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The foraging activity of the juvenile horseshoe crabs Tachypleus tridentatus (Leach, 1819) was examined in natural conditions on a sandy substrate during ebb-tide periods in the intertidal zone at Chingluo Wetland, Taiwan, during July and August 2019. The movement patterns, length and width of the crawling paths and the azimuths of direction to sunlight were examined. Juvenile T. tridentatus at the seventh- to tenth-instars (95.5%, 21of 22) could emerge from sand and start to feed on beach surface. Their crawling trails did not follow a straight-line directed pattern; D: Wall was 0.52±1.99; 0.1-0.83 (mean ± s.d.; range). The juveniles rarely faced the sunlight when departing from the starting point or stayed at the end-point of crawling paths. We first detected a lateral phototaxis tendency of juvenile T. tridentatus that was more often with a body lateral to the sunlight than a direct orientation of head towards (81.8% and 18.2%, Binomial test, N = 22, P < 0.01). Their body left-side was more frequently exposed in direction to sunlight the right-side (75% and 25%, Binomial test, N = 24, P < 0.01). We suppose that such a lateral phototaxis and related movement patterns are adaptive foraging strategies of juveniles of T. tridentatus. [ABSTRACT FROM AUTHOR]

The timing of American horseshoe crab (Limulus polyphemus) spawning behavior along the coast of Florida (United States) is generally associated with the highest tides during the spring and fall lunar cycles. All Florida estuaries support horseshoe crab populations, but tidal characteristics vary markedly among locations, which may influence the timing of horseshoe crab spawning behavior. The Indian River Lagoon is a large microtidal estuary on Florida's east coast. Given the microtidal nature of the lagoon, it is unclear which environmental factors affect horseshoe spawning. In 2019, volunteers of Florida Horseshoe Crab Watch conducted daily surveys at two sites in the northern Indian River Lagoon during peak spawning months (February–April). During each survey, volunteers counted all spawning horseshoe crabs and recorded environmental variables, including water temperature, air temperature, wind speed, wind direction, salinity, and tide height. We developed a suite of negative-binomial regression models to quantify relationships between the number of spawning horseshoe crabs and environmental factors. Modeling results indicated a positive relationship between onshore wind speed and number of spawning horseshoe crabs. Our study suggests that in the absence of tidal cues, onshore wind speed may be an important driver of horseshoe crab spawning activity in microtidal estuarine systems. [ABSTRACT FROM AUTHOR]

While considered ecological generalists in most aspects of their life history, horseshoe crabs (Limulus polyphemus) have traditionally been regarded as reproductive habitat specialists, given that spawning is thought to occur primarily on beaches where conditions for embryonic development are considered optimal. Observations of horseshoe crabs spawning in other habitats were deemed isolated and the behavior non‐adaptive. Here, we used spawning and egg surveys to compare the use of beach and salt marsh habitats for spawning by the horseshoe crab in three US states along the Atlantic coast. We found similar spawning and egg densities in both habitats but were more likely to find eggs in marsh habitats, indicating that spawning in marsh habitats is common and geographically widespread. These results suggest that the conservation of salt marshes may be critical for the protection of this species and that management strategies should be revised to incorporate this generalist behavior. [ABSTRACT FROM AUTHOR]

Chelicerae, distinctive feeding appendages in chelicerates, such as spiders, scorpions, or horseshoe crabs, can be classified based on their orientation relative to the body axis simplified as either orthognathous (parallel) or labidognathous (inclined), exhibiting considerable diversity across various taxa. Among extinct chelicerates, sea scorpions belonging to the Pterygotidae represent the only chelicerates possessing markedly elongated chelicerae relative to body length. Despite various hypotheses regarding the potential ecological functions and feeding movements of these structures, no comprehensive 3D kinematic investigation has been conducted yet to test these ideas. In this study, we generated a comprehensive 3D model of the pterygotid Acutiramus, making the elongated right chelicera movable by equipping it with virtual joint axes for conducting Range of Motion analyses. Due to the absence in the fossil record of a clear indication of the chelicerae orientation and their potential lateral or ventral movements (vertical or horizontal insertion of joint axis 1), we explored the Range of Motion analyses under four distinct kinematic settings with two orientation modes (euthygnathous, klinogathous) analogous to the terminology of the terrestrial relatives. The most plausible kinematic setting involved euthygnathous chelicerae being folded ventrally over a horizontal joint axis. This configuration positioned the chelicera closest to the oral opening. Concerning the maximum excursion angle, our analysis revealed that the chela could open up to 70°, while it could be retracted against the basal element to a maximum of 145°. The maximum excursion in the proximal joint varied between 55° and 120° based on the insertion and orientation. Our findings underscore the utility of applying 3D kinematics to fossilized arthropods for addressing inquiries on functional ecology such as prey capture and handling, enabling insights into their possible behavioral patterns. Pterygotidae likely captured and processed their prey using the chelicerae, subsequently transporting it to the oral opening with the assistance of other prosomal appendages. [ABSTRACT FROM AUTHOR]

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Horseshoe crabs represent the most ancestral chelicerate lineage characterized by marine ecology and the possession of lateral compound eyes. While considered living fossils, recent studies reported an unusual number of Pax6 genes in the Atlantic horseshoe crab Limulus polyphemus. Pax genes encode ancient metazoan transcription factors, which comprise seven subfamilies. Among these, the members of the Pax6 subfamily confer critical functions in the development of the head, the visual system, and further body plan components. Arthropods are generally characterized by two Pax6 subfamily homologs that were discovered in Drosophila and named eyeless (ey) and twin of eyeless (toy). However, whole genome sequence searches uncovered three homologs of ey and two homologs of toy in L. polyphemus. These numbers are explained by the occurrence of likely three whole genome duplications in the lineage to the last common ancestor of L. polyphemus and the three additional members of the extant horseshoe crab species cluster. Here, we report that all five L. polyphemus Pax6 paralogs are conserved in the approximately 135-million-year-old horseshoe crab species cluster and that they evolve under strong purifying selection. Largely homogenous protein sequence diversification rates of ey and toy paralogs suggest subfunctionalization as the likeliest preservation trajectory. However, our studies further revealed evidence that the horseshoe crab ey1 and ey2 paralogs share a derived splice isoform that encodes a unique five amino acid-long insertion in helix 3 of the homeodomain. This suggests that the exceptional expansion of the horseshoe crab Pax6 gene family repertoire was also associated with regulatory diversification and possibly innovation. [ABSTRACT FROM AUTHOR]

The article discusses the role of women dentists in esthetic implant dentistry. It highlights the growing demand for implant dentistry worldwide and the increasing number of women in the dental workforce. However, it also notes that fewer women dentists are attracted to implant dentistry compared to men, which is a concern for the future care of dental patients. The article suggests that the lack of undergraduate education in implant dentistry and the perception of costly and lengthy training may be barriers for women dentists. It emphasizes the importance of providing basic knowledge and training in implant dentistry and encourages women dentists to consider it as a stimulating and enriching discipline for their professional journey. [Extracted from the article]

An ichnoassemblage comprising trackways and trails of horseshoe crabs and fishes has been discovered in the Upper Triassic Wayaobu Formation of the Ordos Basin, Shaanxi Province, northern China. This is a lacustrine coal-bearing succession with sandstones, mudstones and oil shales. Two trace-bearing beds are present, one with fine sandstone, the other being a mudstone layer. The traces are assigned to Kouphichnium isp., different Undichna ichnospecies representing U. bina, U. britannica, U. ?quina, U. unisulca and U. isp., and to an indeterminate trackway. Kouphichnium isp. shows long trackways dominated by impressions of the pusher legs, often accompanied by a telson trace. While these were probably left by bottom walking horseshoe crabs, others showing elongated curved scratches lacking a telson trace might have been left by swimming individuals. Remarkable is the large size of the Kouphichnium trackmaker if compared to known Triassic body fossils. The ichnofauna is described and the ichnotaxonomy of Undichna and similar forms discussed. In the Late Triassic, a depressional lake basin was formed within the Ordos Basin. Bivalve, crustacean and fish body fossils support a lake environment in a semi-arid to humid climate. Discoveries of horseshoe crab and diverse fish traces indicate a rich shallow lake epibenthic community. [ABSTRACT FROM AUTHOR]

Aim: Adult body size often exhibits patterns across large‐scale environmental gradients, creating ecogeographic clines. However, the form of body size clines varies across taxonomic groups, with linear and non‐linear patterns in body size observed in nature. Non‐linear body size clines have received less study, and questions remain about how environmental gradients interact to produce non‐linear clines. We examined the body size of the American horseshoe crab (Limulus polyphemus), a widely distributed marine arthropod, and evaluated the hypothesis that temperature and active season length can interact multiplicatively to result in a dome‐shaped distribution. Location: Fourteen states in the United States of America and three Mexican states, representing the entire geographic range of the species. Methods: We compiled environmental data and body size measurements from more than 49,000 individual horseshoe crabs. For each location, we extracted from the literature or calculated from raw data the mean male prosoma width and the mean female prosoma width. We applied a general additive modelling (GAM) approach to characterize the body size cline, test a hypothesis regarding temperature and season length, and explore evidence for the influence of additional environmental factors. Results: Model results indicate temperature and season length could act multiplicatively to produce dome‐shaped clines, and these findings align with and quantify previous anecdotal reports of a strong dome‐shaped body size cline across latitude for horseshoe crabs. Main Conclusions: Active season length appears to become relatively more influential on horseshoe crab body size in the northern part of their range, while temperature effects per se appear to dominate in southern latitudes. For horseshoe crabs, the pattern of size variation is consistent with the predictions of Optimal Resource Allocation models, but more study is needed to elucidate mechanistic underpinnings. Considering climate change projections, results from our study suggest future shifts in horseshoe crab body sizes. [ABSTRACT FROM AUTHOR]

Tetrodotoxin analogues (TTXs) used in research and development were originated from biological sources for the last decades. Among TTXs‐bearing aquatic animals, horseshoe crab Carcinoscorpius rotundicauda from Vietnam's Coast was reported to contain a high level of TTXs, indicating a promising source for extraction and purification of TTXs. In this work, horseshoe crab C. rotundicauda collected from Can Gio Coast, Vietnam was used for TTX extraction using homogenization‐assisted method with acetic acid solvent. The extraction process was analysed and optimized by single‐factor investigation and response surface methodology (RSM). Single‐factor investigation pointed out that the optimal conditions for TTX recovery yield from C. rotundicauda's soft tissues were homogenization time of 20 min, acetic acid concentration of 1.0%, solvent/matrix ratio of 4 mL/g, extraction temperature of 70°C, extraction time of 30 min and number of extraction of two times. The most significant factors including acetic acid concentration, solvent/matrix ratio and extraction temperature were utilized for constructing the RSM model to predict TTX recovery yield. The maximal TTX recovery yield predicted from RSM model was 97.3% under solvent/matrix ratio of 4 mL/g, extraction temperature of 70°C and acetic acid concentration of 1% (v/v). The RSM model displayed a high stability and precision for prediction of TTX recovery yield from experiments of 1–10 kg C. rotundicauda's soft tissues/batch extractions producing low errors (−1.95% to 1.85%). TTXs in C. rotundicauda's soft tissues were elucidated by HPLC‐MS/MS, revealing the presence of three analogues TTX, 4epi‐TTX and Anh‐TTX with their contents of 43.02, 22.54 and 45.07 μg/g, respectively. [ABSTRACT FROM AUTHOR]

Horseshoe crab Factor G is a heterodimeric serine protease zymogen that is activated by (1→3)-β-D-glucans (BDG) from fungal cell walls. This reaction is used in diagnostic agents for deep-seated mycosis. At present, functional analysis using Factor G from Tachypleus tridentatus has been performed, and genetic information has been published, but reconstitution using recombinant proteins has not yet been achieved. In this study, we cloned the genes for Factor G α and β from Limulus polyphemus; two gene sequences were obtained for Factor G α and seven for β. The obtained L. polyphemus Factor G α was used to specifically remove BDG from the culture medium for eliminating the activator BDG. The optimal combination for each sequence was examined with BDG removal medium, and a combination was found that featured BDG-dependent activity. These results indicate that a BDG assay system using recombinant Factor G is feasible in reconstitution. This research will support future reagent development that does not require natural horseshoe crab resources. Key points: • Cloned novel Factor G α subunit and β subunit genes from L. polyphemus • Proposed a method of removing BDG without reducing culture medium performance • Identified combination of recombinant α and β subunits for BDG-dependent activation [ABSTRACT FROM AUTHOR]

Bleeding of horseshoe crabs (Limulus polyphemus) for the biomedical industry can have both sublethal and lethal impacts. Bleeding induces a significant drop in the concentration of hemolymph hemocyanin, as well as decreased levels of activity. Furthermore, horseshoe crabs with low hemocyanin prior to being bled have been found to be more likely to die after the procedure. The goal of this project was to determine whether feeding horseshoe crabs after bleeding them could enhance the recovery of their hemocyanin levels and, in doing so, improve their physiological status. The feeds tested in separate experiments included (1) natural forage items, blue mussels (Mytilus edulis) or softshell clams (Mya arenaria); (2) a formulated diet containing green crabs (Carcinus maenas) and Limulus hemolymph; and (3) a modified commercially available shrimp (Litopenaeus vannamei) broodstock aquafeed. Horseshoe crabs (n = 63) were bled and then either fed or not fed, and their hemolymph hemocyanin concentrations were measured before they were bled and for the following 6–14 days. An additional 25 horseshoe crabs were treated in the same manner but not bled. In three experiments, horseshoe crabs that were fed consistently showed significantly higher hemolymph hemocyanin concentrations compared to those that were not fed. These data suggest that relatively simple modifications of the industrial bleeding procedure, such as feeding horseshoe crabs after bleeding them, may improve their physiological status prior to release. [ABSTRACT FROM AUTHOR]

Recent arachnid phylogenies support an Arachnopulmonata clade including scorpions, pseudoscorpions and the tetrapulmonate arachnids (i.e. spiders and their closest relatives). The position of the other arachnids is less certain, with molecular data suggesting that Arachnida may be paraphyletic with respect to horseshoe crabs. Here we explore the potential role fossil data can play in this debate. We outline the beneficial aspects of including fossils in phylogenies -- fossils calibrate trees to time -- as well as the challenges integrating these data. We tabulate the oldest occurrences of all major groups and superimpose these on recent phylogenetic hypotheses. Given that a key question is when (and how often) arachnids moved from water onto land, we review the early plant fossil record as a framework for when arthropod life on land may have been viable. In light of the aquatic ecology of horseshoe crabs, we then discuss the implications of placing this group within the arachnids, especially since some extinct lineages differ substantially from living species. In this context we re-assess what a horseshoe crab is from a palaeontological perspective, and speculate that some traditional Xiphosura fossils may actually lie on other parts of the euchelicerate tree. The oldest unequivocal horseshoe crabs are Ordovician in age (ca. 480 Ma), and probably predate complex terrestrial ecosystems. We conclude that recent phylogenetic results are best reconciled with fossils by inferring multiple terrestrialization events, possibly involving quite different approaches to breathing air. The lung-bearing (arachnopulmonate) branch of the tree is well resolved. Future work should focus on the apulmonate arachnids, and integrate the various early horseshoe-crab-like fossils into chelicerate phylogeny. [ABSTRACT FROM AUTHOR]

The elements in blood normally reflect the levels in prey, indicating a recent exposure. Laughing gulls (Leucophaes atricilla) eat mainly horseshoe crab eggs (Limulus polyphemus) in the spring in Delaware Bay, New Jersey. The levels of arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), mercury (Hg), and selenium (Se) in the blood of laughing gulls foraging on crab eggs were examined in Delaware Bay to provide information on a species that is normally a generalist, and to determine if the levels of these elements were similar in 2019 and 2022/2023, were intercorrelated, and were related to those in crab eggs. Hg increased from 2019 (136 ± 31 ng/g) to 2022/2023 (473 ± 75 ng/g), while Cd and Se decreased. There were some significant correlations among elements and a close relationship between the element levels in blood and those in crab eggs collected in the same month (except for As). The levels differed between laughing gulls and three species of shorebirds for As and Cd. The elements in the blood of gulls and shorebirds should be similar because they eat mainly the same eggs in the same places. A significant proportion of laughing gull blood samples had levels of Hg and Se that were above the levels associated with adverse effects, which requires further examination. [ABSTRACT FROM AUTHOR]

While several marine species exhibit biological rhythms of heart rate, gill ventilation, or locomotion, the relationship between these three measures in any species remains unexplored. The American horseshoe crab, Limulus polyphemus Linnaeus, 1758 , expresses circalunidian locomotor rhythms and circadian eye sensitivity rhythms, but it is not clear if either heart and ventilation rates are controlled on a circadian, or circatidal basis or the nature of the relationship between these three measures. We aimed to determine the extent to which the heart and ventilation rates of L. polyphemus are coordinated with its endogenous rhythms of locomotion. We recorded rhythmic beating of the heart and movements of the gill plates in freely moving horseshoe crabs. Most individuals exhibited robust circatidal rhythms of locomotion, heart rate, and ventilation that were highly correlated with each other over three weeks of continuous recording. These results are the first showing long-term rhythms of all three measures in any marine species and suggest that heart rate and ventilation rhythms are coordinated in L. polyphemus , both with each other, and with locomotion, and thus are all modulated on a tidal basis. [ABSTRACT FROM AUTHOR]

Simple Summary: Invertebrates (animals without backbones) make up over 95% of the earth's species yet compared with vertebrates (animals with backbones like fishes, amphibians, reptiles, birds, and mammals) our understanding of and efforts relating to the topic of welfare is relatively minimal. We have selected seven of the most economically important and widely recognized invertebrate taxa to focus the topic of animal welfare on. In these pages the reader will learn about coelenterates (jellyfishes, anemones, and corals), mollusks (snails, slugs, squid, and octopi), crustaceans (lobsters, crabs, and shrimp), echinoderms (sea stars, sea urchins, and sea cucumbers), chelicerates (spiders, scorpions, and horseshoe crabs), myriapods (centipedes and millipedes), and insects (butterflies, honeybees, and fruit flies). In addition to discussing the welfare of these species, other topics, including anatomy, physiology, husbandry, natural history, and environmental diseases, are reviewed. Invertebrates are a diverse group of animals that make up the majority of the animal kingdom and encompass a wide array of species with varying adaptations and characteristics. Invertebrates are found in nearly all of the world's habitats, including aquatic, marine, and terrestrial environments. There are many misconceptions about invertebrate sentience, welfare requirements, the need for environmental enrichment, and overall care and husbandry for this amazing group of animals. This review addresses these topics and more for a select group of invertebrates with biomedical, economical, display, and human companionship importance. [ABSTRACT FROM AUTHOR]

Objective: This paper applies a catch multiple survey analysis (CMSA) to Atlantic horseshoe crabs Limulus polyphemus in the Delaware Bay to generate robust population estimates for harvest management. Currently, horseshoe crabs along the U.S. Atlantic coast are harvested as bait for other fisheries and collected for their blood, which is used in a biomedical industry. The Delaware Bay is home to the largest population of horseshoe crabs and is a significant stopover for shorebirds to rebuild energy by consuming horseshoe crab eggs prior to completing their northward migration. To address this interrelationship, the Adaptive Resource Management (ARM) Framework has been used since 2013 to ensure that horseshoe crab harvest within the region takes into account the forage needs of migratory birds. Since its inception, the ARM Framework has used a single trawl survey's swept area‐based population estimates of horseshoe crab relative abundance and a theoretical population model developed primarily from literature‐derived values. With more data collected in the region in recent years and other sources of mortality that can now be quantified, a catch survey model can provide horseshoe crab population estimates going forward. Methods: A CMSA was used to estimate male and female horseshoe crab population size for 2003–2021 using all quantifiable sources of mortality and three fishery‐independent indices of abundance. Result: The CMSA results indicated that adult abundance of male and female horseshoe crabs was stable from 2003 to 2013 and then began to increase through 2017, a result that is consistent with stock rebuilding following a period of harvest restrictions as recommended by the ARM Framework. Population estimates were lower in recent years but remained above the levels estimated before implementation of the ARM Framework. In 2021, the CMSA estimated that there were over 6 million mature females and nearly 16 million mature male horseshoe crabs in the region. Conclusion: The CMSA provides the best and most comprehensive population estimates of horseshoe crabs in Delaware Bay and will improve modeling efforts within the ARM Framework going forward. Impact statementBeing able to estimate the size of the Atlantic horseshoe crab population in the Delaware Bay will help managers set appropriate harvest levels that will support its fisheries while also ensuring there are enough horseshoe crab eggs to feed migrating shorebirds. [ABSTRACT FROM AUTHOR]

Parasitic infections can have profound implications on host fitness, yet there is minimal information on parasites of the American horseshoe crab (Limulus polyphemus), a species that has experienced recent population declines. Therefore, we aimed to quantify the prevalence, intensity, and gill surface area coverage of the ectoparasite Bdelloura candida in adult (n = 58), sub-adult (n = 7) and juvenile (n = 32) horseshoe crabs (HSCs) collected from coastal waters of Long Island, NY in 2019 and 2022. Sub samples of horseshoe crab gill tissue (10%) were collected from live specimens and B. candida cocoon intensities from individual lamellae were enumerated microscopically. B. candida was present in all adult and sub-adult crabs (100%), whereas juveniles exhibited 6.2% prevalence. 4.0–94.0% of gill lamellae harbored cocoons, with intensities ranging from 0 to 805 cocoons per sub sample. Cocoon covered between 0.06%–14.51% of the gill sub sample surface area, with higher cocoon intensities observed in the ventral-most gill quartiles relative to the dorsal-most regions. Sex was strongly supported as a primary driver behind B. candida infection intensities with adult females harboring higher intensities. These results provide novel insight into B. candida infection dynamics across HSC demographics, but further research is necessary to quantify the physiological impacts of the infection on L. polyphemus. [ABSTRACT FROM AUTHOR]

The suitable spawning habitat of Tachypleus tridentatus was estimated and mapped for the first time using scientific modelling in Tsuyazaki, Fukuoka, Japan. A total of 43 nests were found at five sites from 2018 to 2019. Of these 43 nests, the location information of nine nests at one of the sites was used as 'Training data' for constructing the models.A series of procedures was employed to determine the relationship between the biological data and their physical parameters to estimate the suitable spawning habitat. First, the contribution rates of the physical parameters (beach elevation, slope and sediment) to nest locations were evaluated. Second, physical parameters that showed significant contribution rates were chosen to estimate suitable spawning habitats.It was found that the beach elevation was the most significant parameter for estimating suitable spawning habitats. Mean high water neap to mean higher high water was estimated as suitable spawning habitat, and 74% of the nests were fitted in an area assessed as suitable. The result was consistent with previous studies.The area of suitable spawning habitat was estimated to be only 476 m2 out of 1943 m2, comprising 24% of the sandy beach in the study site. Therefore, it was concluded that the conservation and restoration of spawning grounds is a high‐priority and urgent issue at the site.It is proposed that scientific modelling of nest/egg occurrence and beach elevation can effectively determine suitable spawning habitats. Thus, it is possible to quickly establish the habitat most suitable for spawning in coastal environments and help plan conservation strategies for this globally endangered species. [ABSTRACT FROM AUTHOR]

The document titled "Index to Volume 245, December 2023" is an index of articles published in the Biological Bulletin. It includes a range of topics such as the developmental ontology of salps, the embryonic and early larval development of the Pacific razor clam, the use of chromatophores for cryptic coloration in shrimp, the function of BK channels in nematocyst discharge in sea anemones, and the impacts of increasing temperature on the metabolism of American lobsters. The index provides a comprehensive overview of the articles published in the volume and can be a valuable resource for library patrons conducting research on various biological topics. [Extracted from the article]

Simple Summary: Pain is an unpleasant emotional state that produces behavioural changes to minimize future tissue damage and promote recovery and survival. These behavioural changes have been demonstrated in crustaceans, insects, and, to a lesser extent, spiders. Other arthropod groups have received little attention with respect to pain. The examination of situations in which individuals might attempt to cause pain in order to manipulate others might offer new opportunities for research into pain in arthropods. For example, defensive venom, traumatic mating, and fighting might inflict pain. This might benefit the animal causing the pain and result in a cost to the animal in pain. Pain in response to tissue damage functions to change behaviour so that further damage is minimised whereas healing and survival are promoted. This paper focuses on the behavioural criteria that match the function to ask if pain is likely in the main taxa of arthropods. There is evidence consistent with the idea of pain in crustaceans, insects and, to a lesser extent, spiders. There is little evidence of pain in millipedes, centipedes, scorpions, and horseshoe crabs but there have been few investigations of these groups. Alternative approaches in the study of pain are explored and it is suggested that studies on traumatic mating, agonistic interactions, and defensive venoms might provide clues about pain. The evolution of high cognitive ability, sensory systems, and flexible decision-making is discussed as well as how these might influence the evolution of pain-like states. [ABSTRACT FROM AUTHOR]

The lipopolysaccharide (LPS)-triggered horseshoe crab coagulation cascade is composed of three protease zymogens, prochelicerase C (proC), prochelicerase B (proB) and the proclotting enzyme (proCE). In this study, we found that Ca 2+ ions increase the production of the clotting enzyme as a result of a cascade reaction reconstituted by recombinant proteins of wild-type (WT) proC, WT proB and WT proCE. We divided the cascade into three stages: autocatalytic activation of WT proC on the surface of LPS into WT α-chelicerase C (Stage 1); activation of WT proB on the surface of LPS into WT chelicerase B by WT α-chelicerase C (Stage 2) and activation of WT pro ce into WT CE by chelicerase B (Stage 3). Ca2+ ions enhanced the proteolytic activation in Stage 2, but not those in Stages 1 and 3. Moreover, we performed isothermal titration calorimetry to clarify the interaction of LPS or the recombinant zymogens with Ca2+ ions. LPS interacted with Ca2+ ions at an association constant of K a = 4.7 × 104 M−1, but not with any of the recombinant zymogens. We concluded that LPS bound with Ca2+ ions facilitates the chain reaction of the cascade as a more efficient scaffold than LPS itself. [ABSTRACT FROM AUTHOR]

Understanding variations in metal levels in biota geographically and under different environmental conditions is essential to determining risk to organisms themselves and to their predators. It is often difficult to determine food chain relationships because predators may eat several different prey types. Horseshoe crab (Limulus polyphemus) eggs form the basis for a complex food web in Delaware Bay, New Jersey, USA. Female horseshoe crabs lay thumb-sized clutches of eggs, several cm below the surface, and often dislodge previously laid eggs that are brought to the surface by wave action, where they are accessible and critical food for migrant shorebirds. This paper compares metal and metalloid (chromium [Cr], cadmium [Cd], lead [Pb], mercury [Hg], arsenic [As] and selenium [Se]) concentrations in horseshoe crab eggs collected on the surface with concentrations in eggs from clutches excavated from below the sand surface, as well as examining metals in eggs from different parts of the Bay. The eggs were all collected in May 2019, corresponding to the presence of the four main species of shorebirds migrating through Delaware Bay. These migrating birds eat almost entirely horseshoe crab eggs during their stopover in Delaware Bay, and there are differences in the levels of metals in blood of different shorebirds. These differences could be due to whether they have access to egg clutches below sand (ruddy turnstones, Arenaria interpres) or only to eggs on the surface (the threatened red knot [Calidris canutus rufa] and other species of shorebirds). Correlations between metals in clutches were also examined. Except for As and Cd, there were no significant differences between the metals in crab egg clutches and eggs on the surface that shorebirds, gulls, and other predators eat. There were significant locational differences in metal levels in horseshoe crab eggs (except for Pb), with most metals being highest in the sites on the lower portion of Delaware Bay. Most metals in crab eggs have declined since studies were conducted in the mid-1990s but were similar to levels in horseshoe crab eggs in 2012. The data continue to provide important monitoring and assessment information for a keystone species in an ecosystem that supports many species, including threatened and declining shorebird species during spring migration. [ABSTRACT FROM AUTHOR]

The American horseshoe crab (Limulus polyphemus) is an economically and ecologically important species, which is currently categorized as endangered in Mexico. L. polyphemus, one of four extant horseshoe crab species that constitute the class Merostomata, is distributed along the Atlantic coastline of the USA from Alabama to Maine and has another population on the coastline of Campeche, Yucatan, and Quintana Roo in the Yucatan Peninsula, Mexico. In the present study, we evaluated the genetic diversity and genetic structure of four separated localities along the coast of the Yucatan peninsula (Champoton, CH; Isla Arena, IA; Rio Lagartos, RL; and Holbox Island, HI), using nine microsatellite-type molecular markers for this species. The aim of this study is to obtain a baseline of the current level of genetic diversity, which would allow the monitoring of important changes over time. Multilocus analyses revealed moderate levels of genetic diversity (He, 0.5230 to 0.6389) and genetic structure within the whole study area (FST 0.025). The population from RL showed limited gene flows, differing significantly from the other sampling sites. The genetic information obtained in this study can support the implementation of management and conservation programs for this species in Mexico. [ABSTRACT FROM AUTHOR]

This dialogue has emerged from a project funded by the Leverhulme Trust called "Circulatory Entanglements: Marine Biomaterials and Paradoxes in Ocean Governance." The project explores how marine organisms figure in contradictory narratives of ocean futures. Horseshoe crabs, jellyfish, and shrimp all feature in concerning stories of depleted and damaged oceans. But they also enliven narratives of a prosperous blue economy. Throughout the project and inspired by Helen's contributions, we have begun to interrogate our own entanglements with the subjects of our research. Through a series of interlaced reflections, we weave personal histories together with the political economies and imagined resource futures in which our research is embedded. Circuitously, we collectively arc toward a more "blended inquiry" and new ways of knowing. [ABSTRACT FROM AUTHOR]

There is limited study on DNA barcoding of horseshoe crabs in South Sumatra, Indonesia. The present study was the first to record horseshoe crabs' COI DNA barcoding in three localities of Banyasin estuarine waters. The nucleotide composition was in a strong adenine thymine bias (AT = 63.90%) with high haplotypic diversity (Hd = 0.858) relative to low nucleotide diversity (π = 0.0534). A total of 16 haplotypes were recorded, of which two were in Carat Cape, 4 in Makati Jaya, and 12 in the Banyuasin river estuary (BRE), and Hap 1 was a dominant type (62.5%). The population differentiation (FST) value was varied, and only in the comparison of BRE-Carat Cape was significant (FST = 0.637), while the gene flow (Nm) value in Makati Jaya-BRE was high (6.563). The neutrality test, Tajima's D (0.4142), and Fu's Fs values were negative (-0.492), suggesting these populations have experienced a current bottleneck or multiplication. Analysis of molecular variation (AMOVA) suggested that 68% was distributed within populations. The haplotype network, PCoA, and phylogenetic of COI DNA sequences clustered in three groups correspond to Carcinoscorpius rotundicauda, Tachypleus gigas, and Tachypleus tridentatus. This finding is a matter of concern for managing and conserving horseshoe crab species in Banyuasin estuarine waters. [ABSTRACT FROM AUTHOR]

Background: Horseshoe crab (Tachypleus gigas) amebocytes are useful biomedical components for endotoxin detection, and their growing needs for biomedical purposes cause the horseshoe crab population to decline. Factor C synthesis via genetic engineering offers a solution to replace natural horseshoe crab's factor C and prevent its excessive harvest from nature. In response to these concerns, this study aimed to characterize the amebocyte lysates and factor C protein modeling of T. gigas originated from Banyuasin South Sumatra Estuary. Methods and results: Sampling of T. gigas was carried out in Banyuasin South Sumatra Estuary, Indonesia. The endotoxin test or TAL (Tachypleus amebocyte lysates) assay was performed using gel coagulation method. Protein characterization of protease enzyme was conducted by protease activity, SDS-PAGE, and zymogram analysis. The cDNA of mitochondrial COI gene was amplified for molecular identification followed by cDNA cloning of factor C. Protein modeling was investigated by molecular docking and molecular dynamic (MD) simulation. Endotoxin test results showed that TAL-35 had endotoxin sensitivity in a range of 0.0156–1 EU/ml, while TAL 36 had a sensitivity between 00,625 and 1 EU/ml. T. gigas amebocytes have protease activity in molecular mass sizes less than 60 kDa, with 367 U/ml for TAL 35 and 430 U/ml for TAL 36. The molecular identification revealed 98.68% identity similarity to T. gigas. The docking results suggested three ligands; i.e., diphosphoryl lipid A, core lipid A, and Kdo2 lipid A can be activators of the factor C protein by binding to the region of the receptor to form a ligand-receptor complex. Conclusions: Endotoxins can be detected using horseshoe crab amebocytes. The presence of proteases is considered responsible for this ability, as evidenced by casein zymogram results. According to docking and MD analysis, we found that lipopolysaccharides (LPS) participate to the binding site of factor C. [ABSTRACT FROM AUTHOR]

Despite an abundance of gene expression surveys, comparatively little is known about Hox gene function in Chelicerata. Previous investigations of paralogs of labial (lab) and Deformed (Dfd) in a spider have shown that these play a role in tissue maintenance of the pedipalp segment (lab-1) and in patterning the first walking leg identity (Dfd-1), respectively. However, extrapolations of these data across chelicerates are hindered by the existence of duplicated Hox genes in arachnopulmonates (e.g. spiders and scorpions), which have resulted from an ancient whole genome duplication (WGD) event. Here, we investigated the function of the single-copy ortholog of lab in the harvestman Phalangium opilio , an exemplar of a lineage that was not subject to this WGD. Embryonic RNA interference against lab resulted in two classes of phenotypes: homeotic transformations of pedipalps to chelicerae, as well as reduction and fusion of the pedipalp and leg 1 segments. To test for combinatorial function, we performed a double knockdown of lab and Dfd , which resulted in a homeotic transformation of both pedipalps and the first walking legs into cheliceral identity, whereas the second walking leg is transformed into a pedipalpal identity. Taken together, these results elucidate a model for the Hox logic of head segments in Chelicerata. To substantiate the validity of this model, we performed expression surveys for lab and Dfd paralogs in scorpions and horseshoe crabs. We show that repetition of morphologically similar appendages is correlated with uniform expression levels of the Hox genes lab and Dfd , irrespective of the number of gene copies. [ABSTRACT FROM AUTHOR]

In their piece 'Signs of Life - Hearts, Blood and our Breath: An artistic dialogue on embodiment and boundaries', the authors and interdisciplinary artists Jane Prophet and Tobias Klein discuss three recent collaborative artworks made with Victor Leung and contextualise those works by referencing their individual art practices. Sensemaking with the heart and blood is central to these kinetic installation artworks: 'Blood work 1.0', 'Blood work 2.0: Unruh', and 'Common Datum'. The trio made them by interweaving methods and approaches from arts-based inquiry and computer science within a feminist technoscience framework. Blood has historically been a powerful and often contested symbol in art, described by Anne Pollock, Professor of Global Health and Social Medicine, as 'an object itself and an object within a network of objects'. This article considers the characteristics of blood and what it means to be human by triangulating between the chemical, physical and mechanical characteristics of blood. We focus on blood drawn from both human and nonhuman sources and the passage of air into the blood via the semi-permeable lung-heart connection. The artworks are inspired by the transfusion of blood and the use of organs donated by humans and extracted from nonhumans like horseshoe crabs. These biologically inspired, transparent kinetic sculptures depend on and transform the properties and qualities of blood in different species. The fluidity, coagulation and metal content of blood form the structures and movement of the sculptures. In addition, the artists incorporate shifting energies generated through visible mechanical and invisible magnetic forces to question-through-making the material properties and state change in blood flows. [ABSTRACT FROM AUTHOR]

Consideration of the full annual cycle population dynamics can provide useful insight for conservation efforts, but collecting data needed to estimate demographic parameters is often logistically difficult. For species that breed in remote areas, monitoring is often conducted during migratory stopover or at nonbreeding sites, and the recruitment rate of new breeding adults can be difficult to estimate directly. Here, we present an integrated population model that uses mark‐resight and count data to estimate survival probability, population growth rate, and recruitment rate for an Arctic‐breeding shorebird of conservation concern, the red knot (Calidris canutus rufa), from data collected during spring stopover in Delaware Bay, USA, from 2005 to 2018. At this site, red knots feed primarily on the eggs of spawning horseshoe crabs (Limulus polyphemus), a legally harvested species. We used this model to estimate the relationship between horseshoe crab abundance and red knot demographics, which informed a recent revision to the framework used to establish horseshoe crab harvest regulations. Our analysis indicates that the red knot population was most likely stable from 2005 to 2018 (average λ = 1.03, 95% credible interval [CRI]: 0.961, 1.15) despite low recruitment rates (average ρ = 0.088, 95% CRI: 0.012, 0.18). Adult survival probability was positively associated with horseshoe crab abundance in the same year (β = 0.35, 95% CRI: 0.09, 0.63), but we found no effect of horseshoe crab abundance two years previously on recruitment of new adults (β = −0.08, 95% CRI: −0.41, 0.38). Our approach demonstrates the utility of integrated population models for understanding population dynamics, even when data are only available from migratory stopover monitoring. [ABSTRACT FROM AUTHOR]

Knowledge of the growth and ecdysis or molting process in horseshoe crabs as a primitive member of arthropods is limited. This study aimed to investigate the development and ecdysis in the Asian horseshoe crabs through a Scanning Electron Microscope (SEM) approach. The fertilized eggs of Tachypleus gigas were collected from the natural breeding site at Kg. Johor Lama, Johor, and brought back to the laboratory for incubation and hatching. The molted exoskeletons (exuviae) from the first and second ecdysis were collected right away after each molting process, carefully dried and further processed and critical-point dried before coated with gold. The same preparation was made to examine the morphological feature for instars. They were then examined with the SEM. All prosomal appendages are in a complete form during the first instar stage as well as in the exuviae. The second instar stage is noted with the presence of the telson. The exuviae for the first (from instar 1), and then the second molt (from instar 2) showed consistently the suture opening located along the anterior edge of the prosoma at the exuviation suture. This suture is absent from the exoskeleton which is still intact with the larvae. There are notably two hinge pores located at both ends of the hinge which is the central dorsal part that joins the prosoma and opisthosoma. These pores are absent on the intact larvae's exoskeleton. The findings contribute to further improving the understanding of early growth and ecdysis in this living fossil. [ABSTRACT FROM AUTHOR]

Horseshoe crabs as a group are renowned for their morphological conservatism punctuated by marked shifts in morphology associated with the occupation of non-marine environments and have been suggested to exhibit a consistent developmental trajectory throughout their evolutionary history. Here, we report a new species of horseshoe crab from the Ordovician (Late Sandbian) of Kingston, Ontario, Canada, from juvenile and adult material. This new species provides critical insight into the ontogeny and morphology of the earliest horseshoe crabs, indicating that at least some Palaeozoic forms had freely articulating tergites anterior to the fused thoracetron and an opisthosoma comprising 13 segments. [ABSTRACT FROM AUTHOR]

Horseshoe crabs are famous for their blood lysate that is extensively used for the detection of bacterial endotoxin contamination in injectable drugs and medical equipment. However, their existence is now threatened because of overexploitation for bleeding. Synthetic antimicrobial peptides or proteins created by bioengineering may be effective in solving the present predicament. Factor D (FD) is a bioactive substance that shows significant sensitivity to gram-negative bacteria. However, little is known about the expansion information of FD orthologs. In the present study, a total of nine FD orthologs were detected in horseshoe crabs according to the reference genomes. The composition of the FD orthologs in different species was highly conserved, although the common ancestor of the extant horseshoe crabs dates back to the Silurian period. These data suggested that the composition of FD orthologs in horseshoe crabs was formed before the speciation of these species. Considering that three rounds of whole-genome duplication (WGD) events may expanded the homologs in horseshoe crabs, while only one pair of FD orthologs showed significant collinearity according to the intraspecies comparative analysis. Unexpectedly, tandem duplication events that occurred before speciation also expanded the FD orthologs. In addition, several separately distributed FD orthologs also showed high conservation with each other. These data revealed that transposon-mediated duplication may have expanded the FD orthologs in horseshoe crabs. Intriguingly, the C-terminus of the FD orthologs is extremely conserved, although the expansion occurred more than 400 million years ago. In summary, our research provides evidence for the duplication of FD orthologs in horseshoe crabs. Additionally, by demonstrating the conservation of the segments in the C-terminus of these duplicated orthologs, our results also contributed to understanding the functional differentiation mechanism of the diversified FD orthologs. [ABSTRACT FROM AUTHOR]

Horseshoe crabs (Limulus polyphemus) exhibit ontogenetic and geographic variability in migratory patterns, yet the implications of movement on their resource use dynamics remain poorly understood. Here, we evaluate horseshoe crab resource use across ontogeny (instars 14–18 and adults), sex, seasons, and between two spatially distinct populations that exhibit different migratory patterns. Multi-tissue stable isotope analyses of carbon, nitrogen, and sulfur were used to examine (1) ontogenetic and sex-specific variability in the reliance of resource pools; (2) variation in isotopic niche breadth within and among populations; and (3) seasonal variability in resource use within juvenile life stages. We found evidence for subtle ontogenetic shifts in resource use, with increased contributions of phytoplankton with ontogeny, but all age groups predominantly relied on sedimentary organic matter (SOM) pools. Sex-specific differences in resource use were observed with SOM serving as the predominant source assimilated in males, while females exhibited a higher dependence on phytoplankton resource pools, indicating foraging or spatial preferences may be different between sexes. Low trophic niche overlap between adult and juvenile horseshoe crabs was evident, likely arising from differences in migratory patterns and size constraints. Within juveniles, no seasonal differences in resource use were observed, indicating that dietary patterns may remain static across temporal scales, consistent with limited dispersal of that life stage. Spatial differences in resource use were, however, observed between adult crabs likely reflecting the migratory strategies of different populations. Our results are consistent with previous evidence that horseshoe crabs are dietary generalists but provide novel insights into the linkages between movement and trophic patterns. [ABSTRACT FROM AUTHOR]

Horseshoe crabs have survived until Holocene, but their persistence beyond the Anthropocene is challenged by drastic environment changes that entail impoverishments and the resultant unusual growth sizes. Previously, allometry via morphometric ratio was introduced to classify horseshoe crabs into normal-abnormal growth. However, the descriptive size and weight analysis indicated a considerable portion of Tachypleus gigas with normal allometry. This error was caused by the median sorting of values. Therefore, the same data was treated with correlation before generating a linear equation. By being sexual dimorphs, these arthropods actually have gender-specific morphology indicators which could generate a functional allometry. Since the assessed arthropods were mature, the 19 % yield of smaller female T. gigas was possibly due to degradation effects from poor diets or stress. Yet, for this population, an added risk was female-only harvest. Perhaps, close sizing to male counterparts could be perceived a survival strategy by the female T. gigas. More evidence is needed to strengthen this opinion but for now, this assessment method is novel for accurate allometry assessments in the species with sexual dimorphism. Overall, capture fisheries could have negative impacts and when made severe by sex-specific harvest, the unaccounted practices could collapse sustaining populations. [ABSTRACT FROM AUTHOR]

Pioneering molecular work on chelicerate visual system development in the horseshoe crab Limulus polyphemus surprised with the possibility that this process may not depend on the deeply conserved retinal determination function of Pax6 transcription factors. Genomic, transcriptomic, and developmental studies in spiders now reveal that the arthropod Pax6 homologs eyeless and twin of eyeless act as ancestral determinants of the ocular head segment in chelicerates, which clarifies deep gene regulatory and structural homologies and recommends more unified terminologies in the comparison of arthropod visual systems. Following this phylotypic stage, chelicerate visual system development differs fundamentally from other arthropods during the compartmentalization of the ocular segment in that eye and optic neuropil primordia originate independently from each other. Comparative analyses of this phase identified further gene regulatory homologies but also major differences, most notably the possibly compensatory replacement of Pax6 by Pax2 in lateral eye specification. Also see the video abstract here: https://youtu.be/Hdfr3z5kEXU [ABSTRACT FROM AUTHOR]

Background. An enhanced understanding of larval ecology is fundamental to improve the management of locally depleted horseshoe crab populations in Asia. Recent studies in the northern Beibu Gulf, China demonstrated that nesting sites of Asian horseshoe crabs are typically close to their nursery beaches with high-density juveniles distributed around mangrove, seagrass and other structured habitats. Methods. A laboratory Y-maze chamber was used to test whether the dispersal of earlystage juvenile tri-spine horseshoe crab Tachypleus tridentatus is facilitated by chemical cues to approach suitable nursery habitats. The juvenile orientation to either side of the chamber containing controlled seawater or another with various vegetation cues, as well as their movement time, the largest distance and displacement were recorded. Results. The juveniles preferred to orient toward seagrass Halophila beccarii cues when the concentration reached 0.5 g l-1, but ceased at 2 g l-1. The results can be interpreted as a shelter-seeking process to get closer to the preferred settlement habitats. However, the juveniles exhibited avoidance behaviors in the presence of mangrove Avicennia marina and invasive saltmarsh cordgrass Spartina alterniflora at 2 g l-1. The juveniles also spent less time moving in the presence of the A. marina cue, as well as reduced displacement in water containing the S. alterniflora cue at 1 and 2 g l-1. These results may explain the absence of juvenile T. tridentatus within densely vegetated areas, which have generally higher organic matter and hydrogen sulfide. Conclusion. Early-stage juvenile T. tridentatus are capable of detecting and responding to habitat chemical cues, which can help guide them to high-quality settlement habitats. Preserving and restoring seagrass beds in the intertidal areas should be prioritized when formulating habitat conservation and management initiatives for the declining horseshoe crab populations. [ABSTRACT FROM AUTHOR]

The largest aggregation of spawning American horseshoe crabs in the world occurs in Delaware Bay and supports one of the largest concentrations of shorebirds in the western hemisphere where the birds feed on horseshoe crab eggs during migration. Unregulated harvest in the 1990s is associated with the decline of shorebird populations using the bay, but corresponding baseline information on the horseshoe crab egg food supply that supported peak shorebird populations has been lacking.Past and current measurements of horseshoe crab eggs in the bay indicate that abundance in the 1980s was an order of magnitude greater (x̄ = 156,600/m2) than present‐day estimates (2015–2021 x̄ = 10,243/m2). An additional egg prevalence index, which characterizes the timing and magnitude of horseshoe crab egg output, revealed a similar pattern of higher prevalence in the 1980s (0.89, 95% confidence interval 0.81–0.94) compared with the recent 2015–2021 interval (0.52, 95% confidence interval 0.43–0.60).Declines of egg and shorebird abundance occurred shortly after horseshoe crab harvest reached its peak. Red knot aerial survey counts have stabilized at 30% of the baseline population while ruddy turnstone counts are 40% of baseline estimates. Initially these species were evenly distributed between the New Jersey and Delaware coasts but both species have trended toward predominately occupying New Jersey beaches.A lack of recovery of horseshoe crab egg and shorebird abundance suggests that horseshoe crab harvest management has stabilized populations but progress toward population recovery has been limited. Impacts from bycatch, the pharmaceutical industry and other potential population impacts must be better quantified and mitigated, if necessary, to promote the recovery of horseshoe crab populations. Measurements of horseshoe egg prevalence and abundance are essential metrics for tracking the progress toward management goals for improving shorebird habitat quality. [ABSTRACT FROM AUTHOR]