The Trochidae and Turbinidae of the Kermadec Ridge (Mollusca: Gastropoda)

Abstract

Taieria erebus (Gnaphosidae) was found to be a versatile predator: it captured insects both cursorially (away from webs) and kleptopar-asitically (on alien webs); it captured spiders in both the presence and absence of webs; and it also ate the eggs of host spiders (oophagy). When T. erebus invaded webs, it was as an aggressive mimic — it performed a repertoire of vibratory behaviours to lure the host spider. Although T. erebus pursued and captured spiders on diverse web-types, it was more effective as a predator when invading densely (rather than sparsely) woven cribellate and non-sticky webs, and was especially effective on non-cribellate sticky webs. Gnaphosids are traditionally referred to as hunting spiders, but T. erebus built a small prey-capture web. T. erebus also preyed on segestriid spiders, then used their webs to catch more prey, this being an unusual example of a spider using, as a tool for predation, the spinning-work of another species from an unrelated family. T. erebus used specialised behaviours to prey on nesting cursorial spiders. Prey was either grasped or stabbed; the venom of T. erebus was highly potent against spiders. Experiments indicated that vision was of little or no importance in the predatory behaviour of T. erebus. The behaviour of T. erebus is compared to that of Portia, a web-building salticid spider which is very versatile in its predatory behaviour and has acute vision. T. erebus is discussed in relation to hypotheses concerning gnaphosid and salticid evolution.     

Comparative biology of Portia africana,P. albimana,P. fimbriata,P. labiata,and P. shultzi,araneophagic, web-building jumping spiders (Araneae: Salticidae): Utilisation of webs,predatory versatility,and intraspecific interactions

Abstract

Portia is a behaviourally complex and aberrant salticid genus. The genus is of unusual importance because it is morphologically primitive. Five species were studied in nature (Australia, Kenya, Malaysia, Sri Lanka) and in the laboratory in an effort to clarify the origins of the salticids and of their unique, complex eyes. All the species of Portia studied were both web builders and cursorial. Portia was also an araneophagic web invader, and it was a highly effective predator on diverse types of alien webs. Portia was an aggressive mimic, using a complex repertoire of vibratory behaviour to deceive the host spiders on which it fed. The venom of Portia was unusually potent to other spiders; its easily autotomised legs may have helped Portia escape if attacked by its frequently dangerous prey. Portia was also kleptoparasitic and oophagic when occupying alien webs. P. fimbriata from Queensland, where cursorial salticids were superabundant, used a unique manner of stalking and capturing other salticids. The display repertoires used during intraspecific interactions were complex and varied between species. Both visual (typical of other salticids) and vibratory (typical of other web spiders) displays were used. Portia copulated both on and away from webs and frequently with the female hanging from a dragline. Males cohabited with subadult females on webs, mating after the female matured. Adult and subadult females sometimes used specialised predatory attacks against courting or mating males. Sperm induction in Portia was similar to that in other cursorial spiders. Portia mimicked detritus in shape and colour, and its slow, mechanical locomotion preserved concealment. Portia occasionally used a special defensive behaviour (wild leaping) if disturbed by a potential predator. Two types of webs were spun by all species (Type 1, small resting platforms; Type 2, large prey-capture webs). Two types of egg sacs were made, both of which were highly aberrant for a salticid. Responses of different species and both sexes of Portia were quantitatively compared for different types of prey. Many of the trends in behaviour within the genus, including quantitative differences in predatory behaviour, seemed to be related to differences in the effectiveness of the cryptic morphology of Portia in concealing the spider in its natural habitat (‘effective crypsis’). The results of the study supported, in general, Jackson & Blest’s (1982a) hypothesis of salticid evolution which, in part, proposes that salticid ancestors were web builders with poorly developed vision and that acute vision evolved in conjunction with the ancestral spiders becoming proficient as araneophagic invaders of diverse types of webs.     

Web-invasion and araneophagy by New Zealand and Australian pholcid spiders

Abstract

Pholcus phalangioides, Pholcus ancoralis, and Psilochorus sphaeroides were observed in the field in New Zealand (first species only) and Australia (all three species) to invade the webs of other species. P. phalangioides was observed to feed on spiders in alien webs. Webs of each species were frequently contiguous with webs of other spiders and P. sphaeroides sometimes invaded neighbouring webs in pursuit of insects.     

Predatory and nesting behaviour of Cocalus gibbosus,a spartaeine jumping spider (Araneae: Salticidae) from Queensland

Abstract

Cocalus gibbosus was studied in the field in Queensland and in the laboratory. This is the first behavioural study of a species from the spartaeine genus Cocalus. C. gibbosus often omitted elements which are usually present in the predatory sequences of typical salticids and tended to lunge at prey from close range rather than leap from afar. Experiments showed that C. gibbosus prefers moths to other prey. In nature, C. gibbosus moulted and oviposited on silk sheets spun against tree trunks, and in the laboratory on sides of cages or blocks of wood, but this species never built an enclosing nest like typical salticids nor a large prey-catching web like some other spartaeines. C. gibbosus stalked across alien webs to catch spiders and insects, but it did not make vibratory signals. It did not stick to cribellate or ecribellate glue on alien webs. The behaviour of C. gibbosus is compared to that of other spartaeine salticids.     

Conditional strategies and interpopulation variation in the behaviour of jumping spiders

Abstract

Conditional strategies and interpopulation variation in the mating and predatory behaviour of salticid spiders are reviewed. A functional approach is adopted, and defended, in which specified behavioural phenotypes are accounted for, in large part, by specified selection factors. Courtship versatility, in which a male's behaviour depends on the female's maturity and location, is common in the Salticidae. If a male encounters an adult female in the open, where there is ample ambient light, he performs vision-dependent displays (Type 1 courtship) in front of her. If he encounters an adult female inside her nest, he uses different displays (Type 2 courtship) which are not vision–dependent and consist of various tugging, probing and jerking movements on the silk of the nest. These displays apparently send vibratory stimuli to the female. When a male encounters a subadult female inside her nest, he initially performs Type 2 courtship, then spins a second chamber on the nest and cohabits until the female moults and matures. A modification of optimal foraging theory has been used to examine factors that influence interpopulation variation in male courtship persistence. A study of five populations corroborated predictions from the model. Persistence appears to be related to female availability. Female availability is related to local phenology, which is, in turn, related to local climate. Complex examples of predatory versatility also have evolved in the Salticidae, especially in the genus Portia. All species of Portia studied are araneophagic spiders that invade other spiders' webs and practise aggressive mimicry. Portia fimbriata, uniquely among Portia species studied, uses specialised behaviour to prey on other salticids. Portia fimbriata and one of the salticids on which it preys, Euryattus sp., appear to be co-adapted to each other.     

Conspecific and Heterospecific Attraction: A Mechanism of Web-site Selection Leading to Aggregation Formation by Web-building Spiders

This study investigated whether conspecific and/or heterospecific attraction to silk is a mechanism of web-site selection leading to aggregation formation by two species of web-building spiders, Hypochilus thorelli Marx (Araneae: Hypochilidae) and Achaearanea tepidariorum (C.L. Koch) (Araneac: Theridiidae). We determined that the spatial distribution of these two spiders was clumped and that H. thorelli had a greater tendency to aggregate than did A. tepidariorum. To determine the mechanism responsible for this spatial pattern, we conducted three field experiments. We examined web-site selection by H. thorelli in three contexts: no spiders or webs present (cue removed), vacant webs present, and occupied webs present. In the case where no webs were present, there was no tendency for spiders to choose previously occupied sites as web sites. When vacant webs were present, spiders chose to occupy the vacant webs. When occupied webs were present, spiders either invaded webs and evicted the owners, or settled adjacent to and attached their webs to those of residents. Various microhabitat variables (height, angle, temperature, humidity, and substrate character of the rock surface) of randomly selected unoccupied sites and the web sites chosen by spiders were compared. There were no detectable differences between web sites and unoccupied sites with respect to any of the variables measured. This leads us to conclude that web-site choice by immigrating spiders was based on the presence of silk rather than other features of the site.     

Body size determines the outcome of competition for webs among alien and native sheetweb spiders (Araneae: Linyphiidae)

Abstract 1. Biotic invasions are one of the most important reasons for changes in biodiversity. The alien sheetweb spider Mermessus trilobatus (Araneae: Linyphiidae) has become abundant in large parts of Central Europe within the past three decades. Its invasion might negatively influence native spiders, for instance via competition for webs. 2. Laboratory experiments were developed to test if M. trilobatus is competitively superior to native spiders. The alien M. trilobatus and five native sheetweb spiders (Erigone dentipalpis, E. atra, Gnathonarium dentatum, Dicymbium nigrum and Micrargus herbigradus) were compared with respect to their success to take over occupied webs from E. dentipalpis. 3. The rate of web takeover or defence was determined by body size, whereby individuals with a wider thorax invaded webs more successfully. After taking body size into account, the frequency of defence or web takeover did not differ between species. In 13% of all confrontations, predation against generally smaller opponents was recorded. Contrary to the predictions, raising the web value with food resources did not raise the effort expended on web defence but reduced predation by the web owner. 4. The current study does not indicate that the invasion of the relatively small‐sized M. trilobatus is facilitated by strong competitiveness. Nevertheless, M. trilobatus may displace smaller‐sized immature specimens and thereby threaten native spiders. Still, other reasons are likely to underlie the success of M. trilobatus in Europe, such as rapid reproduction or release from natural enemies.     

The biology of Euryattus sp. indet., a web-building jumping spider (Araneae, Salticidae) from Queensland: utilization of silk, predatory behaviour and intraspecific interactions

The biology of an aberrant saltioid spider, Euryattus Thorell sp. indet., is described from observations in a Queensland rain forest and the laboratory. Pronounced morphological and behavioural changes occur during post-embryological development. Juveniles spin webs, but adult females make 'suspension nests' by suspending a curled-up leaf by heavy guylines from a rock ledge or vegetation. Adult males spin neither webs nor suspension nests. Females oviposit inside their suspension nests, but if denied access to leaves for suspension, they spin and oviposit in webs similar to those spun by juveniles. The flat, papery egg sacs of Euryattus are atypical for a salticid, being more like the egg sacs of many of the Gnaphosidae. Intraspecific display behaviour has characteristics in common with typical salticids, but also includes unique features. Male courtship includes vibratory displays performed on the surface of the suspended leaf. Mating occurs inside the curled-up leaf. Males co-habit with sub-adult females in suspension nests. Females take over suspension nests of other females and eat each other's eggs. Normal locomotion, intraspecific interactions, and predatory behaviour are characterized by frequent leaping. Euryattus routinely makes long and accurate leaps on to prey, including flying insects intercepted in mid-air and spiders and insects located in alien webs. The phylogenetic implications of the unusual characteristics of Euryattus are considered.     

Testing the Functions of Detritus Stabilimenta in Webs of Cyclosa fililineata and Cyclosa morretes (Araneae: Araneidae): Do They Attract Prey or Reduce the Risk of Predation?

Spiders of the genus Cyclosa often add prey remains and other debris to their orb‐webs. The function of silk decorations is generally associated with defense against predators or with the attraction of prey, but few studies have focused on stabilimenta containing detritus. In this study, we used artificial webs with and without the detritus stabilimenta of two species of Cyclosa to investigate whether these structures increase the number of insects intercepted. Artificial models of spiders and stabilimenta were used to compare the frequency of attacks against different shapes. We also conducted choice experiments in laboratory to determine whether detritus columns attracted Drosophila melanogaster (Diptera: Drosophilidae) and Trigona angustula (Hymenoptera: Apidae, Meliponinae) to the webs. The frequency of interception in artificial webs with a stabilimentum was similar to that of webs without such structure. The taxonomic composition and biomass of insects were also similar in both types of artificial webs. The choice experiments showed no significant tendency in attraction to webs with a stabilimentum. However, models of spiders were attacked at a higher frequency than those simulating detritus columns and silk decorations. These findings argue against the prey attraction hypothesis and suggest that the addition of stabilimenta to webs of Cyclosa could reduce the intensity of predation, possibly by disrupting the image of the spider's outline.     

Individual decisions and group dynamics: why pholcid spiders join and leave groups

To examine the role of individual variation in the dynamics of group formation, I conducted a mark-recapture study and a series of laboratory and field experiments with Holocnemus pluchei spiders (Araneae: Pholcidae). These spiders can either share webs or live alone, and individuals shift frequently between these strategies. Spiders' decisions were influenced by size and recent feeding success. In the laboratory, small hungry spiders introduced into a web that held a larger conspecific resident were more likely than small well-fed spiders to abandon the web and build their own web. This behaviour pattern gradually reversed as spiders grew: large hungry spiders were more likely than large well-fed spiders to stay in the shared web. When I introduced spiders into empty webs, they were more likely to stay compared with spiders tested with conspecifics. However, hunger level also influenced behaviour even when conspecifics were not present. Food-deprived spiders were more likely to abandon webs and build their own, consistent with the idea that spiders were following a win-stay/lose-shift strategy. In the field, spiders were more likely to stay in webs overnight when they were given supplemental food. In another experiment, spiders that were found building webs in cleared areas were smaller and thinner than average. Finally, I tested whether the size of the intruder or the resident affected whether spiders joined webs. Large intruders were more successful at remaining in webs than smaller intruders, although spiders of all sizes had some success in joining groups. Additional synthetic theoretical work is needed to integrate the complex processes underlying the formation and persistence of groups.     

Orchestrating the score: complex multimodal courtship in the Habronattus coecatus group of Habronattus jumping spiders (Araneae: Salticidae)

Jumping spiders in the genus Habronattus use complex multimodal signals during courtship displays. In the present study, we describe multimodal displays from the Habronattus coecatus clade, comprising a diverse group of 23 described species. Habronattus coecatus group displays are made up of sex‐specific ornamentation and temporally coordinated combinations of motion displays and vibratory songs. Vibratory songs are complex, consisting of up to 20 elements organized in functional groupings (motifs) that change as courtship progresses. This temporal structuring of displays is analogous to a musical composition. Vibratory elements are associated with movement displays involving coloured and patterned ornaments on the male body. We describe general patterns of multimodal displays for 11 species including one, Habronattus borealis, which appears to have lost complex display behaviour. Habronattus coecatus group courtship is one of the most complex communication systems yet described in arthropods and this group may reveal important factors driving the evolution of complex signals. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 522–547.     

Redescription of Natalaspis leptocarpi n.comb. (Homoptera: Diaspididae)

Abstract

Cyllobelus rufopictus? a salticid species from equatorial Africa, has a large and complex repertoire of displays. These spiders live on and near the ground in habitats of short grass, and build opaque silk nests on dead leaves. Each male uses one of three different mating tactics depending on the female’s maturity and location (communicatory versatility). Type 1 courtship, involving special movements and postures of the legs, palps, and body, occurs if the female is an adult away from the nest; apparently this type of courtship is vision-dependent. If the male encounters an adult female inside her nest, he uses Type 2 courtship, which consists of movements by the male that cause the silk to vibrate. If the female is a subadult inside her nest, the male initially uses Type 2 courtship, then builds a second chamber on the female’s nest, and cohabits until she moults and matures. Other displays occur during male-male and female-female interactions. Biting and pinching are distinctive Type 2 courtship displays that have not been described previously for salticids, and juddering is the most distinctive Type 1 display.     

The biology of Pholcus phalangioides (Araneae, Pholcidae): predatory versatility, araneophagy and aggressive mimicry

Predatory versatility occurs in Pholcus phalangioides (Fuesslin). In addition to building prey-catching space webs, P. phalangioides invades webs of other spiders and feeds on the occupants. It acts as an aggressive mimic by performing specialized vibratory behaviours to which the prey-spider responds as it normally would to its own prey. Prey (spiders and insects) is attacked by wrapping. Prey that trips over lines at the edge of a web of P. phalangioides , but fails to enter the web, is successfully attacked: P. phalangioides leans out of its web to throw silk over the prey, keeping as few as two legs on the silk. However, P. phalangioides does not attack prey that is completely away from webs. Occasionally, P. phalangioides feeds on eggs of other spiders and on ensnared insects it encounters in alien webs. Experimental evidence indicates that vision is of little or no importance in the predatory behaviour of P. phalangioides . Although P. phalangioides invades diverse types of webs, in addition to using its own web, its efficiency as a predator varies with web-type. It is most efficient as a predator of spiders and, especially, insects on its own web, and least efficient as a predator of amaurobiids on their cribellate sheet webs. Sensory, locomotory and other factors which influence differential predatory efficiency are discussed. The behaviour of P. phalangioides is compared to that of Portia , an araneophagic web-invading salticid, and the results of this study are discussed in relation to hypotheses concerning salticid evolution.     

Signaling by decorating webs: luring prey or deterring predators?

Many organisms convey false signals to mislead their prey orpredators. Some orb-weaving spiders build conspicuous structureson webs called decorations. Web decorations and spider colorationsare both suggested to be important signals involved in interactionsbetween spiders and other organisms. There are several hypothesesabout the functions of signaling by decorations, among whichprey attraction had received much support, but empirical evidenceregarding predator defense is controversial. In this study,we conducted field experiments to investigate the effects ofspider decoration and coloration on insect interception ratesof webs built by Argiope aemula and to evaluate whether presenceof decorations may decrease predation risk of spiders. Decoratedwebs with spiders present had the highest prey interceptionrate, followed by undecorated webs with spiders, and then undecoratedwebs without spiders. Such results indicated that decorationsof Argiope spiders functioned as visual lures, and so did spiders'bright body colorations. In the field, almost all wasp attackevents occurred on medium-sized spiders rather than on largeones. Moreover, medium-sized Arg. aemula on decorated webs receivedfar more attacks than those on undecorated webs. Results ofthis study thus show that the signals conveyed by decorationscan visually lure prey but at the cost of an increased predationrisk. Received 20 March 2007; revised 3 August 2007; accepted 5 August 2007.     

Linyphid spider courtship: Releaser and attractant functions of a contact sex pheromone

Experiments with male bowl-and-doily spiders (Frontinella communis) on methanol-washed and unwashed female webs indicate that the courtship of males is chemically released. Parallel experiments on the webs of females of another linyphiid species and on immature F. communis webs indicate that the releaser pheromone is species specific and that it is produced only by mature females. The pheromone that releases male courtship also functions as an attractant, changing the male's orientation from negatively to positively geotactic. The presence or absence of a female on the test web has only a slight effect on the male's behaviour.     

Impact of predation by spiders on a territorial damselfly (Odonata: Calopterygidae)

Summary Predation by orb-weaving spiders and crab spiders on the damselfly Calopteryx haemorrhoidalis was studied at a small stream in Southern France. One species of orb-weaving spider, Larinioides folium, caught 76% of the damselflies which fell prey to spiders. Displacement experiments on spiders on sections of bank and the positioning of webs in male territories show that the density and distribution of damselflies is not influenced by orbweb density or by the position of webs. Predation rates corresponded to orb-web density, but neither for sex nor for stage was there a relationship with damselfly density. Mean daily predation rates ranged between 0.9% for females and 4.1% for adult males. Predation risk to adult damselflies by orb-weaving spiders was male biased, whereas among tenerals there was no bias. Males were captured more frequently at territories near the water. Captures show a maximum at noon when territorial disputes of adult males were most frequent. After orbwebs were placed within territories predation rate of males was strongly increased. Predation risk to adult females in the direct vicinity of the stream was less than in the bank vegetation where they perch close to orbwebs. The risk of predation by crab spiders, which catch damselflies at their perching sites, was not sex-biased.     

Aliens among us: nestmate recognition in the social huntsman spider, Delena cancerides

Unlike all other social spiders, the social huntsman spider, Delena cancerides, has been reported to rapidly respond to non-nestmates with lethal aggression, similar to the behavior of some eusocial insects. We tested for the presence of nestmate recognition in D. cancerides under laboratory conditions by introducing 105 unrelated alien conspecifics into foreign colonies and comparing their behavior to 60 control spiders removed and returned to their natal colony. Spiders demonstrated nestmate recognition by investigating alien spiders far more than nestmates and by resting closer to nestmates than to aliens. Serious attacks or deaths occurred in 23% of all trials; however, aggression was not directed significantly more toward aliens than to nestmates. Most notably, aggression was largely mediated by the adult females (resident or alien), who were most likely to attack or kill other subadult or mature individuals. Young individuals (resident or alien) were largely immune from serious aggression. Spiders recently collected from the field tended to be more aggressive than spiders born and raised in the laboratory, possibly due to blurring of recognition cues related to laboratory husbandry. Our findings support the prediction that nestmate recognition should evolve when there is a benefit to discriminating against non-kin, as in this social spider system where foraging individuals may enter a foreign colony and the colony retreat is a limited resource.     

Site Selection and Foraging in the Eresid Spider Stegodyphus tentoriicola

Habitat selection has profound consequences for survival and reproductive success. We investigated web relocation behaviour in relation to plant structure and body condition as well as the plasticity of foraging behaviour of the spider Stegodyphus tentoriicola. Spiders inhabiting thorny vegetation were larger, built larger webs than spiders in thornless plants and relocated their webs less frequently. Web relocation affected reproductive success through a delay of oviposition. Spiders supplemented with extra food improved body condition and built smaller webs than control spiders implying a crucial role of food in limiting fitness of S. tentoriicola. Reduced investment in webs suggests a trade-off between the benefit of more food against the cost of web-construction. We propose that S. tentoriicola exhibit a “silk and energy saving” strategy when saturated.     

Behavioural evidence of UV sensitivity in jumping spiders (Araneae: Salticidae)

Jumping spiders are known to possess ultraviolet (UV) receptors in the retinas of their large-principal eyes. The existence of UV visual cells, however, does not prove that jumping spiders can see into the UV part of spectrum (300–400 nm) or whether such an ability plays any role in salticid intra-specific interactions. In the study reported herein, we performed behavioural experiments to test whether a UV−reflecting jumping spider, Cosmophasis umbratica, is sensitive to UV wavelengths and whether UV cues are important in intra-specific communication. The absence of UV cues not only affected intra-specific behaviour by significantly reducing the frequency of agonistic displays, but also elicited unprecedented courtship displays in males towards their own mirror images and conspecific opponents. Furthermore, C. umbratica males were able to respond rapidly to changes in UV cues of conspecific mirror images by switching between agonistic and courtship displays. These findings clearly demonstrate that C. umbratica males are capable of seeing UV wavelengths and that UV cues are necessary and sufficient for this species to enable the agonistic displays. Hence, UV light may have an important role to play in intra-specific communication in jumping spiders.     

Effects of male size and female dispersion on male mate-locating success in Nephila clavipes

The reproductive success of sexually reproducing organisms depends on their capacity to locate potential partners. Research on the mating systems of web-building spiders, like other terrestrial invertebrates, has focused around male courtship and the signalling behaviours that facilitate copulation. In contrast, both mate searching and mate location behaviours are largely ignored and rarely quantified in field studies. We conducted a series of field removal experiments to explore the effects of male body size and female dispersion on mate locating behaviour of the golden orb-weaving spider (Nephila clavipes). The number of males that arrived on females’ webs was influenced by travel distance, male body size, male body weight and female dispersal. More males returned to webs that were closer to the release point; smaller males experienced a greater weight loss; and larger numbers of males arrived at webs where males had been previously present. Female dispersion influenced the size but not the number of arriving males: males were no more likely to arrive at solitary than aggregations of webs, but males arriving at solitary webs were typically larger than those arriving at aggregations. We discuss the implications of various male traits that could act as selective pressures on male mate location and mate searching behaviours.