Interaction between spiders and ticks-ancient arthropod predatory behavior?

Ticks are ectoparasite vectors of pathogens affecting human and animal health worldwide. Rational integration of different control interventions including plant-derived repellents and acaricides, management of natural predators, and vaccines is required for innovative approaches to reduce the risks associated with ticks and tick-borne diseases. How tick populations are naturally controlled is always a question. Tick interactions with other arthropods including predators evolved from ancient times. In this study, Cretaceous (ca. 100 Mya) Burmese amber inclusions were identified as probably related to Compluriscutula vetulum (Acari: Ixodida: Ixodidae) tick larvae and spider silk. As illustrated in this study, ancient interactions between ticks and spiders may support arthropod predatory behavior as a natural control intervention. Rational integrative management of different tick control interventions including natural predators under a One Health perspective will contribute to effectively and sustainably reducing the risks associated with ticks and tick-borne diseases.

Venom gland organogenesis in the common house spider.

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.

Envenomation by the Indian ornamental tarantula (Poecilotheria regalis): A case report on treatment with Latrodectus mactans antivenom.

Poecilotheria spiders are considered theraphosids of underestimated clinical importance, with bites from these species inducing symptoms such as severe pain and intense muscle cramps. However, there is no specific treatment for the envenomation caused by these species, which, while native to India and Sri Lanka, are widely distributed worldwide. The present study reports the case of a 31-year-old man bitten by a Poecilotheria regalis specimen. The patient's clinical presentation was similar to Latrodectus envenomation, and patient was treated with an L. mactans antivenom. Most of patient's symptoms improved (fasciculations, pain, erythema, and local swelling), except muscle cramps. A toxicological study conducted on mice did not show that L. mactans antivenom has a neutralizing effect on the toxicity of P. regalis. The present report discusses the envenoming process of Poecilotheria species and the possible neutralizing effect exerted by L. mactans antivenom.

Allometry and ecology shape eye size evolution in spiders.

Eye size affects many aspects of visual function, but eyes are costly to grow and maintain. The allometry of eyes can provide insight into this trade-off, but this has mainly been explored in species that have two eyes of equal size. By contrast, animals possessing larger visual systems can exhibit variable eye sizes within individuals. Spiders have up to four pairs of eyes whose sizes vary dramatically, but their ontogenetic, static, and evolutionary allometry has not yet been studied in a comparative context. We report variable dynamics in eye size across 1,098 individuals in 39 species and 8 families, indicating selective pressures and constraints driving the evolution of different eye pairs and lineages. Supplementing our sampling with a recently published phylogenetically comprehensive dataset, we confirmed these findings across more than 400 species; found that ecological factors such as visual hunting, web building, and circadian activity correlate with eye diameter; and identified significant allometric shifts across spider phylogeny using an unbiased approach, many of which coincide with visual hunting strategies. The modular nature of the spider visual system provides additional degrees of freedom and is apparent in the strong correlations between maximum/minimum investment and interocular variance and three key ecological factors. Our analyses suggest an antagonistic relationship between the anterior and posterior eye pairs. These findings shed light on the relationship between spider visual systems and their diverse ecologies and how spiders exploit their modular visual systems to balance selective pressures and optical and energetic constraints.

Activating an invertebrate bistable opsin with the all-trans 6.11 retinal analog.

Animal vision depends on opsins, a category of G protein-coupled receptor (GPCR) that achieves light sensitivity by covalent attachment to retinal. Typically binding as an inverse agonist, 11-cis retinal photoisomerizes to the all-trans isomer and activates the receptor, initiating downstream signaling cascades. Retinal bound to bistable opsins isomerizes back to the 11-cis state after absorption of a second photon, inactivating the receptor. Bistable opsins are essential for invertebrate vision and nonvisual light perception across the animal kingdom. While crystal structures are available for bistable opsins in the inactive state, it has proven difficult to form homogeneous populations of activated bistable opsins either via illumination or reconstitution with all-trans retinal. Here, we show that a nonnatural retinal analog, all-trans retinal 6.11 (ATR6.11), can be reconstituted with the invertebrate bistable opsin, Jumping Spider Rhodopsin-1 (JSR1). Biochemical activity assays demonstrate that ATR6.11 functions as a JSR1 agonist. ATR6.11 binding also enables complex formation between JSR1 and signaling partners. Our findings demonstrate the utility of retinal analogs for biophysical characterization of bistable opsins, which will deepen our understanding of light perception in animals.

Evolution: Decoding the adaptation of multi-eyed visual systems.

Many invertebrates possess more than two pairs of eyes - but does eye redundancy aid in ecological diversification? A new study finds varied size adaptation of different eye pairs in spiders, demonstrating how developmental modularity of multi-eyed systems effectively balances selective pressures.

Genome of the early spider-orchid Ophrys sphegodes provides insights into sexual deception and pollinator adaptation.

Pollinator-driven evolution of floral traits is thought to be a major driver of angiosperm speciation and diversification. Ophrys orchids mimic female insects to lure male pollinators into pseudocopulation. This strategy, called sexual deception, is species-specific, thereby providing strong premating reproductive isolation. Identifying the genomic architecture underlying pollinator adaptation and speciation may shed light on the mechanisms of angiosperm diversification. Here, we report the 5.2 Gb chromosome-scale genome sequence of Ophrys sphegodes. We find evidence for transposable element expansion that preceded the radiation of the O. sphegodes group, and for gene duplication having contributed to the evolution of chemical mimicry. We report a highly differentiated genomic candidate region for pollinator-mediated evolution on chromosome 2. The Ophrys genome will prove useful for investigations into the repeated evolution of sexual deception, pollinator adaptation and the genomic architectures that facilitate evolutionary radiations.

Infrequent Long-Range Dispersal and Evolution of a Top Terrestrial Arthropod Predator in the Sub-Antarctic.

AbstractThe sub-Antarctic terrestrial ecosystems survive on isolated oceanic islands in the path of circumpolar currents and winds that have raged for more than 30 million years and are shaped by climatic cycles that surpass the tolerance limits of many species. Surprisingly little is known about how these ecosystems assembled their native terrestrial fauna and how such processes have changed over time. Here, we demonstrate the patterns and timing of colonization and speciation in the largest and dominant arthropod predators in the eastern sub-Antarctic: spiders of the genus Myro. Our results indicate that this lineage originated from Australia before the Plio-Pleistocenic glacial cycles and underwent an adaptive radiation on the Crozet archipelago, from where one native species colonized multiple remote archipelagos via the Antarctic circumpolar current across thousands of kilometers. The results indicate limited natural connectivity between terrestrial macroinvertebrate faunas in the eastern sub-Antarctic and partial survival of repeated glaciations in the Plio-Pleistocene. Furthermore, our findings highlight that by integrating arthropod taxa from multiple continents, the climatically more stable volcanic Crozet archipelago played a critical role in the evolution and distribution of arthropod life in the sub-Antarctic.

From fibres to adhesives: evolution of spider capture threads from web anchors by radical changes in silk gland function.

Spider webs that serve as snares are one of the most fascinating and abundant type of animal architectures. In many cases they include an adhesive coating of silk lines-so-called viscid silk-for prey capture. The evolutionary switch from silk secretions forming solid fibres to soft aqueous adhesives remains an open question in the understanding of spider silk evolution. Here we functionally and chemically characterized the secretions of two types of silk glands and their behavioural use in the cellar spider, Pholcus phalangioides. Both being derived from the same ancestral gland type that produces fibres with a solidifying glue coat, the two types produce respectively a quickly solidifying glue applied in thread anchorages and prey wraps, or a permanently tacky glue deployed in snares. We found that the latter is characterized by a high concentration of organic salts and reduced spidroin content, showing up a possible pathway for the evolution of viscid properties by hygroscopic-salt-mediated hydration of solidifying adhesives. Understanding the underlying molecular basis for such radical switches in material properties not only helps to better understand the evolutionary origins and versatility of ecologically impactful spider web architectures, but also informs the bioengineering of spider silk-based products with tailored properties.

Optimal inventorying and monitoring of taxonomic, phylogenetic and functional diversity.

Comparable data is essential to understand biodiversity patterns. While assemblage or community inventorying requires comprehensive sampling, monitoring focuses on as few components as possible to detect changes. Quantifying species, their evolutionary history, and the way they interact requires studying changes in taxonomic (TD), phylogenetic (PD) and functional diversity (FD). Here we propose a method for the optimization of sampling protocols for inventorying and monitoring assemblages or communities across these three diversity dimensions taking sampling costs into account. We used Iberian spiders and Amazonian bats as two case-studies. The optimal combination of methods for inventorying and monitoring required optimizing the accumulation curve of α-diversity and minimizing the difference between sampled and estimated ß-diversity (bias), respectively. For Iberian spiders, the optimal combination for TD, PD and FD allowed sampling at least 50% of estimated diversity with 24 person-hours of fieldwork. The optimal combination of six person-hours allowed reaching a bias below 8% for all dimensions. For Amazonian bats, surveying all the 12 sites with mist-nets and 0 or 1 acoustic recorders was the optimal combination for almost all diversity types, resulting in >89% of the diversity and <10% bias with roughly a third of the cost. Only for phylogenetic α-diversity, the best solution was less clear and involved surveying both with mist nets and acoustic recorders. The widespread use of optimized and standardized sampling protocols and regular repetition in time will radically improve global inventory and monitoring of biodiversity. We strongly advocate for the global adoption of sampling protocols for both inventory and monitoring of taxonomic, phylogenetic and functional diversity.

Broken Ring Speciation in California Mygalomorph Spiders (Nemesiidae, Calisoga).

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.

Spider and Wasp Acylpolyamines: Venom Components and Versatile Pharmacological Leads, Probes, and Insecticidal Agents.

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.

Identification and Evolutionary Analysis of the Widely Distributed CAP Superfamily in Spider Venom.

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.

Does female control and male mating system predict courtship investment and mating outcomes? A comparative study in five widow spider species (genus Latrodectus) tested under similar laboratory conditions.

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. CONCLUSION: 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.

Effect of Phosphate on the Molecular Properties, Interactions, and Assembly of Engineered Spider Silk Proteins.

Phosphate plays a vital role in spider silk spinning and has been utilized in numerous artificial silk spinning attempts to replicate the remarkable mechanical properties of natural silk fiber. Its application in artificial processes has, however, yielded varying outcomes. It is thus necessary to investigate the origins and mechanisms behind these differences. By using recombinant silk protein SC-ADF3 derived from the garden spider Araneus diadematus, here, we describe its conformational changes under various conditions, elucidating the effect of phosphate on SC-ADF3 silk protein properties and interactions. Our results demonstrate that elevated phosphate levels induce the irreversible conformational conversion of SC-ADF3 from random coils to ß-sheet structures, leading to decreased protein solubility over time. Furthermore, exposure of SC-ADF3 to phosphate stiffens already formed structures and reduces the ability to form new interactions. Our findings offer insights into the underlying mechanism through which phosphate-induced ß-sheet structures in ADF3-related silk proteins impede fiber formation in the subsequent phases. From a broader perspective, our studies emphasize the significance of silk protein conformation for functional material formation, highlighting that the formation of ß-sheet structures at the initial stages of protein assembly will affect the outcome of material forming processes.

Changes in the material properties of spider glue droplet proteins accompanied shifts in prey capture biomechanics as cobweb spiders diverged from their orb weaving ancestors.

Although descended from orb weavers, spiders in the family Theridiidae spin cobwebs whose sticky prey capture gumfoot lines extend from a silk tangle to a surface below. When a crawling insect contacts glue droplets at the bottom of a gumfoot line, the line's weak pyriform anchor releases, causing the taut line to contract, pulling the insect from the surface and making its struggles to escape ineffective. To determine if this change in prey capture biomechanics was accompanied by a change in the material properties of theridiid glue, we characterized the elastic modulus and toughness of the glue droplet proteins of four theridiid species at 20-90 % relative humidity and compared their properties with those of 13 orb weaving species in the families Tetragnathidae and Araneidae. Compared to orb weavers, theridiid glue proteins had low extensions per protein volume and low elastic modulus and toughness values. These differences are likely explained by the loss of tension on a gumfoot line when its anchor fails, which may prioritize glue droplet adhesion rather than extension. Similarities in theridiid glue droplet properties did not reflect these species' evolutionary relationships. Instead, they appear associated with differences in web architecture. Two species that had stiffer gumfoot support lines and longer and more closely spaced gumfoot lines also had stiffer glue proteins. These lines may store more energy, and, when their anchors release, require stiffer glue to resist the more forceful upward thrust of a prey. STATEMENT OF SIGNIFICANCE: When a crawling insect contacts glue droplets on a theridiid cobweb's gumfoot line, this taut line's anchor fails and the insect is hoisted upward, rendering its struggles to escape ineffective. This strategy contrasts with that of orb weaving ancestors, which rely on more closely spaced prey capture threads to intercept and retain flying insects. A comparison of the elastic modulus and toughness of gumfoot and orb web glue proteins shows that this change in prey capture biomechanics is associated with reductions in the stiffness and toughness of cobweb glue. Unlike orb web capture threads, whose droplets extend in a coordinated fashion to sum adhesive forces, gumfoot lines become untethered, which prioritizes glue droplet adhesive contact over glue droplet extension.

Warming alters cascading effects of a dominant arthropod predator on fungal community composition in the Arctic.

Rapid climate change in the Arctic is altering microbial structure and function, with important consequences for the global ecosystem. Emerging evidence suggests organisms in higher trophic levels may also influence microbial communities, but whether warming alters these effects is unclear. Wolf spiders are dominant Arctic predators whose densities are expected to increase with warming. These predators have temperature-dependent effects on decomposition via their consumption of fungal-feeding detritivores, suggesting they may indirectly affect the microbial structure as well. To address this, we used a fully factorial mesocosm experiment to test the effects of wolf spider density and warming on litter microbial structure in Arctic tundra. We deployed replicate litter bags at the surface and belowground in the organic soil profile and analyzed the litter for bacterial and fungal community structure, mass loss, and nutrient characteristics after 2 and 14 months. We found there were significant interactive effects of wolf spider density and warming on fungal but not bacterial communities. Specifically, higher wolf spider densities caused greater fungal diversity under ambient temperature but lower fungal diversity under warming at the soil surface. We also observed interactive treatment effects on fungal composition belowground. Wolf spider density influenced surface bacterial composition, but the effects did not change with warming. These findings suggest a widespread predator can have indirect, cascading effects on litter microbes and that effects on fungi specifically shift under future expected levels of warming. Overall, our study highlights that trophic interactions may play important, albeit overlooked, roles in driving microbial responses to warming in Arctic terrestrial ecosystems. IMPORTANCE: The Arctic contains nearly half of the global pool of soil organic carbon and is one of the fastest warming regions on the planet. Accelerated decomposition of soil organic carbon due to warming could cause positive feedbacks to climate change through increased greenhouse gas emissions; thus, changes in ecological dynamics in this region are of global relevance. Microbial structure is an important driver of decomposition and is affected by both abiotic and biotic conditions. Yet how activities of soil-dwelling organisms in higher trophic levels influence microbial structure and function is unclear. In this study, we demonstrate that predicted changes in abundances of a dominant predator and warming interactively affect the structure of litter-dwelling fungal communities in the Arctic. These findings suggest predators may have widespread, indirect cascading effects on microbial communities, which could influence ecosystem responses to future climate change.

Engineering a wolf spider A-family toxin towards increased antimicrobial activity but low toxicity.

Spider-derived peptides with insecticidal, antimicrobial and/or cytolytic activities, also known as spider venom antimicrobial peptides (AMPs), can be found in the venoms of RTA-clade spiders. They show translational potential as therapeutic leads. A set of 52 AMPs has been described in the Chinese wolf spider (Lycosa shansia), and many have been shown to exhibit antibacterial effects. Here we explored the potential to enhance their antimicrobial activity using bioengineering. We generated a panel of artificial derivatives of an A-family peptide and screened their activity against selected microbial pathogens, vertebrate cells and insects. In several cases, we increased the antimicrobial activity of the derivatives while retaining the low cytotoxicity of the parental molecule. Furthermore, we injected the peptides into adult Drosophila suzukii and found no evidence of insecticidal effects, confirming the low levels of toxicity. Our data therefore suggest that spider venom linear peptides naturally defend the venom gland against microbial colonization and can be modified into more potent antimicrobial agents that could help to battle infectious diseases in the future.

HcN57, A Novel Unusual Acidic Silk-Like Matrix Protein from Hyriopsis cumingii, Participates in Framework Construction and Nacre Nucleation During Nacreous Layer Formation.

In the classic molecular model of nacreous layer formation, unusual acidic matrix proteins rich in aspartic acid (Asp) residues are essential for nacre nucleation due to their great affinity for binding calcium. However, the acidic matrix proteins discovered in the nacreous layer so far have been weakly acidic with a high proportion of glutamate. In the present study, several silk-like matrix proteins, including the novel matrix protein HcN57, were identified in the ethylenediaminetetraacetic acid-soluble extracts of the nacreous layer of Hyriopsis cumingii. HcN57 is a highly repetitive protein that consists of a high proportion of alanine (Ala, 34.4%), glycine (Gly, 22.5%), and serine (Ser, 11.4%). It forms poly Ala blocks, GlynX repeats, an Ala-Gly repeat, and a Ser-Ala-rich region, exhibiting significant similarity to silk proteins found in spider species. The expression of HcN57 was specifically located in the dorsal epithelial cells of the mantle pallium and mantle center. Notably, expression of HcN57 was relatively high during nacreous layer regeneration and pearl nacre deposition, suggesting HcN57 is a silk matrix protein in the nacreous layer. Importantly, HcN57 also contains a certain content of Asp residues, making it an unusual acidic matrix protein present in the nacreous layer. These Asp residues are mainly distributed in three large hydrophilic acidic regions, which showed inhibitory activity against aragonite deposition and morphological regulation of calcite in vitro. Moreover, HcN57-dsRNA injection resulted in failure of nacre nucleation in vivo. Taken together, our results show that HcN57 is a bifunctional silk protein with poly Ala blocks and Gly-rich regions that serve as space fillers within the chitinous framework to prevent crystallization at unnecessary nucleation sites and Asp-rich regions that create a calcium ion supersaturated microenvironment for nucleation in the center of nacre tablets. These observations contribute to a better understanding of the mechanism by which silk proteins regulate framework construction and nacre nucleation during nacreous layer formation.

Taxon-dependent diversity response along a temperate elevation gradient covered by grassland.

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 ß-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 ß-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 ß-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.