Characterization of sound production by the pot-bellied seahorse (Hippocampus abdominalis) during feeding.

Sound production during feeding by the pot-bellied seahorse, Hippocampus abdominalis, was quantified with an observation of clicks (acoustic signal) and snicks (visual behavior). Female, male, and juvenile seahorses had feeding sounds characterized for peak (dominant) frequency (Hz), sound pressure level (SPL), and duration (ms). Subject body size and condition was estimated by standard length (SL, cm), to determine an estimate of body condition index (BCI). An inverse correlation between mean peak frequency (Hz) of clicks and SL was found for females. A negative correlation between peak frequency (Hz) of clicks and a residual BCI was determined for both males and females, suggesting that acoustic signals may contain information regarding fitness.

Male courtship signal modality and female mate preference in the wolf spider Schizocosa ocreata: results of digital multimodal playback studies.

Females must be able to perceive and assess male signals, especially when they occur simultaneously with those of other males. Previous studies show female Schizocosa ocreata wolf spiders display receptivity to isolated visual or vibratory courtship signals, but increased receptivity to multimodal courtship. It is unknown whether this is true when females are presented with a choice between simultaneous multimodal and isolated unimodal male courtship. We used digital playback to present females with a choice simulating simultaneous male courtship in different sensory modes without variation in information content: 1) isolated unimodal visual versus vibratory signals; 2) multimodal versus vibratory signals; and 3) multimodal versus visual signals. When choosing between isolated unimodal signals (visual or vibratory), there were no significant differences in orientation latency and number of orientations, approaches or receptive displays directed to either signal. When given a choice between multimodal versus vibratory-only male courtship signals, females were more likely to orient to the multimodal stimulus, and directed significantly more orients, approaches and receptivity behaviors to the multimodal signal. When presented with a choice between multimodal and visual-only signals, there were significantly more orients and approaches to the multimodal signal, but no significant difference in female receptivity. Results suggest that signal modes are redundant and equivalent in terms of qualitative responses, but when combined, multimodal signals quantitatively enhance detection and/or reception. This study confirms the value of testing preference behavior using a choice paradigm, as female preferences may depend on the context (e.g., environmental context and social context) in which they are presented with male signals.

Courtship behavior and coloration influence conspicuousness of wolf spiders (Schizocosa ocreata (Hentz)) to avian predators.

Signalers must balance the benefits of detection by intended receivers with the costs of detection by eavesdroppers. This trade-off is exemplified by sexual signaling systems, in which signalers experience sexual selection for conspicuousness to mates as well as natural selection for crypsis to predators. In this study, we examined how courtship behavior and body coloration influenced the conspicuousness of males to avian predators in the well-studied brush-legged wolf spider system (Schizocosa ocreata (Hentz)). We focused on three behaviors (courtship, walking, and freezing) and two coloration schemes (natural coloration and idealized background-matching coloration). We presented captive blue jays (Cyanocitta cristata) with video playbacks of male spiders in a presence-absence detection task and characterized conspicuousness by measuring response latency and detectability. We found that any type of motion significantly increased detectability, and that body coloration and behavior interacted to determine detectability while the spiders were in motion. Among spiders in motion, courting spiders were detected faster than walking spiders. Stationary (frozen) spiders, in contrast, were rarely detected. These results illustrate that male S. ocreata can be both highly conspicuous and highly cryptic to avian predators. Thus, while we find that courtship is conspicuous to avian predators in this system, we suggest that behavioral plasticity may mitigate some of the predation costs of the sexual signal.

Cross-modal integration of multimodal courtship signals in a wolf spider.

Cross-modal integration, i.e., cognitive binding of information transmitted in more than one signal mode, is important in animal communication, especially in complex, noisy environments in which signals of many individuals may overlap. Males of the brush-legged wolf spider Schizocosa ocreata (Hentz) use multimodal communication (visual and vibratory signals) in courtship. Because females may be courted by multiple males at the same time, they must evaluate co-occurring male signals originating from separate locations. Moreover, due to environmental complexity, individual components of male signals may be occluded, altering detection of sensory modes by females. We used digital multimodal playback to investigate the effect of spatial and temporal disparity of visual and vibratory components of male courtship signals on female mate choice. Females were presented with male courtship signals with components that varied in spatial location or temporal synchrony. Females responded to spatially disparate signal components separated by ≥90° as though they were separate sources, but responded to disparate signals separated by ≤45° as though they originated from a single source. Responses were seen as evidence for cross-modal integration. Temporal disparity (asynchrony) in signal modes also affected female receptivity. Females responded more to male signals when visual and vibratory modes were in synchrony than either out-of-synch or interleaved/alternated. These findings are consistent with those seen in both humans and other vertebrates and provide insight into how animals overcome communication challenges inherent in a complex environment.

Eavesdropping and signal matching in visual courtship displays of spiders.

Eavesdropping on communication is widespread among animals, e.g. bystanders observing male-male contests, female mate choice copying and predator detection of prey cues. Some animals also exhibit signal matching, e.g. overlapping of competitors' acoustic signals in aggressive interactions. Fewer studies have examined male eavesdropping on conspecific courtship, although males could increase mating success by attending to others' behaviour and displaying whenever courtship is detected. In this study, we show that field-experienced male Schizocosa ocreata wolf spiders exhibit eavesdropping and signal matching when exposed to video playback of courting male conspecifics. Male spiders had longer bouts of interaction with a courting male stimulus, and more bouts of courtship signalling during and after the presence of a male on the video screen. Rates of courtship (leg tapping) displayed by individual focal males were correlated with the rates of the video exemplar to which they were exposed. These findings suggest male wolf spiders might gain information by eavesdropping on conspecific courtship and adjust performance to match that of rivals. This represents a novel finding, as these behaviours have previously been seen primarily among vertebrates.

Chemical signaling in a wolf spider: a test of ethospecies discrimination.

Chemical signals from female wolf spiders that elicit exploratory behavior and courtship in males are often assumed to be species-specific, but males of some species court in response to silk cues deposited by closely related heterospecific females. Such is the case with the wolf spiders Schizocosa ocreata and S. rovneri, ethospecies reproductively isolated on the basis of differences in behavioral mechanisms during courtship. We explored whether male S. ocreata and S. rovneri reciprocally discriminate species-specific chemical or mechanical cues associated with female silk by using male behavioral response as an assay. Males were exposed to stimulus treatment categories including silk, washed silk, silk extract, and appropriate controls within conspecific or heterospecific female stimulus categories. Male S. ocreata and S. rovneri did not discriminate between conspecific or heterospecific female stimuli, and courtship intensity was greatest on untreated silk. There were no differences in latency to begin courtship or in rates of courtship behaviors attributed to species origin of silk. However, silk treatment (washed silk, extract) had a significant effect on display and exploratory behaviors (e.g., chemoexplore) in both species. Methanol extraction of female silk successfully removed or inactivated a component necessary to elicit active courtship, but extraction did not significantly reduce exploratory behavior, suggesting that a separate compound may be responsible for releasing this behavior. Together, these experiments support the characterization of S. ocreata and S. rovneri as ethospecies reproductively isolated only by female discrimination of species-specific male courtship, and indicate that chemical, but not mechanical cues associated with silk are critical for eliciting male courtship in both species.

Multisensory cues and multimodal communication in spiders: insights from video/audio playback studies.

Spiders perceive the world using multiple sensory modes, including vibration, vision, and chemical senses, for prey detection and communication. These sensory modes are used in many communication contexts, either individually or in multimodal signaling. Selection for effective signaler-receiver communication and species discrimination is especially strong for these predatory and potentially cannibalistic arthropods, resulting in the evolution of considerable diversity in signaling behaviors. In this paper, we review sensory mechanisms involved in spider signaling and present an overview of recent work done on wolf spiders (Lycosidae) that use multimodal communication (simultaneous visual and vibratory signals) in sexual signals during courtship. The relative importance of visual and vibratory signaling modes, and the use of multiple modes varies among closely related species in the genus Schizocosa, providing a model system for investigating multisensory guidance of complex behavior. Here we examine previous and current research on responses of female spiders to components of male courtship behavior, using several experimental techniques including cue isolation (single sensory modes), video/audio digitization and playback, and cue-conflict (mixed conspecific/heterospecific components) to tease apart elements of multimodal signaling.

Foraging advantages of mixed-species association between solitary and colonial orb-weaving spiders.

This study investigated association between solitary orb-weaving spiders and a colonial orb-weaving spider, Metepeira incrassata (Araneae: Araneidae). Spiders were sampled along transects and an index of species association showed that two of the species were associated more frequently than expected based on a null hipothesis of random co-occurrence. The potential advantages of mixed-species association were investigated by comparing prey-capture success of one of these associates, Nephila clavipes (Araneae: Tetragnathidae), when it occurs alone, in single-species groups, and when associated with M. incrassata colonies. Field observations of prey-capture success by all three of these categories of N. clavipes revealed that individuals in M. incrassata colonies captured significantly more prey than solitaries or individuals in single-species groups. The increase in prey capture by N. clavipes in M. incrassata colonies may result from utilization of a foraging niche which intercepts a diffirent spectrum of prey than that available to single-species groups or solitaries. Related to this enhanced prey consumption is greater fecundity of spiders in association with M. incrassata as compared to solitaries or individuals in single-species groups.

Ontogenetic shifts within the selfish herd: predation risk and foraging trade-offs change with age in colonial web-building spiders.

We examine costs and benefits associated with spatial position relative to spider age (size) in colonial web-building spiders. Predator attack and capture rates vary with position in the colony, and suggest that risk is higher for the smallest and the largest spiders on the periphery, and lower in the central core of the colony. Foraging success is greater on the periphery for small and medium spiders but does not differ significantly with position for larger spiders. Decreased predation risk may be the reason why larger spiders aggressively seek and defend positions in the colony core, demonstrating a "selfish herd effect" (Rayor and Uetz, 1990). Smaller (immature) spiders, unable to compete for protected web positions in the core, must trade-off potentially higher risk of predation to take advantage of higher prey availability on the periphery. Increased foraging success on the periphery may allow juvenile spiders to achieve the larger size necessary to compete successfully for protected core positions as adults. Spatial variation in size-related fitness trade-offs between predation risk and foraging success may explain why colonies are dynamic entities - with individual spiders exhibiting ontogenetic shifts in web location as they grow larger and mature-accounting for the characteristic age (size) structure ofMetepeira incrassata colonies.

Colony size and parasitoid load in two species of colonial Metepeira spiders from Mexico (Araneae: Araneidae).

While a number of advantages may result from group living, it may also lead to increased levels of attack by parasites because groups may be easier to find. This leads to the prediction that levels of parasitism should increase with colony size. We test this prediction by comparing colony size and parasitoid load for two species of colonial orb-weaving spiders from Mexico, Metepeira (undesc. sp., tentatively named atascadero) and Metepeira incrassata, which exhibit contrasting levels of social organization and utilize different habitats. For M. atascadero, which occurs solitarily or in small groups in desert/mesquite grassland habitat, rates of egg-sac parasitism fluctuate widely from year to year, and are closely tied to spider egg output. There is no relationship between colony size and rate of parasitism. For colonial M. incrassata, which occur in tropical rain forest/agricultural habitat, rates of parasitism are relatively constant from year to year. However, there is a positive relationship between colony size and rate of parasitism in this species. These differences are discussed with regard to the stability of the two habitats, prey availability, and the foraging behavior of the respective parasitoids.

The "ricochet effect" and prey capture in colonial spiders.

Increased prey capture efficiency in colonial spiders is a consequence of the "ricochet effect", as prey are captured after they bounce off several webs in succession. In this study, the prey capture of three species of colonial spiders in the genus Metepeira from Mexico are compared. These species, from different habitats, show varying levels of social organization (group size and withingroup spacing) that affect prey capture from ricochets. Metepeira sp. a (a presumed new species tentatively named atascadero) from desert grassland habitats, occur solitarily or in small groups, and gain little from prey ricochets: prey capture rates are low and variance in prey captured/spider is high. M. spinipes, from mesic agricultural sites, occur in groups of 10-150, and show a ricochet effect resulting in more and larger prey, and reduced variance in capture rate. M. incrassata, from tropical rainforest/agricultural sites, occur in large colonies of hundreds to thousands of individuals, and show a similar ricochet effect. The ricochet effect does not influence taxonomic composition of prey in either M. atascadero or M. spinipes, but does in tropical M. incrassata. This result, however, is primarily due to the capacity of certain taxa (eg., Lepidoptera), more common in the tropics, to escape more easily from spider webs. A comparison of prey capture efficiency of colonial M. incrassata with that of solitary M. atascadero shows that the ricochet effect provides an increase in efficiency across all size classes of prey.

Variation in life-history characteristics over a clinal gradient in three populations of a communal orb-weaving spider.

Adult size and fecundity, total reproductive biomass, egg size, and spiderling size and resistance to desiccation were compared in three populations of the communal orb-weaving spider,Metepeira spinipes, in Mexico. In a desert population and in one from a moist tropical forest adult size, fecundity, and total reproductive biomass were similar, but were markedly smaller than in a climatologically intermediate agricultural habitat. Egg size and protein content were greater in the desert and agricultural habitats than in the moist forest, but spiderling size increased from desert to agricultural to moist forest populations. Desert spiderlings survived significantly longer than moist forest spiderlings at all humidity treatments over a 10% to 100% range. An explanation for these results is proposed based on apparent differences in energy allocation and expenditure which arise from the distinct climate, colony structure, and prey and space availability in the three habitats.

THE INHERITANCE OF COURTSHIP BEHAVIOR AND ITS ROLE AS A REPRODUCTIVE ISOLATING MECHANISM IN TWO SPECIES OF SCHIZOCOSA WOLF SPIDERS (ARANEAE; LYCOSIDAE).

The courtship behaviors of two morphologically similar spider species, Schizocosa ocreata and S. rovneri, are distinctive and prevent interbreeding. We used "forced" copulation between these species to investigate the mode of inheritance of the courtship behavior and to determine whether postmating isolating mechanisms exist. F1 hybrids proved to be behaviorally sterile, but they were capable of producing viable offspring when forced to interbreed. Analysis of the courtship behaviors of F1 , F2 , and backcross progeny showed that the inheritance of some aspects of these behaviors is consistent with models involving single autosomal loci. The inheritance of secondary sexual characteristics in the males is also investigated. The genes for courtship behavior and secondary sexual characteristics do not assort independently. The origin of the premating isolating mechanisms may be explained by either an initial habitat separation between the two groups, or by a founding event with each group subsequently diverging in slightly different habitats. It is suggested that the differences in the microhabitats may have a profound effect on what type of signal (visual or vibratory) would be effective.

Abundance and community structure of forest floor spiders following litter manipulation.

We conducted a field manipulation of forest litter to determine effects of litter structure (flat vs curly leaves) on forest floor spiders in natural and artificial leaf litter. Artificial litter made of vinyl, was nondecomposable and non-nutritive. In this way, we separated interactions of effects of litter as a nutritional base and as a spatially heterogeneous environment on litter-dwelling spiders.Structural complexity of litter significantly affected abundances of some forest floor spiders. In particular, abundances of web-building spiders were lower in treatments of flat leaves. Litter nutritional content and structural complexity only slightly affected spider species composition and richness. Results suggest that litter depth is more influential than are litter structural complexity or nutritional content, in organizing forest floor spider communities.

The influence of variation in litter habitats on spider communities.

Spider communities were sampled over an artificial gradient of litter depth (created by raking) and compared to those of two other forests exhibiting natural variation in litter depth. More species of spiders were present in areas of greater depth and/or complexity in all sites. Relative abundance of Lycosidae decreased, while relative abundance of Clubionidae, Thomisidae and Gnaphosidae increased over gradients of increasing depth and complexity. Similarity of species composition between areas within a forest was related to site differences in litter depth and structure.As litter depth increased, there were significant changes in prey species richness, litter complexity, and microclimate. Partial correlation analysis of grouped data from early-, mid-, and late season suggests that influential factors change with season. In the early season, prey abundance and temperature variation account for most of the variation in spider species richness. In mid-season, litter complexity and moisture fluctuations appear to influence richness, with complexity relatively more important. In late season, complexity and temperature range were the primary factors, with temperature relatively more influential. The relative importance of these factors in influencing community structure of spiders is discussed.

Gradient analysis of spider communities in a streamside forest.

Species composition and diversity of a guild of wandering spiders was studied by pitfall trapping over an elevational gradient in an Illinois streamside forest. Differences in flooding frequency and their effect on the litter habitat (removal and/or compression) account for a majority of the variation in the number of species between elevations. Changes in spider communities with elevation over the flooding gradient are indicative of a transition from a harsh to a moderate environment: (1) increased abundance and species diversity; (2) decreased dominance of flood tolerant species accompanied by increased dominance of species with specialized microhabitats found in complex litter; (3) greater similarity in species composition between sites; and, (4) a change in species-abundance curves from a geometric series to a lognormal distribution. The influence of the flooding regime in regulating community structure of spiders is discussed. A multiple regression equation including flood frequency and litter depth as variables was used to predict the impact of altered flooding regimes (due to reservoir construction downstream) on spider diversity.