Project description:In the Paleozoic era, more than 400 Ma, a number of insect groups continued molting after forming functional wings. Today, however, flying insects stop molting after metamorphosis when they become fully winged. The only exception is the mayflies (Paleoptera, Ephemeroptera), which molt in the subimago, a flying stage between the nymph and the adult. However, the identity and homology of the subimago still is underexplored. Debate remains regarding whether this stage represents a modified nymph, an adult, or a pupa like that of butterflies. Another relevant question is why mayflies have the subimago stage despite the risk of molting fragile membranous wings. These questions have intrigued numerous authors, but nonetheless, clear answers have not yet been found. By combining morphological studies, hormonal treatments, and molecular analysis in the mayfly Cloeon dipterum, we found answers to these old questions. We observed that treatment with a juvenile hormone analog in the last nymphal instar stimulated the expression of the Kr-h1 gene and reduced that of E93, which suppress and trigger metamorphosis, respectively. The regulation of metamorphosis thus follows the MEKRE93 pathway, as in neopteran insects. Moreover, the treatment prevented the formation of the subimago. These findings suggest that the subimago must be considered an instar of the adult mayfly. We also observed that the forelegs dramatically grow between the last nymphal instar, the subimago, and the adult. This necessary growth spread over the last two stages could explain, at least in part, the adaptive sense of the subimago.
Project description:The great capability of insects to adapt to new environments promoted their extraordinary diversification, resulting in the group of Metazoa with the largest number of species distributed worldwide. To understand this enormous diversity, it is essential to investigate lineages that would allow the reconstruction of the early events in the evolution of insects. However, research on insect ecology, physiology, development and evolution has mostly focused on few well-established model species. The key phylogenetic position of mayflies within Paleoptera as the sister group of the rest of winged insects and life history traits of mayflies make them an essential order to understand insect evolution. Here, we describe the establishment of a continuous culture system of the mayfly Cloeon dipterum and a series of experimental protocols and omics resources that allow the study of its development and its great regenerative capability. Thus, the establishment of Cloeon as an experimental platform paves the way to understand genomic and morphogenetic events that occurred at the origin of winged insects.
Project description:Testing for toxicity in a number of aquatic organisms is necessary for risk assessments of substances. Yet, aquatic larvae of the so-called EPT (Ephemeroptera, Plecoptera, Trichoptera) taxa are regularly exposed to several environmental contaminants and have been demonstrated to be extremely vulnerable to a variety of environmental pollutants. These results show that existing toxicity testing can result in an underestimating of the risk for EPT taxa and that more toxicity data using EPT taxonomic representatives are needed. Unfortunately, there is a dearth of standardized test techniques and scant published data, particularly for European EPT species. Our study's objective was to create a testing framework for a variety of endpoints in the mayfly Cloeon dipterum. Due to its high prevalence in local waterbodies and its brief lifecycle of a few weeks in the right environmental conditions, C. dipterum was selected as the test organism. To this end, two chronic toxicity tests with semi-static test design and two media renewal per week were performed. Small larvae in the stage L3 based on the wing pad development described by Cianciara (1976) were used in the tests. Four replicates per test concentration and control containing five individuals per replicate were installed. The emergence was determined daily on working days. The tests were conducted at a temperature of 20 °C (± 1 °C) and the illumination was < 1 µE m2s 1 with a light and dark rhythm of 16:8 h. The physico-chemical parameters pH, oxygen concentration, and oxygen saturation were measured using the multiparameter device WTW Multi 1970i at test start, throughout each media renewal, and at test end. Continuous temperature measurements were taken, and weekly lighting assessments were made. Fipronil was administered to C. dipterum larvae in the long-term exposure experiment at nominal concentrations ranging from 0.038 to 0.60 g/L. This test was conducted for 38 days until all larvae had emerged. In the short-term exposure experiment, C. dipterum larvae were exposed to Fipronil in nominal concentrations between 0.038 and 0.30 µg/L for a test duration of seven days. At test end, the larvae were sampled for transcriptome analysis.
Project description:Understanding how novel complex traits originate is a foundational challenge in evolutionary biology. Yet how descent with modification in developmental evolution may lead to morphological innovation remains poorly understood. We investigated the origin of thoracic horns in scarabaeine beetles, one of the most dramatic classes of secondary sexual traits in the animal kingdom. We show that thoracic horns derive from bilateral source tissues, that diverse wing genes are functionally required for instructing this process, and that in the absence of Hox-input thoracic horn primordia transform to contribute to ectopic wings. Once induced, however, the transcriptional profile of thoracic horns diverges markedly from that of wings and other wing serial homologs. Our results provide evidence for the serial homology between thoracic horns and insects wings, and suggest that other insect innovations may similarly derive from wing serial homologs and the concomitant recruitment of diverse genes from outside a wing formation context.
Project description:<p>Aquatic insects are well-adapted to freshwater environments, but metabolic mechanisms of such adaptations, particularly to primary environmental factors (e.g., hypoxia, water pressure, dark light and abundant microbes), are poorly known. Most firefly species (Coleoptera: Lampyridae) are terrestrial, but the larvae of a few species are aquatic. We generated 24 global metabolomic profiles of larvae and adults of <em>Aquatica leii</em> (freshwater) and <em>Lychnuris praetexta</em> (terrestrial) to identify freshwater adaptation-related metabolites (AARMs). We identified 110 differentially abundant metabolites (DAMs) in <em>A. leii</em> (adults vs aquatic larvae) and 183 DAMs in <em>L. praetexta</em> (adults vs terrestrial larvae). Furthermore, 100 DAMs specific to aquatic <em>A. leii</em> larvae were screened as AARMs via interspecific comparisons (<em>A. leii</em> vs <em>L. praetexta</em>), which were primarily involved in antioxidant activity, immune response, energy production and metabolism, and chitin biosynthesis. They were assigned to six categories/superclasses (e.g., lipids and lipid-like molecules, organic acids and derivatives, and organoheterocyclic compound). Finally, ten metabolic pathways shared between KEGG terms specific to aquatic fireflies and enriched by AARMs were screened as aquatic adaptation-related pathways (AARPs). These AARPs were primarily involved in energy metabolism, xenobiotic biodegradation, protection of oxidative/immune damage, oxidative stress response and sense function (e.g., glycine, serine and threonine metabolism, drug metabolism-cytochrome P450 and taste transduction), and certain aspects of morphology (e.g., steroid hormone biosynthesis). These results provide evidence suggesting that abundance changes in metabolomes contribute to freshwater adaptation of fireflies. The metabolites identified here may be vital targets for future work to determine the mechanism of freshwater adaptation in insects.</p>
Project description:Spiders are renowned for their efficient capture of flying insects using intricate aerial webs. How the spider nervous systems evolved to cope with this specialized hunting strategy and various environmental clues in an aerial space remains unknown. Here, we report a brain cell atlas of >30,000 single-cell transcriptomes from a web-building spider (Hylyphantes graminicola). Our analysis revealed the preservation of ancestral neuron types in spiders, including the potential coexistence of noradrenergic and octopaminergic neurons, and many peptidergic neuronal types that are lost in insects. By comparing the genome of two newly sequenced plesiomorphic burrowing spiders with three aerial web-building spiders, we found that the positively selected genes in the ancestral branch of web-building spiders were preferentially expressed (42%) in the brain, especially in the three mushroom body-like neuronal types. By gene enrichment analysis and RNAi experiments, these genes were suggested to be involved in the learning and memory pathway and may influence the spiders’ web-building and hunting behavior. Our results provide key sources for understanding the evolution of behavior in spiders and reveal how molecular evolution drives neuron innovation and the diversification of associated complex behaviors.