Venom is a remarkable innovation found across the animal kingdom, yet the evolutionary origins of venom systems in various groups, including spiders, remain enigmatic. Here, we investigated the organogenesis of the venom apparatus in the common house spider, Parasteatoda tepidariorum. The venom apparatus consists of a pair of secretory glands, each connected to an opening at the fang tip by a duct that runs through the chelicerae. We performed bulk RNA-seq to identify venom gland-specific markers and assayed their expression using RNA in situ hybridisation experiments on whole-mount time-series. These revealed that the gland primordium emerges during embryonic stage 13 at the chelicera tip, progresses proximally by the end of embryonic development and extends into the prosoma post-eclosion. The initiation of expression of an important toxin component in late postembryos marks the activation of venom-secreting cells. Our selected markers also exhibited distinct expression patterns in adult venom glands: sage and the toxin marker were expressed in the secretory epithelium, forkhead and sum-1 in the surrounding muscle layer, while Distal-less was predominantly expressed at the gland extremities. Our study provides the first comprehensive analysis of venom gland morphogenesis in spiders, offering key insights into their evolution and development.

BACKGROUND: Male courtship investment may evolve in response to the male\'s expectation of future mating opportunities or the degree of female control during mating interactions. We used a comparative approach to test this hypotheses by assessing the courtship and mating behaviors of five widow spider species (genus Latrodectus) under common laboratory conditions. We predicted male investment in courtship would be higher in species where males mate only once because of high cannibalism rates (monogyny, L. geometricus, L. hasselti, L. mirabilis), compared to species with rare cannibalism (L. mactans, L. hesperus) in which males should reserve energy for future mating opportunities. Increased male investment, measured as courtship duration, might also evolve with increased female control over mating outcomes if females prefer longer courtships. We tested this by assessing the frequency of copulations, timing of sexual cannibalism, and the degree of female-biased size dimorphism, which is expected to be negatively correlated with the energetic cost of rebuffing male mating attempts.
RESULTS: Copulation frequency was consistently lower in species with extreme female-skewed size dimorphism, and where sexual cannibalism was more prevalent, suggesting the importance of female control for mating outcomes. We confirmed significant interspecific variation in average courtship duration, but contrary to predictions, it was not predicted by male mating system, and there was no consistent link between courtship duration and sexual size dimorphism.
CONCLUSIONS: We show that the degree of sexual dimorphism is not only correlated with sexual cannibalism, but also with mating success since restriction of male copulation frequency by female Latrodectus affects paternity. However, predictions about male mating system or female control affecting courtship duration were not supported. We propose that the form of female control over mating and cannibalism, and male responses, might be more informative for understanding the evolution of courtship duration. For example, male tactics to avoid female aggression may drive lower courtship duration in species like L. mirabilis. Nonetheless, our results differ from inferences based on published studies of each species in isolation, illuminating the need for standardized data collection for behavioural comparative studies.

Field ridges are commonly viewed as the stable semi-natural habitats for maintaining plant diversity in the agricultural landscape. The high plant diversity could further support higher animal diversity. But following the adoption of well-facilitated farmland construction measures in China, many field ridges have been disproportionately neglected or destroyed. Empirical studies delineating the relationships between plant and animal diversity in these field ridges in the paddy landscape remain scant, especially in China, which has the most rice production. A two-year field ridge evaluation was conducted in the Chengdu Plain area, covering 30 paddy landscapes. This investigation scrutinizes the shape attributes of field ridges, their plant diversity, and the associated animal α-diversity and community compositions, including spiders, carabids, birds, frogs, and rice planthoppers. In the results of Pearson\'s correlation analysis, a significant inconsistent correlation was observed between plant diversity and animal diversity. The analysis of community structure heterogeneity also revealed no correspondence for species composition between plant and animal communities (i.e., spiders, carabids, and birds), while the non-metric multidimensional scale analysis indicated a substantial difference in the species composition of spiders or plants even within the same field ridge between 2020 and 2021. We argue that the implementation of intensive management practices in paddy landscapes, such as machine ploughing and harvesting and herbicide spraying with drones, leads to a scarcity of stable animal and plant communities in field ridges. Therefore, besides retaining these field ridges in paddy landscapes, maintaining the long-term stable ridges by refraining from herbicide spraying or artificial weeding, as well as avoiding winter wheat cultivating in field ridges, will contribute to protecting biodiversity of field ridges as semi-natural habitats.

Venom plays a crucial role in the defense and predation of venomous animals. Spiders (Araneae) are among the most successful predators and have a fascinating venom composition. Their venom mainly contains disulfide-rich peptides and large proteins. Here, we analyzed spider venom protein families, utilizing transcriptomic and genomic data, and highlighted their similarities and differences. We show that spiders have specific combinations of toxins for better predation and defense, typically comprising a core toxin expressed alongside several auxiliary toxins. Among them, the CAP superfamily is widely distributed and highly expressed in web-building Araneoidea spiders. Our analysis of evolutionary relationships revealed four subfamilies (subA-subD) of the CAP superfamily that differ in structure and potential functions. CAP proteins are composed of a conserved CAP domain and diverse C-terminal domains. CAP subC shares similar domains with the snake ion channel regulator svCRISP proteins, while CAP subD possesses a sequence similar to that of insect venom allergen 5 (Ag5). Furthermore, we show that gene duplication and selective expression lead to increased expression of CAP subD, making it a core member of the CAP superfamily. This study sheds light on the functional diversity of CAP subfamilies and their evolutionary history, which has important implications for fully understanding the composition of spider venom proteins and the core toxin components of web-building spiders.

Polyamines (PAs) are polycationic biogenic amines ubiquitously present in all life forms and are involved in molecular signaling and interaction, determining cell fate (e.g., cell proliferation, dif-ferentiation, and apoptosis). The intricate balance in the PAs\' levels in the tissues will determine whether beneficial or detrimental effects will affect homeostasis. It\'s crucial to note that endoge-nous polyamines, like spermine and spermidine, play a pivotal role in our understanding of neu-rological disorders as they interact with membrane receptors and ion channels, modulating neuro-transmission. In spiders and wasps, monoamines (histamine, dopamine, serotonin, tryptamine) and polyamines (spermine, spermidine, acyl polyamines) comprise, with peptides and other sub-stances, the low molecular weight fraction of the venom. Acylpolyamines are venom components exclusively from spiders and a species of solitary wasp, which cause inhibition chiefly of iono-tropic glutamate receptors (AMPA, NMDA, and KA iGluRs) and nicotinic acetylcholine receptors (nAChRs). The first venom acylpolyamines ever discovered (argiopines, Joro and Nephila toxins, and philanthotoxins) have provided templates for the design and synthesis of numerous analogs. Thus far, analogs with high potency exert their effect at nanomolar concentrations, with high se-lectivity toward their ionotropic and ligand receptors. These potent and selective acylpolyamine analogs can serve biomedical purposes and pest control management. The structural modification of acylpolyamine with photolabile and fluorescent groups converted these venom toxins into use-ful molecular probes to discriminate iGluRs and nAchRs in cell populations. In various cases, the linear polyamines, like spermine and spermidine, constituting venom acyl polyamine backbones, have served as cargoes to deliver active molecules via a polyamine uptake system on diseased cells for targeted therapy. In this review, we examined examples of biogenic amines that play an essential role in neural homeostasis and cell signaling, contributing to human health and disease outcomes, which can be present in the venom of arachnids and hymenopterans. With an empha-sis on the spider and wasp venom acylpolyamines, we focused on the origin, structure, derivatiza-tion, and biomedical and biotechnological application of these pharmacologically attractive, chemically modular venom components.

Elevational gradients constitute excellent systems for understanding the mechanisms that generate and maintain global biodiversity patterns. Climatic gradients associated with elevation show strong influence on species distribution in mountains. The study of mountains covered by the same habitat type is an ideal scenario to compare alternatives to the energy hypotheses. Our aim was to investigate how changes in climatic conditions along the elevational gradient drive α- and β-diversity of four taxa in a mountain system located within a grassland biome. We sampled ants, spiders, birds and plants, and measured climatic variables at six elevational bands (with 10 sampling sites each) established between 470 and 1,000 masl on a mountain from the Ventania Mountain System, Argentina. Species richness per site and β-diversity (turnover and nestedness) between the lowest band and upper sites were estimated. For most taxa, species richness declined at high elevations and energy, through temperature, was the major driver of species richness for ants, plants and birds, prevailing over productivity and water availability. The major β-diversity component was turnover for plants, spiders and birds, and nestedness for ants. The unique environmental conditions of the upper bands could favour the occurrence of specialist and endemic species.

AbstractIdealized ring species, with approximately continuous gene flow around a geographic barrier but singular reproductive isolation at a ring terminus, are rare in nature. A broken ring species model preserves the geographic setting and fundamental features of an idealized model but accommodates varying degrees of gene flow restriction over complex landscapes through evolutionary time. Here we examine broken ring species dynamics in Calisoga spiders, which, like the classic ring species Ensatina salamanders, are distributed around the Central Valley of California. Using nuclear and mitogenomic data, we test key predictions of common ancestry, ringlike biogeography, biogeographic timing, population connectivity, and terminal overlap. We show that a ring complex of populations shares a single common ancestor, and from an ancestral area in the Sierra Nevada mountains, two distributional and phylogenomic arms encircle the Central Valley. Isolation by distance occurs along these distributional arms, although gene flow restriction is also evident. Where divergent lineages meet in the South Coast Ranges, we find rare lineage sympatry, without evidence for nuclear gene flow and with clear evidence for morphological and ecological divergence. We discuss general insights provided by broken ring species and how such a model could be explored and extended in other systems and future studies.

The major ampullate Spidroin 1 (MaSp1) is the main protein of the dragline spider silk. The C-terminal (CT) domain of MaSp1 is crucial for the self-assembly into fibers but the details of how it contributes to the fiber formation remain unsolved. Here we exploit the fact that the CT domain can form silk-like fibers by itself to gain knowledge about this transition. Structural investigations of fibers from recombinantly produced CT domain from E. australis MaSp1 reveal an α-helix to β-sheet transition upon fiber formation and highlight the helix No4 segment as most likely to initiate the structural conversion. This prediction is corroborated by the finding that a peptide corresponding to helix No4 has the ability of pH-induced conversion into β-sheets and self-assembly into nanofibrils. Our results provide structural information about the CT domain in fiber form and clues about its role in triggering the structural conversion of spidroins during fiber assembly.

Muscles and muscle fibers are volume-constant constructs that deform when contracted and develop internal pressures. However, muscles embedded in hydrostatic skeletons are also exposed to external pressures generated by their activity. For two examples, the pressure generation in spiders and in annelids, we used simplified biomechanical models to demonstrate that high intracellular pressures diminishing the resulting tensile stress of the muscle fibers are avoided in the hydrostatic skeleton. The findings are relevant for a better understanding of the design and functionality of biological hydrostatic skeletons.

Copper (Cu) contamination represents a persistent and significant form of heavy metal pollution in agricultural ecosystems, posing serious threats to organisms in current society. Spiders serve as crucial biological indicators for assessing the impact of heavy metals-induced toxicity. However, the specific molecular responses of spiders to Cu exposure and the mechanisms involved are not well understood. In our study, the wolf pond spiders, Pirata subpiraticus, were exposed to Cu for 21 d, resulting in a notable decline in survival rates compared with the control (n = 50, p < 0.05). We observed an increased expression of enzymes like glutathione peroxidase and superoxide dismutase (p < 0.05), signaling a strong oxidative stress response crucial for counteracting the harmful effects of reactive oxygen species. This response was corroborated by a rise in malondialdehyde levels (p < 0.05), a marker of lipid peroxidation and oxidative damage. Transcriptomic and metabolomic analyses revealed 2004 differentially expressed genes (DEGs) and 220 metabolites (DEMs). A significant number of these DEGs were involved in the glutathione biosynthetic process and antioxidant activity. A conjoint analysis revealed that under the Cu stress, several important enzymes and metabolites were altered (e.g., cathepsin A, legumain, and lysosomal acid lipase), affecting the activities of key biological processes and components, such as lysosome and insect hormone biosynthesis. Additionally, the protein interaction network analysis showed an up-regulation of processes like the apoptotic process, glutamate synthase activity, and peroxisome, suggesting that spiders activate cellular protective strategies to cope with stress and maintain homeostasis. This study not only deepens our understanding of spider biology in the context of environmental stress but also makes a significant contribution to the field of environmental stress biology.