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

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.

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.

Predation Risk Affects Mate Choice in a Gobiid Fish

Infection stress and mate assessment in wolf spiders: female mate choice varies with sensory mode of male courtship

Recent work on the psychophysics of reading has concentrated primarily on achromatic (or luminance) contrast factors (Legge et al, 1985, 1986, 1987). In general, reading is fastest with text of high contrast defined by luminance contours. In the real world, however, chromatic as well as luminance edges abound. While several studies have examined the interaction of chromatic and luminance contrasts on stimuli near threshold (e.g., Mullen, 1987; Knoblauch et al, 1984; Jameson, 1985; Switkes et al, 1988), only a few have investigated suprathreshold levels. Legge et al, (1986) demonstrated that for observers with normal vision, the luminance contrast and not the color of text on a dark background determines reading rate. This finding is consistent with threshold studies that show that the color of a grating does not affect luminance contrast sensitivity either (Nelson and Halberg, 1979), provided that one avoids frequencies near the diffraction limit (Pokorny et al, 1968; Van Nes and Bouman, 1967).

A combined achromatic and chromatic contrast metric for digital images and video is presented in this paper. Our work is aimed at tuning any parametric rendering algorithm in an automated way by computing how much details an observer perceives in a rendered scene. The contrast metric is based on contrast analysis in spatial domain of image sub-bands constructed by pyramidal decomposition of the image. The proposed contrast metric is the sum of the perceptual contrast of every pixel in the image at different detail levels corresponding to different viewing distances. The novel metric shows high correlation with subjective experiments. Important applications involve optimal parameter set of any image rendering and contrast enhancement technique or auto exposure of an image capturing device.

Contour adaptation reduces the spreading of edge induced colors

Male–male competition and female mate choice act contemporaneously in the cockroach Nauphoeta cinerea and the social pheromone of males influences the outcome of both forms of sexual selection. We therefore examined the joint and separate effects of male–male competition and female mate choice to determine if the selective optima for the pheromone were the same or different. Dominant males in a newly established hierarchy mated more frequently, but not exclusively. Manipulations of the multi-component social pheromone produced by males of N. cinerea showed that both long- and close-range attraction of females by males were influenced by the quantity and composition of the pheromone. The most attractive composition, however, differed from that which was most likely to confer high status to males. Since the outcome of male–male competition can conflict with mating preferences exhibited by females, there is balancing sexual selection on the social pheromone of N. cinerea. Such balancing selection might act to maintain genetic variation in sexually selected traits. We suggest that the different forms of sexual selection conflict in N. cinerea because females prefer a blend different to that which is most effective in male–male competition in order to avoid mating with overly aggressive males.

Intraguild predation is described as predation among organisms that exploit similar resources. As wolf spiders (Araneae, Lycosidae) are generalist predators that share habitat and food resources with the ground skink Scincella lateralis, we conducted a series of laboratory experiments to determine if wolf spiders are capable of preying upon ground skinks. Wolf spiders (Gladicosa pulchra) successfully preyed on skinks during 3 of 20 encounters, but did not overtly respond to chemical stimuli from the skinks. Skinks employed antipredatory behaviors (i.e., immobility) when exposed to visual and chemical stimuli from spiders, providing evidence that they recognize spiders as predators prior to an encounter. In an additional experiment, the hypothesis that increased skink movement would lead to an increase in spider attacks was tested. Skinks exhibited high levels of movement in this experiment, with spider predation occurring during 4 of 10 encounters. The presence of structural refugia played a significant role in this predator–prey interaction by increasing the amount of time required for a spider to prey upon a skink. Our results indicate that G. pulchra can prey upon S. lateralis, and that skinks may recognize cues deposited on the substrate by spiders. These data indicate that these two species may interact in an ecologically meaningful manner.

The effect of spatio-temporal chromatic and achromatic contrast on VEPs

In the presence of predators, animal* may reduce or alter their mating activities. There has been little experimental study of whether mating behavior varies with the level of predation risk. Two species of moths, Pseudaletia unipuncta (Noctuidae) and Ostrinia nubilalis (Pyralidae), significantly reduced their mate-seeking behavior under high levels of simulated predation risk. Male moths aborted upwind flight in a pheromone phime, and females stopped releasing pheromone in response to sounds simulating the echolocation calls of bats. For 0. nubilalis, but not for P. unipuncta, the response varied significantly with the level of predation risk. Interspecific differences in behavioral responses likely reflect differences in physiological auditory sensitivity and/or behavioral thresholds. Female behavioral responses to sounds simulating the calls of bats that glean their prey from surfaces were significantly weaker than their responses to sounds resembling the calls of aerially hawking bats; these results support the neurophysiological data that the calls of gleaning bats are relatively inaudible to moths. This study indicates that some animals can modify their reproductive activities in response to auditory cues from predators. Key words: bats, mating behavior, moths, Ostrinia nubilalis, pheromone, predation risk, Pseudaletia unipuncta, ultrasound. [Behav Ecol 9:552-558 (1998)]

Diurnal and nocturnal activity patterns shown by different species will strongly determine the characteristics of signals as well as the sensory channels used during sexual interactions. Despite this, few studies have experimentally tested the effects of lighting and time of day on courtship characteristics in arthropods. Previous studies have shown that the wolf spider Schizocosa malitiosa can be active during the day or at night. We tested whether the period of the day affects the sexual behavior of S. malitiosa, by pairing males and females under diurnal or nocturnal conditions. We carried out mating trials in diurnal and nocturnal conditions in arenas containing female refuges. In diurnal conditions, male leg shaking behavior occurred at higher rates and consisted of greater leg raising angles relatively to nocturnal conditions. We did not find differences in mounts and mount latency between both experimental groups. In nocturnal conditions, female attacks and emergence from refuges were higher. Also, although mount occurrence did not differ between the two treatments, mounts inside the refuge were more frequent in diurnal conditions. Results suggest behavioral flexibility in male courtship and female receptivity responses relative to the time of the day.

The measurement of achromatic sensitivity has been an important tool for monitoring subtle changes in vision as the result of disease or response to therapy. In this study, we aimed to provide a normative data set for achromatic and chromatic contrast sensitivity functions within a common cone contrast space using an abbreviated measurement approach suitable for clinical practice. In addition, we aimed to provide comparisons of achromatic and chromatic binocular summation across spatial frequency. We estimated monocular cone contrast sensitivity functions (CCSFs) using a quick Contrast Sensitivity Function (qCSF) approach for achromatic as well as isoluminant, L/M cone opponent, and S cone opponent stimuli in a healthy population of 51 subjects. We determined the binocular CCSFs for achromatic and chromatic vision to evaluate the degree of binocular summation across spatial frequency for these three different mechanisms in a subset of 20 subjects. Each data set shows consistent contrast sensitivity across the population. They highlight the extremely high cone contrast sensitivity of L/M cone opponency compared with the S-cone and achromatic responses. We also find that the two chromatic sensitivities are correlated across the healthy population. In addition, binocular summation for all mechanisms depends strongly on stimulus spatial frequency. This study, using an approach well suited to the clinic, is the first to provide a comparative normative data set for the chromatic and achromatic contrast sensitivity functions, yielding quantitative comparisons of achromatic, L/M cone opponent, and S cone opponent chromatic sensitivities as a function of spatial frequency.

Conservative biological control promotes the use of native natural enemies to limit the size and growth of pest populations. Although spiders constitute one of the most important groups of native predators in several crops, their trophic ecology remains largely unknown, especially for several generalist taxa. In laboratory, we assessed the predatory behaviour of a wandering spider (the wolf spider Lycosa thorelli (Keyserling, 1877) against several arthropods varying in size and trophic positions, all found in South American soybean and rice crops. As prey we used the bug Piezodorus guildinii (Westwood, 1837) as well as larvae and adults of the moth Spodoptera frugiperda (Smith, 1797), both being considered important pests in Uruguayan crops. We also used several non‐pest arthropods as prey, sarcophagid flies, carabid beetles and wolf spiders. All prey were attacked in more or less high, although not statistically differing, proportions. However, carabids were not consumed, and bugs were consumed in significantly lower proportions than flies. A negative correlation was found between prey size and acceptance rate. Immobilization times were longer against larvae when compared to moths and flies, while predatory sequences were longer for bugs when compared to flies, moths and spiders. In addition, we found a positive effect of prey size on predatory sequence length and complexity. Our results confirm the ability of spiders to attack and feed upon prey with different morphologies, included well‐defended arthropods, and their potential use as natural enemies of several pests in South American crops.

Pigmentation patterns, ultraviolet reflection and fluorescent emission are often involved in mate recognition and mate quality functions in many animal taxa. We investigated the role of wing ultra-violet reflection, fluorescence emission, and pigmentation on age and sexual signals in the damselfly Mnesarete pudica. In this species, wings are sexually dimorphic in colour and exhibit age dependency: males and females show a smoky black colouration when young, turning red in mature males while it turns brown in females. First, we investigated wing UV patterns through reflectance and emission spectra. Second, behavioural experiments were undertaken to show male and female responses to manipulated wing pigmentation and experimentally reduced UV (UV-). Reflectance spectra of the wings of juvenile and mature males and females were used to show the differences between controls and individuals with manipulated colouration used in the behavioural experiment. UV-reduced, females with wings painted red, and control males and females were tethered and presented to conspecific males and females, and their behavioral responses were recorded. The male red wing pigmentation and females with red wings elicited an aggressive response in territorial males and a sexual response in females. Both males and females showed neutral responses towards individuals with reduced UV. Wing signals of juvenile individuals also provoked neutral responses. These results suggest that UV, together with pigmentation, plays a role during mate recognition in males and females. Other than butterflies and spiders, it seems that fluorescence signals and UV reflectance can also be part of communication in odonates.