Agonistic behaviour of female Tegenaria atrica in the presence of different aged spiderlings

The agonistic behaviour of adult female T. atrica increases with increasing age of spiderlings until 80 days post-emergence, then decreases. In all cases, cannibalism of spiderlings increases markedly after completion of their pre-dispersal period with a correlation between the switch of behaviour, from tolerance to cannibalism, and a modification of individual’s cuticular compounds. Experiments that compare spiderlings weight and mobility indicate that female agonistic behaviour are always low with spiderlings in pre-dispersal period, and high with spiderlings in post-dispersal period. Female reproductive state and the weight/mobility of spiderlings are not the only factors controlling the adult female’s agonistic behaviour towards spiderlings on her web, as tactochemical information plays an important role in modulating agonistic behaviour after close contact between female spiders and spiderlings. The agonistic behaviour of females appears to correspond with a change in the increase of polar compound levels (methylesters and fatty acids) and the decrease of apolar compound levels (hydrocarbons) in spiderlings of different ages.     

Agonistic interactions, cuticular and hemolymphatic lipid variations during the foraging period in spider females Brachypelma albopilosa (Theraphosidae)

Agonistic behaviour and lipid state were examined in tarantula Brachypelma albopilosa females during the foraging period. Modulation of the agonistic behaviour of females was not connected to their body size. Results show that the agonistic pattern of females differed significantly from the predation pattern at the behavioural and lipid levels. Aggressive-foraging females had low predation behaviour. Quantitative lipid changes were observed in relation to agonistic behaviour and predation. The total lipid index was studied by colorimetric methods, and lipid compounds were analyzed by gas chromatography-mass spectrometry in cuticle and hemolymph of females. The lipid components were free fatty acids, methyl esters, cholesterol, and long-chain aliphatic hydrocarbons. Methyl esters were much more abundant in cuticular lipids; unsaturated free fatty acids (linoleic and oleic acids) and methyl esters (methyl linoleate and methyl stearate) predominated in the hemolymph. Spider aggression was positively correlated with lipid concentration (cholesterol, fatty acids, methyl esters and hydrocarbons) in the hemolymph and the levels of cuticular fatty acids. Lipid levels are hypothesized to have evolved as a regulatory factor of predation and agonistic behaviours in tarantula females.     

Identification and Synthesis of Branched Wax‐type Esters,Novel Surface Lipids from the Spider Argyrodes elevatus (Araneae: Theridiidae)

The analysis of cuticular extracts from the kleptoparasitic spider Argyrodes elevatus revealed the presence of unusual esters, new for arthropods. These novel compounds proved to be methyl‐branched long‐chain fatty acid esters with methyl branches located either close or remote from the internally located ester group. The GC/MS analysis of the prosoma lipid blend from the male cuticle contained one major component, undecyl 2‐methyltridecanoate ( 1 ). In contrast, four major wax‐type esters, 2‐methylundecyl 2,8‐dimethylundecanoate ( 2 ), 2,8‐dimethylundecyl 2,8‐dimethylundecanoate ( 3 ), heptadecyl 4‐methylheptanoate ( 4 ), and 14‐methylheptadecyl 4‐methylheptanoate ( 5 ), were identified in the lipid blend of female prosomata. Structure assignments were based on mass spectra, gas chromatographic retention indices, and microderivatization. Unambiguous proof of postulated structures was ensured by an independent synthesis of all five esters. Preferentially, odd‐numbered carbon chains pointed to a distinct biosynthetic pathway, different from that of common fatty acids, because one or two C₃ starter units are incorporated during the biosynthesis of all acid and alcohol building blocks present in the five esters. The striking sexual dimorphism together with the unique biosynthesis points to a function of the esters in chemical communication of the spiders, although no behavioral data are currently available to test this assumption.     

Relationships among food and contact signals in experimental group‐living young of Tegenaria atrica

Relationships between the quantity of diet, and group vs. individual rearing toward ontogenesis on degree of cannibalism and cuticular lipid profile of young Tegenaria atrica Araneae, Agelenidae were studied. Ad libitum diet increases the development rate and decreases cannibalism between conspecifics compared to a reduced diet. Individually reared young on the two diets showed no quantitative differences in cuticular lipid profile, but differences were observed in individual vs. group rearing modes. The ad libitum–fed grouped young spiders had notably increased quantities of palmitic acid, 13,17‐,11,17‐, and 9,17‐dimethylhentriacontane, methyl oleate, and n‐heptatriacontane over the reduced diet, cannibalistic group. Arch. Insect Biochem. Physiol. 42:188–197, 1999. © 1999 Wiley‐Liss, Inc.     

Sexual receptivity of Anastrepha obliqua (Diptera: Tephritidae) wild females affected by nutrition and egg load

The influence of feeding, egg load and stage of ovarian development on the sexual receptivity of some insect species has been reported. This work investigated the effects of different brewer's yeast concentrations in the diet offered to females of West Indian fruit fly, Anastrepha obliqua, on their sexual receptivity. Wild females were fed on artificial diets containing 2.0 g brewer's yeast per 100 mL of water (low‐yeast diet, LY diet), 6.5 g yeast per 100 mL of water (high‐yeast diet, HY diet) or only sucrose (Su diet) and then placed with the males. Female sexual receptivity tests were carried out in acrylic boxes in the laboratory under controlled conditions (temperature, humidity and light). Females fed on the HY diet were more sexually receptive to male courtship than the other females. Additionally, when fed on the same diet (HY diet), those females with higher egg load were more sexually receptive. The data suggest that the ingestion of a protein source is essential for increasing sexual receptivity and that egg load is the most important factor affecting sexual receptivity of A. obliqua females.     

Changes in male sexual responses from silk cues of females at different reproductive states in the wolf spider Schizocosa malitiosa

Male wolf spiders are capable of recognising sexual signals associated with female silk threads. In the wolf spider Schizocosa malitiosa variations in female receptivity have been studied, but changes in female silk attractiveness remain unknown. We analysed the sexual responses of adult males (leg shaking, papal drumming and searching) exposed to silk cues from subadult, virgin and mated females of different ages, and females that were or were not carrying an egg-sac. Penultimate and recently moulted adult females elicited low levels of male sexual behaviour, while those of virgin females (21–40 days old) were the most attractive. Silk threads slowly became less attractive after mating. Cues from females carrying an egg-sac as well as females in the inter egg-sac period were fairly attractive. The low attractiveness of recently moulted females disagrees with their high sexual receptivity. In contrast, females continued to elicit strong male responses during a 10-day period after mating, despite the fact that they immediately become sexually reluctant, suggesting strong selection for male searching ability. Low attractiveness during the egg-carrying period could reflect the fact that females do not require any further sperm. Concordances and discordances between attractiveness and sexual receptivity suggest that they respond to different physiological mechanisms.     

Consequences of sexual size dimorphism on energetics and locomotor performance of Grammostola rosea (Araneae; Teraphosidae)

Most male spiders are smaller than females; during sexual maturity, males change their behaviour, abandoning their web or nest to seek out receptive females actively, whereas females stalk prey near their web or nest and tend not to move away from it. Considering this behavioural difference to be associated with increased locomotor activity at maturity, it may be hypothesized that males will have traits that increase locomotor performance. The present study examines the kinetics and energetics of the movements of the mygalomorph spider Grammostola rosea Walckenaer, a large spider with sexual size dimorphism. It is found that males have a higher maximum aerobic speed, average speed, distance travelled and critical angle of climbing than females, indicating better performance. Males also have lower costs of transport than females. These results support the hypothesis that sexual dimorphism in wandering spiders with active males, which are characterized by smaller body size and longer legs than the larger and more static females, is associated with low transport cost, high velocity and better locomotor performance.     

Signalling and Sexual Conflict: Female Spiders Use Stridulation to Inform Males of Sexual Receptivity

The use of acoustic signals by males during courtship and mating is well known. Nevertheless, their association with female unwillingness to mate is much less studied. In spiders, stridulation during sexual interactions is relatively common in some groups, but mainly restricted to males. In the pholcid spider Holocnemus pluchei, both sexes have stridulatory organs. The aims of the present work were (1) to establish whether female stridulation occurs during intra‐ and inter‐sexual interactions, (2) to determine whether female reproductive status affects the likelihood that she will stridulate and (3) to determine whether female stridulation is influenced by male sexual behaviour. We found that female stridulation usually occurs both during intrasexual interactions and, most frequently, during intersexual interactions. Females with more previous matings stridulated more frequently. Stridulation intensity was higher in females that did not accept new copulations compared with those that copulated. Female stridulation did not vary in elaborated and non‐elaborated courtship. Thus, females use stridulation to communicate levels of sexual receptivity. It is also possible that females use stridulation to indirectly assess male ability to persist and persuade.     

Cuticular hydrocarbons as contact sex pheromone in the parasitoid Dibrachys cavus

Cuticular hydrocarbons (CHCs) cover the cuticle of virtually any insect and do not only protect them from desiccation, but also possess various communicative functions. Previous studies suggested a function as contact sex pheromones in the parasitic wasp family Pteromalidae, but further species need to be studied before more general conclusions are possible. Here, we demonstrate a contact sex pheromone in females of Dibrachys cavus (Walker) (Hymenoptera: Pteromalidae). Males of this parasitoid were arrested on cadavers of 1‐ to 2‐day‐old females, but neither on newly emerged females nor on males. Extracts from 1‐ to 2‐day‐old females and non‐polar fractions were also behaviorally active suggesting a non‐polar contact sex pheromone. Chemical analyses of bioactive and non‐active CHC profiles by gas chromatography–mass spectrometry and subsequent principal component analysis (PCA) revealed that the bioactive profiles from 1‐ to 2‐day‐old females were clearly distinguishable from all other profiles. Among the chemicals showing the strongest impact in the PCA were the two 3‐methylalkanes 3‐methylnonacosane and 3‐methylhentriacontane, which were absent or trace components in the inactive profiles and whose relative amounts increased in females when they became sexually attractive. The putative function of 3‐methylalkanes as key components of the contact sex pheromones in Pteromalidae is discussed.     

Different positions of males approaching towards females and male choices between webs with and without stabilimentum in a sexually cannibalistic orb‐web spider,Argiope bruennichi

Males of the orb‐weaving spider species Argiope bruennichi (Araneidae) are frequently victims of sexual cannibalism. Therefore, a male spider approaching a female should have strategies to avoid being killed before copulation. Our present field study detected six types of A. bruennichi male positions vis‐à‐vis the female web. In 78% of situations (39/50), only one male attached to a female. Two males attached to the same female in 11 cases. We observed no cases of three or more males on the same female web. We most commonly observed the situation of a male staying in its own web and connecting to a female's web with its silk thread (46% of cases). Of the female webs chosen by males, 68% were decorated with both an upper and lower portion of stabilimentum – a conspicuous white silk structure that reflects much more ultraviolet light than other spider silks in the web. Only 14% (7/50) of the selected webs lacked stabilimentum. Therefore, we conducted an experiment to investigate the males' choice between females' webs with and without stabilimentum. Of the 24 males used in the experiment, 10 chose webs with stabilimentum. This result did not show a strong preference of the male for stabilimentum between equally sized webs, and thus did not support an earlier suggestion that stabilimentum in A. bruennichi might function to guide males to females for mating.     

Effect of the mating plug on female chemical attractiveness and mating acceptance in a scorpion

After mating, females may experience a decline in sexual receptivity and attractiveness that may be associated with changes in the production and emission of sex pheromones. In some cases, these changes are produced by chemical substances or structures (e.g., mating plugs) produced by males as a strategy to avoid or reduce sperm competition. In scorpions, sex pheromones may be involved in finding potential mates and starting courtship. Here, we tested the hypothesis that the males of Urophonius brachycentrus, a species that produces a mating plug, use chemical communication (sex pheromones) to detect, localize, and discriminate females according to their mating status (virgin or inseminated), aided by chemical signaling. We also explored the effect of extracting of the mating plug on chemical communication and mating acceptance. We used Y‐maze olfactometers with different stimuli to analyze male choice and exploration time. To evaluate mating acceptance, we measured the attractiveness and receptivity of females of different mating status. We found that chemical communication occurs through volatile pheromones, but not contact pheromones. Males equally preferred sites with virgin or inseminated females with removed mating plug. In turn, females with these mating statuses were more attractive and receptive for males than inseminated females. This study suggests that the mating plug significantly affects female chemical attractiveness with an effect on volatile pheromones and decreasing sexual mating acceptance of females. The decline in the female's sexual receptivity is a complex process that may respond to several non‐exclusive mechanisms imposed by males and strategically modulated by females.     

Male adaptations to minimize sexual cannibalism during reproduction in the funnel‐web spider Hololena curta

Males of many spider species risk being attacked and cannibalized while searching for, courting, and mating with conspecific females. However, there are exceptions. We show that the funnel‐web spider, Hololena curta, has 3 adaptations that minimize risk to males during courtship and mating, and enhance reproductive success. First, males detected chemical or tactile signals associated with webs of virgin females, and differentiated them from webs of mated females, enabling males to increase encounter rates with virgin females and avoid aggressive mated females. Second, males produced stereotyped vibrational signals during courting which induced female quiescence and suppressed female aggression. Third, when touched by males, sexually receptive females entered a cataleptic state, allowing males to safely approach and copulate. Because males can mate multiple times and the sex ratio in natural populations of H. curta is female biased, overall reproductive output is likely increased by males of this species avoiding sexual cannibalism.     

Small Organic Solutes in Sticky Droplets from Orb Webs of the Spider Zygiella atrica (Araneae; Araneidae): β‐Alaninamide Is a Novel and Abundant Component

In northeastern North America, Zygiella atrica often build their orb webs near the ocean. We analyzed individual field‐built Z. atrica webs to determine if organic low‐molecular‐mass solutes (LMM) in their sticky droplets showed any unusual features not previously seen in orb webs of other species living in less salty environments. While two of the three most abundant organic LMM (putrescine (butane‐1,4‐diamine) and GABamide (4‐aminobutanamide)) are already well‐known from webs of inland spiders, the third major LMM, β‐alaninamide (3‐aminopropanamide), a homolog of GABamide, has not been detected in sticky droplets from any other araneoid spiders (27 species). It remains to be established, however, whether or not use of β‐alaninamide is related to proximity to saltwater. We observed variability in organic LMM composition in Z. atrica webs that appeared to be influenced more by an undetermined factor associated with different collecting locations and/or collection dates than by different genders or instars. Shifts in composition when adult females were transferred from the field to the laboratory were also observed. Structural similarities and inverse correlations among β‐alaninamide, GABamide, and N‐acetylputrescine suggest that they may form a series of LMM fulfilling essentially the same, as yet unknown, role in the webs of those species in which they occur.     

Mated Redback Spider Females Re-Advertise Receptivity Months after Mating

In many species, selection acts on males to recognize female reproductive status at a distance using pheromones. Unmated females may actively seek to attract males; however, mated females may become cryptic to avoid attracting additional males if multiple matings are costly. Although females of many species cease pheromone production after mating, it is often unclear whether this is a strategic part of a female reproductive strategy, or whether this is because of chemical manipulation by males. If variation in pheromone production is part of the female’s strategy, then we predicted mated females should eventually re‐advertise receptivity if the benefits of multiple mating increase with time since copulation (e.g. because of sperm depletion). Here, we tested this prediction in Australian redback spiders (Latrodectus hasselti). First, we replicated earlier results by showing that virgin males discriminate female maturity and mating status based exclusively on web‐borne chemicals. Our results show this difference must arise from a change in chemical deposition in the web as we controlled for web volume differences between mated and virgin females. Male activity on extracts from webs of virgin females exceeded activity on a solvent control and on extracts of webs of just‐mated females—confirming that female redbacks cease pheromone production immediately after mating. Second, we tested a new prediction that mated females might re‐advertise receptivity near the end of their normal breeding season to replenish diminished sperm stores prior to overwintering. Consistent with the prediction of strategic advertisement, we show that male activity on extracts from females’ webs increased significantly 3 mo after the female first mated (typical length of the breeding season). Thus, these females had begun to add pheromone to their web again. At this time, 26% of these females re‐mated with a second male. If females re‐advertise receptivity to ensure adequate sperm stores, then we predicted a positive relationship between female reproductive output during the 3‐mo interval after copulation and the subsequent intensity of male response to web extracts. However, differences in male activity time were not related to the total number of spiderlings or the number of egg sacs a female had produced during the 3‐mo interval after the first copulation. This result could arise if male chemical manipulation of female receptivity decreases with time after copulation, or if the testing interval used in our study was too long to reveal variation in sperm depletion in females. Thus, although our results are consistent with the idea that females strategically alter pheromonal advertisement, we cannot distinguish this from the hypothesis that female receptivity arises from chemical manipulation by males.     

Changes in cuticular hydrocarbon composition in relation to age and sexual behavior in the female Calliphora Vomitoria (Diptera)

Qualitative and quantitative changes in epicuticular hydrocarbon synthesis/release were observed during the first gonadotrophic cycle of Calliphora vomitoria.Up to 12 hours after eclosion, hydrocarbon synthesis/release is low, with little change in the relative proportions of the compounds detected. At 24 hours there is a marked increase in hydrocarbon synthesis/release, especially in the monomethylalkanes (both absolute and relative amounts). Between 48 and 72 hours, hydrocarbon synthesis stabilizes. At 83 hours, two hydrocarbon patterns can be distinguished, depending on the state of receptiveness of the females.The results show for the first time that differences in age, sexual attractiveness and receptivity are accompanied by characteristic changes in cuticular n-alkanes and mono-methylalkanes.     

Are you Paying Attention? Female Wolf Spiders Increase Dragline Silk Advertisements When Males do not Court

Females of many spider species invest in chemical advertisements to attract males, yet variation in investment relative to the presence or quality of males remains poorly understood. Males of the wolf spider Pardosa milvina court females longer and more intensively when in contact with female silk and also court more intensively when encountering silk from virgin rather than mated females; therefore, females may use silk as a medium to advertise their receptivity to mate. We estimated female investment in advertisements by measuring variation in the quantity and type of silk deposited by females in the presence or absence of males and among males that varied in their courtship intensity. We measured dragline silk, cord silk, and attachment disk deposition from females on gridded sheets of paper in response to four stimuli over a 30‐min period (n = 39/treatment): (1) an intensively (high) courting male with access to female silk, (2) a weakly courting or non‐courting male (low) without access to female silk, (3) no male present, but female silk present (silk control), and (4) no stimulus present (control). Females produced significantly more dragline silk and significantly less cord silk in the presence of low‐courting males compared to any other treatment, but we found no difference in attachment disk deposition across treatments. Our results suggest that females invest more heavily in dragline deposition when encountering low‐courting males. Additional studies are necessary to determine the relative role of different silk types in male–female sexual communication.     

Female fecundity and offspring survival are not increased through sexual cannibalism in the spider Larinioides sclopetarius

Many hypotheses explaining the evolution and maintenance of sexual cannibalism incorporate the nutritional aspect of the consumption of males. Most studies have focused on a fecundity advantage through consumption of a male; however, recent studies have raised the intriguing possibility that consumption of a male may also affect offspring quality. In particular, recent studies suggest prolonged survival for offspring from sexually cannibalistic females. Here, we measured the protein and lipid content of males compared to insect prey (crickets), quantified female nutrient intake of both prey types and finally assessed how sexual cannibalism affects female fecundity and spiderling quality in the orb‐web spider Larinioides sclopetarius. We found no evidence that sexual cannibalism increased fecundity when compared to a female control group fed a cricket. Contrary to previous studies, spiderlings from females fed a male showed reduced survival under food deprivation compared to spiderlings from the control group. Offspring from females fed a male also tended to begin web construction sooner. The low lipid content of males compared to crickets may have reduced offspring survival duration. Whether additional proteins obtained through consumption of a male translate to enhanced silk production in offspring requires further investigation.     

Behavioral correlates to gonadal state in the lizard, Anolis carolinensis

Female Anolis carolinensis of unknown reproductive condition were introduced into cages containing a sexually active male and the resulting sexual behavior was noted. Female sexual receptivity was found to be correlated with the stages of follicular maturation. These results suggest that sexual receptivity in female A. carolinensis is restricted to a time immediately preceding the ovulation of each follicle and is dependent upon hormonal conditions normally arising during follicular development. Evidence is offered to suggest that during the breeding season, female sexual receptivity is rhythmical and contingent upon the cyclic ovarian changes peculiar to lizards of this genus.     

Pheromones exchanged during mating: a mechanism for mate assessment in Drosophila

Many insect species are sexually dimorphic for volatile compounds associated with the cuticle. In these species, females may acquire volatile compounds from males through direct contact with males during mating. In some cases, these compounds function as antiaphrodisiacs, which inhibit subsequent male precopulatory behaviour. During mating, males may also acquire female compounds, which normally stimulate males to court. Contact during mating thus results in a mutual exchange of compounds usually found primarily, or exclusively, on one or the other sex. Drosophila melanogaster is a sexually dimorphic dipteran species in which predominant male and female cuticular hydrocarbons are mutually exchanged during mating. Using synthetic compounds, the effect of this exchange on the post-mating sexual attractiveness of both males and females was tested. The sex-predominant hydrocarbons acquired during mating decreased the attractiveness of both males and females to members of the other sex. Mated females are courted less actively than virgins, and are usually unwilling to re-mate. Similarly, recently mated males are less attractive to females than virgin males are, and may be less fertile. Thus, cuticular hydrocarbons acquired by the other sex during mating could allow both males and females to assess the immediate reproductive potential of prospective mates.     

Ovarian development of Agrilus planipennis: effects of age and mating status and influence on attraction to host volatiles

Emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is a major pest of ash trees, Fraxinus spp. (Oleaceae), in North America. This study investigated the timing of reproductive development in female beetles and the influence of female reproductive maturity on attraction to host volatiles. Based on dissections of females of increasing age, females with access to males for mating, and thus presumed mated, developed mature eggs only after 18–24 days. In contrast, female beetles reared without access to males, and thus unmated, did not develop mature eggs at any age. Chemical analysis of cuticular hydrocarbons detected the contact sex pheromone, 9‐methyl‐pentacosane, in cohorts of females which were 8–9 days old and older, supporting previous research that this compound signals sexual maturity to males. Results from field‐trapping bioassays demonstrated that stage of female reproductive maturity influenced their attraction to host volatiles: females caught on traps baited with foliar volatiles contained eggs and ovarioles that were significantly less developed than those on traps baited with bark sesquiterpenes. However, our results revealed that females with immature stages of ovarioles and undeveloped eggs, such as those observed in unmated females, were rarely ever caught on traps baited with either of the host volatile lures. Further research on host compounds attractive to immature females is critical for early detection and possible control of A. planipennis populations during the extended pre‐oviposition period.