Male Schizocosa Ocreata Research Articles

Background contrast affects detection and recognition of courting wolf spiders by intended and unintended receivers

We used video playback of courting male Schizocosa ocreata wolf spiders to examine responses of intended receivers (conspecific females) and eavesdroppers (competitor males, predatory spiders, toads) to manipulations of spider color (natural color, monochromatic gray, monochromatic RBG average) displayed against complex leaf litter backgrounds (color, grayscale). Models of chromatic and achromatic contrast between spider stimuli and backgrounds were used to predict receiver responses. The results support the hypothesis that interactions between spider and background coloration affect detection and recognition, although responses varied with receiver type. Detection responses of intended receivers (female S. ocreata) did not fit predictions of the chromatic contrast model in some cases, but showed a fair fit to the achromatic model. Detection responses of social eavesdroppers (male S. ocreata) fit the chromatic and achromatic contrast models slightly better than did female responses (poor fit and very good fit, respectively). Eavesdropping wolf spider predators (Rabidosa) exhibited detection responses that significantly matched predictions of the chromatic (very good fit) and achromatic (excellent fit) models. Whereas jumping spiders (Phidippus) showed a good fit to the chromatic and achromatic contrast models, toad predators had a good fit only to the chromatic model. Recognition responses revealed a different pattern of fit to the chromatic and achromatic models across receiver types, although Rabidosa again indicated a significant fit to both models. Taken together, the results of this study identify both chromatic and achromatic features of spider appearance as likely explanations for differences in behavioral responses of intended and unintended receivers. This outcome suggests the possibility that both sexual and natural selection likely target different features of male appearance during courtship.

Trail-following behavior by males of the wolf spider, Schizocosa ocreata (Hentz)

Male spiders are able to detect and respond to chemical cues deposited by females in the environment. In many species, detection of these chemicals may be the first indication a male has to the presence of a nearby female. In wolf spiders (Lycosidae), which do not produce webs, females leave a trail of silk and chemical cues as they move through the leaf-litter habitat. Males could increase encounter rates with receptive females if they were able to follow these trails. We used behavioral assays to determine whether male Schizocosa ocreata (Hentz) wolf spiders are able to detect and respond to cues resulting from a single-pass trail by a female, and whether they are able to determine the direction of female travel. Our focal males responded to virgin adult female trails with following behavior, but showed no propensity to follow trails from other conspecifics (subadult females or males). While males were able to follow a female trail, our observations and analysis indicates that they are not able to determine trail directionality.

The role of social experience in eavesdropping by male wolf spiders (Lycosidae)

When reproductive success is limited by mate search costs, males can reduce costs by eavesdropping and initiating displays if conspecific courtship is detected. Here, we examine eavesdropping by male Schizocosa ocreata wolf spiders, with field studies, laboratory studies using video playback and live exposure studies. In field enclosure experiments, introduced males responded with increased courtship signalling behaviour in the presence of a courting male. In the laboratory, field-collected males spent more time engaged in interaction behaviours and performed more bouts of courtship activity in response to a courting video male stimulus than did laboratory-reared males, suggesting that eavesdropping might arise as a consequence of field experience. To explore this further, we conducted associative learning studies on naïve, laboratory-reared males, pairing video playback of male courtship with sensory cues indicating female presence. Results showed that males with no prior exposure learned to associate courtship of other males with cues indicating the presence of females. In subsequent video playback experiments, field-collected males recognized differences in male behaviour, responding with courtship more often and for longer periods to video stimuli of courting male spiders than to walking males or an empty leaf litter background (no spider). Additional studies showed that males spent significantly more time in courtship displays when presented with two to three live or video male stimuli simultaneously. Together, these findings confirm that male wolf spiders meet assumptions of eavesdropping behaviour, and suggest that social experience arising from exposure to courtship interactions of conspecifics may impact male eavesdropping and subsequent courtship behaviour. • We examined eavesdropping by male Schizocosa ocreata wolf spiders in the field and laboratory. • In the field, males showed more courtship signalling behaviour in the presence of a courting male. • Field-collected males were more responsive to videos of courting males than lab-reared males. • Naïve lab-reared males learned to associate courtship of other males with female presence. • Males courted longer when two to three live or video males were presented simultaneously.

Multimodal signals increase active space of communication by wolf spiders in a complex litter environment

Multimodal signals may compensate for environmental constraints on communication, as signals in different modalities vary in efficacy. We examined the influence of complex microhabitats on transmission of vibratory and visual signals of courting male Schizocosa ocreata wolf spiders (Araneae: Lycosidae) with laser Doppler vibrometry (LDV) and behavioral observations in lab and field. We measured maximum potential detection distance of visual and vibratory signals by females in laboratory mesocosms, recorded vibration signal attenuation on different substrates, and estimated transmission distances for male vibration signals in the field. We also determined effective line-of-sight visual detection distances in the field with laser distance measures. Together, these data were used to estimate the potential and effective active space of multimodal signals. LDV measures show leaves are highly conductive substrates for wolf spider vibratory signals compared to others (soil, wood, rock). For both visual and vibratory modes, lab estimates of maximum potential distance for signal transmission and detection (behavior studies) exceeded estimates of effective active space (signal attenuation, “vanishing point,” and “line-of-sight” measures). Field estimates of transmission distance for signal modes overlap, such that in close range (<20 cm), vibratory signals are more likely to be detected, while farther away, visual signals are more likely to be seen. These findings thus support current hypotheses regarding how multimodal communication might extend the range of overall signal active space or compensate for environmental constraints.

Experience with chemotactile cues indicating female feeding history impacts male courtship investment in the wolf spider Schizocosa ocreata

Male fitness is often determined by the ability of the male to gain access to multiple mates, although in species that exhibit sexual cannibalism, males might increase their likelihood of being cannibalized with each encounter. This risk should create selection for males who are able to perceive potential risks associated with mating encounters. We studied male Schizocosa ocreata wolf spiders to determine whether they use female chemotactile cues (silk, excreta) as indicators of potential risks and how these cues affected subsequent male courtship behaviors. Female treatments included satiated females vs. starved females, as well as a treatment where females had recently cannibalized a male S. ocreata. We performed experiments to assess (1) if males use female chemotactile cues to determine potential risks associated with differing female feeding treatments and alter courtship investment, and 2) how male experience with female chemotactile cues affected courtship investment in subsequent female encounters. At first encounter, males do not vary courtship investment (number of bouts, duration, and vigor) with different female feeding treatments. However, male behaviors during subsequent encounters with female chemotactile cues varied in complex ways, depending on female feeding treatment and male first encounter experience. These data suggest that male experience impacts perception of female chemical cues and offers the male opportunity to avoid sexual cannibalism in high-risk situations.

Multimodal communication of wolf spiders on different substrates: evidence for behavioural plasticity

Communication in complex environments poses challenges of potential loss of intended messages, but some animals may compensate by using multimodal signalling. Courtship displays of male Schizocosa ocreata (Hentz) wolf spiders are multimodal, consisting of visual and seismic signals. The microhabitat of S. ocreata is complex, including leaf litter, wood/bark, soil and rocks. Results from laser vibrometer measurements in the present study indicated that leaf litter transmitted male courtship signals with greater efficacy. Mating success was significantly greater on leaf litter (∼85%) compared to other substrates (∼30%), even though latency to male courtship did not vary among substrates. Given these results, selection should favour spiders that increase their mating potential on nonconducting substrates. We tested whether spiders detect substrate differences in a choice test, and found that when males and females visited all substrates, they spent significantly more time on leaf litter. We isolated courting male spiders on each substrate and scored courtship behaviours to see whether signals varied with substrate. Males used significantly more visual signals (waves and arches) on substrates that attenuated seismic signals (soil and rocks), but other behaviours showed no differences. Taken together, these results suggest that combined visual/seismic components of multimodal displays may serve as ‘backup signals’, ensuring reception under different environmental conditions. Results also suggest that male S. ocreata have the flexibility to compensate for environmental constraints by seeking microhabitats with more effective vibration conduction properties, and/or by increasing visual signals on substrates where seismic communication is less effective.

Effect of visual background complexity and light level on the detection of visual signals of male Schizocosa ocreata wolf spiders by female conspecifics

For visual signaling to be effective, animal signals must be detected and discriminated by receivers, often against complex visual backgrounds with varying light levels. Accordingly, in many species, conspicuous visual displays and ornaments have evolved as a means to enhance background contrast and thereby increase the detection and discrimination of male courtship signals by females. Using video playbacks, we tested the hypothesis that visual courtship displays and leg decorations of male Schizocosa ocreata wolf spiders are more conspicuous against complex leaf-litter backgrounds. Video exemplars of courting males with manipulated leg tufts were superimposed on different backgrounds (complex leaf litter in sun or shade, featureless gray background) and presented to female spiders. Females were more likely to orient to males presented against lighter backgrounds (litter in sun, gray) than the darker ones (litter—shade). Males with larger tufts were also more likely to be detected, as latency to orient was shortest for enlarged and longest for removed tufts. Latency of females to approach was shorter against lighter backgrounds, and approach latency was longest for males without tufts. Female receptivity scores were significantly greater for males against lighter backgrounds, and males with larger tufts had higher scores. These results suggest that both complexity and light level of display backgrounds affect the detection of male visual courtship signals by females and that aspects of the male phenotype may increase chances of detection (and receptivity) against visually complex backgrounds.

Antipredator responses of wolf spiders (Araneae: Lycosidae) to sensory cues representing an avian predator

Predator detection and subsequent antipredator response behaviours have been documented in many vertebrate and invertebrate animals, although the degree of specificity in predator recognition and response varies. We examined responses of actively courting adult male Schizocosa ocreata (Hentz) wolf spiders to cues indicating the presence of an avian predator, including visual, seismic (substrate vibration) and acoustic (airborne) stimuli. Spiders responded to acoustic (bird call) and seismic (simulated beak tap) stimuli with cessation of courtship and movement, but increased locomotion when presented with a visual stimulus (bird shadow). Spiders responded to experimental playback of avian acoustic stimuli with antipredator behaviour significantly more often and took longer to return to courtship than when exposed to nonthreatening stimuli. Tests of responses on different substrata to isolate sensory modes revealed that spiders perceive airborne sound from bird calls as substratum-conducted vibration. Results indicate that S. ocreata are capable of recognizing sensory cues associated with avian predators and distinguishing them from nonthreatening stimuli, suggesting that bird predation has been a selection factor in shaping behaviour of this wolf spider species.

Foreleg Autotomy Reduces Mating Success of Male Schizocosa ocreata Wolf Spiders

Autotomy is a taxonomically widespread antipredator tactic that allows animals to escape life-threatening situations. Opposing the benefits of survival, animals that have autotomized appendages may later suffer reduced ability in important determinants of fitness. Male Schizocosa ocreata wolf spiders use their forelegs during courtship for visual displays, for tactile courtship, and to defend against attacks by females. In nature they are often found missing one, and sometimes both, forelegs. We found that autotomy of one foreleg has little effect on male ability to mate with virgin females, but that autotomy of both forelegs causes a significant reduction in mating success. Among males that mated, autotomy of one or both forelegs did not influence latency until mating, period spent mounted, probability that his mate would accept a subsequent suitor, or probability that his mate would kill a subsequent suitor.

MATING IN THE ABSENCE OF VISUAL CUES BY SCHIZOCOSA OCREATA (HENTZ 1844) WOLF SPIDERS (ARANEAE, LYCOSIDAE)

Abstract Male Schizocosa ocreata (Hentz 1844) wolf spiders court females with multi-modal displays that include both seismic and visual components. The seismic components are thought to be ancestral whereas the visual components are thought to have been more recently derived. We here present evidence that, despite the evolution of elaborate visual display components in males, female S. ocreata remain able to derive sufficient information about males through the seismic display components alone. We compared the mating tendency of females courted by males in the light (seismic and visual components present) and in the dark (only seismic components present). With a sample of 79 pairs in each condition, pairs were not significantly less likely to mate when in the dark (62%) than when in the light (73%). While all males performed courtship, and latency from the release of males until the onset of courtship was similar in the light and in the dark, latency until mounting tended to be much longer in the dark. Th...

Consequences of complex signaling: predator detection of multimodal cues

Animals often evolve complex signals to enhance their detectability by intended receivers. But signals that are more detectable by intended receivers may also be more likely to be intercepted by others, including predators. Courtship signaling in male Schizocosa ocreata wolf spiders (Lycosidae) includes morphological traits (prominent foreleg tufts) and active behaviors that together produce a complex signal with simultaneous broadcast of visual and seismic components. Females respond more readily to males with large tufts and are more likely to respond when multiple modalities (visual and seismic) are present in a complex signal. These spiders cooccur with active predators that may intercept these conspicuous courtship signals and use them as hunting cues. We used video/seismic playback to experimentally isolate and manipulate aspects of the complex signal produced by male S. ocreata. We found that increasing the size of a visual signal (male tufts) and increasing the complexity of the courtship signal by adding a second modality (visual plus seismic versus visual alone) increased the speed with which a common predator, the jumping spider Phidippus clarus (Salticidae), responded to playbacks of courting male S. ocreata. These results indicate that the benefits of increased signaling efficacy of large visual signaling ornaments and complex, multimodal signaling may be countered by increased predation risks.

Absence of social facilitation of courtship in the wolf spider, Schizocosa ocreata (Hentz) (Araneae: Lycosidae)

Males of many animal species are reproductively limited by the difficulty and time costs of finding mates. Males of such species should be selected to take advantage of any cues that might reveal the location of prospective mates. Cues to female location are not restricted to those produced by females, but might also include the highly apparent courtship displays of males that have already found a female. By “eavesdropping” on these courting rivals, initiating sexual displays when courting rivals are detected (i.e., social facilitation of displays); males might effectively exploit the mate-searching efforts of their rivals. We tested the possibility that male Schizocosa ocreata wolf spiders exhibit social facilitation of courtship behaviors using a combination of live behavioral trials and video playback with single stimulus presentations. When exposed to visual cues from another male, male S. ocreata can discern the presence of another individual whether that individual is courting or not. However, we found no evidence of social facilitation of courtship or chemoexploratory behaviors in response to seismic or visual cues presented in isolation or combined. While complex, multimodal, male courtship signals are important in mate choice by female S. ocreata, males do not appear to use these cues to socially facilitate their own courtship.

Compensation for Injury? Modified Multi-Modal Courtship of Wolf Spiders Following Autotomy of Signalling Appendages.

Male Schizocosa ocreata wolf spiders court females using displays that involve dramatic waving motions of their ornamented forelegs. In nature males are often found missing one, and sometimes both, of these legs. We here find that, when exposed to female draglines, males missing these signalling appendages perform a high intensity courtship element (‘jerky tapping’) at a greater rate than intact males. Loss of forelegs was also associated with changes in chemoexploration activity, tendency to stand stationary, and performance of a low intensity courtship element (‘tapping’). The age of the virgin female from which draglines were collected also had an important influence on male courtship behaviour; males on the draglines of old females were less likely to court and, if they did court, did so at a lower rate. These data indicate that courtship behaviour of male S. ocreata is flexible, varying both with the state of the male himself and the state of the female whose draglines he has encountered. Such indivi...

Compensation for Injury? Modified multi-modal courtship of wolf spiders following autotomy of signalling appendages

Male Schizocosa ocreata wolf spiders court females using displays that involve dramatic waving motions of their ornamented forelegs. In nature males are often found missing one, and sometimes both, of these legs. We here find that, when exposed to female draglines, males missing these signalling appendages perform a high intensity courtship element (‘jerky tapping’) at a greater rate than intact males. Loss of forelegs was also associated with changes in chemoexploration activity, tendency to stand stationary, and performance of a low intensity courtship element (‘tapping’). The age of the virgin female from which draglines were collected also had an important influence on male courtship behaviour; males on the draglines of old females were less likely to court and, if they did court, did so at a lower rate. These data indicate that courtship behaviour of male S. ocreata is flexible, varying both with the state of the male himself and the state of the female whose draglines he has encountered. Such individual courtship flexibility raises challenging questions of what processes and trade-offs underlie male courtship decision-making, and whether autotomy-induced changes in courtship activity represent adaptive compensation.

Sexual cannibalism and mate choice decisions in wolf spiders: influence of male size and secondary sexual characters

Sexual cannibalism may influence expression of elaborate male traits by either reinforcing or opposing sexual selection. Male Schizocosa ocreata (Hentz) wolf spiders (Lycosidae) have tufts of bristles on the first pair of legs that may function as a condition-indicating signal trait. We paired virgin and previously mated adult females with males under seminatural conditions (laboratory containers with leaf litter). For males encountering virgin females, probability of attempted premating cannibalism varied with male size, body condition, tuft size, fluctuating asymmetry of tufts (FA) and female size (larger females attacked smaller males and males in poor condition with smaller, more asymmetrical tufts). Probability of successful cannibalism varied with the relative size of both sexes and female body condition, but not male tuft size (smaller males were cannibalized by larger females in better condition). Males with larger tufts (relative to body size) were more likely to mate, but no other traits (male or female) were associated with mating success. Postmating cannibalism risk was associated with female size and age, and male size, body condition and tuft size (larger, older females cannibalized smaller males in poor condition with smaller tufts). For males paired with previously mated females, probability of cannibalism was influenced by size of both sexes and male tuft size (larger females cannibalized smaller males with smaller tufts). While no morphological characteristics (male or female) influenced the probability of second matings, recently matured females were more likely to mate twice. Results suggest that both mate choice and sexual cannibalism can impose reinforcing directional selection on male size and secondary sexual characters.

Flexibility in the multi-modal courtship of a wolf spider, Schizocosa ocreata

Male Schizocosa ocreata wolf spiders court females with synchronous visual and seismic displays. We tested whether male S. ocreata modify their courtship in relation to light environment, and associated utility of the visual components. Males were generally more active and more likely to perform the major courtship element (‘jerky tapping’) when in the light. One courtship element (‘arching’) was only observed in the light while another (‘vertical leg-extend’) was only observed in the dark. Courtship in the dark retained ‘visual’ components, suggesting spiders cannot disengage these components of multi-modal display even when superfluous. Once initiated, there was no evidence that performance rate or time spent in each courtship element differed in the light and in the dark.

Species-Specificity of Chemical Signals: Silk Source Affects Discrimination in a Wolf Spider (Araneae: Lycosidae)

Female spiders deposit chemical cues that elicit male courtship behavior with silk. These cues are often assumed to be species-specific although male spiders may court in response to chemical cues of closely-related species. We used behavioral assays to test the extent of species discrimination of female chemical cues by male Schizocosa ocreata, a wolf spider (Lycosidae). Discrimination, expressed as relative courtship intensity of males, varied significantly with phylogenetic distance. Males did not discriminate between female cues of conspecifics and a sibling species, S. rovneri. Courtship response was intermediate for another species within the ocreata clade and not different from control for spiders outside the clade. These findings support the sibling species status of S. ocreata and S. rovneri, and also suggest the composition of female chemical signals is conserved across closely related wolf spider species.

INFLUENCE OF FEEDING REGIME ON BODY SIZE, BODY CONDITION AND A MALE SECONDARY SEXUAL CHARACTER IN SCHIZOCOSA OCREATA WOLF SPIDERS (ARANEAE, LYCOSIDAE): CONDITION-DEPENDENCE IN A VISUAL SIGNALING TRAIT

Abstract Male Schizocosa ocreata (Hentz) wolf spiders (Araneae, Lycosidae) have tufts of elongated, dark bristles on the patella and tibia of the forelegs, which are involved in visual signaling. Previous research has suggested that these tufts are used by females as a criterion in mate choice, raising the question of whether they might serve as indicators of male condition. We tested the hypothesis that tufts are condition-dependent indicator traits with a laboratory rearing study subjecting spiders to lifelong feeding regimens representing successful (high food) and unsuccessful (low food) foraging history, after which males were measured upon reaching adulthood. Mortality varied significantly with experimental treatment, and had a disproportionate impact on some egg sacs assigned to the low food treatment. Age at sexual maturity and several body size measures varied significantly with feeding history. Well-fed spiders survived better, matured earlier, were significantly larger, and were in relatively b...

Asymmetry in a visual signaling character and sexual selection in a wolf spider

Fluctuating asymmetry (FA) can indicate developmental instability in bilaterally symmetric organisms, and studies have shown that the degree of asymmetry in male secondary sexual characters influences female mate choice in a number of taxa. In male Schizocosa ocreata wolf spiders, conspicuous tufts of bristles on the forelegs are a critical component of visual courtship signals, which appear to play a role in female mate choice. Previous studies have shown that females exhibit reduced receptivity to males with regenerative asymmetry, a consequence of leg loss and regeneration that causes males to be grossly asymmetric with respect to this important signaling character. We provide data on the occurrence of FA in the tufts of S. ocreata, and examine further the influence of asymmetry on female mate choice. The distribution of tuft area asymmetry values from a sample of field-collected males was normal, with a mean value of zero, indicating true FA. For a subset of males measured directly after field collection and prior to feeding, tuft asymmetry was significantly negatively correlated with measures of body size (body length) and condition (abdomen volume/cephalothorax width). Receptivity responses of females to visual signals from live males of similar size varied with the degree of asymmetry in male tufts. Since FA covaries with male body size and condition, which may also influence behavioral vigor, we used video image manipulation to alter the degree of asymmetry in tufts of a courting male while holding size and condition constant. Asymmetry treatments represented values within the range of natural FA variation as well as more extreme values characteristic of regenerative asymmetry. With the confounding effects of male size, condition, and behavior held constant, female spiders exhibited reduced receptivity responses to all experimental asymmetric video images relative to a control video stimulus. There were no differences in the frequency of female receptivity among the various asymmetry treatments, suggesting that discrimination against asymmetry in conspecific male signal characters is not simply a rejection of extreme phenotypes. Results suggest that asymmetry in a key male secondary character used in visual signaling, independent of any concomitant behavioral or size factor, is an important criterion in mate choice.

Preliminary isolation of male-inhibitory pheromone of the spiderSchizocosa ocreata (Araneae, Lycosidae)

Compounds with pheromone activity were extracted from maleSchizocosa ocreata silk using methanol as the solvent. Behavioral data suggest that these compounds mediate agonistic encounters among male spiders. Preliminary chemical analyses indicate that the pheromones are low-molecular-weight lipids, one being slightly polar, the other nonpolar.