Body-colour variation in an orb-web spider and its effect on predation success

Relationship between body colour and microhabitat breadth in an orb-web spider

Habitat use often differs among intraspecific individuals, and the degree to which individual animals use specific habitats, i.e. microhabitat breadth, can also vary. Variation in body colour sometimes emerges as dark vs. bright coloration, which can be related to habitat selectivity. The aim of this study was to examine whether darker animals prefer shady sites to avoid overheating from direct sunlight exposure, whereas brighter animals would use both shady and open sites. Orb-web spiders, Cyclosa argenteoalba, have a silver dorsal abdomen with black markings; the proportion of these black markings varies between 20 and 100% among individuals. In summer, there was less variation in the duration of direct sunlight hitting the webs of darker spiders compared with that of brighter spiders. This indicated a narrower microhabitat range for darker spiders, which preferred shady sites. This pattern was not observed in spring and autumn, when thermal conditions were less severe. These results are consistent with the hypothesis that when the temperature is high, darker animals are microhabitat specialists, whereas brighter animals are generalists. A previous study found that darker spiders capture more prey than brighter spiders, and the amount of black markings is considered to be a trade-off between foraging success and microhabitat availability.

Color lures in orb-weaving spiders: a meta-analysis

Lures are deceptive strategies that exploit sensory biases in prey, usually mimicking a prey’s mate or food item. Several predators exploit plant–pollinator systems, where visual signals are an essential part of interspecific interactions. Many diurnal, and even nocturnal, orb-web spiders present conspicuous body coloration or bright color patches. These bright colors are regarded as color-based lures that exploit biases present in insect visual systems, possibly mimicking flower colors. The prey attraction hypothesis was proposed more than 20 years ago to explain orb-web spider coloration. Although most data gathered so far has corroborated the predictions of the prey attraction hypothesis, there are several studies that refute these predictions. We conducted a multilevel phylogenetic meta-analysis to assess the magnitude of the effect of conspicuous orb-web spider body coloration on prey attraction. We found a positive effect in favor of the prey attraction hypothesis; however, there was substantial heterogeneity between studies. Experimental designs comparing conspicuous spiders to painted spiders or empty webs did not explain between-studies heterogeneity. The lack of theoretical explanation behind the prey attraction hypothesis makes it challenging to address which components influence prey attraction. Future studies could evaluate whether color is part of a multicomponent signal and test alternative hypotheses for the evolution of spider colors, such as predator avoidance and thermoregulation.

The timing of female genital mutilation and the role of contralateral palpal insertions in the spider Cyclosa argenteoalba

Some male spiders exhibit female genital mutilation behaviour (FGM) by removing the female genital appendage (scape) to control the mating frequency of females. Female spiders have two, i.e. right and left, genital openings connected with separate spermathecae into which males transfer sperm successively using one pedipalp (secondary genitalia) at a time. Thus, males must complete at least two palpal insertions to fill both spermathecae, before FGM. The present study examined whether (i) scape removal is only associated with the second palpal insertion (one-action hypothesis) or (ii) two contralateral palpal insertions facilitate FGM, with each insertion cutting the basal part of the scape halfway (two-actions hypothesis). Experiments in which females were replaced after a male had made the first insertion did not support the one-action hypothesis, because scapes remained intact after the newly introduced virgin females received their first palpal insertion, which was the second insertion by the males. In comparison, mating experiments using two half-eunuchs (i.e. one of the palps of each male had been manually removed, forcing them to fill female spermatheca on one side only) supported the two-actions hypothesis. FGM was more frequent in females that received two contralateral palpal insertions than in females that received ipsilateral insertions.

Luring prey to the web: the case of Argiope and Nephila

The view that orb webs are imperceptible traps has changed since it was discovered that some spiders possess body colorations or web designs that are attractive to prey. Spiders of the genera Argiope and Nephila exemplify both cases and are able to adjust their webs to increase foraging success. In this study, I compared the foraging strategies of A. submanorica and N. clavipes as they foraged on the same natural prey (stingless bees). Argiope submanorica adds UV-reflective decorations while N. clavipes builds non-UV-reflective golden webs. Based on studies that suggest a lack of niche separation between these two species, the objective of this study was to test whether this hypothesis holds when the spiders are competing for a limited resource. In addition, I investigated whether the colorations of the spiders influence their foraging success. The golden webs of N. clavipes intercepted more bees than the decorated webs of A. submanorica, suggesting that some type of niche separation must occur in nature, as otherwise competition would lead to the local extinction of A. submanorica. These differences in foraging success, leading to its ability to outcompete other spider species exploiting the same resource, could explain in part the abundance and distribution of the N. clavipes on the American continent.

Female genital mutilation and monandry in an orb-web spider

Monandry, in which a female has only one mating partner during the reproductive period, is established when a female spontaneously refrains from re-mating, or when a partner male interferes with the attempts of a female to mate again. In the latter case, however, females often have countermeasures against males, which may explain why polyandry is ubiquitous. Here, I demonstrate that the genital appendage, or scape, of the female orb-web spider (Cyclosa argenteoalba) is injured after her first mating, possibly by her first male partner. This female genital mutilation (FGM) permanently precludes copulation, and females appear to have no countermeasures. FGM is considered to confer a strong advantage to males in sexual conflicts over the number of female matings, and it may widely occur in spiders.