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A fundamental understanding of animal sensory systems is crucial for comprehending their interactions with the environment and with other conspecifics. However, knowledge gaps persist, particularly in arachnids like the order Solifugae. While certain solifuge setae and palpal papillae have been studied structurally and electrophysiologically, providing evidence of chemoreception and mechanoreception, the sensilla on their walking legs remain unexplored. Notably, elongated sensilla on the femur and tibia of the 4th walking legs resemble trichobothria in other arachnid orders yet their function remains unknown. Thus, this study investigates whether these sensilla serve a mechanosensory function. Using electrophysiological and behavioral assays on Eremobates pallipes (Eremobatidae), we assessed the response of the elongated 4th leg sensilla to- (i) air particle movement and- (ii) air pressure changes. Air particle movement stimuli were generated using a speaker placed in the near field of the elongated sensilla that emitted low-frequency pure tones (10-1000 Hz). Air pressure stimuli involved forceful blowing on the sensilla. No response to air particle movement was observed, but a mechanosensory response to air pressure stimuli was detected. Electrophysiological data identified a fast-adapting and fast-recovering cell, and behavioral observations revealed a startle response. Our electrophysiology results suggest a mechanosensory role of elongated sensilla on the 4th walking legs of solifuge, indicating that although they are not sensitive enough to detect air particle movement stimuli, they can receive and respond to air pressure stimuli. Our behavioral experiments similarly show that these sensilla are not sensitive enough to detect air particle movement but respond to more forceful mechanosensory stimuli., Competing Interests: Declarations. Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)

To understand how global warming will impact biodiversity, we need to pay attention to those species with higher vulnerability. However, to assess vulnerability, we also need to consider the thermoregulatory mechanisms, body size, and thermal tolerance of species. Studies addressing thermal tolerance on small ectotherms have mostly focused on insects, while other arthropods, such as arachnids remain understudied. Here, we quantified the physiological thermal sensitivity of the pseudoscorpion Dactylochelifer silvestris using a respirometry setup with a ramping temperature increase. Overall, we found that D. silvestris has a much lower metabolic rate than other organisms of similar size. As expected, metabolic rate increased with body size, with adults having larger metabolic rates, but the overall metabolic scaling exponent was low. Both the temperature at which metabolism peaked and the critical thermal maxima were high (>44°C) and comparable to those of other arachnids. The activation energy, which characterizes the rising portion of the thermal sensitivity curve, was 0.66 eV, consistent with predictions for insects and other taxa in general. Heat tolerances and activation energy did not differ across life stages. We conclude that D. silvestris has low metabolic rates and a high thermal tolerance, which would likely influence how all stages and sexes of this species could endure climate change., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology.)

Previous studies have shown that whip spiders (Amblypygi) can use a variety of cues to navigate to and recognize a home refuge. The current study aimed to determine whether whip spiders were capable of using the boundary geometry of an experimental space (geometric information) to guide goal-directed navigation and to investigate any preferential use of geometric or feature (visual) information. Animals were first trained to find a goal location situated in one corner of a rectangular arena (geometric information) fronting a dark-green-colored wall, which created a brightness contrast with the other three white walls (feature information). Various probe trials were then implemented to determine cue use. It was found that animals were capable of directing their choice behavior towards geometrically correct corners at a rate significantly higher than chance, even when the feature cue was removed. By contrast, choice behavior dropped to random chance when geometric information was removed (test in a square arena) and only feature information remained. Choice behavior was also reduced to chance when geometric and feature information were set in conflict (by moving the feature cue to one of the longer walls in the rectangular arena). The data thus suggest that whip spiders are capable of using geometric information to guide goal-directed navigation and that geometric information is preferred over feature guidance, although a feature cue may set the context for activating geometry-guided navigation. Experimental design limitations and future directions are discussed., (© 2023. The Psychonomic Society, Inc.)

To expand the scope of soundscape ecology to encompass substrate-borne vibrations (i.e. vibroscapes), we analyzed the vibroscape of a deciduous forest floor using contact microphone arrays followed by automated processing of large audio datasets. We then focused on vibratory signaling of ground-dwelling Schizocosa wolf spiders to test for (i) acoustic niche partitioning and (ii) plastic behavioral responses that might reduce the risk of signal interference from substrate-borne noise and conspecific/heterospecific signaling. Two closely related species - S. stridulans and S. uetzi - showed high acoustic niche overlap across space, time, and dominant frequency. Both species show plastic behavioral responses - S. uetzi males shorten their courtship in higher abundance of substrate-borne noise, S. stridulans males increased the duration of their vibratory courtship signals in a higher abundance of conspecific signals, and S. stridulans males decreased vibratory signal complexity in a higher abundance of S. uetzi signals., (© 2024. The Author(s).)

A new evolutionary model of mate choice copying, published in PLOS Biology, aims to reconcile mismatches between theory and data by proposing that juvenile females mistakenly imprint on male phenotypes that were not in fact preferred by the female they copied., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Mendelson et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

From both comparative biology and translational research perspectives, there is escalating interest in understanding how animals navigate their environments. Considerable work is being directed towards understanding the sensory transduction and neural processing of environmental stimuli that guide animals to, for example, food and shelter. While much has been learned about the spatial orientation behavior, sensory cues, and neurophysiology of champion navigators such as bees and ants, many other, often overlooked animal species possess extraordinary sensory and spatial capabilities that can broaden our understanding of the behavioral and neural mechanisms of animal navigation. For example, arachnids are predators that often return to retreats after hunting excursions. Many of these arachnid central-place foragers are large and highly conducive to scientific investigation. In this review we highlight research on three orders within the Class Arachnida: Amblypygi (whip spiders), Araneae (spiders), and Scorpiones (scorpions). For each, we describe (I) their natural history and spatial navigation, (II) how they sense the world, (III) what information they use to navigate, and (IV) how they process information for navigation. We discuss similarities and differences among the groups and highlight potential avenues for future research., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Female cichlid fish living in African great lakes are known to have sensory systems that are adapted to ambient light environments. These sensory system adaptations are hypothesized to have influenced the evolution of the diverse male nuptial coloration. In rock-dwelling Lake Malawi mbuna cichlids, however, the extent to which ambient light environments influence female sensory systems and potentially associated male nuptial coloration remains unknown. Yet, the ubiquitous blue flank coloration and UV reflection of male mbuna cichlids suggest the potential impacts of the blue-shifted ambient light environment on these cichlid's visual perception and male nuptial coloration in the shallow water depth in Lake Malawi. In the present study, we explored whether and how the sensory bias of females influences intersexual communication in the mbuna cichlid, Metriaclima zebra . A series of choice experiments in various light environments showed that M. zebra females 1) have a preference for the blue-shifted light environment, 2) prefer to interact with males in blue-shifted light environments, 3) do not show a preference between dominant and subordinate males in full-spectrum, long-wavelength filtered, and short-wavelength filtered light environments, and 4) show a "reversed" preference for subordinate males in the UV-filtered light environment. These results suggest that the visual perception of M. zebra females may be biased to the ambient light spectra in their natural habitat by local adaptation and that this sensory bias may influence the evolution of blue and UV reflective patterns in male nuptial coloration., (© The Author(s) 2023. Published by Oxford University Press on behalf of Editorial Office, Current Zoology.)

AbstractLight availability is highly variable, yet predictable, over various timescales and is expected to play an important role in the evolution of visual signals. Courtship displays of the wolf spider genus Schizocosa always involve the use of substrate-borne vibrations; however, there is substantial variation in the presence and complexity of visual displays among species. To gain insight into the role the light environment plays in the evolution of courtship displays, we tested the function of visual courtship signaling across distinct light environments in four species of Schizocosa that vary in their degree of ornamentation and dynamic visual signals. We ran mating and courtship trials at three light intensities (bright, dim, and dark) and tested the hypothesis that ornamentation interacts with light environment. We also examined each species' circadian activity patterns. The effects of the light environment on courtship and mating varied between species, as did circadian activity patterns. Our results suggest that femur pigmentation may have evolved for diurnal signaling, whereas tibial brushes may function to increase signal efficacy under dim light. Additionally, we found evidence for light-dependent changes in selection on male traits, illustrating that short-term changes in light intensity have the potential for strong effects on the dynamics of sexual selection.

AbstractTheory predicts that the strength of sexual selection (i.e., how well a trait predicts mating or fertilization success) should increase with population density, yet empirical support remains mixed. We explore how this discrepancy might reflect a disconnect between current theory and our understanding of the strategies individuals use to choose mates. We demonstrate that the density dependence of sexual selection predicted by previous theory arises from the assumption that individuals automatically sample more potential mates at higher densities. We provide an updated theoretical framework for the density dependence of sexual selection by (1) developing models that clarify the mechanisms through which density-dependent mate sampling strategies might be favored by selection and (2) using simulations to determine how sexual selection changes with population density when individuals use those strategies. We find that sexual selection may increase strongly with density if sampling strategies change adaptively in response to density-dependent sampling costs, whereas within-individual plasticity in sampling over time (e.g., due to adaptation to increasing sampling costs as the breeding season progresses) produces weaker density-dependent sexual selection. Our findings suggest that density dependence of sexual selection depends on the ecological context in which mate sampling has evolved.

The evolution of complex signals has often been explored by testing multiple functional hypotheses regarding how independent signal components provide selective benefits to offset the costs of their production. In the present study, we take a different approach by exploring the function of complexity per se . We test the hypothesis that increased vibratory signal complexity-based on both proportional and temporal patterning-provides selective benefits to courting male Schizocosa stridulans wolf spiders. In support of this hypothesis, all of our quantified metrics of vibratory signal complexity predicted the mating success of male S. stridulans. The rate of visual signalling, which is mechanistically tied to vibratory signal production, was also associated with mating success. We additionally found evidence that males can dynamically adjust the complexity of their vibratory signalling. Together, our results suggest that complexity per se may be a target of female choice.

Members of the Nearctic spider genus Schizocosa Chamberlin, 1904 have garnered much attention in behavioral studies and over many decades, a number of species have developed as model systems for investigating patterns of sexual selection and multimodal communication. Many of these studies have employed a comparative approach using putative, but not rigorously tested, sister species pairs that have distinctive morphological traits and attendant behaviors. Despite past emphasis on the efficacy of these presumably comparative-based studies of closely related species, generating a robust phylogenetic hypothesis for Schizocosa has been an ongoing challenge. Here, we apply a phylogenomic approach using anchored hybrid enrichment to generate a data set comprising over 400 loci representing a comprehensive taxonomic sample of 23 Nearctic Schizocosa. Our sampling also includes numerous outgroup lycosid genera that allow for a robust evaluation of genus monophyly. Based on analyses using concatenation and coalescent-based methods, we recover a well-supported phylogeny that infers the following: 1) The New World Schizocosa do not form a monophyletic group; 2) Previous hypotheses of North American species require reconsideration along with the composition of species groups; 3) Multiple longstanding model species are not genealogically exclusive and thus are not "good" species; 4) This updated phylogenetic framework establishes a new working paradigm for studying the evolution of characters associated with reproductive communication and mating. Ancestral character state reconstructions show a complex pattern of homoplasy that has likely obfuscated previous attempts to reconstruct relationships and delimit species. Important characters presumably related to sexual selection, such as foreleg pigmentation and dense bristle formation, have undergone repeated gain and loss events, many of which have led to increased morphological divergence between sister-species. Evaluation of these traits in a comparative framework illuminates how sexual selection and natural selection influence character evolution and provides a model for future studies of multimodal communication evolution and function., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)