Sociality in a bark-dwelling huntsman spider from Australia,Delena cancerides Walckenaer (Araneae: Sparassidae)

Summary Social behavior is reported for the first time in a member of the family Sparassidae (Araneae), the Australian huntsman spiderDelena cancerides Walckenaer. Unlike any previously known social spider, this is a bark dwelling species and, thus, its sociality cannot have its basis on an aerial web, the structure that has been considered central to the evolution of sociality in other spider species. Colonies ofD. cancerides may comprise up to 300 individuals living in close physical contact under the exfoliating bark of deadAcacia, Callitris andCasuarina species. Specimens maintained in the laboratory feed communally and capture prey jointly. Although this intranest tolerance and communal feeding behavior is reminiscent of other highly social spiders,D. cancerides notably differs from these other species in the extreme aggression shown towards members of foreign colonies, its outbred population structure, and lack of sex ratio bias. We suggest that sociality in this species may have been facilitated by the presence of extended maternal care in the ancestral phylogenetic lineage, as suggested by the occurrence of such behavior in related nonsocial species, and that colonial living may have arisen as a consequence of the reduction and fragmentation ofDelena's habitat associated with the rise to dominance of the eucalypts. The apparent colony recognition observed may have evolved becauseDelena's hunting habits may require mechanisms to locate one's own colony after foraging expeditions and to exclude wandering outsiders from entering one's nest, in contrast to web-bound species that do not need to leave their nest to forage. How the observed outbreeding is accomplished in the face ofDelena's extreme intolerance to members of other nests, as well as how new colonies are formed, are issues that have yet to be investigated.     

中国稻田蜘蛛优势种及其成因探讨

文中介绍了中国稻田蜘蛛26个优势种在全国117个样点中的发生现状；论述了稻田蜘蛛优势种在中国稻区的地理分布概况；分析了稻田生态系统主要生态因子对稻田优势种蜘蛛发生发展的影响；重点探讨了稻田蜘蛛优势种的成因，提出了稻田蜘蛛优势种形成的主要条件和关键因子，为有的放矢地保护利用蜘蛛优势种群控制稻早效能提供了科学依据。     

Life-history variation in closely related generalist predators living in the same habitat: a case study with three Cyclosa spiders

1. Generalist predators sharing similar food resources and phenologies as well as having no competitive interactions are expected to have a similar life-history pattern, but some closely related web spiders show different life-history traits. The present paper clarifies possible selection pressures affecting life-history traits of the three coexisting Cyclosa spiders and explores the significance of the life-history variation.
2. Cyclosa argenteoalba had lower daily survival rate and higher growth rate, C. sedeculata had higher daily survival rate and lower growth rate, and C. octotuberculata showed intermediate levels. This implies that the selection pressures these spiders experience differ appreciably even in the same habitat.
3. The significance of the life-history characteristics of the three species was evaluated by general life-history theories. Cyclosa argenteoalba showed distinguishing reproductive traits: shorter time to maturation, larger reproductive effort, larger relative clutch size, decreased clutch size with the number of clutches, and smaller egg size. These characteristics may have evolved in response to the larger ratio of juvenile to adult survivorship. Cyclosa octotuberculata had a clutch size much larger than the other two species, but relative clutch sizes accounting for body size were similar between C. octotuberculata and C. sedeculata . Also, the two species showed a similar time to maturation despite having different selection pressures. Probably, higher growth rate compensates for lower survivorship, leading to the similarity in some reproductive traits.     

Spider silk reduces insect herbivory

The role of predators in food webs extends beyond their ability to kill and consume prey. Such trait-mediated effects occur when signals of the predator influence the behaviour of other animals. Because all spiders are silk-producing carnivores, we hypothesized that silk alone would signal other arthropods and enhance non-lethal effects of spiders. We quantified the herbivory inflicted by two beetle species on green bean plants (Phaseolus vulgaris) in the presence of silkworm silk and spider silk along with no silk controls. Single leaflets were treated and enclosed with herbivores in the laboratory and field. Another set of leaflets were treated and left to experience natural herbivory in the field. Entire plants in the field were treated with silk and enclosed with herbivores or left exposed to herbivory. In all cases, the lowest levels of herbivory occurred with spider silk treatments and, in general, silkworm silk produced intermediate levels of leaf damage. These results suggest that silk may be a mechanism for the trait-mediated impacts of spiders and that it might contribute to integrated pest management programmes.     

Human dimensions of wolf (<Emphasis Type="Italic">Canis lupus</Emphasis>) conflicts in Finland

The growth of the Finnish wolf (Canis lupus) population during the last years has highlighted people’s contradictory attitudes toward wolves. The supranational conservation objectives brought on by Finland’s membership in the European Union (EU) and the regional application of the official policy on wolves have led to conflicts. This article is based on the preparation process of the wolf management plan in Finland. As a part of the process, a nationwide hearing was arranged in 2004. Fear of wolves is widespread and even more common in areas with low wolf population. People living in areas where wolves occur feel that they can no longer influence decision making which affects them and that the authorities, conservationists, and the EU do not listen to their opinions. Numerous requests have been made for the legislation and its interpretation, and concessions to these requests would promote consensus and increase tolerance for wolves. Proposed changes include reforming the damage compensation system and formulating a clearer interpretation of the conservation status of wolves. However, it seems impossible to create a policy that would be universally supported. As the wolf question has become more central in environmental policy, the conservation and management of the species have become more complicated, and the cooperation between various interest groups has declined. The wolf conflict could be mitigated by compromises, but because the conflict is value-based, solutions are illusive.     

Distortion of the local magnetic field appears to neither disrupt nocturnal navigation nor cue shelter recognition in the amblypygid Paraphrynus laevifrons

Many arthropods are known to be sensitive to the geomagnetic field and exploit the field to solve spatial problems. The polarity of the geomagnetic field is used, for instance, as an orientation cue by leafcutter ants as they travel on engineered trails in a rainforest and by Drosophila larvae as they move short distances in search of food. A ubiquitous orientation cue like the geomagnetic field may be especially useful in complex, cluttered environments like rainforests, where the reliability of celestial cues used to navigate in more open environments may be poor. The neotropical amblypygid Paraphrynus laevifrons is a nocturnal arachnid that wanders nightly in the vicinity of its shelter and occasionally travels 30 m or more in the rainforest understory before it returns to its shelter. Here, we conducted a field experiment to determine whether navigation by P. laevifrons is guided by the ambient magnetic field and a complimentary laboratory experiment to assess whether a magnetic anomaly could be used to pinpoint the entrance of a shelter. In the field experiment, subjects were fitted with a radio transmitter and a small, powerful magnet or a similar-sized brass disk and displaced 10 m from their shelter. The return rate of magnet-fitted subjects was similar to that of brass-fitted subjects and to that of subjects in an earlier study fitted with only a radio transmitter. In the laboratory experiment, we trained P. laevifrons with a protocol under which the amblypygid Phrynus marginemaculatus rapidly learns—in 1–14 trials over two daily sessions—to associate an olfactory stimulus with access to a shelter. The conditioned stimulus here was a magnetic anomaly characterized by a high total field intensity and a 180° reversal of the polarity of the ambient magnetic field. The magnetic anomaly-shelter contingency was not learned in 50 trials conducted over 10 daily sessions. These results imply prima facie that P. laevifrons does not rely on a magnetic compass to locate or recognize a shelter and, perhaps, that the magnetic field cannot be detected, but alternative explanations are discussed.     

Discrimination and release of unpalatable butterflies by Nephila clavipes, a neotropical orb-weaving spider

Abstract. 1. Nephila clavipes (L.), a common spider in neotropical forests, discriminates some unpalatable prey and releases them unharmed from its web. Release is not accidental but results from a specific behavioural sequence.
2. Field trials with twenty-seven butterfly species showed that spiders respond consistently to butterfly species and higher taxa. Ithomiinae and some Danainae are almost always released while Heliconiinae, Nymphalinae, Acraeinae, Pieridae and Papilionidae are usually eaten.
3. Paired tests showed that an immediately preceding experience with a different butterfly did not reveal any change in the spider's usual response to a particular butterfly.
4. Warning coloration is not involved in spider response. Spiders rejected the models but ate the mimics of two different butterfly species pairs. Distastefulness is probably signalled by chemical cues.
5. Some unpalatable butterflies stay motionless when entangled and while the spiders release them. Motionlessness in webs seems to be a requisite to allow recognition of their distastefulness without being bitten by the spider.
6. Spiders differ from vertebrates in the prey accepted and in rejection mechanics. Although there is no indication of learning, spiders may select butterflies for distastefulness, chemical signals and motionlessness, at the individual level.