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The camouflage of crab spiders on flowers have been extensively studied, primarily focusing on species with uniform coloration. In reality, more than 50 flower-visiting spider species from seven families do not possess uniform coloration. However, there is a lack of exploration regarding them, leaving their cryptic nature uncertain. Additionally, little is known about the flower-visiting strategies employed by spiders at different developmental stages. To address these issues, we investigated Ebrechtella tricuspidata, a crab spider species exhibiting distinct abdomen and carapace colors. Notably, during our earlier field survey, we found that the juvenile spiders appeared on chamomile flowers (Matricaria recutita) significantly more frequently compared to the females. Our visual modeling showed that the spider's carapace on flower petals was detectable, whereas the abdomen matched the flower petals in both chromatic and achromatic contrast, making it unlikely to be detected by avian. Our predation experiment revealed that the probability of being detected and attacked was significantly lower for spiders on flower petals. Moreover, the attacked percentage of juveniles on petals was significantly lower than that of females. Combined with our previous field findings, we predict that spiders in different developmental stages may employ different flower-visiting strategies according to their predation risk. Overall, our study demonstrated that imperfect crypsis of E. tricuspidata on flower prevents avian predation effectively, and the higher presence of juvenile spiders on flowers may be attributed to their lower predation risk. Significance statement: Crab spiders are renowned sit-and-wait predators and provide an ideal model for studying animal camouflage. It is widely acknowledged that these spiders exploit flowers of matching hues to deceive their prey. However, there is a pressing need for broader investigations encompassing the camouflage of crab spiders with non-uniform body colors to predators and their flower visiting strategies during ontogeny. To investigate these questions, we conducted avian visual modeling and behavioral experiments. Our findings demonstrated that distinct local body part did not significantly impact overall concealment, suggesting that camouflage is prevalent not only among flower-visiting spiders sporting uniform coloration but also among those with different colored abdomen and carapace. Furthermore, juvenile spiders on flower experienced lower predation risk than females, indicating that spiders at different stages face distinct levels of predation risk. Combined with our previous field findings that juvenile spiders were significantly more commonly found on flowers than females, we predict that spiders may employ varied flower-visiting strategies throughout their developmental stages, where the increasing predation risk leads to a decreased presence of spiders on flowers as they mature during ontogeny. [ABSTRACT FROM AUTHOR]

Understanding the complex interplay of factors shaping polymorphic changes within individuals represents a longstanding conundrum in biology. Some crab spiders (Thomisidae) are examples of sit-and-wait predators that can change their body coloration. Many factors may influence crab spider color polymorphism with multiple explanations receiving various levels of support. Here we examined the daytime and nighttime activities and predator and prey interactions for two yellow-white polymorphic crab spiders, Thomisus labefactus and Ebrechtella tricuspidatus in the field. We thereupon conducted a manipulative experiment using dummies with color morphs visibly resembling the spiders when placed on background-matched flowers. We measured the spectra reflected from the dummies and their floral backgrounds and used insect visual models to determine if they are likely to be visible to a range of insects by night and day. We found that both color morphs of each species were more active by night than by day. Our visual models revealed that the spider's bodies were unlikely to be cryptic. Together, these results suggest that the crab spiders might exploit flower colorations during the night but not during the day. They also indicated that explanations of why crab spiders utilize certain color polymorphs are context dependent and will vary with time, and whether predators, prey, or both, are present. Significance statement: Crab spiders are an excellent model for investigating a long-standing challenge in evolutionary biology: understanding the causes and consequences of polymorphic coloration in animals. Studies have postulated a range of explanations with some support for each. Broader studies encompassing all interactions between spiders and their predators and prey across the day and night are urgently needed. Here we combined an around-the-clock spider activity survey with field experiments and insect visual models to show that the types of interactions between spider color morphs and their predators and prey differ over the day and night. Our study suggests that outcomes of experiments examining the adaptive drivers of polymorphisms may be dependent upon the context within which the observations were made, and that examining interactions across temporal contexts is required to fully uncover the various drivers of the polymorphisms. [ABSTRACT FROM AUTHOR]

Crab spiders (Thomisidae) are known by their ability to change their body colouration via change in epithelial pigments. However, the crab spider genus Stephanopis appears to match the colouration of the bark they are sitting on by having debris attached to its dorsal cuticle. The functional morphology, colouration, and evolution of this phenomenon were investigated in Stephanopis cf. scabra and S. cambridgei. Analysis under the microscope revealed that debris originated from the bark they were sitting on. Using scanning electron microscopy, three different types of setae likely related in the retention of debris were found in S. cf. scabra and one in S. cambridgei. These setae are branched and possess barbs, unlike the more filiform setae found in other crab spider species. In addition, the presence of debris improved the brightness background matching of spiders against the bark, but not hue and chroma matching. Ancestral character state reconstruction suggested that presence of debris evolved two to three times within Thomisidae. The evolution of both masking and colour change among crab spiders indicates that they are under a strong selection to avoid detection. [ABSTRACT FROM AUTHOR]

Mobile predators employ a variety of locomotor tasks in hunting, avoiding predators and searching for mates. However, few studies have evaluated the performances of a population's members in all of their major locomotor tasks, even though all of these performances may affect both an individual's fitness and how members of a population exploit resources. Male crab spiders Misumena vatia, diminutive members of an extremely sexually dimorphic species, regularly run, climb and cross silken lines. For the most part, individuals moved at similar speeds relative to each other in the three tasks: the 15th fastest runner was approximately 15th fastest in the other two moves as well. Thus, these spiders provided little evidence that any individual excelled at one task or another, relative to other members of its population, thereby exhibiting a marked behavioral syndrome. However, large individuals moved faster than small ones in these tasks, especially when climbing. Although the gravity and bridging hypotheses predict that small individuals climb and cross silken lines faster than larger ones, at ca. 4.15 mg (extremes of 2.5-8.0 mg), male Misumena, and most terrestrial invertebrates, fall well below weight constraints currently predicted by either hypothesis. Data on sexual cannibalism, overwintering, and lifespan suggest possible countering advantages of small size, and hence balancing selection, which may contribute to Misumena's striking sexual size dimorphism and explain the males' wide size range. [ABSTRACT FROM AUTHOR]

Predators hunting for cryptic prey use search images, but how do prey search for cryptic predators? We address this question using the interaction between bumblebees and the colour-changing crab spider Misumena vatia which can camouflage itself on some flowers. In laboratory experiments, we exposed bumblebees to an array of flowers concealing robotic predators (a trapping mechanism combined with a 3D life-sized model of a crab spider or a circle). Groups of bees were trained to avoid either cryptic yellow spiders or yellow circles (equal area to the spiders) or remained predator naive. The bees were then exposed to a new patch of white flowers containing some cryptic predators (either white spiders, white circles or a mixture of both). We monitored individual foraging choices and used a 3D video tracking system to quantify the bees' flight behaviour. The bees trained to avoid cryptic spiders, chose 40% fewer spider-harbouring flowers than expected by chance, but were indifferent to cryptic circles. They also aborted a higher proportion of landings on flowers harbouring spiders, ultimately feeding from half as many 'dangerous' flowers as naive bees. Previous encounters with cryptic spiders also influenced the flight behaviour of bees in the new flower patch. Experienced bees spent more time inspecting the flowers they chose to reject (both with and without concealed spiders) and scanned from side to side more in front of the flowers to facilitate predator detection. We conclude that bees disentangle shape from colour cues and thus can form a generalised search image for spider shapes, independent of colour. [ABSTRACT FROM AUTHOR]

Mimicry is used widely by arthropods to survive in a hostile environment. Often mimicry is associated with the production of chemical compounds such as pigments. In crab spiders, the change of color is based on a complex physiological process that still is not understood. The aim of this study was to identify and quantify the ommochrome pigments and precursors responsible for the color change in the mimetic crab spider Misumena vatia (Thomisidae). A modified high performance reverse phase ion-pair chromatography technique enabled us to separate and quantify the ommochrome pigments, their precursors, and related metabolites in individual spiders. Compounds such as tryptophan, kynurenine, and kynurenic acid occurred only or mainly in white crab spiders. In contrast, compounds such as 3-hydroxy-kynurenine, xanthommatin, and ommatin D occurred only or mainly in yellow crab spiders. Factor analysis ranked the different color forms in accordance with their metabolites. The biochemical results enabled us to associate the different phases of formation of pigment granules with specific metabolites. Yellow crab spiders contain many unknown ommochrome-like compounds not present in white crab spiders. We also found large quantities of decarboxylated xanthommatin, whose role as precursor of new pathways in ommochrome synthesis needs to be assessed. The catabolism of ommochromes, a process occurring when spiders revert from yellow to white, warrants further study. [ABSTRACT FROM AUTHOR]

Some crab spiders reflect UV-light, thereby creating a deceptive signal that attracts prey to the flowers that they sit on. We conducted a survey of several Australian and European species of crab spiders and found that UV-reflection is common in Australian species but absent from European species. Furthermore, honeybees are attracted to UV-reflecting Australian spiders while they are either indifferent to or repelled by European crab spiders. We do not know if UV-reflection evolved once or several times independently in crab spiders endemic to Australia or whether UV-reflective spiders arrived in Australia more recently. [ABSTRACT FROM AUTHOR]

The perception of ultraviolet (UV) light by spiders has so far been only demonstrated in salticids. Crab spiders (Thomisidae) hunt mostly on flowers and need to find appropriate hunting sites. Previous studies have shown that some crab spiders that reflect UV light use UV contrast to enhance prey capture. The high UV contrast can be obtained either by modulation of body colouration or active selection of appropriate backgrounds for foraging. We show that crab spiders ( Thomisus sp.) hunting on Spathiphyllum plants use chromatic contrast, especially UV contrast, to make themselves attractive to hymenopteran prey. Apart from that, they are able to achieve high UV contrast by active selection of non-UV reflecting surfaces when given a choice of UV-reflecting and non-UV reflecting surfaces in the absence of odour cues. Honeybees ( Apis cerana) approached Spathiphyllum plants bearing crab spiders on which the spiders were high UV-contrast targets with greater frequency than those plants on which the UV contrast of the spiders was low. Thus, crab spiders can perceive UV and may use it to choose appropriate backgrounds to enhance prey capture, by exploiting the attraction of prey such as honeybees to UV. [ABSTRACT FROM AUTHOR]

Abstract  A new type of pycnostad has been identified in the western subtropical-subarctic transition region of the North Pacific, based on the intensive hydrographic survey carried out in July, 2002. The potential density, temperature and salinity of the pycnostad were found to be 26.5–26.7 σ θ , 5�–7�C and 33.5–33.9 psu respectively. The pycnostad is denser, colder and fresher than those of the North Pacific Central Mode Water and different from those of other known mode waters in the North Pacific. The thickness of the pycnostad is comparable to that of other mode waters, spreading over an area of at least 650 � 500 km around 43�N and 160�E in the western transition region. Hence, we refer to the pycnostad as Transition Region Mode Water (TRMW). Oxygen data, geostrophic current speed and climatology of mixed layer depth in the winter suggest that the TRMW is formed regularly in the deep winter mixed layer near the region where it was observed. Analysis of surface heat flux also supports the idea and suggests that there is significant interannual variability in the property of the TRMW. The TRMW is consistently distributed between the Subarctic Boundary and the Subarctic Front. It is also characterized by a wide T-S range with similar density, which is the characteristic of such a transition region between subtropical and subarctic water masses, which forms a density-compensating temperature and salinity front. The frontal nature also tends to cause isopycnal intrusions within the pycnostad of the TRMW. [ABSTRACT FROM AUTHOR]

Examines the interaction of residency status, experience, and body size on fighting success of the crab spider Misumenoides formosipes. Adjustment of contestants' strategy to the value of the resource and the resource holding potential of their opponent; Advantage of residents over intruders in contests between adult males with no contest experience; Suggestion that crab spiders learn strategies through experience.

Size and species composition of flower patches were manipulated to determine whether these factors exerted indirect effects on the hunting success of flower-dwelling spiders via direct effects on insect pollinators. Multivariate analysis of variance (MANOVA) of two pollinator response variables (visitation rate and visitor size) revealed a significant pollinator preference for Bidens aristosa (tickseed sunflower) over Solidago juncea (goldenrod) and for large patches of a given plant species over small patches. Bidens received significantly more pollinator visits per floral unit per unit time and attracted significantly larger insects than Solidago. The significant patch size effect seen in the MANOVA was driven by the strong impact of patch size on the size of insects visiting the experimental patches: the size (mass) of insects visiting large patches was significantly greater than the size of insects visiting small patches of a given plant species, but visitation rates to large and small patches of a given plant species were similar. MANOVA indicated that hunting success of a flower-dwelling crab spider, Misumenoides formosipes, was also significantly affected by species composition and size of flower patches. Three measures of spider hunting success (rate of mass gain and its components, total prey mass captured per spider per day, and number of prey captured per spider per day) were evaluated, and the experimental treatments exerted similar effects on all three measures. Spiders occupying Bidens patches experienced greater hunting success than spiders occupying Solidago patches, and in patches of a given plant species, spiders occupying large patches experienced greater hunting success than spiders occupying small patches. The pattern of spider hunting success most closely paralleled the pattern described by the size of insects visiting the patches (BL>BS=SL>SS), suggesting that the size of visiting pollinators, rather than frequency of visitation, exerted a greater influence on spider hunting success. Taxonomic composition of a spider's diet varied with the plant species occupied. The size of insects captured by spiders was significantly greater than average size of insects visiting the patches, indicating that spiders selectively captured larger pollinator taxa. Spider movements among patches revealed a pattern of migration from Solidago to Bidens. [ABSTRACT FROM AUTHOR]

Novel disulfide-containing polypeptide toxin was discovered in the venom of the Tibellus oblongus spider. We report on isolation, spatial structure determination and electrophysiological characterization of this 41-residue toxin, called ω-Tbo-IT1. It has an insect-toxic effect with LD50 19 μg/g in experiments on house fly Musca domestica larvae and with LD50 20 μg/g on juvenile Gromphadorhina portentosa cockroaches. Electrophysiological experiments revealed a reversible inhibition of evoked excitatory postsynaptic currents in blow fly Calliphora vicina neuromuscular junctions, while parameters of spontaneous ones were not affected. The inhibition was concentration dependent, with IC50 value 40 ± 10 nM and Hill coefficient 3.4 ± 0.3. The toxin did not affect frog neuromuscular junctions or glutamatergic and GABAergic transmission in rat brains. Ca2+ currents in Calliphora vicina muscle were not inhibited, whereas in Periplaneta americana cockroach neurons at least one type of voltage gated Ca2+ current was inhibited by ω-Tbo-IT1. Thus, the toxin apparently acts as an inhibitor of presynaptic insect Ca2+ channels. Spatial structure analysis of the recombinant ω-Tbo-IT1 by NMR spectroscopy in aqueous solution revealed that the toxin comprises the conventional ICK fold containing an extended β-hairpin loop and short β-hairpin loop which are capable of making 'scissors-like mutual motions'. [ABSTRACT FROM AUTHOR]

Examines the camouflage strategy of crab spiders. Adaptation of the entire body color of female crab spiders to that of the flowers on which they are trying to hide; Difference between the visual systems and the range of sensitivity of crab spiders; Analysis of spider crypsis with respect to potential predators and prey.