Male Silk Research Articles

The wolf spider Pardosa milvina varies silk deposition in response to self and same‐sex conspecific silk

AbstractSilk is an important communication medium for spiders with roles in species recognition, sex identification, and mating status assessment. Spiders may benefit by discriminating between their own or another same‐sex conspecific's silk. Silk‐mediated self‐recognition could allow spiders to identify areas that they have previously visited, competitively block silk advertisements from sexual rivals or minimize redundant signaling in an area. Silk deposition behavior may also be contingent upon silk cues detected from same‐sex conspecifics. We tested if males and females of the wolf spider Pardosa milvina show different silk deposition patterns when encountering their own silk versus the silk of another spider of the same sex. Using a within‐between‐subjects design, we quantified male and female deposition of three silk types: draglines, cord silk, and attachment disks on substrates containing either their own silk or the silk of an adult same‐sex conspecific (N = 23 males, 28 females). Both males and females significantly increased dragline and cord silk deposition on substrates containing conspecific rather than their own silk with males producing more cord silk than females. Males significantly increased attachment disk deposition on conspecific male silk compared to their own while females showed the opposite response, decreasing attachment disk deposition on conspecific female silk. Both male and female P. milvina can recognize their own silk, but we found significant qualitative and quantitative sex differences in silk deposition suggesting sex‐specific functions for attachment disks compared to cord or dragline silk.

Analysis of Odor-Tracking Performance of Silk Moth Using a Sensory-Motor Intervention System.

Animals can adaptively behave in different environmental conditions by converting environmental information obtained from their sensory organs into actions. This sensory-motor integration enables the accomplishment of various tasks and is essential for animal survival. This sensory-motor integration also plays an important role in localization to females, relying on sex pheromones floating in space. In this study, we focused on the localization behavior of the adult male silk moth, Bombyx mori. We investigated sensory-motor integration against time delay using odor plume tracking performance as an index when we set a certain time delay for the sensory and motor responses. Given that it is difficult to directly intervene in the sensory and motor functions of the silk moth, we constructed an intervention system based on a mobile behavior measurement system controlled by them. Using this intervention system, not only can timing the detection of the odor in the environment and timing the presentation of the odor to the silk moth be manipulated, but timing the reflection of the movement of the silk moth can also be manipulated. We analyzed the extent to which the localization strategy of the silk moth could tolerate sensory delays by setting a delay to the odor presentation. We also evaluated behavioral compensation by odor sensory feedback by setting a delay to the motor. The results of the localization experiment have shown that the localization success rate did not decrease when there was a motor delay. However, when there was a sensory delay, the success rate decreased depending on the time delay. Analysis of the change in behavior after detection of the odor stimulus has shown that the movement was more linear when we set a motor delay. However, the movement was accompanied by a large rotational movement when there was a delay in the sensory input. This result has suggested that behavior is compensated for the delay in motor function by feedback control of odor sensation, but not when accompanied by sensory delay. To compensate for this, the silk moth may acquire appropriate information from the environment by making large body movements.

Robust Moth-Inspired Algorithm for Odor Source Localization Using Multimodal Information.

Odor-source localization, by which one finds the source of an odor by detecting the odor itself, is an important ability to possess in order to search for leaking gases, explosives, and disaster survivors. Although many animals possess this ability, research on implementing olfaction in robotics is still developing. We developed a novel algorithm that enables a robot to localize an odor source indoors and outdoors by taking inspiration from the adult male silk moth, which we used as the target organism. We measured the female-localization behavior of the silk moth by using a virtual reality (VR) system to obtain the relationship between multiple sensory stimuli and behavior during the localization behavior. The results showed that there were two types of search active and inactive depending on the direction of odor and wind detection. In an active search, the silk moth moved faster as the odor-detection frequency increased, whereas in the inactive search, they always moved slower under all odor-detection frequencies. This phenomenon was constructed as a robust moth-inspired (RMI) algorithm and implemented on a ground-running robot. Experiments on odor-source localization in three environments with different degrees of environmental complexity showed that the RMI algorithm has the best localization performance among conventional moth-inspired algorithms. Analysis of the trajectories showed that the robot could move smoothly through the odor plume even when the environment became more complex. This indicates that switching and modulating behavior based on the direction of odor and wind detection contributes to the adaptability and robustness of odor-source localization.

Male silk moths for the post-mating activities of female Silkmoth Bombyx mori L.

Male silk moths for the post-mating activities of female Silkmoth Bombyx mori L.

Learning a Generic Olfactory Search Strategy From Silk Moths by Deep Inverse Reinforcement Learning

Despite their simple nervous systems, insects efficiently search for and find sources of odorants. Hence, it is necessary to model and implement such behavior in artificial agents (robots), to enable them to detect dangerous substances such as drugs, gas leaks, and explosives. Previous studies have approached behavioral modeling with either statistical or machine-learning methods. In this study, we determined the behavior trajectories of male silk moths using a virtual reality (VR) system. We then modeled these trajectories as a Markov decision process (MDP) and employed inverse reinforcement learning (IRL) to learn their reward function. Furthermore, we estimated the optimal policy from the learned reward function. We then conducted olfactory search simulations and determined that the IRL-based policy could locate odor sources with a high success rate. This was also investigated under environmental conditions different from those faced by real moths on the VR system. The obtained results indicate that IRL can generically represent olfactory search strategies that are adaptable to various environments.

Silk-borne chemicals of spider nuptial gifts elicit female gift acceptance.

Chemical communication is important in a reproductive context for conveying information used for mate recognition and/or assessment during courtship and mating. Spider silk is a common vehicle for chemical communication between the sexes. However, despite being well described in females, male silk-borne chemicals remain largely unexplored. Males of the spider Pisaura mirabilis silk-wrap prey (i.e. nuptial gifts) that is offered to females during courtship and eaten by the female during mating. Interestingly, rejected males often add more silk to their gift which leads to successful mating, suggesting the presence of silk-borne chemicals that facilitate female gift acceptance. To test this hypothesis, we offered females standardized gifts covered with male silk that was either washed in solvents or unwashed, respectively, to remove or not any chemically active components. We scored female gift acceptance, and as expected in the case chemicals that mediate female mating behaviour are present in male silk, females were more likely to accept gifts covered with unwashed silk. Our findings suggest that silk-borne chemicals of nuptial gifts prime female responses, potentially signalling male quality or manipulating females into mating beyond their interests given the occurrence of male cheating behaviour via nutritionally worthless gifts in this system.

Regulation of olfactory-based sex behaviors in the silkworm by genes in the sex-determination cascade.

Insect courtship and mating depend on integration of olfactory, visual, and tactile cues. Compared to other insects, Bombyx mori, the domesticated silkworm, has relatively simple sexual behaviors as it cannot fly. Here by using CRISPR/Cas9 and electrophysiological techniques we found that courtship and mating behaviors are regulated in male silk moths by mutating genes in the sex determination cascade belonging to two conserved pathways. Loss of Bmdsx gene expression significantly reduced the peripheral perception of the major pheromone component bombykol by reducing expression of the product of the BmOR1 gene which completely blocked courtship in adult males. Interestingly, we found that mating behavior was regulated independently by another sexual differentiation gene, Bmfru. Loss of Bmfru completely blocked mating, but males displayed normal courtship behavior. Lack of Bmfru expression significantly reduced the perception of the minor pheromone component bombykal due to the down regulation of BmOR3 expression; further, functional analysis revealed that loss of the product of BmOR3 played a key role in terminating male mating behavior. Our results suggest that Bmdsx and Bmfru are at the base of the two primary pathways that regulate olfactory-based sexual behavior.

Pore-ridge nanostructures on the surface of trichoid sensilla of the male silkmoth Bombyx mori: Aerodynamic trapping and transporting of the pheromone molecules

This paper tries to reveal the mechanism of the high-efficient adsorption of the sex pheromone by the trichoid sensilla of the male silk moth Bombyx mori. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to acquire the topographies and nanostructures of the surfaces of the trichoid sensilla. SEM and AFM images present mostly regular pore-ridge nanostructures on the sensilla, and all the pores are located at or near the feet of the ridges. AFM phase-shift images demonstrate that the variation of phase-shift, which appears along the ridge cannot simply be attributed to heterogeneity in surface lipid properties, for the phase-shift was present in the same region with the sudden difference in height. Simulations of computational fluid dynamics were applied to investigate the effects on the airflow velocity field and streamlines by the pore-ridge nanostructures and the antenna vibration. Simulation results indicate that the airflow vortexes that form on the sensillum surface are generated by the combined effect of ambient airflow and pore-ridge structure as well as spontaneous vibration of the antenna. We suggest that the vortex intercepts and traps the pheromone molecules passing nearby, and transports them through its periodical movement to the pore. We speculate that the vortex is the aerodynamic factor benefitting the highly efficient adsorption of pheromone molecules.

A review of the mechanisms and functional roles of male silk use in spider courtship and mating

Spiders are well known for using chemical, vibratory, tactile, and visual signals within mating contexts. All spiders produce silk, and even in non-web building spiders, silk is intimately tied to courtship and mating. Silk produced by females provides a transmission channel for male vibratory courtship signals, while webs and draglines provide a substrate for female sex pheromones. Observations of male spiders producing silk during sexual interactions are also common across phylogenetically widespread taxa. However, the function of male-produced silk in mating has received very little study. Exploring the function of male silk use during mating will provide a deeper understanding of the complex mating systems of spiders and allow tests of hypotheses about the evolution of male and female traits under sexual selection and/or conflict. In this review, we outline functional hypotheses that may explain each of the following three main categories of silk deposition males exhibit during courtship and mating: (1) silk deposition on females' webs or other silk structures, (2) silk deposition on females (‘bridal veils') and (3) silk associated with nuptial gifts. We then summarize the current knowledge of silk use by male spiders within these three categories and the types of mechanisms that may lead to functional effects, and discuss areas where future work can be targeted.

Does silk mediate chemical communication between the sexes in a nuptial feeding spider?

Chemical signals play a crucial role in reproduction as a means for locating mates and/or gaining information about their quality, ultimately affecting mating system dynamics and mate choice. In spiders, one of the potential sources of chemical signalling is silk. However, while female silk is known to attract mates and/or elicit courtship, due to sex-specific roles in mate searching, male silk-related signals are often neglected. In the hunting spider Pisaura mirabilis (Pisauridae), both sexes leave silk draglines during movements while males additionally use silk to wrap nuptial gifts (food donations to females at mating). We explored the potential for both silk types (draglines and gift silk) to release signals and tested the hypothesis that chemical compounds bound to gifts’ silk serve to elicit female attraction. We conducted behavioural choice assays for dragline and gift silk, and their putative transmission mode (airborne or contact) by testing (i) male and female attraction towards draglines of the opposite sex and (ii) female attraction towards gift silk. Whereas males were attracted to female draglines (contact cues), females did not respond to male silk of any type. We suggest that females use draglines for advertisement to secure copulation and foraging of nuptial gifts. If these signals ease male mate searching, attractive male draglines are unnecessary. Overall, males may not invest in chemical stimulation but rather exploit female foraging interests through gift giving. Alternatively, they may release signals that prime other female sexual behaviours or towards which females may have evolved resistance. Animals commonly use chemical signals to communicate during reproduction, and spiders have the potential to release such signals from their silk. We investigated whether two silk types, draglines released during movements and silk covering male nuptial gifts (prey offered to females at mating) are attractive to the opposite sex in a hunting spider. While males were attracted to female draglines, females did not respond to male silk of any type. Females may be using silk to advertise themselves to secure matings and food through reception of nuptial gifts. If males can successfully locate females, attracting females through draglines may be unnecessary. The finding that males do not release attractant signals in the silk cover of their nuptial gifts further suggests that rather than attempting to increase their attractiveness by using chemical stimulation, males may be uniquely exploiting females’ interest in food through gift giving behaviour.

The role of silk in courtship and chemical communication of the false widow spider, Steatoda grossa (Araneae: Theridiidae)

In spiders, sex pheromones are often associated with silk produced by females, and function in mate attraction, recognition, and evaluation. Silk-bound pheromones typically elicit courtship behaviour in web-building spiders. Here we (1) describe courtship interactions of Steatoda grossa males with virgin or mated females, and (2) show that silk and methanol extracts of silk produced by virgin females trigger courtship behaviour (silk production) by males, whereas silk of mated females does not. Our results indicate that (1) virgin females produce a silk-bound sex pheromone, (2) males discriminate between virgin and mated females based on silk cues, and (3) male silk likely functions in sexual communication.

FemalePardosa milvinawolf spiders increase silk advertisements when in the presence of silk from courting males

Abstract Female wolf spider silk is known to elicit searching and courtship behavior among adult males, however variation in the types of silk females deposit, the context in which it occurs, and the role of male silk in courtship displays and female responses has rarely been examined. We measured male Pardosa milvina (Hentz 1844) silk deposition while performing courtship displays. We then examined whether female silk deposition changes when encountering silk produced from a courting rather than a non-courting male and compared these conditions to female silk deposition in the absence of male silk. We measured the quantity of three different types of silk (draglines, cord silk, and attachment disks) deposited by females across substrates previously occupied by a courting male, a non-courting male, or no male. Females significantly increased attachment disk deposition in the presence of silk from a courting rather than a non-courting male. Females also showed elevated dragline deposition in the presence o...

Web reduction by courting male black widows renders pheromone-emitting females' webs less attractive to rival males

Male adaptations that limit sperm competition include guarding females, applying mating plugs and chemically reducing the attractiveness or receptivity of females. In many web-building spider species, females attract males with silk-borne volatile pheromones. In widow spiders (Latrodectus, 30 species), the courting male often engages in web reduction behaviour during which he excises and bundles sections of the female's web and wraps them with his own silk. Hypothesized functions of this widespread behaviour include sexual communication (e.g. through dissemination of male sex pheromone) and/or decreasing the female's attractiveness to rivals. The latter function was previously demonstrated in a single spider species, Neriene litigiosa, but the extent to which web reduction may decrease male–male competition has never been quantified in the field. In a dense population of western black widows, Latrodectus hesperus, we ran mate attraction experiments to test the hypothesis that web reduction and/or male silk addition decrease web attractiveness to potential rivals. Webs reduced by males attracted three times fewer males than intact webs; webs with a similar proportion of silk experimentally removed attracted as many males as intact webs. However, the experimental addition of male silk did not affect the attractiveness of intact webs. We conclude that web reduction in black widows limits male–male competition by reducing the attraction of rival males to females' webs. This effect is probably mediated through targeted excision of pheromone-laden silk by courting males, possibly in combination with the male's silk forming a physical barrier to pheromone emission.

FemalePardosa milvinawolf spiders increase silk advertisements when in the presence of silk from courting males

Female wolf spider silk is known to elicit searching and courtship behavior among adult males, however variation in the types of silk females deposit, the context in which it occurs, and the role of male silk in courtship displays and female responses has rarely been examined. We measured male Pardosa milvina (Hentz 1844) silk deposition while performing courtship displays. We then examined whether female silk deposition changes when encountering silk produced from a courting rather than a non-courting male and compared these conditions to female silk deposition in the absence of male silk. We measured the quantity of three different types of silk (draglines, cord silk, and attachment disks) deposited by females across substrates previously occupied by a courting male, a non-courting male, or no male. Females significantly increased attachment disk deposition in the presence of silk from a courting rather than a non-courting male. Females also showed elevated dragline deposition in the presence of male silk but whether or not the male was courting had no effect on dragline deposition. Female cord silk deposition did not vary across treatments. Courting males produced significantly fewer attachment disks than non-courting males while dragline and cord silk deposition did not vary. We conclude that females can discriminate between silk from courting and non-courting males and increase attachment disk deposition in the presence of courting males. The number of male attachment disks deposited may be one mechanism by which females can discriminate between silk produced by courting rather than non-courting males.

Dyeing of male silk fibers with reactive dyes

A study of the dyeing behavior of male silk fibers (obtained from silk cocoons spun by male worms) was undertaken. Normal silk (composed of filaments made by male and female worms) was also dyed for comparison purposes. Physical and chemical characteristics of silk which may affect dyeing behavior were also investigated using scanning electron microscope (SEM) and Fourier transform infrared (FT‐IR) spectroscopy. From the results obtained in this research work, it can be concluded that male silk fibers tend to be finer than the normal silk fibers. The male silk fibers’ dye uptake was tested and found to be lower than that of normal silk. Adjustment of exhaustion salt and dyeing temperature to higher levels had significant improvement on dye uptake and K/S value for male silk.

Mate binding: male adaptation to sexual conflict in the golden orb-web spider (Nephilidae: Nephila pilipes)

To counter female resistance to mating and cannibalism, males of many animal species have evolved a variety of behavioural adaptations. Here we investigated a novel copulatory courtship behaviour, mate binding, in which the male deposits fine silk onto the female’s body in between copulation bouts, in an orb-web nephilid spider, Nephila pilipes. We hypothesized that mate binding might reduce female aggressiveness and sexual cannibalism and that both tactile and chemical cues play a role. We performed a series of mating trials, in which we blocked (1) the females’ tactile perception, (2) the females’ chemoreceptors, and (3) both types of communication. We also manipulated male spinnerets and thus male silk production. As predicted, mate binding reduced both female resistance to repeated mating and levels of sexual cannibalism. Our results suggest that both tactile and chemical cues are crucial for mate binding to succeed in rendering females less aggressive, but that tactile cues are more important. We conclude that mate binding prolongs total copulation duration, whereby the male maximizes his paternity. Therefore, mate binding may serve as a mechanism countering sexual conflict over repeated mating and sexual cannibalism.

Silk release by copulating Schizocosa malitiosa males (Araneae, Lycosidae): a bridal veil

We report release of silk threads by males of Schizocosa malitiosa (Tullgren 1905) during copulation. The silk is deposited over the female's front legs and near her mouthparts. Possible functions for this behavior could be inhibiting female aggressiveness through chemicals deposited on the silk, inducing female catalepsy during copulation or repelling other males. We propose future studies manipulating male silk release to test these hypotheses.

Thermal characterization of social vespid silk

In this paper we try to establish a link between the microclimate in the wasp nest and the structure and thermal stability of vespid silk. We suggest that there are at least two types of water that is absorbed by the silk of Oriental hornets, namely, surface water and intrinsic structural water. The release of both types of water was found to be reversible. The enthalpy values of the endothermic peaks associated with the release of water from different silk samples do not differ substantially and are in the range of 106 to 130 J g-1 for the Vespa orientalis male larvae silk (sample #1), Paravespula germanica (yellowjacket) worker larvae silk (#3) and Vespa orientalis nest envelope(#4). For the Vespa orientalis worker larvae silk (sample #2), however, it is twice as large (228 J g-1). This is in agreement with the increased total amount of absorbed water. The silk studied has a fibrilar structure with interconnecting surfaces overlying entire regions. It is assumed that the initial water loss stems from water evaporation from the coat of the fibers - a daily occurrence in the hornets' nest. Heating to above 70°C may result in structural changes in the silk core.

Role of Nosema bombycis infected male silk moths in the venereal transmission of pebrine disease in Bombyx mori (Lep., Bombycidae)

Abstract: The role of male moths of silkworm in the spread of pebrine spores (disease) has been studied using appropriate crossings and examining the multiplication of spores in the testis. Sections of infected testis reveal the presence of spores in the peritoneal sheath, spermatids but not in the sperm. A large number of spores was observed in the bursa copulatrix of the uninfected female moth mated with an infected male moth. This is a first record of venereal transmission of pebrine spores in silkworms. Venereally transmitted spores do not contribute to transovarial transmission, but give a false positive indication during mother‐moth examination. An alternative method for mother‐moth testing has also been discussed.

Signal conflict in spider webs driven by predators and prey

Variation in the sensory physiologies of organisms can bias the receptions of signals, driving the direction of signal evolution. Sensory drive in the evolution of signals may be particularly important for organisms that confront trade–offs in signal design between the need for conspicuousness to allow effective transfer of information and the need for crypsis of the signal to unintended receivers. Several genera of orb–weaving spiders include conspicuous silk designs, stabilimenta, in the centre of their webs. Stabilimenta can be highly visible signals to predators, warning them of the presence of a noxious, sticky silk web. However, stabilimenta can also be used by prey as a signal in avoidance of webs, creating a trade–off in signal visibility. I argue that the derived spectral properties of stabilimentum silk have resulted in part from this conflict. The innate colour preferences of insects, their ability to learn colours, and the spectral properties of flowers all suggest that the reflectance spectra of stabilimenta renders them relatively cryptic to many insect prey, while maintaining their visibility to vertebrate predators.