Land-use change affects size spectra, energy flux and ecosystem functions in litter and soil invertebrates

In Focus: Potapov, A. M., Klarner, B., Sandmann, D., Widyastuti, R. and Scheu, S. (2019). Linking size spectrum, energy flux and trophic multifunctionality in soil food webs of tropical land-use systems. Journal of Animal Ecology, 88, 1845-1859. https://doi.org/10.1111/1365-2656.13027 Potapov et al. (2019) advance our understanding of the various levels of the consequences of human impact on ecosystems. They examine the communities of litter and soil invertebrates in four different forests (from rainforest to oil palm plantations). Data on abundance, body masses and trophic guild in litter and soil invertebrates are expanded to a study towards biodiversity, biomass, energy flux and ecosystem functions. Their results show that size spectra are affected differently for decomposers, herbivores, omnivores and predators. Most of these groups decrease in abundance with increasing land use, and only large decomposers increase strongly. Moreover, creating trophic-group food webs for litter and soil invertebrates of each forest demonstrates the changes in energy flux and ecosystem functions. With their study, Potapov et al. (2019) present new insights into ecosystem functions and the sensitivity of communities to changes in land use.

Identification and Description of the Key Molecular Components of the Egg Strings of the Salmon Louse (Lepeophtheirus salmonis)

The salmon louse Lepeophtheirus salmonis is a parasite of Atlantic salmon and other salmonids. Every year, it causes high costs for the Norwegian aquaculture industry. While the morphology of the female genital tract has been described, knowledge of the molecular basis of reproduction is very limited. We identified nine genes which are expressed exclusively in the female cement gland, the organ responsible for cement production, which is used to hold the eggs together and keep them attached to their mother in egg strings. Six of these genes encode proteins with signal peptides and probably form the main component of the cement. Two other genes are peroxidases, which are probably important in the cement formation. The last gene is not similar to any known protein, but contains a transmembrane domain. A knockdown of all these genes leads to missing or deformed egg strings, preventing reproduction of the lice. The correct assemblage of the cement in the cement gland is essential for successful reproduction of salmon lice. Similar proteins seem to be present in other copepod species, as well.

Comparative studies of endocannabinoid modulation of pain

Cannabinoid-based therapies have long been used to treat pain, but there remain questions about their actual mechanisms and efficacy. From an evolutionary perspective, the cannabinoid system would appear to be highly conserved given that the most prevalent endogenous cannabinoid (endocannabinoid) transmitters, 2-arachidonyl glycerol and anandamide, have been found throughout the animal kingdom, at least in the species that have been analysed to date. This review will first examine recent findings regarding the potential conservation across invertebrates and chordates of the enzymes responsible for endocannabinoid synthesis and degradation and the receptors that these transmitters act on. Next, comparisons of how endocannabinoids modulate nociception will be examined for commonalities between vertebrates and invertebrates, with a focus on the medicinal leech Hirudo verbana. Evidence is presented that there are distinct, evolutionarily conserved anti-nociceptive and pro-nociceptive effects. The combined studies across various animal phyla demonstrate the utility of using comparative approaches to understand conserved mechanisms for modulating nociception. This article is part of the Theo Murphy meeting issue 'Evolution of mechanisms and behaviour important for pain'.

Dark Ophiuroid Biodiversity in a Prospective Abyssal Mine Field

The seafloor contains valuable mineral resources, including polymetallic (or manganese) nodules that form on offshore abyssal plains. The largest and most commercially attractive deposits are located in the Clarion Clipperton Fracture Zone (CCZ), in the eastern Pacific Ocean (EP) between Hawaii and Mexico, where testing of a mineral collection system is set to start soon [1]. The requirement to establish pre-mining environmental management plans has prompted numerous recent biodiversity and DNA barcoding surveys across these remote regions. Here we map DNA sequences from sampled ophiuroids (brittle stars, including post-larvae) of the CCZ and Peru Basin onto a substantial tree of life to show unprecedented levels of abyssal ophiuroid phylogenetic diversity including at least three ancient (>70 Ma), previously unknown clades. While substantial dark (unobserved) biodiversity has been reported from various microbial meta-barcoding projects [2, 3], our data show that we have considerably under-estimated the biodiversity of even the most conspicuous mega-faunal invertebrates [4] of the EP abyssal plain.

Storage of Carotenoids in Crustaceans as an Adaptation to Modulate Immunopathology and Optimize Immunological and Life-History Strategies

Why do some invertebrates store so much carotenoids in their tissues? Storage of carotenoids may not simply be passive and dependent on their environmental availability, as storage variation exists at various taxonomic scales, including among individuals within species. While the strong antioxidant and sometimes immune-stimulating properties of carotenoids may be beneficial enough to cause the evolution of features improving their assimilation and storage, they may also have fitness downsides explaining why massive carotenoid storage is not universal. Here, the functional and ecological implications of carotenoid storage for the evolution of invertebrate innate immune defenses are examined, especially in crustaceans, which massively store carotenoids for unclear reasons. Three testable hypotheses about the role of carotenoid storage in immunological (resistance and tolerance) and life-history strategies (with a focus on aging) are proposed, which may ultimately explain the storage of large amounts of these pigments in a context of host-pathogen interactions.

Diurnal variation around an optimum and near-critically high temperature does not alter the performance of an ectothermic aquatic grazer

The growing threat of global climate change has led to a profusion of studies examining the effects of warming on biota. Despite the potential importance of natural variability such as diurnal temperature fluctuations, most experimental studies on warming are conducted under stable temperatures. Here, we investigated whether the responses of an aquatic invertebrate grazer (Lymnaea stagnalis) to an increased average temperature differ when the thermal regime is either constant or fluctuates diurnally. Using thermal response curves for several life-history and immune defense traits, we first identified the optimum and near-critically high temperatures that Lymnaea potentially experience during summer heat waves. We then exposed individuals that originated from three different populations to these two temperatures under constant or fluctuating thermal conditions. After 7 days, we assessed growth, reproduction, and two immune parameters (phenoloxidase-like activity and antibacterial activity of hemolymph) from each individual. Exposure to the near-critically high temperature led to increased growth rates and decreased antibacterial activity of hemolymph compared to the optimum temperature, whilst temperature fluctuations had no effect on these traits. The results indicate that the temperature level per se, rather than the variability in temperature was the main driver altering trait responses in our study species. Forecasting responses in temperature-related responses remains challenging, due to system-specific properties that can include intraspecific variation. However, our study indicates that experiments examining the effects of warming using constant temperatures can give similar predictions as studies with fluctuating thermal dynamics, and may thus be useful indicators of responses in nature.

Antibiotics as chemical warfare across multiple taxonomic domains and trophic levels in brown food webs

Bacteria and fungi secrete antibiotics to suppress and kill other microbes, but can these compounds be agents of competition against macroorganisms? We explore how one competitive tactic, antibiotic production, can structure the composition and function of brown food webs. This aspect of warfare between microbes and invertebrates is particularly important today as antibiotics are introduced into ecosystems via anthropogenic activities, but the ecological implications of these introductions are largely unknown. We hypothesized that antimicrobial compounds act as agents of competition against invertebrate and microbial competitors. Using field-like mesocosms, we tested how antifungal and antibacterial compounds influence microbes, invertebrates, and decomposition in the brown food web. Both antibiotics changed prokaryotic microbial community composition, but only the antibacterial changed invertebrate composition. Antibacterials reduced the abundance of invertebrate detritivores by 34%. However, the addition of antimicrobials did not ramify up the food web as predator abundances were unaffected. Decomposition rates did not change. To test the mechanisms of antibiotic effects, we provided antibiotic-laden water to individual invertebrate detritivores in separate microcosm experiments. We found that the antibiotic compounds can directly harm invertebrate taxa, probably through a disruption of endosymbionts. Combined, our results show that antibiotic compounds could be an effective weapon for microbes to compete against both microbial and invertebrate competitors. In the context of human introductions, the detrimental effects of antibiotics on invertebrate communities indicates that the scope of this anthropogenic disturbance is much greater than previously expected.

Network Degeneracy and the Dynamics of Task Switching in the Feeding Circuit in Aplysia

The characteristics of a network are determined by parameters that describe the intrinsic properties of the component neurons and their synapses. Degeneracy occurs when more than one set of parameters produces the same (or very similar) output. It is not clear whether network degeneracy impacts network function or is simply a reflection of the fact that, although it is important for a network to be able to generate a particular output, it is not important how this is achieved. We address this issue in the feeding network of the mollusc Aplysia In this system, there are two stimulation paradigms that generate egestive motor programs: repetition priming and positive biasing. We demonstrate that circuit parameters differ in the 2 cases (e.g., egestive repetition priming requires activity in an interneuron, B20, which is not essential for positive biasing). We show that degeneracy has consequences for task switching. If egestive repetition priming is immediately followed by stimulation of an ingestive input to the feeding central pattern generator, the first few cycles of activity are egestive (not ingestive). In this situation, there is a task switch cost. This "cost" is in part due to the potentiating effect of egestive repetition priming on B20. In contrast, there is no switch cost after positive biasing. Stimulation of the ingestive central pattern generator input immediately triggers ingestive activity. Our results indicate that the mechanisms used to pattern activity can impact network function in that they can determine how readily a network can switch from one configuration to another.SIGNIFICANCE STATEMENT A particular pattern of neural activity can be generated by more than one set of circuit parameters. How or whether this impacts network function is unclear. We address this issue in the feeding network of Aplysia and demonstrate that degeneracy in network function can have consequences for task switching. Namely, we show that, when egestive activity is generated via one set of circuit modifications, an immediate switch to ingestive activity is not possible. In contrast, rapid transitions to ingestive activity are possible if egestive activity is generated via a different set of circuit modifications.

Alternatively spliced down syndrome cell adhesion molecule (Dscam) controls innate immunity in crab

Alternatively-spliced hypervariable immunoglobulin domain-encoding molecules, called Down syndrome cell adhesion molecule (Dscam), have been widely detected as components of the arthropod immune system. Although its ability to specifically bind pathogens and enable phagocytosis of bacteria has been elucidated, the signal transduction mechanisms or effectors that activate post-Dscam-binding pathogens remain poorly characterized. Here, we reveal the alternative splicing exons of Dscam's cytoplasmic tail and its isoforms in the hemocytes of crab (Eriocheir sinensis), showing that the expression of Dscam was acutely induced after an immune challenge, which suggested its functioning for innate immunity. Significantly decreased expression levels of antimicrobial molecular peptides (AMPs) were detected in Dscam-silenced crab hemocytes in vitro, which coincided with their vulnerability to infection by Staphylococcus aureus and higher bacterial concentrations occurring in Dscam-silenced crabs in vivo Further experimental investigation demonstrated that Dscam-regulated AMP expression via the Src homology (SH)3-binding domain in the first constant exon translated protein of the cytoplasmic tail bound with the SH3 domain of the Dock, an SH3/SH2 adaptor protein required for axon guidance. Dock promoted extracellular signal-regulated kinase (ERK) phosphorylation via indirect binding and then regulated dorsal phosphorylation and translocation from the cytoplasm to the nucleus, subsequently promoting AMP expression for the effective removal of bacteria. To the best of our knowledge, this comprehensive study is the first to highlight the critical role of the alternatively-spliced Dscam cytoplasmic tail in antimicrobial control activity. It also suggests possible cross-talk occurring between Dscam and other pattern recognition receptors.

EVALUATION OF EUTHANASIA OF MOON JELLYFISH (AURELIA AURITA) USING SIMPLE SALT SOLUTIONS

Immersion euthanasia methods reported over the most recent decades for aquatic invertebrates use organic alcohols or halogenated hydrocarbons that can interfere with nuclear magnetic resonance (NMR) analysis. A rolling study design evaluated potassium chloride (KCl), magnesium chloride (MgCl₂), and magnesium sulfate (MgSO₄) as potential ion-based euthanasia methods for moon jellyfish (Aurelia aurita) destined for metabolomic analysis by NMR spectroscopy. Death was defined as the cessation of autonomous bell pulsing and response to external stimulus. MgCl₂ applied at a dose of 142 g/L provided euthanasia within 32 sec of applications without the untoward effects observed with the other two salts. Euthanasia with KCl at the doses tested was associated with abnormal behavior and tissue degradation during dissection. MgSO₄ at the doses tested resulted in abnormal behavior and failed to provide rapid euthanasia.

A Na+ leak channel cloned from Trichoplax adhaerens extends extracellular pH and Ca2+ sensing for the DEG/ENaC family close to the base of Metazoa

Acid-sensitive ion channels belonging to the degenerin/epithelial sodium channel (DEG/ENaC) family activate in response to extracellular protons and are considered unique to deuterostomes. However, sensitivity to pH/protons is more widespread, where, for example, human ENaC Na⁺ leak channels are potentiated and mouse BASIC and Caenorhabditis elegans ACD-1 Na⁺ leak channels are blocked by extracellular protons. For many DEG/ENaC channels, extracellular Ca²⁺ ions modulate gating, and in some cases, the binding of protons and Ca²⁺ is interdependent. Here, we functionally characterize a DEG/ENaC channel from the early-diverging animal Trichoplax adhaerens, TadNaC6, that conducts Na⁺-selective leak currents in vitro sensitive to blockade by both extracellular protons and Ca²⁺. We determine that proton block is enhanced in low external Ca²⁺ concentration, whereas calcium block is enhanced in low external proton concentration, indicative of competitive binding of these two ligands to extracellular sites of the channel protein. TadNaC6 lacks most determinant residues for proton and Ca²⁺ sensitivity in other DEG/ENaC channels, and a mutation of one conserved residue (S353A) associated with Ca²⁺ block in rodent BASIC channels instead affected proton sensitivity, all indicative of independent evolution of H⁺ and Ca²⁺ sensitivity. Strikingly, TadNaC6 was potently activated by the general DEG/ENaC channel blocker amiloride, a rare feature only reported for the acid-activated channel ASIC3. The sequence and structural divergence of TadNaC6, coupled with its noncanonical functional features, provide unique opportunities for probing the proton, Ca²⁺, and amiloride regulation of DEG/ENaC channels and insight into the possible core-gating features of ancestral ion channels.

Abyssal deposit-feeding rates consistent with the metabolic theory of ecology

The Metabolic Theory of Ecology (MTE) posits that metabolic rate controls ecological processes, such as the rate of resource uptake, from the individual‐ to the ecosystem‐scale. Metabolic rate has been found empirically to be an exponential function of whole organism body mass. We test a fundamental assumption of MTE, whether resource uptake scales to metabolism, by examining detritivores accessing a single common resource pool, an ideal study case. We used an existing empirical model of ingestion for aquatic deposit feeders adjusted for temperature to test whether ingestion by abyssal deposit feeders conforms to MTE‐predicted feeding rates. We estimated the sediment deposit‐feeding rates of large invertebrates from two abyssal study sites using time‐lapse photography, and related those rates to body mass, environmental temperature, and sediment organic matter content using this framework. Ingestion was significantly related to individual wet mass, with a mass‐scaling coefficient of 0.81, with 95% confidence intervals that encompass the MTE‐predicted value of 0.75, and the same pattern determined in other aquatic systems. Our results also provide insight into the potential mechanism through which this fundamental assumption operates. After temperature correction, both deep‐ and shallow‐water taxa might be summarized into a single mass‐scaled ingestion rate.

Identification and Function of GnRH-like Peptide in the Pacific Abalone, Haliotis discus hannai

Gonadotropin-releasing hormone (GnRH) is an important regulator of reproductive function in various vertebrates and invertebrates. In the present study, we have identified the GnRH-like peptide cDNA and peptide from the cerebral ganglion (CG) of the Pacific abalone, Haliotis discus hannai. Pacific abalone GnRH-like peptide (hdhGnRH-like peptide) cDNA encodes precursor, which possesses the typical organization of the known mollusk GnRH-like peptide precursors, including a hydrophobic signal peptide, GnRH-like peptide, and a cleavage site followed by a GAP-like peptide region. Three hdhGnRH-like peptides, pQNYHFSNGWHAamide (hdhGnRH-11amide), pQNYHFSNGWHA (hdhGnRH-11OH), and pQNYHFSNGWHAG (hdhGnRH-12OH), were determined from the acid/acetone extract of the CG by mass spectrometry (LC-MS/MS) analysis. The hdhGnRH-like peptide mRNA expression was detected not only in the CG but also in gonads, and hdhGnRH-11amide was also detected in the extract of gonads. The mRNA expression of hdhGnRH-like peptide in the CG was lower in spawned males than in non-spawned animals, while no change in hdhGnRH-like peptide mRNA expression was shown in both ovulated and non-ovulated abalone. The hdhGnRH-11amide induces spawning and ovulation of both mature males and females in a concentration-dependent fashion following intramuscular injection. These results indicate that three hdhGnRH-like peptides are yielded from a single hdhGnRH-like peptide precursor, and that at least hdhGnRH-11amide is involved in the control of reproduction of the Pacific abalone.

Is reproductive strategy a key factor in understanding the evolutionary history of Southern Ocean Asteroidea (Echinodermata)?

Life traits such as reproductive strategy can be determining factors of species evolutionary history and explain the resulting diversity patterns. This can be investigated using phylogeographic analyses of genetic units. In this work, the genetic structure of five asteroid genera with contrasting reproductive strategies (brooding: Diplasterias, Notasterias and Lysasterias versus broadcasting: Psilaster and Bathybiaster) was investigated in the Southern Ocean. Over 1,400 mtDNA cytochrome C oxidase subunit I (COI) sequences were analysed using five species delineation methods (ABGD, ASAP, mPTP, sGMYC and mGMYC), two phylogenetic reconstructions (ML and BA), and molecular clock calibrations, in order to examine the weight of reproductive strategy in the observed differences among phylogeographic patterns. We hypothesised that brooding species would show higher levels of genetic diversity and species richness along with a clearer geographic structuring than broadcasting species. In contrast, genetic diversity and species richness were not found to be significantly different between brooders and broadcasters, but broadcasters are less spatially structured than brooders supporting our initial hypothesis and suggesting more complex evolutionary histories associated to this reproductive strategy. Broadcasters' phylogeography can be explained by different scenarios including deep-sea colonisation routes, bipolarity or cosmopolitanism, and sub-Antarctic emergence for the genus Bathybiaster; Antarctic- New Zealand faunal exchanges across the Polar Front for the genus Psilaster. Brooders' phylogeography could support the previously formulated hypothesis of a past trans-Antarctic seaway established between the Ross and the Weddell seas during the Plio-Pleistocene. Our results also show, for the first time, that the Weddell Sea is populated by a mixed asteroid fauna originating from both the East and West Antarctic.

Application of PEG-Covered Non-Biodegradable Polyelectrolyte Microcapsules in the Crustacean Circulatory System on the Example of the Amphipod Eulimnogammarus verrucosus

Layer-by-layer assembled microcapsules are promising carriers for the delivery of various pharmaceutical and sensing substances into specific organs of different animals, but their utility in vivo inside such an important group as crustaceans remains poorly explored. In the current study, we analyzed several significant aspects of the application of fluorescent microcapsules covered by polyethylene glycol (PEG) inside the crustacean circulatory system, using the example of the amphipod Eulimnogammarus verrucosus. In particular, we explored the distribution dynamics of visible microcapsules after injection into the main hemolymph vessel; analyzed the most significant features of E. verrucosus autofluorescence; monitored amphipod mortality and biochemical markers of stress response after microcapsule injection, as well as the healing of the injection wound; and finally, we studied the immune response to the microcapsules. The visibility of microcapsules decreased with time, however, the central hemolymph vessel was confirmed to be the most promising organ for detecting the spectral signal of implanted microencapsulated fluorescent probes. One million injected microcapsules (sufficient for detecting stable fluorescence during the first hours after injection) showed no toxicity for six weeks, but in vitro amphipod immune cells recognize the PEG-coated microcapsules as foreign bodies and try to isolate them by 12 h after contact.

Histologic Findings in Captive American Horseshoe Crabs (Limulus polyphemus)

Histopathology of 61 captive American horseshoe crabs (HSCs; Limulus polyphemus) is reviewed. HSC organs evaluated histologically included body wall (chitin, epidermis, dermis, and skeletal muscle), hepatopancreas, gut, gonads, book gills, eyes, heart, brain, and coxal gland. In descending order, lesions were most frequently identified in compound eye, body wall, book gills, hepatopancreas, chitinous gut, nonchitinous gut, heart, and brain; lesions were not observed in coxal gland or gonads. Hemocytes (also called amoebocytes) surrounded infectious agents and occluded ulcers. Large hemocyte aggregates had a central eosinophilic coagulum (ie, hemocyte coagulum). Cutaneous ulceration (34/60 cases), branchitis (29/48 cases), and ophthalmitis (17/20 cases) were common lesions and consistently associated with fungi, which were invasive into subjacent tissues, and/or bacteria, which were usually superficial. Fungal culture was performed in 3 cases and isolated Fusarium spp., although fungal morphology varied and multiple fungal species may have been present. Presumptive green algae were associated with ulceration in 1 case with minimal to no inflammation. Presumptive cyanobacteria were identified within a biofilm overlying the gills in 4 of 48 cases and were not invasive. Multifocal, random hepatopancreatitis was identified in 16 of 57 cases, 10 of which were associated with bacteria. Metacercarial cysts were identified in 25 of 61 cases and associated with minimal to no inflammation. Depleted eosinophilic globules in hepatopancreatic interstitial cells were interpreted as decreased nutritional status in 12 of 57 cases.

Developmental and Immune Role of a Novel Multiple Cysteine Cluster TLR From Eisenia andrei Earthworms

Earthworms are not endowed with adaptive immunity and they are rely on the tools of innate immunity. Cells of the innate immune system utilize pattern recognition receptors, such as Toll-like receptors, to detect the pathogen-associated molecular patterns (PAMPs). The first earthworm TLR was isolated from Eisenia andrei earthworms (EaTLR), which belongs to the single cysteine cluster TLR (sccTLR). Here, we identified a new multiple cysteine cluster TLR (mccTLR) in E. andrei earthworms. Phylogenetic DNA analysis revealed that it has no variability within one earthworm as well as in the population. By screening of the tissue expression profile, the TLR was expressed primarily in earthworm seminal vesicles and receptacles suggesting a connection to sperm cells. Seminal vesicles are often heavily infected by gregarine parasites. As a sign of immune response, a strong melanization reaction is visible around parasites. Stimulation experiments with profilin from related parasite Toxoplasma gondii, led to the upregulation of mccEaTLR in the earthworm seminal vesicles. Also, profilin activated prophenoloxidase cascade, the efficient mechanism of innate immunity. However, its involvement in the NF-κB signaling was not proven. Further, we provide evidence that the antibiotics metronidazole and griseofulvin destroyed the developing spermatocytes. The observed decrease in the mccEaTLR mRNA levels after the antibiotic treatment of parasites is caused by the decline of sperm cells numbers rather than by diminution of the parasites. Since earthworms with extensively reduced parasite load had a similar amount of mccEaTLR mRNA, presumably, earthworm sperm cells have a certain level of mccEaTLR expressed as a standard, which can be augmented by particular antigenic stimulation. Also, mccEaTLR was expressed mainly in the early stages of earthworm development and presumably is primarily involved in early embryonic development. Expression of mccEaTLR in seminal vesicles correlates with the expression of endothelial monocyte-activation polypeptide II. High-throughput sequencing of gregarine DNA from seminal vesicles of individual earthworms resulted in great diversity of the observed genotypes. Phylogenetically, all observed OTUs belong to the clade of earthworm gregarines suggesting host specificity. Overall, mccEaTLR is supposed to play a function role in early embryonic development and potentially it participates in immune response against parasites.

Trait-based ecology of terrestrial arthropods

In focusing on how organisms' generalizable functional properties (traits) interact mechanistically with environments across spatial scales and levels of biological organization, trait-based approaches provide a powerful framework for attaining synthesis, generality and prediction. Trait-based research has considerably improved understanding of the assembly, structure and functioning of plant communities. Further advances in ecology may be achieved by exploring the trait-environment relationships of non-sessile, heterotrophic organisms such as terrestrial arthropods, which are geographically ubiquitous, ecologically diverse, and often important functional components of ecosystems. Trait-based studies and trait databases have recently been compiled for groups such as ants, bees, beetles, butterflies, spiders and many others; however, the explicit justification, conceptual framework, and primary-evidence base for the burgeoning field of 'terrestrial arthropod trait-based ecology' have not been well established. Consequently, there is some confusion over the scope and relevance of this field, as well as a tendency for studies to overlook important assumptions of the trait-based approach. Here we aim to provide a broad and accessible overview of the trait-based ecology of terrestrial arthropods. We first define and illustrate foundational concepts in trait-based ecology with respect to terrestrial arthropods, and justify the application of trait-based approaches to the study of their ecology. Next, we review studies in community ecology where trait-based approaches have been used to elucidate how assembly processes for terrestrial arthropod communities are influenced by niche filtering along environmental gradients (e.g. climatic, structural, and land-use gradients) and by abiotic and biotic disturbances (e.g. fire, floods, and biological invasions). We also review studies in ecosystem ecology where trait-based approaches have been used to investigate biodiversity-ecosystem function relationships: how the functional diversity of arthropod communities relates to a host of ecosystem functions and services that they mediate, such as decomposition, pollination and predation. We then suggest how future work can address fundamental assumptions and limitations by investigating trait functionality and the effects of intraspecific variation, assessing the potential for sampling methods to bias the traits and trait values observed, and enhancing the quality and consolidation of trait information in databases. A roadmap to guide observational trait-based studies is also presented. Lastly, we highlight new areas where trait-based studies on terrestrial arthropods are well positioned to advance ecological understanding and application. These include examining the roles of competitive, non-competitive and (multi-)trophic interactions in shaping coexistence, and macro-scaling trait-environment relationships to explain and predict patterns in biodiversity and ecosystem functions across space and time. We hope this review will spur and guide future applications of the trait-based framework to advance ecological insights from the most diverse eukaryotic organisms on Earth.

Replanting of first-cycle oil palm results in a second wave of biodiversity loss

Conversion of forest to oil palm plantations results in a significant loss of biodiversity. Despite this, first-cycle oil palm plantations can sustain relatively high biodiversity compared to other crops. However, the long-term effects of oil palm agriculture on flora and fauna are unknown. Oil palm has a 25-year commercial lifespan before it must be replanted, due to reduced productivity and difficulty of harvesting. Loss of the complex vegetation structure of oil palm plantations during the replanting process will likely have impacts on the ecosystem at a local and landscape scale. However, the effect of replanting on biodiversity is poorly understood.Here, we investigate the effects of replanting oil palm on soil macrofauna communities. We assessed ordinal richness, abundance, and community composition of soil macrofauna in first- (25- to 27-year-old) and second-cycle oil palm (freshly cleared, 1-year-old, 3-year-old, and 7-year-old mature).Macrofauna abundance and richness drastically declined immediately after replanting. Macrofauna richness showed some recovery 7 years after replanting, but was still 19% lower than first-cycle oil palm. Macrofauna abundance recovered to similar levels to that of first-cycle oil palm plantations, 1 year after replanting. This was mainly due to high ant abundance, possibly due to the increased understory vegetation as herbicides are not used at this age. However, there were subsequent declines in macrofauna abundance 3 and 7 years after replanting, resulting in a 59% drop in macrofauna abundance compared to first-cycle levels. Furthermore, soil macrofauna community composition in all ages of second-cycle oil palm was different to first-cycle plantations, with decomposers suffering particular declines.After considerable biodiversity loss due to forest conversion for oil palm, belowground invertebrate communities suffer a second wave of biodiversity loss due to replanting. This is likely to have serious implications for soil invertebrate diversity and agricultural sustainability in oil palm landscapes, due to the vital ecosystem functions that soil macrofauna provide.

Nitrogen Inputs by Marine Vertebrates Drive Abundance and Richness in Antarctic Terrestrial Ecosystems

Biodiversity is threatened by climate change and other human activities [1], but to assess impacts, we also need to identify the current distribution of species on Earth. Predicting abundance and richness patterns is difficult in many regions and especially so on the remote Antarctic continent, due to periods of snow cover, which limit remote sensing, and the small size of the biota present. As the Earth's coldest continent, temperature and water availability have received particular attention in understanding patterns of Antarctic biodiversity [2], whereas nitrogen availability has received less attention [3]. Nitrogen input by birds is a major nutrient source in many regions on Earth [4-7], and input from penguins and seals is associated with increased plant growth [8-10] and soil respiration [11-13] at some Antarctic locations. However, the consequences of increased nitrogen concentrations in Antarctic mosses and lichens for their associated food web has hardly been addressed [14, 15], despite the fact that nutrient status of primary producers affects the abundance and diversity of higher trophic levels [16, 17]. We show that nitrogen input and δ¹⁵N signatures from marine vertebrates are associated with terrestrial biodiversity hotspots well beyond (>1,000 m) their immediate colony borders along the Antarctic Peninsula. Invertebrate abundance and richness was two to eight times higher under penguin and elephant seal influence. The nitrogen footprint area was correlated with the vertebrate population size. These findings improve our ability to predict biogeographical patterns of Antarctic terrestrial biodiversity through knowledge of the location and size of penguin and elephant seal concentrations.

Retinoid receptor-based signaling plays a role in voltage-dependent inhibition of invertebrate voltage-gated Ca2+ channels

The retinoic acid receptor (RAR) and retinoid X receptor (RXR) mediate the cellular effects of retinoids (derivatives of vitamin A). Both RAR and RXR signaling events are implicated in hippocampal synaptic plasticity. Furthermore, retinoids can interact with calcium signaling during homeostatic plasticity. We recently provided evidence that retinoids attenuate calcium current (I _Ca) through neuronal voltage-gated calcium channels (VGCCs). We now examined the possibility that constitutive activity of neuronal RXR and/or RAR alters calcium influx via the VGCCs. We found that in neurons of the mollusk Lymnaea stagnalis, two different RXR antagonists (PA452 and HX531) had independent and opposing effects on I _Ca that were also time-dependent; whereas the RXR pan-antagonist PA452 enhanced I _Ca, HX531 reduced I _Ca Interestingly, this effect of HX531 occurred through voltage-dependent inhibition of VGCCs, a phenomenon known to influence neurotransmitter release from neurons. This inhibition appeared to be independent of G proteins and was largely restricted to Ca_v2 Ca²⁺ channels. Of note, an RAR pan-antagonist, LE540, also inhibited I _Ca but produced G protein-dependent, voltage-dependent inhibition of VGCCs. These findings provide evidence that retinoid receptors interact with G proteins in neurons and suggest mechanisms by which retinoids might affect synaptic calcium signaling.

Pharmacological evidence for the role of RAR in axon guidance and embryonic development of a protostome species

Retinoic acid (RA), the active metabolite of vitamin A, functions through nuclear receptors, one of which is the retinoic acid receptor (RAR). Though the RAR is essential for various aspects of vertebrate development, little is known about the role of RAR in nonchordate invertebrates. Here, we examined the potential role of an invertebrate RAR in mediating chemotropic effects of retinoic acid. The RAR of the protostome Lymnaea stagnalis is present in the growth cones of regenerating cultured motorneurons, and a synthetic RAR agonist (EC23), was able to mimic the effects of retinoic acid in inducing growth cone turning. We also examined the ability of the natural retinoids, all-trans RA and 9-cis RA, as well as the synthetic RAR agonists, to disrupt embryonic development in Lymnaea. Developmental defects included delays in embryo hatching, arrested eye, and shell development, as well as more severe abnormalities such as halted development. Developmental defects induced by some (but not all) synthetic RAR agonists were found to mimic those induced by addition of high concentrations of the natural retinoid isomers. These pharmacological data support a possible physiological role for the RAR in axon guidance and embryonic development of an invertebrate protostome species.

A meta food web for invertebrate species collected in a European grassland

Patterns of feeding interactions between species are thought to influence the stability of communities and the flux of nutrients and energy through ecosystems. However, surprisingly few well-resolved food webs allow us to evaluate factors that influence the architecture of species interactions. We constructed a meta food web consisting of 714 invertebrate species collected over 9 years of suction and pitfall sampling campaigns in the Jena Experiment, a long-term grassland biodiversity experiment located in Jena, Germany. We summarize information on the 51,496 potential trophic links, which were established using information on diet specificity and species traits that typically constrain feeding interactions (trophic group, body size, and vertical stratification). The list of species identities, traits, and link-derivation rules will be useful not only for tests of plant diversity effects on food web structure within the Jena Experiment, but also for considering consistent construction of food webs from empirical data, and for comparisons of network structure across ecosystems. No copyright or proprietary restrictions are associated with the use of this data set other than citation of this Data Paper.

Neurite Development and Repair in Worms and Flies

How the nervous system is wired has been a central question of neuroscience since the inception of the field, and many of the foundational discoveries and conceptual advances have been made through the study of invertebrate experimental organisms, including Caenorhabditis elegans and Drosophila melanogaster. Although many guidance molecules and receptors have been identified, recent experiments have shed light on the many modes of action for these pathways. Here, we summarize the recent progress in determining how the physical and temporal constraints of the surrounding environment provide instructive regulations in nervous system wiring. We use Netrin and its receptors as an example to analyze the complexity of how they guide neurite outgrowth. In neurite repair, conserved injury detection and response-signaling pathways regulate gene expression and cytoskeletal dynamics. We also describe recent developments in the research on molecular mechanisms of neurite regeneration in worms and flies.