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В статье впервые для Сахалинской области отмечаются Dolomedes senilis Simon, 1880 и Agelenopsis potteri (Blackwall, 1846). Они известны с сопредельных с Сахалином территорий, однако для самого острова виды не указывались. Обсуждается распространение D. senilis и A. potteri, а также видовой состав других представителей семейств Pisauridae и Agelenidae в Сахалинской области. Даны главные определительные признаки видов. Приведены фотографии внешнего вида пауков, эпигины самки D. senilis и пальпы самца A. potteri.

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. [ABSTRACT FROM AUTHOR]

Contact with environmental microbes are arguably the most common species interaction in which any animal participates. Studies have noted diverse relationships between hosts and resident microbes, which can have strong consequences for host development, physiology, and behavior. Many of these studies focus specifically on pathogens or beneficial microbes, while the benign microbes, of which the majority of bacteria could be described, are often ignored. Here, we explore the nature of the relationships between the grass spider Agelenopsis pennsylvanica and bacteria collected from their cuticles in situ. First, using culture-based methods, we identified a portion of the cuticular bacterial communities that are naturally associated with these spiders. Then, we topically exposed spiders to a subset of these bacterial monocultures to estimate how bacterial exposure may alter 3 host behavioral traits: boldness, aggressiveness, and activity level. We conducted these behavioral assays 3 times before and 3 times after topical application, and compared the changes observed in each trait with spiders that were exposed to a sterile control treatment. We identified 9 species of bacteria from the cuticles of 36 spiders and exposed groups of 20 spiders to 1 of 4 species of cuticular bacteria. We found that exposure to Dermacoccus nishinomiyaensis and Staphylococcus saprophyticus was associated with a 10-fold decrease in the foraging aggressiveness of spiders toward prey in their web. Since bacterial exposure did not have survival consequences for hosts, these data suggest that interactions with cuticular bacteria, even non-pathogenic bacteria, could alter host behavior. [ABSTRACT FROM AUTHOR]

Trait consistency over time is one of the cornerstones of animal personality. Behavioral syndromes are the result of correlations between behaviors. While repeatability in behavior is not a requirement for behavioral syndromes, the two concepts studied together provide a more comprehensive understanding of how behavior can change over ontogeny. The roles of ontogenetic processes in the emergence of personality and behavioral syndromes have received much individual attention. However, the characterization of both individual trait consistency and behavioral syndromes across both sexes, as in our study, has been relatively rare. Ontogeny refers to changes that occur from conception to maturation, and juveniles might be expected to undergo different selection pressures than sexually mature individuals and also will experience profound changes in hormones, morphology, and environment during this period. In this study, we test for behavioral trait consistency and behavioral syndromes across six time points during ontogenetic development in the desert funnel-web spider ( Agelenopsis lisa). Our results indicate behavioral traits generally lack consistency (repeatability) within life stages and across ontogeny. However, penultimate males and mature females do exhibit noticeable mean-level changes, with greater aggressive responses toward prey, shorter latencies to explore their environment and in the exhibition of risk-averse responses to predatory cues. These traits also show high repeatability. Some trait correlations do exist as well. In particular, a strong correlation between aggressiveness toward prey and exploration factors is observed in mature males. However, because correlations among these factors are unstable across ontogeny and vary in strength over time, we conclude that behavioral syndromes do not exist in this species. Nevertheless, our results indicate that increased consistency, increasing average trait values, and varying correlations between traits may coincide with developmentally important changes associated with sexual maturation, albeit at different time points in males and females. This period of the life cycle merits systematic examination across taxa. [ABSTRACT FROM AUTHOR]

The Nearctic agelenid spider genus Agelenopsis Giebel 1896 is revised, with redescriptions of the 13 known species including: A. actuosa (Gertsch & Ivie 1936), A. aleenae Chamberlin & Ivie 1935, A. aperta (Gertsch 1934), A. emertoni Chamberlin & Ivie 1935, A. kastoni Chamberlin & Ivie 1941, A. longistyla (Banks 1901), A. naevia (Walckenaer 1841), A. oklahoma (Gertsch 1936), A. oregonensis Chamberlin & Ivie 1935, A. pennsylvanica (C.L. Koch 1843), A. potteri (Blackwall 1846), A. spatula Chamberlin & Ivie 1935, and A. utahana (Chamberlin & Ivie 1933). We also include an identification key to the species and a species distribution map. Our cladistic analysis of Agelenopsis is based upon 31 genitalic and somatic characters using Hololena hola (Chamberlin 1928) as the outgroup taxon and including three species of Barronopsis Chamberlin & Ivie 1941 in the analysis since Barronopsis has been considered a sister taxon to Agelenopsis in previous work. The cladistic analysis found 22 most parsimonious trees unambiguously supporting Agelenopsis monophyly. The majority rule consensus provides support for a clade including ((( A. pennsylvanica + A. potteri) + A. actuosa) + A. emertoni); another clade including (((( A. aleenae + A. spatula) + A. aperta) + A. kastoni) + A. naevia); and a third clade including (( A. oregonensis + A. utahana) + A. longystyla). Our analysis supports species groups proposed by researchers using molecular characters. [ABSTRACT FROM AUTHOR]

Precopulatory sexual cannibalism is an extreme form of sexual conflict that can entail significant costs to the cannibalized individual and a variety of costs and benefits to the cannibal itself. Characterizing these costs and benefits is fundamental to our understanding of how this behavior evolves. Using the spider Agelenopsis pennsylvanica, we tested the reproductive consequences of precopulatory sexual cannibalism by staging cannibalization events and comparing the performance of experimental cannibals against natural cannibals (i.e., those that cannibalized on their own) and non-cannibals. We found two performance benefits associated with precopulatory sexual cannibalism: first, experimental cannibals were more likely to produce egg cases than non-cannibals, and second, egg cases from experimental cannibals and natural cannibals were significantly more likely to hatch than those produced by non-cannibals. We then tested whether males were more likely to approach the webs of experimental cannibals vs. non-cannibalistic control females. Our data demonstrate that sexual cannibalism increases female attractiveness to males. Although this result seems counterintuitive, in fact, rates of precopulatory sexual cannibalism were much lower in females that had already cannibalized their first male: 38% of sexually naïve females engaged in precopulatory sexual cannibalism, whereas only 5% of females engaged in cannibalism a second time. Thus, males that approach cannibals receive two benefits: they are less likely to be cannibalized precopula, and they have the possibility of mating with females that have a higher probability of producing viable egg cases. Taken together, our data suggest that precopulatory sexual cannibalism affords females numerous benefits and may have a hand in shaping male mate choice decisions. [ABSTRACT FROM AUTHOR]

Although there is much interest in behavioral syndromes, very little is known about how syndromes are generated in wild populations. Here, we assess the roles of correlated selection and divergent rearing environments in generating a syndrome between foraging aggressiveness and boldness in the spider Agelenopsis pennsylvanica. We first tested for and confirmed the presence of a behavioral syndrome between boldness and foraging aggressiveness in wild penultimate A. pennsylvanica ( r = 0.24). Then, to assess the effects of rearing environment on the boldness-aggressiveness syndrome, we compared the behavioral tendencies of field- vs. laboratory-reared spiders over the course of their development. The presence of the boldness-aggressiveness syndrome differed based on spiders' developmental stage and rearing environment: field-reared juveniles did not exhibit a syndrome between boldness and foraging aggressiveness, but field-reared penultimates did. In contrast, laboratory-reared spiders never exhibited a behavioral syndrome, regardless of their developmental stage. Thus, the boldness-aggressiveness syndrome in A. pennsylvanica manifests only when individuals are reared in the field. Selection data from a mark-recapture study failed to indicate any signature of correlated selection, despite our finding that at least one element of the syndrome (foraging aggressiveness) can respond to selection (Heritability h2 = 0.27, from mid-parent breeding study). Thus, contemporary correlated selection does not appear to be a major driver of the boldness-aggressiveness syndrome of A. pennsylvanica. Taken together, our data are consistent with the hypothesis that the boldness-aggressiveness syndrome exhibited by wild A. pennsylvanica develops as a result of environmentally induced phenotypic plasticity, and not correlated selection. [ABSTRACT FROM AUTHOR]

Although the study of ecological interactions often takes into account functional variation between species, intraspecific variation is commonly ignored. Here, we investigate the importance of an intraspecific polymorphism in shaping interspecific interactions in a habitat-building species. Colonies of the social spider Anelosimus studiosus provide habitat for dozens of arthropod species, and colony members exhibit markedly polymorphic behavioral temperaments (BT): "aggressive" or "docile." We manipulated the phenotypic compositions of colonies (100% aggressive, 50% aggressive and 50% docile, 100% docile) and measured the nature and magnitude of interactions between A. studiosus and two heterospecific web associates, Larinioides cornutus and Agelenopsis emertoni. We found that BT composition significantly affected the outcome of interspecific interactions, changing the relationship between A. studiosus and its web associates from an ammensalism (where A. studiosus experiences reduced fecundity and survival) to a commensalism or mutualism. Our study successfully illustrates the potential of BTs to impact whole community dynamics, and conversely, for community structure to influence the maintenance of BTs. [ABSTRACT FROM AUTHOR]

1. Many animals are adapted for a ‘feast or famine’ existence, and will opportunistically engage in gluttonous foraging bouts. However, how gluttonous feeding influences individual performance (e.g. running speed) and the fitness consequence of modified performance are not frequently considered. 2. Using laboratory track trials I establish baseline locomotor performances (burst speed) for four spider species: two active foragers ( Hogna helluo and Schizocosa ocreata (family: Lycosidae)), and two sit-and-wait foragers ( Agelenopsis emertoni and Barronopsis texana (family: Agelenidae)). I then fed each species ad libitum, assessed what influence this meal had on individuals’ burst speed relative to baseline performance, and performed a field census to assess selection on running speed for all four species. 3. Sit-and-wait foragers fed significantly more than active foragers and slowed significantly after feeding; however, neither active forager was slowed by their meal. 4. My field census detected no selection on speed for sit-and-wait foragers, and positive directional selection on speed for both active foragers. 5. The negative association between the amount of food consumed and selection on burst speed suggests that selection pressures to maintain locomotor performance may set an upper limit to how much an animal can, or will, eat during a foraging bout. [ABSTRACT FROM AUTHOR]

1. Locomotor performance can influence individual fitness through several ecological contexts, such as prey capture and predator escape. One means of determining which contexts act as significant selective forces on running speed is to quantify individual speed in each context. The underlying hypothesis is that animals will exhibit their highest speeds in contexts most crucial to fitness. 2. We measured running speeds in three ecological contexts (prey capture, fleeing predators and territory defence) in lab-reared offspring of the funnel-web spider Agelenopsis aperta collected from two arid grassland and two riparian populations. Arid populations experience little predation pressure, are prey limited, and are highly territorial; riparian populations experience high predation, have high prey availability, and are less territorial in nature. 3. The offspring of arid individuals exhibited their highest burst speeds in territory defence, and ran more slowly in response to predator threats. The offspring of riparian populations, however, ran fastest when responding to predatory threats and displayed lower velocities in prey capture and territory defence. Thus, our findings support the hypothesis that A. aperta are selected to exhibit their highest speeds in contexts most important to their fitness. 4. Contextual use of running speed can differ among conspecific populations experiencing differing selective forces on locomotion. [ABSTRACT FROM AUTHOR]

The pandemic distribution of Wolbachia (alpha-proteobacteria) across arthropods is largely due to the ability of these maternally inherited endosymbionts to successfully shift hosts across species boundaries. Yet it remains unclear whether Wolbachia has preferential routes of transfer among species. Here, we examined populations of eight species of the North American funnel-web spider genus Agelenopsis to evaluate whether Wolbachia show evidence for host specificity and the relative contribution of horizontal vs. vertical transmission of strains within and among related host species. Wolbachia strains were characterized by multilocus sequence typing (MLST) and Wolbachia surface protein (WSP) sequences, and analysed in relation to host phylogeny, mitochondrial diversity and geographical range. Results indicate that at least three sets of divergent Wolbachia strains invaded the genus Agelenopsis. After each invasion, the Wolbachia strains preferentially shuffled across species of this host genus by horizontal transfer rather than cospeciation. Decoupling of Wolbachia and host mitochondrial haplotype (mitotypes) evolutionary histories within single species reveals an extensive contribution of horizontal transfer also in the rapid dispersal of Wolbachia among conspecific host populations. These findings provide some of the strongest evidence to support the association of related Wolbachia strains with related hosts by means of both vertical and horizontal strain transmission. Similar analyses across a broader range of invertebrate taxa are needed, using sensitive methods for strain typing such as MLST, to determine if this pattern of Wolbachia dispersal is peculiar to Agelenopsis (or spiders), or is in fact a general pattern in arthropods. [ABSTRACT FROM AUTHOR]

Abstract: Linear free polyamines were characterized in the venom of the spiders Agelenopsis aperta, Hololena curta, and Paracoelotes birulai by RP-HPLC coupled to mass spectrometry. The several linear polyamines found were tetramine, pentamine, and hexamine derivatives. Some of these natural products were identified as N-hydroxylated, guanidylated, or acetylated compounds. In addition, the biosynthetical pathway leading to the formation of acylpolyamines in spider venoms is discussed. [Copyright &y& Elsevier]

Abstract: Intra- and interspecific relationships of 12 out of 13 described species as well as a potential new species in the spider genus Agelenopsis (Araneae: Agelenidae) were analyzed using sequence data from two mitochondrial genes, cytochrome oxidase I (COI) and 16S ribosomal RNA. Approximately half of the species examined formed well-supported monophyletic groups, whereas the rest of the species were part of well-supported monophyletic species groups. Rather than viewing cases where species were not identified as being monophyletic as poor taxonomy, these cases more likely represent recent speciation and offer insights into the process of speciation. The clade with the lowest levels of interspecific sequence divergence was found in eastern North America, whereas western species displayed much higher levels of interspecific divergence. These patterns appear to extend below the species level as well, with southwestern species exhibiting the highest levels of intraspecific sequence divergence and geographic structuring. The relationship between Agelenopsis and Barronopsis, a genus once considered a sub-genus of Agelenopsis, was also examined. The two genera are reciprocally monophyletic but more generic level sampling is needed to confirm an apparent sister relationship between the two. [Copyright &y& Elsevier]

We investigated the mechanism by which courting males of the desert spider, Agelenopsis aperta, induce a quiescent state in females. We experimentally induced quiescence in two ways. First, we suspended courting males below females who were housed within netted isolation chambers. Second, we exposed females to air passed over a homogenate of male tissue. Both treatments induced a quiescent state in test females, supporting the hypothesis that an airborne chemical emitted by males elicits female quiescence. Additional tests involving the female isolation chamber indicated that this molecule has an effective range of about 3 cm, and that male drumming of the palpal appendages during courtship may direct the pheromone plume towards the female. [ABSTRACT FROM AUTHOR]

The influence of historical climatic vs. geological changes on species diversification patterns was investigated in a widely distributed North American desert spider,Agelenopsis aperta(Araneae: Agelenidae), with particular reference to Pleistocene glacial cycles and earlier patterns of mountain building. Levels of sequence divergence obtained from the mitochondrial gene, cytochrome oxidase I, dated to the Pleistocene, eliminating Rocky Mountain orogeny as a cause of diversification, as orogeny ended 4 million years ago. The results of phylogenetic and network analyses showed the presence of three geographically defined clades, which were consistent with the presence of at least three glacial refugia: (i) east of the Rocky Mountains; (ii) between the Rocky Mountains and Sierra Nevadas; and (iii) west of the Sierra Nevadas. In addition, populations within the Rocky Mountains exhibited significantly lower genetic diversity than populations east of the Rocky Mountains and the haplotypes found within the Rockies were a subset of eastern haplotypes. These patterns suggest that a post-Pleistocene range expansion occurred out of an eastern glacial refugium into the Rocky Mountains. Examination of phylogeographical studies of other North American desert taxa indicated that mountain building explained diversification patterns more effectively for some taxa but Pleistocene climate change was more important for others, includingA. aperta. [ABSTRACT FROM AUTHOR]

The fragmentation mechanism of the acylpentamine toxins 1–4 found in the venom of the spider Agelenopsis aperta has been investigated in detail. To identify the origin of the two doublets of unexpected fragment ions at m/z 129/112 and m/z 115/98, three synthetic 15N-labeled analogs 5–7 have been prepared and subjected to CID fragmentation on a triple quadrupole mass spectrometer. It appears that the unexpected doublet of fragment ions arises from an internal portion of the polyamine backbone after either a transaminative Zip reaction or a sequential fragmentation of the quasi-molecular ion. The second option has been proven by in-source CID experiments. The detailed knowledge of acylpentamine fragmentation mechanisms is essential for the correct characterization of isomeric compounds, particularly for coeluting compounds within complex mixtures such as spider venoms. [Copyright &y& Elsevier]

Agatoxins from Agelenopsis aperta venom target three classes of ion channels, including transmitter-activated cation channels, voltage-activated sodium channels, and voltage-activated calcium channels. The α-agatoxins are non-competitive, use-dependent antagonists of glutamate receptor channels, and produce rapid but reversible paralysis in insect prey. Their actions are facilitated by the μ-agatoxins, which shift voltage-dependent activation of neuronal sodium channels to more negative potentials, causing spontaneous transmitter release and repetitive action potentials. The ω-agatoxins target neuronal calcium channels, modifying their properties in distinct ways, either through gating modification (ω-Aga-IVA) or by reduction of unitary current (ω-Aga-IIIA). The α-agatoxins and ω-agatoxins modify both insect and vertebrate ion channels, while the μ-agatoxins are selective for insect channels. Agatoxins have been used as selective pharmacological probes for characterization of ion channels in the brain and heart, and have been evaluated as candidate biopesticides. [Copyright &y& Elsevier]

Presents a study which explored the hypothesis that spiders choose to mate with heavier males for the genes for behavioral aggressiveness they offer their offspring in the desert spider, Agelenopsis aperta. Materials and methods; Results; Discussion.

The hypothesis that superfluous killing, partial consumption, and abandonment of prey is a consequence of adaptation to food-limited environments was tested in two feeding trials on a desert spider, Agelenopsis aperta. First, we made comparisons among populations inhabiting sites of high prey (HP) or low prey (LP) availability that differed in their degree of genetic isolation. Typically, A. aperta entirely consumed one or two of the prey items it captured in a feeding bout. Additional prey were partially consumed or abandoned without eating. Spiders from the genetically isolated HP population, however, captured fewer prey and showed a higher incidence of full feeding on prey than did individuals from the other populations. Only one spider from this population captured a prey item that it failed to feed on, whereas spiders from LP populations failed to feed on high numbers of captured prey. The greatest variability in feeding behavior was exhibited in the HP population that experienced gene flow. The second test was based on the finding that aggressiveness is largely a sex-linked trait in A. aperta: the aggressiveness of the female parent only is inherited by male offspring, whereas both parents contribute to this trait in female offspring. All female F1 hybrids between LP and HP parental types exhibited high levels of superfluous killing, as did male F1 hybrids derived from LP females. F1 hybrid males derived from HP females exhibited extremely low levels of superfluous killing. Superfluous killing thus has its basis in the genetic control of levels of aggression. [ABSTRACT FROM AUTHOR]

Investigates the role of chemical communication in complex male-female courtship sequence of the desert spider, Agelenopsis aperta. Emission of sex pheromones by male spider to attract the female; Leg waving, lung and retreat actions in the presence of female spiders; Factors influencing the behavior of male spiders after pheromone emission by female.

Discusses the results of experiments on the monogamous desert, funnel-web spider, Agelenopsis aperta, to test male mate choice with respect to female body weight and reproductive status in a three-choice arena system. Comparison of findings to field data on male visits at female sites in a marked population; Virgin females' emission of a pheromone that cues male courtship.

The predictions of game theory concerning the use of resource assessment strategies by animals in conflict situations were tested through study of the agonistic behavior of the funnel-web spider, Agelenopsis aperta, in disputes over web sites and associated territories. Specifically, contest cost was considered relative to resource value (i.e., the quality and availability of territories). 2. The contest methodology was similar to that described in Riechert (1978 a) with weight controlled to eliminate size bias. In addition, relative contest costs were converted to joules using resting metabolism under field conditions as a reference. Estimates of territory quality and availability were made through the application of a model of spider reproductive success to the results of discriminant analyses of site characteristics. 3. The immediate and ultimate benefits of ownership of specific territories accounts for a significant amount of the within-population variability in dispute cost the greater the benefit, the greater the total cost of the dispute. The territory owner is shown to determine the level of escalation reached in these contests, while the intruder merely adjusts its behavior to that of its opponent. 4. Contest behavior is also shown to vary according to the relative availability of territories: more energy is expended in maintaining and winning territories in a habitat near saturation (desert grassland) than where territories are in ready supply (desert riparian). 5. A greater range of benefits was available to spiders occupying specific sites in the desert grassland study area than to the riparian population. This was emphasized by the greater variability in contest cost, richness, and in the total number of acts exhibited in the sequences involving desert grassland spiders. Prey availability and ultimately reproductive success were found to be correlated with web-site quality in the desert grassland habitat, whereas differential utilization of specific habitat types by the riparian spiders corresponded not to reproductive potential but to the ease of web placement. 6. The correspondance existing between within-population contest cost and site quality reflects active resource assessment on the part of the territory owner, while population differences observed in the level of escalation achieved in disputes over territories is attributed to selection pressure for evolved differences in level of aggression. These findings are discussed in terms of optimization and relative to the predictions of game theory. [ABSTRACT FROM AUTHOR]

1. The agonistic behavior of the funnel-web building spider, Agelenopsis aperta (Gertsch), was studied using induced encounters between adult females at natural web sites. All behavior exhibited by either individual during the course of an encounter was recorded. The results were analyzed through the use of transition matrices and the following multivariate treatments: factor analysis, ordination, and multiple regression. These latter methods were used to provide insight into possible sources of variability and their underlying causes. 2. Sequence outcome is primarily determined by the relative weight of the two contestants engaged in a territorial dispute. If the size difference is large, the larger of the two individuals wins in a significant number of cases. Home bias is evidenced in cases where body weights are close. 3. A stereotypy measure is devised that reflects the percent similarity of each sequence of events to an expected sequence (average). The frequency distribution, presence-absence or duration of all behavior patterns observed during the course of the disputes are utilized in measuring stereotypy. The territorial disputes of A. aperta exhibit low stereotypy, averaging 43% on a scale from 0 to 100%. 4. Low stereotypy is, in part, related to the utilization of 33 different action patterns by spiders in these disputes. Factor analysis is used to express these action patterns in terms of five functional groups including locating behavior, signaling behavior, threat behavior, contact behavior, and a multiple function category. The order of these categories represents increasing cost based on relative estimates of the energy expenditure necessary to complete a specific behavior pattern and the potential for injury through the use of it. 5. A Bray and Curtis ordination shows the important sources of between sequence variability to be the total energetic cost of the dispute and the complexity of behavior exhibited in it. The factors, in turn, depend on the resident-visitor status of the losing spider and on the relative size of the two contestants. The energetic cost of a dispute is markedly higher in those disputes in which the resident loses her territory. The number of action patterns and total frequency of acts observed are also greater in encounters in which the resident is the losing spider. Behavioral complexity is higher as well in cases where the weights of the two contestants are close. 6. The variation in the pathways through which the sequences progress is shown to reflect the operation of assessment strategies by A. aperta. Initial assessment of the relative weights of the opponent is made through movements on the web at a distance (locating behavior). Subsequent activities depend on the results of this assessment, the predominant strategy being 'retaliator' (Maynard Smith and Price, 1973) in which an individual responds to escalation with further escalation. Spiders with a large weight advantage over the opponent tend to escalate directly to threat and contact behavior ('hawk' strategy). The corresponding strategy for a much smaller visiting spider is immediate retreat ('mouse'). A much smaller resident spider, however, will exhibit the 'retaliator' strategy to the 'hawk' rather than the more conservative 'mouse' strategy. The particular stategy exhibited, then, also depends on the energetic investment a particular individual has in the contended resource. 7. Within functional group variability is shown to significantly affect the outcome of territorial disputes. Winning spiders exhibit an average of 20% less stereotypy than losing spiders. Unpredictable behavior possibly confuses the opponent, causing it to make inaccurate assessments of the weights of the opponent relative to it. Retreat follows. This behavior is linked to the 'protean displays' exhibited in defense against predators (Humphries and Driver, 1967). [ABSTRACT FROM AUTHOR]