A minimally invasive technique to assess several life‐history characteristics of the endangered great hammerhead shark Sphyrna mokarran

A dorsal‐fin photo‐identification technique paired with a non‐invasive parallel laser photogrammetry technique was used to non‐invasively identify individual Sphyrna mokarran over time. Based on the data collected over a duration of 59 days, 16 different S. mokarran (mean ± s.d . pre‐caudal length: 220·82 ± 13·66 cm; mean ± s.d . cephalofoil width: 71·38 ± 7·94 cm) were identified using dorsal‐fin photo‐identification, with a mean ± s.d . shark re‐sighting frequency of 4·05 ± 3·06 at‐sea days. The results illustrate a high S. mokarran sighting rate and therefore, the utilization of parallel laser photogrammetry and dorsal‐fin photo‐identification may be a plausible multi‐year approach to aid in non‐invasively determining the growth rate and inter‐annual site fidelity of these animals.     

Prey Luring Coloration of A Nocturnal Semi‐Aquatic Predator

Body coloration serves a variety of purposes in animals. Diurnal and nocturnal predators such as spiders may use their body coloration to lure prey. We predicted here that the white patches on the forelegs on females of the nocturnal semi‐aquatic spider Dolomedes raptor lure prey, explaining why they are primarily displayed when the spider forages along the water edge. To test our prediction, we developed a color vision model assessing whether the patches are visible to pygmy grasshoppers, the spider's primary prey. We conducted a field experiment using cardboard dummies that resemble D. raptor in size, shape, and color, but with half of them lacking leg patches, and we staged interactions between pygmy grasshoppers and D. raptor with and without leg patches in a greenhouse. We found the white patches to be visible to grasshoppers. The dummies with white patches attracted more grasshopper prey than the dummies without the patches. Moreover, grasshoppers were more attracted to spiders when their white patches were present. Our results supported the hypothesis that the white patches of D. raptor lure prey. Our findings, nevertheless, could not be explained as the spider's body coloration acting as a sensory trap but it should not be ruled out. More studies on a wider range of predators and prey will give more meaningful insights into the co‐evolution of predatory lures and prey sensory modalities.     

Are you what you eat? A highly transient and prey‐influenced gut microbiome in the grey house spider Badumna longinqua

Stable core microbial communities have been described in numerous animal species and are commonly associated with fitness benefits for their hosts. Recent research, however, highlights examples of species whose microbiota are transient and environmentally derived. Here, we test the effect of diet on gut microbial community assembly in the spider Badumna longinqua. Using 16S rRNA gene amplicon sequencing combined with quantitative PCR, we analyzed diversity and abundance of the spider's gut microbes, and simultaneously characterized its prey communities using nuclear rRNA markers. We found a clear correlation between community similarity of the spider's insect prey and gut microbial DNA, suggesting that microbiome assembly is primarily diet‐driven. This assumption is supported by a feeding experiment, in which two types of prey—crickets and fruit flies—both substantially altered microbial diversity and community similarity between spiders, but did so in different ways. After cricket consumption, numerous cricket‐derived microbes appeared in the spider's gut, resulting in a rapid homogenization of microbial communities among spiders. In contrast, few prey‐associated bacteria were detected after consumption of fruit flies; instead, the microbial community was remodelled by environmentally sourced microbes, or abundance shifts of rare taxa in the spider's gut. The reshaping of the microbiota by both prey taxa mimicked a stable core microbiome in the spiders for several weeks post feeding. Our results suggest that the spider's gut microbiome undergoes pronounced temporal fluctuations, that its assembly is dictated by the consumed prey, and that different prey taxa may remodel the microbiota in drastically different ways.     

Resource Management in the Orb-Weaving Spider Zygiella x-notata: I. Influence of Spider Behaviour and Available Prey

Management of resource exploitation by the orb-weaving spider Zygiella x-notata was investigated in relation to available prey. Prey capture is studied according to prey type (cricket or fly), and the spider's behaviour (waiting without prey or consuming other prey), at the moment when a prey item was placed onto the web. Characteristics of the spider's exploitation of the previous item (feeding time, and quantities ingested) were analysed according to the type and quantity of prey presented, (1 or 2 items at 1-h intervals). Capture time did not vary in relation to prey type, nor spider activity. However, duration and quantities of certain behavioural components (biting and wrapping) did vary according to prey type and the spider's behaviour, at the moment of presentation of prey. Whatever the type of prey received, if the first item consumed was a cricket, the spiders reduced time spent feeding on this prey without any decrease in the quantities ingested.     

Lethal and sublethal effects of Embelia ribes and two commercial pesticides on a generalist predator

Even as new substances show promise as biopesticides for controlling pests due to their natural properties and high effectiveness in inhibiting pests, their side effects on non‐target organisms must nevertheless be evaluated before they can be included into integrated pest management systems. In this study, a crude extract from dried leaves of Embelia ribes was evaluated together with two commercial pesticides: azadirachtin (a natural product) and amitraz (a synthetic acaricide). We examined both lethal and sublethal effects on the predatory potential of the lynx spider Oxyopes lineatipes, which is among the most dominant predator in tropical agricultural agroecosystems. We found that the spider's mortality increased with rising concentration of both commercial products, azadirachtin and amitraz, but not with rising concentration of the extracts from E. ribes. The greatest mortality occurred when amitraz was used. That material caused almost 100% spider mortality in the doses recommended for field spraying. Azadirachtin significantly reduced the rate at which O. lineatipes captured prey, while there was no significant difference in capture rates among spiders exposed to a control treatment and the E. ribes treatment. Considering its absence of unfavourable impacts on O. lineatipes in terms of mortality and predatory activity, the plant extract from E. ribes shows promise as a new biopesticide material. In contrast, azadirachtin, which has been considered as safe for non‐target organisms, exhibited slight lethal effect only in higher concentrations and strong sublethal effect by reducing spiders’ predation rate.     

Experimental Evidence that a Desert Parasitoid Keeps its Host Cool

The wasp parasitoid Pseudopompilus humboldti (Hymenoptera; Pompilidae) in the Negev desert of Israel stores its paralyzed host, the spider Stegodyphus lineatus (Araneae; Eresidae), at the entrance of the spider's nest. The spider is moved by the wasp from the depth of the nest to the entrance in spite of increased exposure to visually-searching predators, such as birds. We examined the hypothesis that this behaviour has evolved to prevent the wasp's host from overheating in this hot desert. Experimental manipulations of the position of the parasitized spiders demonstrated that spiders and wasp larvae could not survive the heat experienced deep in the spider's nest during summer. By contrast, in the cooler nest entrance, spiders and larvae survived, if they were overlooked by predators. This host-storing behaviour is an adaptive trade-off between thermoregulatory requirements and predation risk. This appears to be the first evidence that a parasitoid manipulates the temperature of its host, albeit for its own ultimate gain.     

SIGNAL POLYMORPHISM IN THE WEB-DECORATING SPIDER ARGIOPE ARGENTATA IS CORRELATED WITH REDUCED SURVIVORSHIP AND THE PRESENCE OF STINGLESS BEES, ITS PRIMARY PREY

Abstract.— Many spiders, and in particular those in the genus Argiope, spin highly visible web decorations whose function and significance are the subject of spirited debate. In this work, we present data to address two of the competing hypotheses that fuel this controversy. In particular, we examine the relationship between the presence of web decorations and spider survivorship (predator‐protection hypothesis) and the relationship between the presence of prey and spider decorating behavior (the prey‐attraction hypothesis). Our laboratory studies reveal that the decorating behavior of the spider A. argentata has a genetic component but that the expression of decorating behavior tends to be elicited only when a spider is well fed. Furthermore, our field studies show that in the presence of abundant stingless bees, spider decorating behavior is induced. Nevertheless, our field surveys also suggest that spiders that decorate their webs show reduced survivorship. We propose that the high correlation between web decorating in the presence of stingless bees supports the hypothesis that A. argentata engage in decorating behavior when attracting or targeting specific prey types. However, we also propose that web decorations attract the predators of A. argentata because high‐frequency decorators suffer lower survivorship than spiders that decorate moderately or rarely. These findings suggest that spider web decorating behavior is affected by conflicting selection pressures: the positive effect of prey attraction versus the negative effect of predator attraction. Due to the heritable component of decorating behavior, web decorating among A. argentata is likely to be particularly sensitive to the spider's local ecology as well as local patterns of gene flow.     

Resource Management in the Orb-Weaving Spider Zygiella x-notata II. Ability to Manage a Set of Various Prey

Management of a set of various prey received ‘simultaneously’ by the orb-weaving spider Zygiella x-notata is investigated in relation to prey species, weight, order of arrival in the web, and factors concerning the spider's state of nourishment. When the spiders encountered several different prey ‘simultaneously’, they subdued all of them, took one of them to begin consumption, and stored the others in the web. The first item for consumption was chosen according to the characteristics of the available prey. Factors concerning previous feeding influenced the spiders's choice of the first item to be ingested. Exploitation of the first item, estimated by the quantity of food extracted and the time necessary for this extraction, depended on the type and the quantity of prey at the spider's disposal. When the spiders received several prey, they spent less time feeding on the first cricket compared with spiders receiving only one cricket, while no difference was found when the first prey item exploited was a fly.     

Emergent properties in the behaviour of a virtual spider robot

Using a virtual spider robot, we studied hypotheses about the weaving behaviour of orb spiders. Our model spiders built virtual webs that mimicked perfectly the visual architecture of real webs of the garden cross spider Araneus diadematus. The matching of capture spiral and auxiliary spiral pitch was an apparently emergent property in both types of web. This validated our interpretation of the garden spider''s web-building decision rules, which use strictly local interactions with previously placed threads to generate global architecture.     

Immunocytochemical localization of GAD isoforms in the CNS ganglia of the cobweb spider,Achaearanea tepidariorum

Glutamic acid decarboxylase (GAD) is an enzyme that catalyzes the decarboxylation of glutamate to γ‐aminobutyric acid (GABA) and CO₂. It has been discovered that the GAD has a restricted tissue distribution and it is highly expressed in the cytoplasm of GABAergic neurons in the CNS where GABA is used as a neurotransmitter. We have examined the microstructure of ganglionic neurons and nerves arising from the CNS and describe here the immunocytochemical localization of GAD isoforms to reveal the ecophysiological significance of GABA for the web‐building spider's behavior. In the CNS of the cobweb spider, Achaearanea tepidariorum, immunocytochemical localization of GAD isoforms can be detected in the neurons and neuropiles of the optic lobes. In addition, GAD‐like immunoreactive cell bodies are observed at the intrinsic cell bodies near the central body and the symmetric cell clusters of the protocerebrum. However, the fibrous masses within the protocerebral ganglion are not labeled at all. Based on its interconnection with other regions of the CNS, our findings suggest that the central body in the web‐building spider may act as an association center as well as a visual center.     

Behavioral manipulation of the orb‐weaver spider Argiope argentata (Araneae: Araneidae) by Acrotaphus chedelae (Hymenoptera: Ichneumonidae)

We observed the first case of host‐behavioral manipulation of an orb‐weaver spider Argiope argentata induced by a parasitoid wasp of the genus Acrotaphus. The modified web is similar of those constructed by other orb weavers attacked by wasps of the close related genus Hymenoepimecis. The stick spirals and radii are absent and the web is composed of a three‐dimensional structure of non adhesive threads. The discovery of the ability to induce changes in host's web‐building behavior in Acrotaphus is indicative that this trait may be primitively present in the clade that includes the genus Hymenoepimecis.     

Tool Use by Spiders: Stone Selection and Placement by Corolla Spiders Ariadna (Segestriidae) of the Namib Desert

The corolla spider (Araneae: Segestriidae: Ariadna) of the Namib Desert gravel plains typically places seven or eight stones in a circle around its burrow entrance. It was examined whether the spider selects and places stones according to physical characteristics. Circle composition can be explained by the allometric scaling to spider size of the burrow entrance and the stones. The stones were usually placed with the narrowest side or point towards the burrow. Quartz crystals were preferred to four other stone types available. The spiders could detect prey brushing the outside of the circle stones that were about as wide as the spider's path of attack. I conclude that corolla spiders use the selected stones as tools to extend their foraging range.     

Fine structure of the CNS ganglia in the geometric spider Nephila clavata (Araneae: Nephilidae)

As web spiders usually hang with their head downward, geometrical differences in body position could affect the organization of their central nervous system (CNS). Nevertheless, most of our knowledge of spider's CNS is dependent on what has been revealed from wandering spiders. To fill the gap, we describe here the fine structural organization of the ganglionic neurons and nerves in the geometric orb web spider Nephila clavata. Nerve cells in the supraesophageal ganglion in N. clavata are packed in the frontal, dorsal and lateral regions, but the nerve cells of the subesophageal mass are only restricted to the ventral and ventrolateral regions. High resolution transmission electron microscopy (TEM) reveals the fine structural details of the neuroglial cells and the neuronal cells which have a conspicuous Golgi apparatus, rough ER, free ribosomes and well‐developed mitochondria. Comparing fine structural characteristics of the CNS ganglia with those of wandering spiders in most respects, it has been revealed that the geometrical difference may affects to the arrangement of receptors in the central body known as an important association center for web building behavior. In particular, remarkable differences can be detected in the protocerebral area by the extraordinary development of the central body including absence of the globuli and associated mushroom bodies.     

A derivative of the orb web and its evolutionary significance

Abstract

This paper describes a new kind of ladder-web structure in which there are two ladders, one above and one below a centrally positioned orb. It differs from previously described ladder-webs, not only because of the two ladders but also because of its 24 h (or more) duration, its vertical placement against the trunks of trees, and the fact that it apparently offers the spider protection against parasitism. Both the spider (Araneus atrihastulus) and its ladder-web are ideally adapted to the tree-trunk: the web with regard to its position, shape, and lack of visibility; and the spider in respect of its coloration, daytime posture, and proximity to the snare. It is concluded that the design of this web offers a number of advantages which evidently enhance the spider's survival and increase its capture potential over and above that of the simple orb.     

Spider mite infestations reduce Bacillus thuringiensis toxin concentration in corn leaves and predators avoid spider mites that have fed on Bacillus thuringiensis corn

Perceived benefits of insecticidal transgenic crops include reduced usage of broad‐based insecticides, and therefore lower risk to non‐target organisms. Numerous studies have documented low or no direct toxicity of Bacillus thuringiensis (Bt)‐derived toxins against non‐target organisms, but there has been less research on (a) effects of secondary pest infestations on Bt expressing in crops and (b) behavioural responses by predators feeding on host arthropods from Bt crops – both topics are investigated in this study. We quantified predation by the obligate spider mite predator Phytoseiulus persimilis of carmine spider mites (Tetranychus cinnabarinus), reared on Bt or non‐Bt corn (Zea mays). Both no‐choice and two‐choice studies were conducted. In addition, we quantified toxin levels in corn leaves with/without spider mite infestation. Under no‐choice conditions, P. persimilis consumed non‐Bt spider mites at a faster rate than Bt spider mites. Under two‐choice conditions, P. persimilis spent more time in the vicinity of non‐Bt spider mites than near Bt spider mites. Corn infested with spider mites exhibited lower toxin levels than non‐infested plants. These results suggest potentially complex interactions among non‐target herbivores, their natural enemies and Bt crops.     

A phylogenetic analysis of the British flora sheds light on the evolutionary and ecological factors driving plant invasions

Darwin's naturalization hypothesis predicts that invasive species should perform better in their novel range in the absence of close relatives in the native flora due to reduced competition. Evidence from recent taxonomic and phylogenetic‐based studies, however, is equivocal. We test Darwin's naturalization hypothesis at two different spatial scales using a fossil‐dated molecular phylogenetic tree of the British native and alien flora (ca. 1600 species) and extensive, fine‐scale survey data from the 1998 Countryside Survey. At both landscape and local scales, invasive species were neither significantly more nor less related to the native flora than their non‐invasive alien counterparts. Species invasiveness was instead correlated with higher nitrogen and moisture preference, but not other life history traits such as life‐form and height. We argue that invasive species spread in Britain is hence more likely determined by changes in land use and other anthropogenic factors, rather than evolutionary history. Synthesis. The transition from non‐invasive to invasive is not related to phylogenetic distinctiveness to the native community, but instead to their environmental preferences. Therefore, combating biological invasions in the Britain and other industrialized countries need entirely different strategies than in more natural environments.     

Spiders,microbes and sex: Bacterial exposure on copulatory organs alters mating behaviour in funnel‐web spiders

Environmental microbes have the potential to be involved in nearly all behavioural processes. For example, mating systems where males use intromittent organs to transfer sperm to females represent a means by which environmental microbes collected by males can breach entry into females' body cavities during mating. However, the degree to which the acquisition of environmental microbes onto important sex structures alters courtship behaviours remains unknown. Here, we collected bacteria from the copulatory organs of Agelenopsis pennsylvanica funnel‐weaving spiders in situ to test whether exposure to bacteria on copulatory organs can alter hosts' courtship behaviour, reproductive success and survival. We used a standardized assay to repeatedly measure each spider's aggressiveness, a behavioural component of both male courtship and female sexual receptivity. Then, we experimentally altered the bacteria present on male and female spiders' copulatory organs with an application of either (a) a mixture of bacteria collected from conspecifics to increase bacterial presence, (b) an antibiotic to reduce bacterial presence or (c) a procedural control. Each spider was paired with a size‐matched spider of the opposite sex whose copulatory organs were unaltered, and we measured the latency until the onset and the duration of courtship. Spiders were then isolated, and we measured each individual's time until death and female fecundity over the next 40 days. We found that female exposure to bacteria had multiple effects on mating dynamics. Males took over four times longer to begin courting females that had been exposed to bacteria compared to unexposed and antibiotic‐treated females. Only when courting these bacteria‐exposed females, males began courtship sooner when females were more aggressive. Lastly, females whose mate had been exposed to bacteria experienced reduced survival. These data suggest that bacteria present on animals' copulatory organs can alter courtship behaviours, female survivorship, and may potentially play a role in mating dynamics.     

The effect of colour variation in predators on the behaviour of pollinators: Australian crab spiders and native bees

1. Australian crab spiders exploit the plant–pollinator mutualism by reflecting UV light that attracts pollinators to the flowers where they sit. However, spider UV reflection seems to vary broadly within and between individuals and species, and we are still lacking any comparative studies of prey and/or predator behaviour towards spider colour variation. 2. Here we looked at the natural variation in the coloration of two species of Australian crab spiders, Thomisus spectabilis and Diaea evanida, collected from the field. Furthermore, we examined how two species of native bees responded to variation in colour contrast generated by spiders sitting in flowers compared with vacant flowers. We used data from a bee choice experiment with D. evanida spiders and Trigona carbonaria bees and also published data on T. spectabilis spiders and Austroplebeia australis bees. 3. In the field both spider species were always achromatically (from a distance) undetectable but chromatically (at closer range) detectable for bees. Experimentally, we showed species‐specific differences in bee behaviour towards particular spider colour variation: T. carbonaria bees did not show any preference for any colour contrasts generated by D. evanida spiders but A. australis bees were more likely to reject flowers with more contrasting T. spectabilis spiders. 4. Our study suggests that some of the spider colour variation that we encounter in the field may be partly explained by the spider's ability to adjust the reflectance properties of its colour relative to the behaviour of the species of prey available.     

Structural analysis of theridiid spider's testicular cyst using 3D reconstruction rendering

A three dimensional reconstruction technique was used for the analysis of a theridiid spider's (Achaearanea tepidariorum) testicular cyst. Although microscopic techniques have greatly improved, most of the information gathered is still based on two‐dimensional images. Particularly in spiders, it is very difficult to count the exact number of sperm in a single cyst, since their spermatogenetic processes takes place within the spherical cysts through the flagellar coiling process. Since morphological features of spider sperm provide detailed information on the whole spermatogenetic processes, we analyzed the exact number of germ cells per cyst in A. tepidariorum through a three‐dimensional image reconstruction technique. For image processing, serially sectioned histological images were scanned using a light microscope and 3D rendering images were reconstructed from these sections. Based on the three dimensional image analysis of the testicular cyst, the number of secondary spermatocytes per cyst was calculated to be 32 (2⁵). Therefore the total number of sperm produced from a single cyst can be calculated as 64 (2⁶), which indicates that a single spermatogonium undergoes four mitotic divisions and an additional two meiotic divisions to produce mature spermatozoa.     

Spider silk as a resource for future biotechnologies

Insect silks have been used by mankind for millennia to produce textiles and in particular, the cocoon silk of Bombyx mori was the base of one of the most important industries in history. In fact, B. mori is probably the only domesticated insect if not invertebrate in its true and strict sense, comparable to cattle and other livestock that humans have known and bred since the Neolithic period. In contrast, reports regarding the use of spider silk throughout history have the character of travellers’ tales or anecdotes, and serious attempts to exploit these biomaterials on a large scale have not been undertaken until recently. Indeed, the cannibalism of these carnivores makes their farming difficult and the production of significant yields of spider silk virtually impossible. Only today, with recombinant technologies available, does this problem seem to have been overcome. But why use spider silk at all – if we have the infrastructure to produce significant yields of silk from Bombyx? In contrast to most insects, spiders do not spin from labial glands, and many spiders possess different types of gland, most of them active throughout the whole lifespan. Typical orb‐weavers (Araneoidea) for instance possess up to seven different types of silk gland to produce different silk fibers and glues. Each of these products has evolved for a particular use and the respective material properties are highly adapted to that use. As the group of Araneae is about 400 million years old, the oldest fossil orb‐weaver is dated about 150 million years, and the use of silk is crucial to a spider's survival, we can expect that evolution will have “squeezed out every iota” to achieve optimum performance at minimum cost. Indeed, some dragline silks such as the major ampullate silks of some Nephila species show amazing mechanical properties that, in terms of toughness, are far superior to Bombyx silk. Labels like “stronger than steel” or “even better than Kevlar” were attached to them, and the Canadian‐based biotech company Nexia created the trademark “bio‐steel” for their prospective product. The discovery of these exceptional mechanical properties of those protein fibers triggered intense research on spider silk, with the goal of their commercial exploitation. But there is more to Arachne's weave and science is beginning to pick up those threads.