomyosin contractility prevent patency. Our findings reveal a key role of cell vertices as gateways controlling paracellular transport and demonstrate that dynamic regulation of adhesion and actomyosin contractility at vertices governs epithelial barrier properties.

Phylogeography of higher Diptera in glacial and postglacial grasslands in western North America

BackgroundPleistocene glaciations have had an important impact on the species distribution and community composition of the North American biota. Species survived these glacial cycles south of the ice sheets and/or in other refugia, such as Beringia. In this study, we assessed, using mitochondrial DNA from three Diptera species, whether flies currently found in Beringian grasslands (1) survived glaciation as disjunct populations in Beringia and in the southern refugium; (2) dispersed northward postglacially from the southern refugium; or (3) arose by a combination of the two. Samples were collected in grasslands in western Canada: Prairies in Alberta and Manitoba; the Peace River region (Alberta); and the southern Yukon Territory. We sequenced two gene regions (658 bp of cytochrome c oxidase subunit I, 510 bp of cytochrome b) from three species of higher Diptera: one with a continuous distribution across grassland regions, and two with disjunct populations between the regions. We used a Bayesian approach to determine population groupings without a priori assumptions and performed analysis of molecular variance (AMOVA) and exact tests of population differentiation (ETPD) to examine their validity. Molecular dating was used to establish divergence times.ResultsTwo geographically structured populations were found for all species: a southern Prairie and Peace River population, and a Yukon population. Although AMOVA did not show significant differentiation between populations, ETPD did. Divergence time between Yukon and southern populations predated the Holocene for two species; the species with an ambiguous divergence time had high haplotype diversity, which could suggest survival in a Beringian refugium.ConclusionsPopulations of Diptera in Yukon grasslands could have persisted in steppe habitats in Beringia through Pleistocene glaciations. Current populations in the region appear to be a mix of Beringian relict populations and, to a lesser extent, postglacial dispersal northward from southern prairie grasslands.

A review and illustrated description of Musca crassirostris, one of the most neglected haematophagous livestock flies

Tabanids, stomoxyine flies, hippoboscids and tsetse flies are the most well‐known brachyceran biting flies of livestock. Only a few other higher Diptera have developed the unique mouthparts required for blood feeding. These neglected blood feeders can also have direct effects on hosts through blood loss, and are likely to contribute to the transmission of pathogens. Musca crassirostris (Diptera: Muscidae) is one of the most abundant of the muscid flies with this haematophagous lifestyle; it is widespread in the Palaearctic, Afrotropical and Oriental regions. The present study reviews and summarizes the biology and morphology of this species, and its potential for impact on animals and humans. The study also provides a fully illustrated description of the fly to facilitate its identification, and reviews information on abundance, with a focus on recent trapping surveys in Thailand. When sampled using traps designed for other biting flies, M. crassirostris appears to be four and 45 times more abundant than stomoxyines and tabanids, respectively. High numbers of M. crassirostris in the vicinity of livestock have also been associated with outbreaks of disease, such as that of a fatal plague in bovine farms in Egypt. This calls for a reconsideration of its potential impacts on livestock economics and health, and thus the development of suitable control methods.

Comparative Evidence of an Exceptional Impact of Gene Duplication on the Developmental Evolution of Drosophila and the Higher Diptera

The importance of gene duplication in developmental body plan evolution is well established, but for many megadiverse clades such as true flies (Diptera), a comprehensive understanding is still just emerging through comparative genomics. In a survey of 377 developmental gene families, we found that in addition to the pea aphid, which has been previously shown to be genome-wide enriched with gene duplicates and was included as positive control, more than twice as many expanded developmental gene families were observed in Drosophila (49) compared to mosquito (21), flour beetle (20), and honey bee (14). Synonymous sequence divergence estimates and ortholog conservation analyses in additional dipteran genomes revealed that most Drosophila gene duplicates are ancient and accumulated during a time window that reaches back to the origin of brachyceran flies, approximately 180 million years ago. Further, available genetic data suggest that more than half of the Drosophila developmental gene duplicates remained partially or even fully redundant despite their ancient separation. We therefore speculate that the exceptional accumulation of developmental gene duplicates in Drosophila and the higher Diptera was proximally driven by the evolution of fast development, benefiting from increased genetic robustness. At the same time, the concomitant increase of opportunities for gene duplicate diversification appears to have been a source for developmental and phenotypic innovation during the unparalleled diversification of brachyceran Diptera.

Specific expression and function of the Six3 optix in Drosophila serially homologous organs.

ABSTRACTOrgan size and pattern results from the integration of two positional information systems. One global information system, encoded by the Hox genes, links organ type with position along the main body axis. Within specific organs, local information is conveyed by signaling molecules that regulate organ growth and pattern. The mesothoracic (T2) wing and the metathoracic (T3) haltere of Drosophila represent a paradigmatic example of this coordination. The Hox gene Ultrabithorax (Ubx), expressed in the developing T3, selects haltere identity by, among other processes, modulating the production and signaling efficiency of Dpp, a BMP2-like molecule that acts as a major regulator of size and pattern. However, the mechanisms of the Hox-signal integration in this well-studied system are incomplete. Here, we have investigated this issue by studying the expression and function of the Six3 transcription factor optix during Drosophila wing and haltere development. We find that in both organs, Dpp defines the expression domain of optix through repression, and that the specific position of this domain in wing and haltere seems to reflect the differential signaling profile among these organs. We show that optix expression in wing and haltere primordia is conserved beyond Drosophila in other higher diptera. In Drosophila, optix is necessary for the growth of wing and haltere. In the wing, optix is required for the growth of the most anterior/proximal region (the ‘marginal cell’) and for the correct formation of sensory structures along the proximal anterior wing margin; the halteres of optix mutants are also significantly reduced. In addition, in the haltere, optix is necessary for the suppression of sensory bristles.

Multispecies Analysis of Expression Pattern Diversification in the Recently Expanded Insect Ly6 Gene Family.

Gene families often consist of members with diverse expression domains reflecting their functions in a wide variety of tissues. However, how the expression of individual members, and thus their tissue-specific functions, diversified during the course of gene family expansion is not well understood. In this study, we approached this question through the analysis of the duplication history and transcriptional evolution of a rapidly expanding subfamily of insect Ly6 genes. We analyzed different insect genomes and identified seven Ly6 genes that have originated from a single ancestor through sequential duplication within the higher Diptera. We then determined how the original embryonic expression pattern of the founding gene diversified by characterizing its tissue-specific expression in the beetle Tribolium castaneum, the butterfly Bicyclus anynana, and the mosquito Anopheles stephensi and those of its duplicates in three higher dipteran species, representing various stages of the duplication history (Megaselia abdita, Ceratitis capitata, and Drosophila melanogaster). Our results revealed that frequent neofunctionalization episodes contributed to the increased expression breadth of this subfamily and that these events occurred after duplication and speciation events at comparable frequencies. In addition, at each duplication node, we consistently found asymmetric expression divergence. One paralog inherited most of the tissue-specificities of the founder gene, whereas the other paralog evolved drastically reduced expression domains. Our approach attests to the power of combining a well-established duplication history with a comprehensive coverage of representative species in acquiring unequivocal information about the dynamics of gene expression evolution in gene families.

Organophosphate and Pyrethroid Hydrolase Activities of Mutant Esterases from the Cotton Bollworm Helicoverpa armigera

Two mutations have been found in five closely related insect esterases (from four higher Diptera and a hymenopteran) which each confer organophosphate (OP) hydrolase activity on the enzyme and OP resistance on the insect. One mutation converts a Glycine to an Aspartate, and the other converts a Tryptophan to a Leucine in the enzymes’ active site. One of the dipteran enzymes with the Leucine mutation also shows enhanced activity against pyrethroids. Introduction of the two mutations in vitro into eight esterases from six other widely separated insect groups has also been reported to increase substantially the OP hydrolase activity of most of them. These data suggest that the two mutations could contribute to OP, and possibly pyrethroid, resistance in a variety of insects. We therefore introduced them in vitro into eight Helicoverpa armigera esterases from a clade that has already been implicated in OP and pyrethroid resistance. We found that they do not generally enhance either OP or pyrethroid hydrolysis in these esterases but the Aspartate mutation did increase OP hydrolysis in one enzyme by about 14 fold and the Leucine mutation caused a 4–6 fold increase in activity (more in one case) of another three against some of the most insecticidal isomers of fenvalerate and cypermethrin. The Aspartate enzyme and one of the Leucine enzymes occur in regions of the H. armigera esterase isozyme profile that have been previously implicated in OP and pyrethroid resistance, respectively.

The mushroom bodies of the lower nematocera: A link between those of the higher diptera and other mecopteroids

Nematoceran Diptera are nonuniform in the structure of their mushroom bodies. Members of the more basal families (Ptychopteridae, Pediciidae, and Tipulidae) have bipartite mushroom bodies, characteristic of members of the other mecopteroid complex orders. In members of Bibionomorpha (Bibionidae and Anisopodidae), tripartite mushroom bodies have been found characteristic of Brachycera Orthorrhapha.

Insect photoperiodism: seeing the light

This review examines the spectral sensitivities of photoperiodic responses in insects and mites in relation to circadian‐based models for the photoperiodic clock. It concludes that there are probably a number of different photoreceptors at both the organ and molecular levels. These latter probably fall into two classes: (i) a blue‐light sensitive photoreceptor and (ii) a range of opsins (i.e. opsin proteins conjugated with a vitamin A based pigment) absorbing light at a range of wavelengths. In flesh flies (Sarcophaga spp. and possibly other higher Diptera), which are considered to exemplify the ‘external coincidence’ model, entrainment of the photoperiodic oscillator probably involves a blue‐light photoreceptor of Drosophila‐type CRYPTOCHROME (CRY1) absorbing maximally at approximately 470 nm, whereas opsins absorbing at longer wavelengths may be involved in the photo‐inductive process (diapause/nondiapause regulation) that occurs when dawn light coincides with the photo‐inducible phase. In the parasitic wasp Nasonia vitripennis, on the other hand, a species that lacks CRY1 but expresses the nonphotosensitive ‘mammalian‐type’ CRY2, and is considered to exemplify ‘internal coincidence’, entrainment of the dawn and dusk oscillators may involve opsin‐based photoreceptors absorbing light at longer wavelengths as far as the red end of the spectrum. In the Lepidoptera, which express both CRY1 and CRY2, properties of both external and internal coincidence may be evident. The presence or absence of cry1 in the genome may thus emerge as a key to the photoperiodic mechanism on its light input pathway.

Observations on antennal morphology in Diptera, with particular reference to the articular surfaces between segments 2 and 3 in the Cyclorrhapha

The main features of antennal segments 2 and 3 seen in the higher Diptera are described, including many that are not or inadequately covered in available publications. The following terms are introduced or clarified: for segment 2 or the pedicel—annular ridge, caestus, chin, collar, conus, distal articular surface, encircling furrow, foramen of articulation, foraminal cusp, foraminal ring, pedicellar button, pedicellar cup, rim; for segment 3 or the postpedicel—basal foramen, basal hollow, basal stem, postpedicellar pouch, sacculus, scabrous tongue, sub-basal caecum; for the stylus or arista—stylar goblet. Particular attention is given to the occurrence and position of the pedicellar button. The button is the cuticular component of a chordotonal organ, which perhaps has the role of a baroreceptor. It is present in the majority of families of Diptera, and possibly was present in the ancestral dipteran. Some generalizations about antennal structure are made, and a diagram showing the main trends in antennal evolution in the Eremoneura is provided. The general form of the antenna shows a transition from approximate radial symmetry (e.g., in Empis, Microphor, and Opetia) through to superficial bilateral symmetry (in many taxa of Eumuscomorpha), though there is usually much asymmetry in detail. More detailed descriptions and illustrations are given for selected taxa of Cyclorrhapha. The phenomenon of an additional concealed segment-like structure between segments 2 and 3, found among the Chloropidae, Pyrgotidae, etc., and formed from the basally flexible conus, is described. Some antennal features of the Calyptratae suggest a relationship to the Tephritoidea. Critical comments are made with regard to the recently published phylogenetic association of the Ironomyiidae with the Phoridae and the Pallopteridae with the Neurochaetidae. In discussing relationships of some taxa, a few non-antennal features, some needing further study, are mentioned, e.g., variation in separation of abdominal tergites 1 and 2 in the Opetiidae and other lower cyclorrhaphous families; the presence of supplementary claw-like terminal tarsal processes in the Lonchopteridae; the apparent restriction of the presence of barbed macrotrichia to the Phoridae, among lower cyclorrhaphans; variation in structure of the prelabrum in the Pyrgotidae; the microstructure of the facial cuticle in the Syringogastridae as compared with that of other families; the calyptrate-like development of the squama in some tephritoid taxa; variation in the subscutellum in the Conopidae; a feature of the larval posterior spiracles diagnostic for Coelopidae.

Larval fat body cells die during the early pupal stage in the frame of metamorphosis remodelation in Bombyx mori

In holometabolus insects, morphology of the larval fat body is remodeled during metamorphosis. In higher Diptera, remodeling of the fat body is achieved by cell death of larval fat body cells and differentiation of the adult fat body from primordial cells. However, little is known about remodeling of the fat body at pupal metamorphosis in Lepidoptera. In this study, we found that cell death of the larval fat body in Bombyx mori occurs at shortly after pupation. About 30% of the fat body cells underwent cell death on days 1 and 2 after pupation. The cell death involved genomic DNA fragmentation, a characteristic of apoptosis. Surgical manipulation and in vitro culture of fat body cells revealed that 20-hydroxyecdysone and juvenile hormone had no effect on either initiation or progression of cell death. During cell death, a large increase in activity of caspase-3, a key enzyme of cell death, was observed. Western blot analysis of the active form of caspase-3-like protein revealed that the length of caspase-3 of B. mori was much larger than that of caspase-3 in other species. The results suggest that larval fat body cells of B. mori are removed through cell death, which is mediated by a caspase probably categorized in a novel family.

Sexually dimorphic regulation of the Wingless morphogen controls sex-specific segment number in Drosophila

Sexual dimorphism is widespread throughout the metazoa and plays important roles in mate recognition and preference, sex-based niche partitioning, and sex-specific coadaptation. One notable example of sex-specific differences in insect body morphology is presented by the higher diptera, such as Drosophila, in which males develop fewer abdominal segments than females. Because diversity in segment number is a distinguishing feature of major arthropod clades, it is of fundamental interest to understand how different numbers of segments can be generated within the same species. Here we show that sex-specific and segment-specific regulation of the Wingless (Wg) morphogen underlies the development of sexually dimorphic adult segment number in Drosophila. Wg expression is repressed in the developing terminal male abdominal segment by the combination of the Hox protein Abdominal-B (Abd-B) and the sex-determination regulator Doublesex (Dsx). The subsequent loss of the terminal male abdominal segment during pupation occurs through a combination of developmental processes including segment compartmental transformation, apoptosis, and suppression of cell proliferation. Furthermore, we show that ectopic expression of Wg is sufficient to rescue this loss. We propose that dimorphic Wg regulation, in concert with monomorphic segment-specific programmed cell death, are the principal mechanisms of sculpting the sexually dimorphic abdomen of Drosophila.

Clusters of Temporal Discordances Reveal Distinct Embryonic Patterning Mechanisms in Drosophila and Anopheles

Author SummaryLinking genotype to phenotype is a major undertaking in modern biological research. A variety of strategies are used but have generally failed to explain the maintenance and acquisition of new phenotypic traits in changing populations. We propose that whole-genome cross-species comparisons can be used to identify gene clusters underlying phenotypic variation. In the present study we used gene expression datasets collected during fruit fly and mosquito embryogenesis to identify temporal changes in gene expression. We found that differentially represented tissue types (such as extraembryonic serosa) were clearly manifested by clusters of local discordances in gene expression. Discordances were also observed for a suite of maternally expressed genes, consistent with the notion that the abrupt maternal-zygotic transition seen in Drosophila is an evolutionary innovation of higher Diptera. We propose that gene clustering by expression discordance can be used to determine the genetic basis of phenotypic variation.

Effects of Habitat Size, Vegetation Cover, and Surrounding Land Use on Diptera Diversity in Temperate Nearctic Bogs

Higher Diptera (Schizophora) are taxonomically and ecologically diverse, and include bog specialist and bog-associated species known to respond to peatland disturbance. We examined the effects of three factors (habitat size, vegetation cover and surrounding land use measured in concentric circles of 500, 1000, 1500, and 2000 m radii from the sampling location) on Schizophora species richness, diversity, and composition in six temperate eastern Nearctic bogs. A total of 381 species of Schizophora were collected with observed species richness among sites ranging from 96 to 182. Assemblages in apparently similar peatlands were highly variable, but characterized by a few highly dominant species, most of which are not peatland specialists. Bog size had no influence on species richness or diversity. Vegetation cover at the sampling sites and surrounding land use at the largest scales measured (1500 and 2000 m) both influenced species assemblages.

Spatial scale and nested patterns of beta-diversity in temperate forest Diptera

Abstract. 1. We examined whether local assemblages of temperate forest Diptera are structured or simply random sets of species, and at what scale any patterns become apparent. Nested patterns of α-, β-, and γ-diversity in higher Diptera (Schizophora) were described using additive partitioning, to determine the spatial scale contributing the most to species richness. Patterns were examined for Schizophora, two subordinate taxonomic groups (Calyptratae, Acalyptratae) and common versus rare species. 2. A hierarchically nested design was used with three spatial scales: three sites, four stands per site, six trees per stand. Flies were sampled using trunk traps and flight intercept traps in June-July 2008 in sugar maple stands in southwestern Quebec forest fragments. 3. Species diversity and composition were non-random at all scales, and varied across scales and among subgroups. Smaller scales (β1: between trees) seem to structure species composition of Schizophora, Calyptratae and Acalyptratae. Common species varied more at finer scales (α1: within trees); rare species varied more at large scales (β3: between sites). The scale contributing the most to γ-diversity varied across the groups, but β1 was the overall trend. 4. Diversity patterns differed from those in other forest arthropod taxa, in which larger scales drive overall patterns. This may be explained by the high ecological diversity in Diptera, in which species occurrence is often dictated by the presence of ephemeral, patchy resources within larger sites. The overall similarity from site to site is difficult to explain without genetic evidence as to the extent of dispersal of Diptera between sites.

Rodney Warren Rickards 1934 - 2007

Rod Rickards graduated with first class honours from the University of Sydney in 1955 and began his academic career at the University of Manchester in close association with Arthur Birch. In 1966 he returned to Australia to a foundation appointment in the Research School of Chemistry at the Australian National University, where he spent the remainder of his career. His research was primarily concerned with the organic and biological chemistry of compounds of medical, biological, agricultural and veterinary importance, and was characterized by an integration of organic synthesis, biomimetic synthesis, structural and stereochemical studies, and biosynthetic studies using isotopically labelled precursors in vivo. His interests ranged widely and included antibiotics, regulatory factors that initiate antibiotic production and control cell differentiation and sexuality in microorganisms, elicitors that communicate between bacteria and plants, mammalian hormones of the prostaglandin group that control many aspects of human physiology, juvenile hormones, which mediate the development and reproductive physiology of higher dipteran insects and the therapeutically active components of Cannabis resin.

Rapid evolution of a novel signalling mechanism by concerted duplication and divergence of a BMP ligand and its extracellular modulators

Gene duplication and divergence is widely considered to be a fundamental mechanism for generating evolutionary novelties. The Bone Morphogenetic Proteins (BMPs) are a diverse family of signalling molecules found in all metazoan genomes that have evolved by duplication and divergence from a small number of ancestral types. In the fruit fly Drosophila, there are three BMPs: Decapentaplegic (Dpp) and Glass bottom boat (Gbb), which are the orthologues of vertebrate BMP2/4 and BMP5/6/7/8, respectively, and Screw (Scw), which, at the sequence level, is equally divergent from Dpp and Gbb. It has recently been shown that Scw has arisen from a duplication of Gbb in the lineage leading to higher Diptera. We show that since this duplication event, Gbb has maintained the ancestral BMP5/6/7/8 functionality while Scw has rapidly diverged. The evolution of Scw was accompanied by duplication and divergence of a suite of extracellular regulators that continue to diverge together in the higher Diptera. In addition, Scw has become restricted in its receptor specificity: Gbb proteins can signal through the Type I receptors Thick veins (Tkv) and Saxophone (Sax), while Scw signals through Sax. Thus, in a relatively short span of evolutionary time, the duplication event that gave rise to Scw produced not only a novel ligand but also a novel signalling mode that is functionally distinct from the ancestral Gbb mode. Our results demonstrate the plasticity of the BMP pathway not only in evolving new family members and new functions but also new signalling modes by redeploying key regulators in the pathway.

A systematic analysis of the gap gene system in the moth midge Clogmia albipunctata

The segmentation gene hierarchy of Drosophila melanogaster represents one of the best understood of the gene networks that generate pattern during embryogenesis. Some components of this network are ancient, while other parts of the network have evolved within the higher Diptera. To further understand the evolution of this gene network, we are studying the role of gap genes in a representative of a basally diverging dipteran lineage, the moth midge Clogmia albipunctata. We have isolated orthologues of all of the Drosophila trunk gap genes from Clogmia, and determined their domains of expression during the blastoderm stage of development, in relation to one another, and in relation to the expression of even-skipped (Calb-eve), a component of the pair-rule system that is directly regulated by the gap genes in Drosophila. We find that hunchback (Calb-hb), Krüppel (Calb-Kr), knirps (Calb-knl), giant (Calb-gt) and tailless (Calb-tll) are all expressed in patterns consistent with a gap segmentation role during blastoderm formation, but huckebein (Calb-hkb) is not. In the anterior half of the embryo, the relative positions of the gap gene expression domains in relation to one another, and in relation to the eve stripes, are rather well conserved. In the posterior half of the embryo, there are significant differences. Posteriorly, Calb-gt is expressed only transiently and very weakly, in a domain that overlaps entirely with that of Calb-knl. At late blastoderm stages, none of the candidate genes we have tested is expressed in the region between the posterior Calb-knl domain and Calb-tll. It is likely that the regulation of Calb-eve expression in this posterior region depends on combinations of gap gene factors that differ from those utilised for the same stripes in Drosophila. Both the gap and the pair-rule patterns of gene expression are dynamic in Clogmia, as they are in Drosophila, shifting anteriorly as blastoderm development proceeds.