Across the animal kingdom, exaggerated weaponry is frequently used by one sex to contest access for potential mates. Within species, if disproportionate investment in weaponry confers an advantage to ...larger individuals, this may result in positive static allometry. It is predicted that the same selective pressures may also lead to positive evolutionary allometry, where larger species bear disproportionately large weapons on average, compared with smaller species. Furthermore, in species with stronger sexual selection, the static allometries of those weapons are expected to steepen. All adult males across the New Zealand sheetweb spider genus Cambridgea bear exaggerated chelicerae, which are used to compete for control of females' webs. Here, we characterize the distribution of chelicera lengths within each sex of 12 Cambridgea species to show that chelicerae almost always exhibit positive static allometry in males while female chelicera lengths are consistently isometric. We use comparative phylogenetic methods to demonstrate that the slopes of static allometries steepen in males of larger species but that the ratio of average chelicera length to cephalothorax width is tightly conserved across taxa, leading to an isometric evolutionary allometry. While static allometries indeed steepen in larger species, possibly due to stronger sexual selection, this conservation of relative trait size suggests that chelicera length is subject to other stabilizing selective pressures. Changes to species body plans might be constrained, while still allowing for disproportionate investment in weapon traits in the upper range of intraspecific body sizes.
Weapons used in intrasexual competition frequently scale disproportionately with body size with large individuals developing disproportionately large traits (known as ‘positive static allometry’). This scaling relationship is heritable and, in New Zealand sheetweb spiders (Cambridgea spp.), we found that male chelicerae almost uniformly exhibit positive static allometries and that these steepen in the largest species. Despite this, it is likely that the importance of chelicerae for foraging conserves the average ratio of chelicera length to body size across species meaning that, while chelicera length scales disproportionately within species, the body plan of the ‘average’ male looks much the same across the genus.
Novel anthropogenic noise has received considerable attention in behavioural ecology, but the natural acoustic environment has largely been ignored as a niche axis.
Using arrays of speakers, we ...experimentally broadcasted whitewater river noise continuously for three summers, and monitored spider abundance and behaviour across 15 sites, to test our hypothesis that river noise is an important structuring force as a niche axis.
We find substantial evidence that orb‐weaving spiders (Araneidae and Tetragnathidae) are more abundant in high sound level environments, but are not affected by background noise spectrum.
We explore multiple possible mechanisms underlying these patterns, such as loss of vertebrate predators and increased prey capture, and assess spider web‐building behaviour and body condition in noise. Continued research on the natural and anthropogenic acoustic environment will likely reveal a web of connections hidden within this neglected ecological niche axis.
A free Plain Language Summary can be found within the Supporting Information of this article.
A free Plain Language Summary can be found within the Supporting Information of this article.
Triage in conservation biology necessitates the prioritization of species and ecosystems for conservation. Although highly diverse, ecologically important, and charismatic, spiders are rarely ...considered. With 2,253 known species, South Africa's spider diversity is among the highest in the world. A 22-year initiative culminating in a national assessment of all the South African species saw a 33% increase in described species and a 350% rise in specimen accessions of the national collection annually. Endemism is high, at 60% of all South African species. Levels of endemicity are particularly high in Fynbos, Succulent Karroo and Forests. Relative to its area, Forests have three times more endemics than any of the other biomes, followed by the Indian Ocean Coastal Belt. A total of 127 species (5.7%) are either rare or endangered. Threats to these species are largely linked to habitat destruction in the form of urbanization and agriculture. The bulk (62.8%) of taxa are of least concern, but many species are data deficient (27%). Predicted large-scale diversity patterns are confounded by the localised nature of distribution records. Best estimates of compositional turnover point to an east-west bias in our understanding and conservation of spiders in the country, a bias that is most acute in the north-western parts of the country because this region has seen less collecting and has fewer conservation estates. In general, rare and threatened species are mainly ground-dwelling taxa that are either relictual or have poor dispersal abilities. Complemented with long-term surveys that will provide insights into population dynamics of spiders, exploring the use of species traits in predicting extinction probability could provide additional criteria for conservation prioritization. Based on these assessments, targeted species-level interventions might provide a platform for more public awareness and institutional involvement.
Sphagnum farming is paludiculture aiming to produce Sphagnum biomass as a sustainable alternative to peat in horticultural growing media. Here we focus on the habitat value of artificial Sphagnum ...farming sites for peatland species. We report results from seven years of biodiversity monitoring (2011–2018) in a 14 ha Sphagnum farm in north western Germany, using spiders and harvestmen as indicator groups for succession of invertebrate communities. Species richness and abundance more than doubled in the first two years of Sphagnum growth, but remained rather constant since then. Peatland generalists rapidly colonized the site and constitute some 30%–40% of activity dominance since the second year. Stenotopic peatland spiders arrived later, but their abundance proportion increased significantly from 2014 to 2017. Nevertheless, the spider communities remain distinct from (semi-)natural reference sites. Highly characteristic species of pristine bogs are still lacking. We conclude that a novel community has assembled that bears only moderate resemblance to natural peatlands. Persisting high annual turnover rates in terms of species composition and dominance structure (both > 30%) corroborate high levels of ongoing dynamics and the significance of stochastic processes. The long-term trajectory of community succession in the Sphagnum farm remains vague.
A main goal of ecological and evolutionary biology is understanding and predicting interactions between populations and both abiotic and biotic environments, the spatial and temporal variation of ...these interactions, and the effects on population dynamics and performance. Trait-based approaches can help to model these interactions and generate a comprehensive understanding of ecosystem functioning. A central tool is the collation of databases that include species trait information. Such centralized databases have been set up for a number of organismal groups but is lacking for one of the most important groups of predators in terrestrial ecosystems – spiders. Here we promote the collation of an open spider traits database, integrated into the global Open Traits Network. We explore the current collation of spider data and cover the logistics of setting up a global database, including which traits to include, the source of data, how to input data, database governance, geographic cover, accessibility, quality control and how to make the database sustainable long-term. Finally, we explore the scope of research questions that could be investigated using a global spider traits database.
Scorpions have always inspired fear and fascination because of the potency of their venoms. Although this ancient arachnid group is relatively small (ca. 2400 species) and has been continuously ...studied for the past century, the taxonomy is still in a state of flux and the correct identification of species often remains difficult. With more than 725 species and 9000 specimens, the Zoological Museum in Hamburg (ZMH) holds one of the largest and most significant scorpion collections in the world. This collection also contains many historical types described by Karl Kraepelin in the early 20
th
century. In order to contribute to a more stable scorpion taxonomy and to assist future scorpion researchers, we present an illustrated and annotated catalogue of the ZMH scorpion collections. The type specimens of 89 species belonging to 10 families are documented, imaged and assessed alongside their primary data. For practical reasons, only the taxa belonging to the parvorder Iurida Soleglad et Fet, 2003 are presented here whilst the Parvorder Buthida Soleglad et Fet, 2003 will be catalogued in a second publication.
Orb-weaver spiders produce upwards of seven different types of silk, each with unique material properties. We focus on the adhesive within orb-weaving spider webs, aggregate glue silk. These droplets ...are composed of three main components: water, glycoproteins, and a wide range of low molecular mass compounds (LMMCs). These LMMCs are known to play a crucial role in maintaining the material properties of the glycoproteins, aid in water absorption from the environment, and increase surface adhesion. Orb-weavers within the Cyrtarachninae subfamily are moth specialists and have evolved glue droplets with novel material properties. This study investigated the biochemical composition and diversity of the LMMCs present in the aggregate glue of eight moth-specialist species and compared them with five generalist orb-weavers using nuclear magnetic resonance (NMR) spectroscopy. We hypothesized that the novel drying ability of moth-specialist glue was accompanied by novel LMMCs and lower overall percentages by silk weight of LMMCs. We measured no difference in LMMC weight by the type of prey specialization, but observed novel compositions in the glue of all eight moth-catching species. Further, we quantified the presence of a previously reported but unidentified compound that appears in the glue of all moth specialists. These silks can provide insight into the functions of bioadhesives and inform our own synthetic adhesives.
The navigation by scene familiarity hypothesis provides broad explanatory power for how bees and ants navigate from the hive to distant food sources and back. The premise is that the visual world is ...decomposed into pixelated matrices of information that are stored and readdressed as the insects retrace learned routes. Innate behaviors in these insects (including learning walks/flights and path integration) provide the important goal-directed views to allow the initial retracing (i.e., the insect must learn the scene while moving toward the goal because everything looks different while moving away). Scorpion navigation may use a similar premise, with the chemical and textural features of the environment substituting for visual input. Scorpion pectines support thousands of chemo- and mechano-sensitive units called peg sensilla, each containing at least 10 energetically expensive sensory neurons. We have long wondered why pectines have so many pegs and associated neurons. Many sand scorpions emerge onto the surface from their home burrows at night to pursue insect prey and somehow find their way back to their burrows. Based on the measured resolution of peg sensilla, we have calculated that sufficient information exists in sand's texture to enable scorpions to retrace previously experienced paths with little to no chance of confusion. Preliminary evidence of learning walks and path integration in scorpions is also congruent with the navigation by chemo-textural familiarity hypothesis.
Spiders use various combinations of silks, adhesives, and behaviors to ensnare prey. One common but difficult-to-catch prey is moths. They easily escape typical orb-webs because their bodies are ...covered in tiny sacrificial scales that flake off when in contact with the web's adhesives. This defense is defeated by spiders of the sub-family of Cyrtarachninae-moth-catching specialists who combine changes in orb-web structure, predatory behavior, and chemistry of the aggregate glue placed in those webs. The most extreme changes in web structure are shown by the bolas spiders which create only one or two glue droplets at the end of a single thread. They prey on male moths by releasing pheromones to draw them close. Here, we confirm the hypothesis that the spinning behavior of the spider is directly used to spin its glue droplets using a high-speed video camera to observe the captured behavior of the bolas spider
as it actively spins its body and bolas. We use the kinematics of the spider and bolas to begin to quantify and model the physical and mechanical properties of the bolas during prey capture. We then examine why this species chooses to spin its body, an energetically costly behavior, during prey capture. We test the hypothesis that spinning helps to spread pheromones by creating a computational fluid dynamics model of airflow within an open field and comparing it to that of airflow within a tree, a common environment for bolas spiders that do not spin. Spinning in an open environment creates turbulent air, spreading pheromones further and creating a pocket of pheromones. Conversely, spinning within a tree does little to affect the natural airflow.
Fossil spiders Selden, Paul A.; Penney, David
Biological reviews of the Cambridge Philosophical Society,
02/2010, Letnik:
85, Številka:
1
Journal Article
Recenzirano
Over the last three decades, the fossil record of spiders has increased from being previously biased towards Tertiary ambers and a few dubious earlier records, to one which reveals a much greater ...diversity in the Mesozoic, with many of the modern families present in that era, and with clearer evidence of the evolutionary history of the group. We here record the history of palaeoarachnology and the major breakthroughs which form the basis of studies on fossil spiders. Understanding the preservation and taphonomic history of spider fossils is crucial to interpretation of fossil spider morphology. We also review the more recent descriptions of fossil spiders and the effect these discoveries have had on the phylogenetic tree of spiders. We discuss some features of the evolutionary history of spiders and present ideas for future work.
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