Major Arthropod Groups Research Articles

New evidence for five cephalic appendages in trilobites and implications for segmentation of the trilobite head

AbstractHead segments play a critical role in revealing the relationships within major arthropod groups but the accurate determination of their number and relationship is challenging because of the decoupling of dorsal tergites and ventral appendages. In recent decades, trilobites have been considered to have four pairs of cephalic appendages and, commonly, five dorsal segments, which has served as the basis for understanding euarthropod cephalic evolution. Based on multiple analytical techniques applied to well‐preserved soft‐bodied specimens of the Upper Ordovician olenid Triarthrus eatoni and middle Cambrian corynexochid Olenoides serratus, we argue that an additional pair of cephalic biramous appendages occurred just behind the antennae, indicating that trilobites had five pairs of cephalic appendages and six dorsally expressed segments. We propose that the mismatch between the four dorsal furrows and five ventral appendages in Olenoides may be reconciled by considering the morphology of the hypostome that marks the position of the antenna and the bifurcation of the first glabellar furrow that has two muscle attachment sites fused. The fusion of clustered attachment sites of the cephalic biramous appendages may have aided feeding ability by gathering the limb bases close to the mouth.

Sexual selection and predation drive the repeated evolution of stridulation in Heteroptera and other arthropods.

Acoustic and substrate-borne vibrations are among the most widely used signalling modalities in animals. Arthropods display a staggering diversity of vibroacoustic organs generating acoustic sound and/or substrate-borne vibrations, and are fundamental to our broader understanding of the evolution of animal signalling. The primary mechanism that arthropods use to generate vibroacoustic signals is stridulation, which involves the rubbing together of opposing body parts. Although stridulation is common, its behavioural context and evolutionary drivers are often hard to pinpoint, owing to limited synthesis of empirical observations on stridulatory species. This is exacerbated by the diversity of mechanisms involved and the sparsity of their description in the literature, which renders their documentation a challenging task. Here, we present the most comprehensive review to date on the systematic distribution and behavioural context of stridulation. We use the megadiverse heteropteran insects as a model, together with multiple arthropod outgroups (arachnids, myriapods, and selected pancrustaceans). We find that stridulatory vibroacoustic signalling has evolved independently at least 84 times and is present in roughly 20% of Heteroptera, representing a remarkable case of convergent evolution. By studying the behavioural context of stridulation across Heteroptera and 189 outgroup lineages, we find that predation pressure and sexual selection are the main behaviours associated with stridulation across arthropods, adding further evidence for their role as drivers of large-scale signalling and morphological innovation in animals. Remarkably, the absence of tympanal ears in most Heteroptera suggests that they typically cannot detect the acoustic component of their stridulatory signals. This demonstrates that the adoption of new signalling modalities is not always correlated with the ability to perceive those signals, especially when these signals are directed towards interspecific receivers in defensive contexts. Furthermore, by mapping their morphology and systematic distribution, we show that stridulatory organs tend to evolve in specific body parts, likely originating from cleaning motions and pre-copulatory displays that are common to most arthropods. By synthesising our understanding of stridulation and stridulatory organs across major arthropod groups, we create the necessary framework for future studies to explore their systematic and behavioural significance, their potential role in sensory evolution and innovation, and the biomechanics of this mode of signalling.

A simple and low-cost method to visualize musculature and other aspects of anatomy by confocal microscopy.

Confocal microscopy study of musculature and other anatomical structures in whole-mount preparations of arthropods and some other cuticle-bearing animals often presents a significant difficulty because the cuticle poses a barrier to fluorescent dyes and their pigmented tissues can cause attenuation of fluorescent signal. This paper describes a simple and inexpensive procedure based on the use of clove oil as a tissue-clearing, staining, and mounting medium that helps overcome the problem of slow dye penetration and tissue opaqueness and allows muscles and several other organ systems to be visualized by confocal or epifluorescent microscopy. This clove oil-induced fluorescence (COIF) method relies on the ability of clove oil to accumulate in muscles and some other tissues and become steadily fluorescent if irradiated at 488 nm. For this method, animals were fixed in 70% ethanol or 4% formaldehyde, then dehydrated and mounted in clove oil. Heavily pigmented animals were additionally bleached in hydrogen peroxide prior to the dehydration step. The COIF method showed excellent results in all major groups of arthropods and some mollusks and annelids revealing the three-dimensional arrangement of muscles, gonads, glands, cellular nuclei and some parts of the nervous and digestive systems. In the other animal groups tested, clove oil stained all tissues making it difficult to observe the anatomical details. The COIF method is advantageous in some respects over other methods such as phalloidin staining because of its tissue penetration and clearing abilities, low cost of the reagents, resistance to photodamage and the possibility of staining museum specimens.

Was There a Cambrian Explosion on Land? The Case of Arthropod Terrestrialization.

Simple SummaryThe transition of life from the aquatic realm onto land represented one of the fundamental episodes in the evolution of the Earth that laid down the foundations for modern ecosystems as we know them today. This key transition in the history of life is poorly known, owing to the scarcity of ancient terrestrial fossil deposits; complex terrestrial ecosystems with plants and animals appear in the fossil record during the Silurian and Devonian. However, recent molecular clock studies and new lines of palaeontological evidence point to a possibly much earlier origin of life on land, dating back as far as the Cambrian. Here, we review this controversy, using the arthropods as a case study of the possible cryptic Cambrian explosion on land. In particular, we highlight approaches for reconciling the disagreement between molecular clock estimates and the fossil record for the arthropod colonization of land.Arthropods, the most diverse form of macroscopic life in the history of the Earth, originated in the sea. Since the early Cambrian, at least ~518 million years ago, these animals have dominated the oceans of the world. By the Silurian–Devonian, the fossil record attests to arthropods becoming the first animals to colonize land, However, a growing body of molecular dating and palaeontological evidence suggests that the three major terrestrial arthropod groups (myriapods, hexapods, and arachnids), as well as vascular plants, may have invaded land as early as the Cambrian–Ordovician. These dates precede the oldest fossil evidence of those groups and suggest an unrecorded continental “Cambrian explosion” a hundred million years prior to the formation of early complex terrestrial ecosystems in the Silurian–Devonian. We review the palaeontological, phylogenomic, and molecular clock evidence pertaining to the proposed Cambrian terrestrialization of the arthropods. We argue that despite the challenges posed by incomplete preservation and the scarcity of early Palaeozoic terrestrial deposits, the discrepancy between molecular clock estimates and the fossil record is narrower than is often claimed. We discuss strategies for closing the gap between molecular clock estimates and fossil data in the evolution of early ecosystems on land

Global Analysis of Gene Expression Profiles Provides Novel Insights into the Development and Evolution of the Large Crustacean Eriocheir sinensis

Chinese mitten crab (Eriocheir sinensis) is an important aquaculture species in Crustacea. Functional analysis, although essential, has been hindered due to the lack of sufficient genomic or transcriptomic resources. In this study, transcriptome sequencing was conducted on 59 samples representing diverse developmental stages (fertilized eggs, zoea, megalopa, three sub-stages of larvae, juvenile crabs, and adult crabs) and different tissues (eyestalk, hepatopancreas, and muscle from juvenile crabs, and eyestalk, hepatopancreas, muscle, heart, stomach, gill, thoracic ganglia, intestine, ovary, and testis from adult crabs) of E. sinensis. A comprehensive reference transcriptome was assembled, including 19,023 protein-coding genes. Hierarchical clustering based on 128 differentially expressed cuticle-related genes revealed two distinct expression patterns during the early larval developmental stages, demonstrating the distinct roles of these genes in “crab-like” cuticle formation during metamorphosis and cuticle calcification after molting. Phylogenetic analysis of 1406 one-to-one orthologous gene families identified from seven arthropod species and Caenorhabditis elegans strongly supported the hypothesis that Malacostraca and Branchiopoda do not form a monophyletic group. Furthermore, Branchiopoda is more phylogenetically closely related to Hexapoda, and the clade of Hexapoda and Branchiopoda and the clade of Malacostraca belong to the Pancrustacea. This study offers a high-quality transcriptome resource for E. sinensis and demonstrates the evolutionary relationships of major arthropod groups. The differentially expressed genes identified in this study facilitate further investigation of the cuticle-related gene expression networks which are likely associated with “crab-like” cuticle formation during metamorphosis and cuticle calcification after molting.

Inside the head of a cybertype – three-dimensional reconstruction of the head muscles of Ommatoiulus avatar (Diplopoda: Juliformia: Julidae) reveals insights into the feeding movements of Juliformia

AbstractThe origin and diversification of the arthropod head is one of the major topics in the field of evolutionary morphology of Arthropoda. Among the major arthropod groups, Myriapoda and, more precisely Diplopoda, are generally poorly studied regarding their head anatomy. However, this group is of pivotal importance to understand the evolutionary functional morphology of the arthropod head. In this study, we investigate the complete musculoskeletal system of the diplopod head with a detailed description of the cephalic anatomy of the recently described species Ommatoiulus avatar. The comparison of our data with the literature on the few other species available show that the morphology of the musculoskeletal system within Juliformia, a subgroup of the Diplopoda, is relatively conservative. Using video recordings of the feeding movements in addition to the anatomical data, we revise the mechanism of the mandibular movements in Juliformia. There was a controversy whether mandibular abduction is an active process, facilitated by contraction of an abductor muscle, or if it is a passive process, mediated by tentorial and gnathochilarial movements not involving a direct abduction by muscular contraction. We show that mandibular abduction in Ommatoiulus is an active movement involving the contraction of an abductor muscle. This is similar to the mandibular abduction in other arthropod groups.

Consuming alternative prey does not influence the DNA detectability half-life of pest prey in spider gut contents.

BackgroundKey natural enemy-pest interactions can be mapped in agricultural food webs by analysing predator gut content for the presence of a focal pest species. For this, PCR-based approaches are the most widely used methods providing the incidence of consumption of a focal pest in field sampled predators. To interpret such data the rate of prey DNA decay in the predators’ gut, described by DNA detectability half-life (t1/2), is needed. DNA decay may depend on the presence of alternative prey in the gut of generalist predators, but this effect has not been investigated in one of the major predatory arthropod groups, spiders.MethodsIn a laboratory feeding experiment, we determined t1/2 of the key cereal pest virus vector leafhopper Psammotettix alienus in the digestive tracts of its natural enemy, the spider Tibellus oblongus. We followed the fate of prey DNA in spiders which received only the focal prey as food, or as an alternative prey treatment they also received a meal of fruit flies after leafhopper consumption. After these feeding treatments, spiders were starved for variable time intervals prior to testing for leafhopper DNA in order to establish t1/2.ResultsWe created a PCR protocol that detects P. alienus DNA in its spider predator. The protocol was further calibrated to the digestion speed of the spider by establishing DNA decay rate. Detectability limit was reached at 14 days, where c. 10% of the animals tested positive. The calculated t1/2 = 5 days value of P. alienus DNA did not differ statistically between the treatment groups which received only the leafhopper prey or which also received fruit fly. The PCR protocol was validated in a field with known P. alienus infestation. In this applicability trial, we showed that 12.5% of field collected spiders were positive for the leafhopper DNA. We conclude that in our model system the presence of alternative prey did not influence the t1/2 estimate of a pest species, which makes laboratory protocols more straightforward for the calibration of future field data.

Relationships between attentional network functioning and spontaneous EEG activity in patients with coronary artery disease

Chinese mitten crab (Eriocheir sinensis) is an important aquaculture species in Crustacea. Functional analysis, although essential, has been hindered due to the lack of sufficient genomic or transcriptomic resources. In this study, transcriptome sequencing was conducted on 59 samples representing diverse developmental stages (fertilized eggs, zoea, megalopa, three sub-stages of larvae, juvenile crabs, and adult crabs) and different tissues (eyestalk, hepatopancreas, and muscle from juvenile crabs, and eyestalk, hepatopancreas, muscle, heart, stomach, gill, thoracic ganglia, intestine, ovary, and testis from adult crabs) of E. sinensis. A comprehensive reference transcriptome was assembled, including 19,023 protein-coding genes. Hierarchical clustering based on 128 differentially expressed cuticle-related genes revealed two distinct expression patterns during the early larval developmental stages, demonstrating the distinct roles of these genes in “crab-like” cuticle formation during metamorphosis and cuticle calcification after molting. Phylogenetic analysis of 1406 one-to-one orthologous gene families identified from seven arthropod species and Caenorhabditis elegans strongly supported the hypothesis that Malacostraca and Branchiopoda do not form a monophyletic group. Furthermore, Branchiopoda is more phylogenetically closely related to Hexapoda, and the clade of Hexapoda and Branchiopoda and the clade of Malacostraca belong to the Pancrustacea. This study offers a high-quality transcriptome resource for E. sinensis and demonstrates the evolutionary relationships of major arthropod groups. The differentially expressed genes identified in this study facilitate further investigation of the cuticle-related gene expression networks which are likely associated with “crab-like” cuticle formation during metamorphosis and cuticle calcification after molting.

Morphological description, character conceptualization and the reconstruction of ancestral states exemplified by the evolution of arthropod hearts.

Arthropods are the most species-rich taxon within Metazoa and have gone through major evolutionary changes with regard to body organization. Arthropod hearts and their associated vascular systems are thus morphologically highly disparate: while some arthropods exhibit very powerful hearts and complex vascular systems, other arthropods do not possess any kind of vascular system or heart at all. A comprehensive study investigating the structure of arthropods hearts has never been undertaken. In this study, we therefore investigate the hearts of 34 species from all major arthropod groups using various imaging techniques (confocal laser scanning microscopy, micro-computed tomography, histology) and describe them by addressing different aspects of heart morphology, e.g. the structure of the myocard or the composition of ostia. In a next step, we conceptualize 18 characters related to heart morphology and their respective character states and–using additional data from the literature–score a matrix for a total of 45 species from 38 supraspecific taxa. We map the characters onto prevailing phylogenetic hypotheses and perform parsimony-based ancestral state reconstruction to trace the evolutionary transformations undergone by arthropod hearts. An exploration of the character concepts (as explanatory hypotheses) reveals ontological peculiarities of character statements that clearly distinguish them in terms of ontological status from descriptive statements (i.e. descriptions of morphemes). The implications of these findings influence the interpretation of ground patterns as explanations. This first phylogenetic approach to heart morphology in the arthropod ground pattern reveals numerous new putative synapomorphies and leads to a reconsideration of the morphology of circulatory systems in early arthropods. Hypotheses on the evolution of hearts in (Pan-) Arthropoda are illustrated and discussed.

Genome size in arthropods; different roles of phylogeny, habitat and life history in insects and crustaceans.

Despite the major role of genome size for physiology, ecology, and evolution, there is still mixed evidence with regard to proximate and ultimate drivers. The main causes of large genome size are proliferation of noncoding elements and/or duplication events. The relative role and interplay between these proximate causes and the evolutionary patterns shaped by phylogeny, life history traits or environment are largely unknown for the arthropods. Genome size shows a tremendous variability in this group, and it has a major impact on a range of fitness‐related parameters such as growth, metabolism, life history traits, and for many species also body size. In this study, we compared genome size in two major arthropod groups, insects and crustaceans, and related this to phylogenetic patterns and parameters affecting ambient temperature (latitude, depth, or altitude), insect developmental mode, as well as crustacean body size and habitat, for species where data were available. For the insects, the genome size is clearly phylogeny‐dependent, reflecting primarily their life history and mode of development, while for crustaceans there was a weaker association between genome size and phylogeny, suggesting life cycle strategies and habitat as more important determinants. Maximum observed latitude and depth, and their combined effect, showed positive, and possibly phylogenetic independent, correlations with genome size for crustaceans. This study illustrate the striking difference in genome sizes both between and within these two major groups of arthropods, and that while living in the cold with low developmental rates may promote large genomes in marine crustaceans, there is a multitude of proximate and ultimate drivers of genome size.

Trophic interactions among soil arthropods in contrasting land-use systems in Kenya, studied with stable isotopes

Understanding how land use intensification changes organism communities and trophic interactions in soil is important for development of sustainable agriculture and forestry.We analysed the food web of soil arthropods with help of natural 13C/12C and 15N/14N ratios (δ13C and δ15N) in two habitats in the Kenyan Highland – a natural forest and an agricultural site on former forest land. Aims of the study: (1) to describe the structure and feeding relationships in the two systems for major soil arthropod groups, (2) to find differences in feeding strategies within major arthropod groups, (3) to determine if soil arthropod groups have the same trophic positions in forest and agricultural soil, (4) to evaluate if δ13C and δ15N can be explained by additional reasons, e.g. the physiology and C:N ratios of organisms.This is one of few studies of the trophic structure of soil arthropod communities in tropical ecosystems. It confirms that the structure is similar to comparable systems in the temperate zones. There was a large variation in δ15N among families of Oribatida, Mesostigmata and Collembola (the most common groups) indicating great variety in feeding ecology. Collembola and Diplopoda had comparatively high δ15N, indicating a contribution of animals to the diet. Although lower abundance and diversity of arthropods in the agricultural soil, the trophic positions of particular taxa, indicated as δ15N level, were similar to the forest. The δ13C values were negatively correlated to the C:N ratio, therefore increasing values of δ13C with trophic level could not be demonstrated.

From success to persistence: Identifying an evolutionary regime shift in the diverse Paleozoic aquatic arthropod group Eurypterida, driven by the Devonian biotic crisis.

Mass extinctions have altered the trajectory of evolution a number of times over the Phanerozoic. During these periods of biotic upheaval a different selective regime appears to operate, although it is still unclear whether consistent survivorship rules apply across different extinction events. We compare variations in diversity and disparity across the evolutionary history of a major Paleozoic arthropod group, the Eurypterida. Using these data, we explore the group's transition from a successful, dynamic clade to a stagnant persistent lineage, pinpointing the Devonian as the period during which this evolutionary regime shift occurred. The late Devonian biotic crisis is potentially unique among the "Big Five" mass extinctions in exhibiting a drop in speciation rates rather than an increase in extinction. Our study reveals eurypterids show depressed speciation rates throughout the Devonian but no abnormal peaks in extinction. Loss of morphospace occupation is random across all Paleozoic extinction events; however, differential origination during the Devonian results in a migration and subsequent stagnation of occupied morphospace. This shift appears linked to an ecological transition from euryhaline taxa to freshwater species with low morphological diversity alongside a decrease in endemism. These results demonstrate the importance of the Devonian biotic crisis in reshaping Paleozoic ecosystems.

Agatoxin-like peptides in the neuroendocrine system of the honey bee and other insects

We investigated the peptide inventory of the corpora cardiaca (CC) of the honey bee, Apis mellifera, by direct tissue profiling using MALDI-TOF MS combined with proteomic approaches focusing on cysteine-containing peptides. An agatoxin-like peptide (ALP) was identified as a component of the glandular part of the CC and was associated with the presence of the adipokinetic hormone in mass spectra. Although abundant in the CC, ALP does not belong to the toxins observed in the venom gland of A. mellifera. Homologs of ALP are highly conserved in major groups of arthropods and in line with this we detected ALP in the CC of non-venomous insects such as cockroaches and silverfish. In the American cockroach, Periplaneta americana, ALP was also identified in the CNS and stomatogastric nervous system. This is the first report that establishes the presence of ALPs in the neuroendocrine tissues of insects and further studies are necessary to reveal common functions of these peptides, e.g. as antimicrobial agents, ion channel modulators or classical neuropeptides. Biological significanceAmong the messenger molecules of the nervous system, neuropeptides represent the structurally most diverse class and basically participate in the regulation of all physiological processes. The set of neuropeptides, their functions and spatial distribution are particularly well-studied in insects. Until now, however, several potential neuropeptide receptors remained orphan, which indicates the existence of so far unknown ligands. In our study, we used proteomic methods such as cysteine modification, enzymatic digestion and peptide derivatization, combined with direct tissue profiling by MALDI-TOF mass spectrometry, for the discovery of novel putative messenger molecules in the neuroendocrine system. The described presence of agatoxin-like peptides in the nervous system of the honey bee and other insects was overseen so far and is thus a remarkable addition to the very well studied neuropeptidome of insects. It is not yet clear, if these toxin-like peptides act as antimicrobial agents, ion channel modulators or classical neuropeptides.

Comparative genomic study of arachnid immune systems indicates loss of beta-1,3-glucanase-related proteins and theimmune deficiency pathway.

Analyses of arthropod genomes have shown that the genes in the different innate humoral immune responses are conserved. These genes encode proteins that are involved in immune signalling pathways that recognize pathogens and activate immune responses. These immune responses include phagocytosis, encapsulation of the pathogen and production of effector molecules for pathogen elimination. So far, most studies have focused on insects leaving other major arthropod groups largely unexplored. Here, we annotate the immune-related genes of six arachnid genomes and present evidence for a conserved pattern of some immune genes, but also evolutionary changes in the arachnid immune system. Specifically, our results suggest that the family of recognition molecules of beta-1,3-glucanase-related proteins (βGRPs) and the genes from the immune deficiency (IMD) signalling pathway have been lost in a common ancestor of arachnids. These findings are consistent with previous work suggesting that the humoral immune effector proteins are constitutively produced in arachnids in contrast to insects, where these have to be induced. Further functional studies are needed to verify this. We further show that the full haemolymph clotting cascade found in the horseshoe crab is retrieved in most arachnid genomes. Tetranychus lacks at least one major component, although it is possible that this cascade could still function through recruitment of a different protein. The gel-forming protein in horseshoe crabs, coagulogen, was not recovered in any of the arachnid genomes; however, it is possible that the arachnid clot consists of a related protein, spätzle, that is present in all of the genomes.

Identification of Odorant Binding Proteins and Chemosensory Proteins in Antennal Transcriptomes of the Jumping Bristletail Lepismachilis y-signata and the Firebrat Thermobia domestica: Evidence for an Independent OBP-OR Origin.

Chemosensory protein (CSP) and gustatory receptor genes have been identified in all major arthropod groups. However, odorant binding proteins (OBP) and olfactory receptor genes are insect specific, suggesting that both gene families originated after the Hexapoda-Crustacea split (~470 million years ago). The seemingly parallel diversification of OBP and olfactory receptors has been suggested as coevolution between these genes after insect terrestrialization. To test this hypothesis we used the recently published transcriptomes of the jumping bristletail Lepismachilis y-signata and the firebrat Thermobia domestica to search for putative OBP and CSP sequences and analyzed their relationship to binding proteins of other insects and crustaceans. Our results suggest an evolution and expansion of OBPs as an adaptation to a terrestrial insect lifestyle, independently from the emergence of olfactory receptors.

Expression study of the hunchback ortholog in embryos of the onychophoran Euperipatoides rowelli.

Zinc finger transcription factors encoded by hunchback homologs play different roles in arthropods, including maternally mediated control, segmentation, and mesoderm and neural development. Knockdown experiments in spider and insect embryos have also revealed homeotic effects and gap phenotypes, the latter indicating a function of hunchback as a "gap gene". Although the expression pattern of hunchback has been analysed in representatives of all four major arthropod groups (chelicerates, myriapods, crustaceans and insects), nothing is known about its expression in one of the closest arthropod relatives, the Onychophora (velvet worms). We therefore examined the expression pattern of hunchback in embryos of the onychophoran Euperipatoides rowelli. Our transcriptomic and phylogenetic analyses revealed only one hunchback ortholog in this species. The putative Hunchback protein contains all nine zinc finger domains known from other protostomes. We found no indication of maternally contributed transcripts of hunchback in early embryos of E. rowelli. Its initial expression occurs in the ectodermal tissue of the antennal segment, followed by the jaw, slime papilla and trunk segments in an anterior-to-posterior progression. Later, hunchback expression is seen in the mesoderm of the developing limbs. A second "wave" of expression commences later in development in the antennal segment and continues posteriorly along each developing nerve cord. This expression is restricted to the neural tissues and does not show any segmental pattern. These findings are in line with the ancestral roles of hunchback in mesoderm and neural development, whereas we find no evidence for a putative function of hunchback as a "gap gene" in Onychophora.

Comparative Genomics Reveals the Origins and Diversity of Arthropod Immune Systems.

Insects are an important model for the study of innate immune systems, but remarkably little is known about the immune system of other arthropod groups despite their importance as disease vectors, pests, and components of biological diversity. Using comparative genomics, we have characterized the immune system of all the major groups of arthropods beyond insects for the first time—studying five chelicerates, a myriapod, and a crustacean. We found clear traces of an ancient origin of innate immunity, with some arthropods having Toll-like receptors and C3-complement factors that are more closely related in sequence or structure to vertebrates than other arthropods. Across the arthropods some components of the immune system, such as the Toll signaling pathway, are highly conserved. However, there is also remarkable diversity. The chelicerates apparently lack the Imd signaling pathway and beta-1,3 glucan binding proteins—a key class of pathogen recognition receptors. Many genes have large copy number variation across species, and this may sometimes be accompanied by changes in function. For example, we find that peptidoglycan recognition proteins have frequently lost their catalytic activity and switch between secreted and intracellular forms. We also find that there has been widespread and extensive duplication of the cellular immune receptor Dscam (Down syndrome cell adhesion molecule), which may be an alternative way to generate the high diversity produced by alternative splicing in insects. In the antiviral short interfering RNAi pathway Argonaute 2 evolves rapidly and is frequently duplicated, with a highly variable copy number. Our results provide a detailed analysis of the immune systems of several important groups of animals for the first time and lay the foundations for functional work on these groups.

Arthropods Associated with Corn Planted in the Marginal Uplands of Inopacan, Leyte

A study was conducted to assess and identify the arthropods associated with corn planted in the marginal uplands of Inopacan, Leyte, using pan trap and sweep net methods, done biweekly during the two cropping periods. Two major groups of arthropods were recorded which included the Arachnids and the insect group, consisting of nine (11) orders of insects represented by 59 insects species and 20 spiders. These arthropods belonged to phytophagous groups (chewing and sucking arthropods); natural enemies (predators and parasitoids) and the innocuous groups or considered “others” (scavengers and saprophagous) The most abundant insect pest species in corn were the Chrysomelidae and Scarabaeidae beetles, while leafhoppers (Homoptera) were moderately abundant in the crop. The predators were mostly ants (Hymenoptera), the spiders (Arachnids), and coccinellid beetles. The parasitoids included the braconid, ichneumonid, and chalcid wasps. The most abundant non-pest and innocuous species are the Dipterans which are potential hosts or prey of the biotic agents in the corn ecosystem. The abundance of pest species in corn is not yet alarming, which indicates that the pests are not attracted to the crops which were marginal in growth. The natural enemies were also occurring in moderate numbers adequate to suppress abundance of pest species. However, from the results, the corn planted in the marginal upland with chicken dung was observed to have the higher number of insect associations than the other treatments.

A Silurian short-great-appendage arthropod

A new arthropod, Enalikter aphson gen. et sp. nov., is described from the Silurian (Wenlock Series) Herefordshire Lagerstätte of the UK. It belongs to the Megacheira (=short-great-appendage group), which is recognized here, for the first time, in strata younger than mid-Cambrian age. Discovery of this new Silurian taxon allows us to identify a Devonian megacheiran representative, Bundenbachiellus giganteus from the Hunsrück Slate of Germany. The phylogenetic position of megacheirans is controversial: they have been interpreted as stem chelicerates, or stem euarthropods, but when Enalikter and Bundenbachiellus are added to the most comprehensive morphological database available, a stem euarthropod position is supported. Enalikter represents the only fully three-dimensionally preserved stem-group euarthropod, it falls in the sister clade to the crown-group euarthropods, and it provides new insights surrounding the origin and early evolution of the euarthropods. Recognition of Enalikter and Bundenbachiellus as megacheirans indicates that this major arthropod group survived for nearly 100 Myr beyond the mid-Cambrian.

First biosynthetic pathway of 1-hepten-3-one in Iporangaia pustulosa (Opiliones).

Arthropods produce a great variety of natural compounds, many of which have unexplored biosynthesis. Among the armored harvestmen (Arachnida: Opiliones) of the suborder Laniatores, the defensive gland exudates contain vinyl ketones and other constituents of supposed polyketide origin. We have studied the biosynthesis of 1-hepten-3-one in the Neotropical harvestman Iporangaia pustulosa by feeding individuals with 13C-labeled precursors, demonstrating its mixed acetate/propionate origin. 13C NMR spectroscopy showed an unusual labeling pattern suggesting different propionate sources for starting and extender units. Our analysis also indicates the presence of methylmalonyl-CoA mutase, converting acetate into propionyl-CoA via succinyl-CoA, together with other C3 unit routes. This is the first biosynthetic study of alkyl vinyl ketones in arthropods. Our results shed light on the origin and diversification of chemical compounds in a major arthropod group.