Male Wolf Spiders Research Articles

Approach Strategy by which Male Mediterranean Tarantulas Adjust to the Cannibalistic Behaviour of Females

AbstractIn sexually cannibalistic species, selection is thought to have favoured the evolution of male approaching behaviour that reduces the probability that the female will kill the male. However, investigations of behaviours that could reduce the probability of sexual cannibalism are few. We examine the hypothesis that male wolf spiders,Lycosa tarantula(L.) (Araneae, Lycosidae), decides to approach females in periods when they are less dangerous. Males of this species approach females for mating during the daytime only. While attending females, males stay farther from the female's burrow at night than during the daytime. In field experiments, we offered a grasshopper (typical prey) or a maleL. tarantulato females at night and during the day, and our findings show that the diel changes in the male's approaching behaviour matches diurnal changes in the female's tendency to attack both the grasshopper and the male spider. These findings support our hypothesis that a diel change in female responsiveness to prey has been a selection pressure influencing the evolution of male approach behaviour in a sexually cannibalistic species.

Sexual advertisement and immune function in an arachnid species (Lycosidae)

A simple version of the immunocompetence handicap hypothesizes that through condition-dependence, the size of the sexual trait may be positively related to immune function at the population level. In the present study, we investigated the relationship between sexual advertisement and immune function in a natural population of male wolf spiders, Hygrolycosa rubrofasciata (Araneae: Lycosidae). Males of H. rubrofasciata have a costly and condition-dependent acoustic signal, courtship drumming. In the mating season, males drum against dry leaves while wandering around the habitat searching for receptive females. Males increase their mating success by increasing their drumming rate and mobility. We used drumming rate and mobility measured without female proximity as estimates of sexual advertisement. As estimates of male immune function, we used encapsulation rate and lytic activity. Encapsulation rate is a common challenging technique, which measures immune response against multicellular parasites. Lytic activity is a monitoring technique, which measures immune response against pathogens. Our results show that males with higher drumming rate had higher encapsulation rate. This suggests that females might use drumming rate as a signal for choosing males with good immunocompetence. Moreover, our results show that males with higher mobility had higher lytic activity. As females are more likely to encounter those males that have higher mobility, this might also select males with better immune function. Our results suggest that the immunocompetence handicap might work also among spiders, although we could not assess the causality of the relationship between sexual selection and immune function in this correlational study.

Assessment of Potential Predation Costs of Male Decoration and Courtship Display in Wolf Spiders Using Video Digitization and Playback

We used video digitization and playback techniques to examine the potential predation risk of leg decorations and visual displays of male wolf spiders, which vary across the genus Schizocosa (Araneae: Lycosidae). Video images of courting males of four Schizocosa species were modified by adding or removing tufts and presented on LCD minitelevisions to the wolf spider Hogna helluo, a common predator of Schizocosa. Predatory responses of H. helluo varied significantly among stimuli and were highest for S. ocreata (which has decorative tufts and leg-waving displays) and lower for S. rovneri, S. duplex, and S. uetzi (which lack decorations and visual displays). Removal of tufts from S. ocreata significantly reduced predatory responses of H. helluo, but addition of tufts to other species had no effect. Results suggest that leg decorations may increase detection of active leg-waving displays and thereby increase predation risk.

Leg ornamentation and the efficacy of courtship display in four species of wolf spider (Araneae: Lycosidae)

This study used both correlative and experimental video playback methods to test the hypothesis that the secondary sexual traits of male wolf spiders act to increase the efficacy of visual courtship displays. Direct observations of courtship of several lycosid genera and a review of the literature revealed a significant association between ornamentation and visual courtship displays. This suggests that the ornamentation may be playing the role of amplifier for a visual display. To test this hypothesis, male courtship behaviors of four Schizocosa species were experimentally manipulated using video-imaging techniques. Females of species with non-visually displaying, non-ornamented males (Schizocosa duplex and S. uetzi) did not increase in frequency of receptivity when tufts were added to conspecific males. In a species with a visual display and foreleg pigmentation (S. stridulans), the addition of foreleg tufts increased female receptivity. In a tufted species (S. crassipes), females tended to decrease their receptivity when male ornamentation was completely removed. In visually displaying species, ornamentation acts to increase female receptivity, supporting its role as an amplifier of a visual display.

Female responses to isolated signals from multimodal male courtship displays in the wolf spider genusSchizocosa(Araneae: Lycosidae)

Male wolf spiders within the genusSchizocosadisplay considerable variation in foreleg ornamentation as well as in courtship communication. Multiple modes of male signalling have evolved in a number of species. Divergence in courtship signals among species within this genus may be directly associated with variation in the sensory sensitivities of conspecific females. We isolated the visual and vibratory courtship cues of four species ofSchizocosaand recorded conspecific female receptivity to each isolated cue. We also examined female receptivity to complete multimodal courtship signals. We found that the sensory sensitivities of conspecific females were associated with the predominant modes of male courtship communication. Species in which females use mostly stridulatory cues in assessing conspecific males tended to have stridulation-based male courtship displays (S.duplexandS.uetzi) while the opposite was true for species in which females used more visual cues in male assessment (S.stridulansandS.crassipes). This study suggests coevolution between male signal design and female sensory design. We discuss possible scenarios that could be driving this coevolution, including hypotheses of sensory bias and environmental constraints.

Age and Sex-Based Differences in the Use of Prey Sensory Cues in Wolf Spiders (Araneae: Lycosidae)

Differences in foraging patterns mediated by sensory cues were examined between adult and juvenile male and female wolf spiders (Schizocosa rovneri; Lycosidae). Patch residence time for thirty-one spiders were tested among juveniles and adults in artificial foraging patches. Patches varied in sensory information provided by live prey (crickets) as follows: visual stimuli alone; vibratory stimuli alone; visual and vibratory stimuli together; and control (no stimuli). Spiders moved between patches for one hour, but could not feed. Adult Schizocosa rovneri use primarily visual information to determine patch residence time, but juveniles use vibratory cues as well. Significant age and sex-based differences in the use of sensory cues suggest that observed divergent foraging strategies are partly due to the use of different perceptual cues in prey detection.

Male display rate reveals ejaculate characteristics in the Trinidadian guppy,Poecilia reticulata.

Previous work (Reynolds and Gross 1992) has demonstrated that mate choice enables female guppies, Poecilia reticulata , to obtain heritable benefits (‘good genes’) for their offspring. It is not yet known whether males also signal their functional fertility, that is, their viability as fathers, to female guppies. Our study tested the hypothesis that a male9s behaviour reveals characteristics of his ejaculate. We uncovered a strong correlation between display rate and sperm number in male guppies derived from two wild Trinidadian populations. This result indicates that information on the functional fertility of potential mates is available to females. However, our investigation also found a significant relationship between the frequency of sneaky mating and sperm number. Female guppies in wild populations, particularly those experiencing a high predation regime, are constantly subjected to sneaky mating attempts. As the males responsible for these sneaky matings have highest reserves of sperm they may have the capacity to undermine female choice. The implications of these findings for sperm competition are discussed.

Female choice and pre-existing bias: visual cues during courtship in two Schizocosawolf spiders (Araneae: Lycosidae)

Abstract. Male wolf spiders, Schizocosa ocreata, possess tufts of bristles on the forelegs, which are used in visual courtship displays, but males of a closely related species, S. rovneri , lack tufted forelegs. In studies with live males, female S. ocreata showed receptivity more often to males with larger tufts than to males with smaller or shaved tufts. Male body size and/or shaving of tufts may affect male courtship behaviour, however, which could influence female receptivity. Manipulated video images of the same courting male were used to control for male behaviour and to test the hypothesis that these tufts influence female choice. Video images of S. ocreata , and images of S. rovneri males (control: without tufts; experimental: with tufts added) were shown to females of both species. Female S. ocreata showed lowered receptivity to a video of a male with tufts removed and equal receptivity to a video of a male with enhanced tufts compared to a control video of a conspecific male with typical tufts. Responses of female S. ocreata to heterospecific video male S. rovneri were significantly lower than to conspecifics. In contrast, female S. rovneri are more receptive to video images of conspecific males with tufts added and heterospecific male S. ocreata than to control images. Phylogenetic analyses suggest that tufts are apomorphic, and that S. rovneri is more basal within the clade than S. ocreata . Since female S. rovneri respond receptively to both conspecific and heterospecific males with tufts and/or active leg waving displays, these results may provide evidence of pre-existing bias and/or sexual selection for a novel trait.

Acoustic Communication and Reproductive Isolation in Two Species of Wolf Spiders

Sound production by male wolf spiders during courtship is critical for behavioral reproductive isolation of two sibling species. Females only respond to and copulate with conspecific males, and acoustic signals through a substrate are necessary to induce receptivity. No reproductive barriers that could arise during mating (such as genital or mechanical incompatibility) or after mating (infertility) are in effect between the species, since forced interspecific matings produce viable offspring.

RECDIS: A BASIC program for computing interindividual distances within a rectangular area

A variety of investigators have observed freely behaving rats in circular open fields and have used interindividual distances as a quantitative measure of social attraction or gregariousness (Barefoot, Aspey, & Olson, 1975; Eckman, Meltzer, & Latane, 1969; Latane, 1969; Latane, Cappell, & Joy, 1970; Latane & Glass, 1968). To facilitate such raw data collection and organization, Aspey (in press-b) developed a computer program (CIRDIS) for determining interindividual distances between any two subjects when observed in a circular open field marked off into 49 sectors. The program RECDIS refers to distances, and extends the generality and applicability of determining interindividual distances by specifying locations in terms of numbered sectors to rectangular test areas of variable length and width. The program is written for a rectangular test area marked off into any number of identified squares of equal size and shape. Length and width are user specified, and the program is applicable to a variety of research situations whenever two animals' locations can be specified in terms of the N squares. In an ethological research example, Aspey (in press-a) computed the theoretical personal space among groups of adult male wolf spiders by determining interindividual distances during agonistic encounters when tested under varying social, spatial, and population densities. Diagrams of the rectangular area, marked off into a numbered grid (Figure 1), make useful data sheets for recording subjects' locations during testing, or for transcribing tape-recorded protocol. Additionally, a theoretical, chance interindividual distance can be computed by entering all combinations of the numbered squares and obtaining the mean of all possible distances. Furthermore, control distances can be computed by recording each partner's location when tested alone and computing the distances as if the partners had been tested together. This measure provides an indication of the expected interindividual distance between subjects if they were to move through the rectangular field independently of each other. Description. After operationally defining location (e.g., as that numbered square where a spider's right palp is located during a given trial), the numbers of the squares are recorded where each member of a subject