Hot and scared: how do heatwaves and predation risk impact resource acquisition and allocation?

Heatwaves are increasingly prevalent and can constrain investment into important life-history traits. In addition to heatwaves, animals regularly encounter threats from other organisms in their environments, such as predators. The combination of these two environmental factors introduces a decision-making conflict-heat exposure requires more food intake to fuel investment into fitness-related traits, but foraging in the presence of predators increases the threat of mortality. Thus, we used female variable field crickets (Gryllus lineaticeps) to investigate the effects of heatwaves in conjunction with predation risk (exposed food and water sources, and exposure to scent from black widow spiders, Latrodectus hesperus) on resource acquisition (food intake) and allocation (investment into ovarian and somatic tissues). A simulated heatwave increased food intake and the allocation of resources to reproductive investment. Crickets exposed to high predation risk reduced food intake, but they were able to maintain reproductive investment at an expense to investment into somatic tissue. Thus, heatwaves and predation risk deprioritized investment into self-maintenance, which may impair key physiological processes. This study is an important step towards understanding the ecology of fear in a warming world.

Foraging rates from metabarcoding: Predators have reduced functional responses in wild, diverse prey communities.

Functional responses describe foraging rates across prey densities and underlie many fundamental ecological processes. Most functional response knowledge comes from simplified lab experiments, but we do not know whether these experiments accurately represent foraging in nature. In addition, the difficulty of conducting multispecies functional response experiments means that it is unclear whether interaction strengths are weakened in the presence of multiple prey types. We developed a novel method to estimate wild predators' foraging rates from metabarcoding data and use this method to present functional responses for wild wolf spiders foraging on 27 prey families. These field functional responses were considerably reduced compared to lab functional responses. We further find that foraging is sometimes increased in the presence of other prey types, contrary to expectations. Our novel method for estimating field foraging rates will allow researchers to determine functional responses for wild predators and address long-standing questions about foraging in nature.

Morphological ant mimics: constrained to imperfection?

Adaptive evolution relies on both heritable variation and selection. Variation is the raw material upon which selection acts, so any mechanism that limits or prevents the generation of heritable variation reduces the power of selection to lead to adaptation. Such limitations are termed evolutionary constraints. While it is widely accepted that constraints play an important role in shaping evolutionary outcomes, their relative importance, as opposed to adaptation, in determining evolutionary outcomes remains a subject of debate. Evolutionary constraints are often evoked as the reason behind the persistence of inaccurate mimicry. Here, we compared the variation and accuracy of body-shape mimicry in ant-mimicking spiders with that of ant-mimicking insects, predicting greater constraints, and hence inaccuracy, in spiders mimicking ants, due to their evolutionary distance from the ant model. We found high inter-species variation in mimetic accuracy, but dorsally, no overall difference in mimetic accuracy between spider and insect mimics, which is inconsistent with a constraint causing inaccurate mimicry. Our study provides empirical evidence suggesting that imperfect mimicry in spiders and insects is predominantly shaped by adaptive processes rather than constraints or chance. Our findings contribute to our understanding of the mechanisms underlying evolutionary diversity and the processes that shape phenotypic outcomes.

Sexual cannibalism as a female resistance trait: a new hypothesis.

Female spiders and praying mantises are renowned for their cannibalism of male partners before, during, or after mating. While several hypotheses have been proposed to explain species-specific examples of sexual cannibalism, much variation remains unexplained, including why the timing of cannibalism varies across taxa. Here, I outline how sexually cannibalistic behavior could evolve via sexually antagonistic selection as a type of behavioral resistance to male-imposed mating costs, and how such a generalizable interpretation provides a framework for understanding the evolution of both sexual cannibalism in females and anti-cannibalistic traits in males. I discuss how differences between mating systems that physiologically constrain males to mate only once (monogyny) or twice (bigyny) and systems where the sexes can potentially mate multiply (polygyny and polyandry) are likely to influence how sexual conflict shapes cannibalistic behavior. I review key examples from the literature that suggest how sexually cannibalistic behavior might function as a female resistance trait and provide comprehensive predictions for testing this hypothesis empirically.

Background matching can reduce responsiveness of jumping spiders to stimuli in motion.

Motion and camouflage were previously considered to be mutually exclusive, as sudden movements can be easily detected. Background matching, for instance, is a well-known, effective camouflage strategy where the colour and pattern of a stationary animal match its surrounding background. However, background matching may lose its efficacy when the animal moves, as the boundaries of the animal become more defined against its background. Recent evidence shows otherwise, as camouflaged objects can be less detectable than uncamouflaged objects even while in motion. Here, we explored whether the detectability of computer-generated stimuli varies with the speed of motion, background (matching and unmatching) and size of stimuli in six species of jumping spiders (Araneae: Salticidae). Our results showed that, in general, the responsiveness of all six salticid species tested decreased with increasing stimulus speed regardless of whether the stimuli were conspicuous or camouflaged. Importantly, salticid responses to camouflaged stimuli were significantly lower compared with those to conspicuous stimuli. There were significant differences in motion detectability across species when the stimuli were conspicuous, suggesting differences in visual acuity in closely related species of jumping spiders. Furthermore, small stimuli elicited significantly lower responses than large stimuli across species and speeds. Our results thus suggest that background matching is effective even when stimuli are in motion, reducing the detectability of moving stimuli.

Physiological sensing system integrated with vibration sensor and frequency gel dampers inspired by spider.

Recent advances in bioelectronics in mechanical and electrophysiological signal detection are remarkable, but there are still limitations because they are inevitably affected by environmental noise and motion artifacts. Thus, we develop a gel damper-integrated crack sensor inspired by the vibration response of the viscoelastic cuticular pad and slit organs in a spider. Benefitting from the specific crack structure design, the sensor possesses excellent sensing behaviors, including a low detection limit (0.05% strain), ultrafast response ability (3.4 ms) and superior durability (>300 000 cycles). Such typical low-amplitude fast response properties allow the ability to accurately perceive vibration frequency and waveform. In addition, the gel damper exhibits frequency-dependent dynamic mechanical behavior that results in improved stability and reliability of signal acquisition by providing shock resistance and isolating external factors. They effectively attenuate external motion artifacts and low-frequency mechanical noise, resulting in cleaner and more reliable signal acquisition. When the gel damper is combined with the crack-based vibration sensor, the integrated sensor exhibits superior anti-interference capability and frequency selectivity, demonstrating its effectiveness in extracting genuine vocal vibration signals from raw voice recordings. The integration of damping materials with sensors offers an efficient approach to improving signal acquisition and signal quality in various applications.

Dynamic evolution of locomotor performance independent of changes in extended phenotype use in spiders.

Many animals use self-built structures (extended phenotypes) to enhance body functions, such as thermoregulation, prey capture or defence. Yet, it is unclear whether the evolution of animal constructions supplements or substitutes body functions-with disparate feedbacks on trait evolution. Here, using brown spiders (Araneae: marronoid clade), we explored if the evolutionary loss and gain of silken webs as extended prey capture devices correlates with alterations in traits known to play an important role in predatory strikes-locomotor performance (sprint speed) and leg spination (expression of capture spines on front legs). We found that in this group high locomotor performance, with running speeds of over 100 body lengths per second, evolved repeatedly-both in web-building and cursorial spiders. There was no correlation with running speed, and leg spination only poorly correlated, relative to the use of extended phenotypes, indicating that web use does not reduce selective pressures on body functions involved in prey capture and defence per se. Consequently, extended prey capture devices serve as supplements rather than substitutions to body traits and may only be beneficial in conjunction with certain life-history traits, possibly explaining the rare evolution and repeated loss of trapping strategies in predatory animals.

Miniaturization does not change conserved spider anatomy, a case study on spider Rayforstia (Araneae: Anapidae).

Miniaturization is an evolutionary trend observed in many animals. Some arachnid groups, such as spiders and mites, demonstrate a strong tendency toward miniaturization. Some of the most miniaturized spiders belong to the family Anapidae. In this study, using light and confocal microscopy and 3D modelling, we provide the first detailed description of the anatomy of a spider of the genus Rayforstia, which is only 900 µm long. In comparison with larger spiders, Rayforstia has no branching of the midgut in the prosoma and an increased relative brain volume. In contrast to many miniature insects and mites, the spider shows no reduction of whole organ systems, no allometry of the digestive and reproductive systems, and also no reduction of the set of muscles. Thus, miniature spider shows a more conserved anatomy than insects of a similar size. These findings expand our knowledge of miniaturization in terrestrial arthropods.

Multi-elemental consumer-driven nutrient cycling when predators feed on different prey.

Predators play a fundamental role in cycling nutrients through ecosystems, by altering the amount and compositions of waste products and uneaten prey parts available to decomposers. Different prey can vary in their elemental content and the deposition of elements in predator waste can vary depending on which elements are preferentially retained versus eliminated as waste products. We tested how feeding on different prey (caterpillars, cockroaches, crickets, and flies) affected the concentrations of 23 elements in excreta deposited by wolf spider across 2 seasons (spring versus fall). Spider excreta had lower concentrations of carbon and higher concentrations of many other elements (Al, B, Ba, K, Li, P, S, Si, and Sr) compared to prey remains and whole prey carcasses. In addition, elemental concentrations in unconsumed whole prey carcasses and prey remains varied between prey species, while spider excreta had the lowest variation among prey species. Finally, the concentrations of elements deposited differed between seasons, with wolf spiders excreting greater concentrations of Fe, Mg, Mn, Mo, S, and V in the fall. However, in the spring, spiders excreted higher concentrations of Al, B, Ba, Ca, Cd, Cu, K, P, Na, Si, Sr, and Zn. These results highlight that prey identity and environmental variation can determine the role that predators play in regulating the cycling of many elements. A better understanding of these convoluted nutritional interactions is critical to disentangle specific consumer-driven effects on ecosystem function.

The evolution of prey-attraction strategies in spiders: the interplay between foraging and predator avoidance.

Lures and other adaptations for prey attraction are particularly interesting from an evolutionary viewpoint because they are characterized by correlational selection, involve multicomponent signals, and likely reflect a compromise between maximizing conspicuousness to prey while avoiding drawing attention of enemies and predators. Therefore, investigating the evolution of lure and prey-attraction adaptations can help us understand a larger set of traits governing interactions among organisms. We review the literature focusing on spiders (Araneae), which is the most diverse animal group using prey attraction and show that the evolution of prey-attraction strategies must be driven by a trade-off between foraging and predator avoidance. This is because increasing detectability by potential prey often also results in increased detectability by predators higher in the food chain. Thus increasing prey attraction must come at a cost of increased risk of predation. Given this trade-off, we should expect lures and other prey-attraction traits to remain suboptimal despite a potential to reach an optimal level of attractiveness. We argue that the presence of this trade-off and the multivariate nature of prey-attraction traits are two important mechanisms that might maintain the diversity of prey-attraction strategies within and between species. Overall, we aim to stimulate research on this topic and progress in our general understanding of the diversity of predator and prey interactions.

Positive tree diversity effects on arboreal spider abundance are tied to canopy cover in a forest experiment.

Human actions are decreasing the diversity and complexity of forests, and a mechanistic understanding of how these changes affect predators is needed to maintain ecosystem services, including pest regulation. Using a large-scale tree diversity experiment, we investigate how spiders respond to trees growing in plots of single or mixed species combinations (4 or 12) by repeatedly sampling 540 trees spanning 15 species. In 2019 (6 years post-establishment), spider responses to tree diversity varied by tree species. By 2021, diversity had a more consistently positive effect, with trees in 4- or 12-species plots supporting 23% or 50% more spiders, respectively, compared to conspecifics in monocultures. Spiders showed stronger tree species preferences in late summer, and the positive impact of plot diversity doubled. In early summer, the positive diversity effect was tied to higher canopy cover in diverse plots, leading to higher spider densities. This indirect path strengthened in late summer, with an additional direct effect of plot diversity on spiders. Prey availability was higher in diverse plots but was not tied to spider density. Overall, diverse plots supported more predators, partly by increasing available habitat. Adopting planting strategies focused on species mixtures may better maintain higher trophic levels and ecosystem functions.

Assessing the impact of fire on spiders through a global comparative analysis.

In many regions fire regimes are changing due to anthropogenic factors. Understanding the responses of species to fire can help to develop predictive models and inform fire management decisions. Spiders are a diverse and ubiquitous group and can offer important insights into the impacts of fire on invertebrates and whether these depend on environmental factors, phylogenetic history or functional traits. We conducted phylogenetic comparative analyses of data from studies investigating the impacts of fire on spiders. We investigated whether fire affects spider abundance or presence and whether ecologically relevant traits or site-specific factors influence species' responses to fire. Although difficult to make broad generalizations about the impacts of fire due to variation in site- and fire-specific factors, we find evidence that short fire intervals may be a threat to some spiders, and that fire affects abundance and species compositions in forests relative to other vegetation types. Orb and sheet web weavers were also more likely to be absent after fire than ambush hunters, ground hunters and other hunters suggesting functional traits may affect responses. Finally, we show that analyses of published data can be used to detect broad-scale patterns and provide an alternative to traditional meta-analytical approaches.

Chronic Engineered Nanoparticle Additions Alter Insect Emergence and Result in Metal Flux from Aquatic Ecosystems into Riparian Food Webs.

Freshwater ecosystems are exposed to engineered nanoparticles (NPs) through discharge from wastewater and agricultural runoff. We conducted a 9-month mesocosm experiment to examine the combined effects of chronic NP additions on insect emergence and insect-mediated contaminant flux to riparian spiders. Two NPs (copper, gold, plus controls) were crossed by two levels of nutrients in 18 outdoor mesocosms open to natural insect and spider colonization. We collected adult insects and two riparian spider genera, Tetragnatha and Dolomedes, for 1 week on a monthly basis. We estimated a significant decrease in cumulative insect emergence of 19% and 24% after exposure to copper and gold NPs, irrespective of nutrient level. NP treatments led to elevated copper and gold tissue concentrations in adult insects, which resulted in terrestrial fluxes of metals. These metal fluxes were associated with increased gold and copper tissue concentrations for both spider genera. We also observed about 25% fewer spiders in the NP mesocosms, likely due to reduced insect emergence and/or NP toxicity. These results demonstrate the transfer of NPs from aquatic to terrestrial ecosystems via emergence of aquatic insects and predation by riparian spiders, as well as significant reductions in insect and spider abundance in response to NP additions.

Passive electrolocation in terrestrial arthropods: Theoretical modelling of location detection.

The recent discovery that some terrestrial arthropods can detect, use, and learn from weak electrical fields adds a new dimension to our understanding of how organisms explore and interact with their environments. For bees and spiders, the filiform mechanosensory systems enable this novel sensory modality by carrying electric charge and deflecting in response to electrical fields. This mode of information acquisition opens avenues for previously unrealised sensory dynamics and capabilities. In this paper, we study one such potential: the possibility for an arthropod to locate electrically charged objects. We begin by illustrating how electrostatic interactions between hairs and surrounding electrical fields enable the process of location detection. After which we examine three scenarios: (1) the determination of the location and magnitude of multiple point charges through a single observation, (2) the learning of electrical and mechanical sensor properties and the characteristics of an electrical field through several observations, (3) the possibility that an observer can infer their location and orientation in a fixed and known electrical field (akin to "stellar navigation"). To conclude, we discuss the potential of electroreception to endow an animal with thus far unappreciated sensory capabilities, such as the mapping of electrical environments. Electroreception by terrestrial arthropods offers a renewed understanding of the sensory processes carried out by filiform hairs, adding to aero-acoustic sensing and opening up the possibility of new emergent collective dynamics and information acquisition by distributed hair sensors.

Prey localization in spider orb webs using modal vibration analysis.

Spider webs are finely tuned multifunctional structures, widely studied for their prey capture functionalities such as impact strength and stickiness. However, they are also sophisticated sensing tools that enable the spider to precisely determine the location of impact and capture the prey before it escapes. In this paper, we suggest a new mechanism for this detection process, based on potential modal analysis capabilities of the spider, using its legs as distinct distributed point sensors. To do this, we consider a numerical model of the web structure, including asymmetry in the design, prestress, and geometrical nonlinearity effects. We show how vibration signals deriving from impacts can be decomposed into web eigenmode components, through which the spider can efficiently trace the source location. Based on this numerical analysis, we discuss the role of the web structure, asymmetry, and prestress in the imaging mechanism, confirming the role of the latter in tuning the web response to achieve an efficient prey detection instrument. The results can be relevant for efficient distributed impact sensing applications.

Fast acrobatic maneuvers enable arboreal spiders to hunt dangerous prey.

Spiders, the most specious taxon of predators, have evolved an astounding range of predatory strategies, including group hunting, specialized silk traps, pheromone-loaded bolas, and aggressive mimicry. Spiders that hunt prey defended with behavioral, mechanical, or chemical means are under additional selection pressure to avoid injury and death. Ants are considered dangerous because they can harm or kill their predators, but some groups of spiders, such as the Theridiidae, have a very high diversification of ant-hunting species and strategies [J. Liu et al., Mol. Phylogenet. Evol. 94, 658-675 (2016)]. Here, we provide detailed behavioral analyses of the highly acrobatic Australian ant-slayer spider, Euryopis umbilicata (Theridiidae), that captures much larger and defended Camponotus ants on vertical tree trunks. The hunting sequence consists of ritualized steps performed within split seconds, resulting in an exceptionally high prey capture success rate.

DNA metabarcoding of gut contents reveals key habitat and seasonal drivers of trophic networks involving generalist predators in agricultural landscapes.

BACKGROUND: Understanding the networks of trophic interactions into which generalist predators are embedded is key to assessing their ecological role of in trophic networks and the biological control services they provide. The advent of affordable DNA metabarcoding approaches greatly facilitates quantitative understanding of trophic networks and their response to environmental drivers. Here, we examine how key environmental gradients interact to shape predation by Lycosidae in highly dynamic vegetable growing systems in China. RESULTS: For the sampled Lycosidae, crop identity, pesticide use and seasons shape the abundance of prey detected in spider guts. For the taxonomic richness of prey, local- and landscape-scale factors gradients were more influential. Multivariate ordinations confirm that these crop-abundant spiders dynamically adjust their diet to reflect environmental constraints and seasonal availability to prey. CONCLUSION: Plasticity in diet composition is likely to account for the persistence of spiders in relatively ephemeral brassica crops. Our findings provide further insights into the optimization of habitat management for predator-based biological control practices. © 2022 Society of Chemical Industry.

Regularly occurring bouts of retinal movements suggest an REM sleep-like state in jumping spiders.

Sleep and sleep-like states are present across the animal kingdom, with recent studies convincingly demonstrating sleep-like states in arthropods, nematodes, and even cnidarians. However, the existence of different sleep phases across taxa is as yet unclear. In particular, the study of rapid eye movement (REM) sleep is still largely centered on terrestrial vertebrates, particularly mammals and birds. The most salient indicator of REM sleep is the movement of eyes during this phase. Movable eyes, however, have evolved only in a limited number of lineages-an adaptation notably absent in insects and most terrestrial arthropods-restricting cross-species comparisons. Jumping spiders, however, possess movable retinal tubes to redirect gaze, and in newly emerged spiderlings, these movements can be directly observed through their temporarily translucent exoskeleton. Here, we report evidence for an REM sleep-like state in a terrestrial invertebrate: periodic bouts of retinal movements coupled with limb twitching and stereotyped leg curling behaviors during nocturnal resting in a jumping spider. Observed retinal movement bouts were consistent, including regular durations and intervals, with both increasing over the course of the night. That these characteristic REM sleep-like behaviors exist in a highly visual, long-diverged lineage further challenges our understanding of this sleep state. Comparisons across such long-diverged lineages likely hold important questions and answers about the visual brain as well as the origin, evolution, and function of REM sleep.

The global spread of misinformation on spiders.

In the internet era, the digital architecture that keeps us connected and informed may also amplify the spread of misinformation. This problem is gaining global attention, as evidence accumulates that misinformation may interfere with democratic processes and undermine collective responses to environmental and health crises1,2. In an increasingly polluted information ecosystem, understanding the factors underlying the generation and spread of misinformation is becoming a pressing scientific and societal challenge3. Here, we studied the global spread of (mis-)information on spiders using a high-resolution global database of online newspaper articles on spider-human interactions, covering stories of spider-human encounters and biting events published from 2010-20204. We found that 47% of articles contained errors and 43% were sensationalist. Moreover, we show that the flow of spider-related news occurs within a highly interconnected global network and provide evidence that sensationalism is a key factor underlying the spread of misinformation.