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. Received: 29 December 1997 / Received in revised form: 23 October 1999 / Accepted: 13 December 1999     

Male signaling behavior and sexual selection in a wolf spider (Araneae: Lycosidae): a test for dual functions

Male signaling behaviors are often studied in a single context but may serve multiple functions (e.g., in male–male competition and female mate choice). We examined the issue of dual function male signals in a wolf spider species Schizocosa ocreata (Hentz) that displays the same species-specific signaling behaviors in both male–male and male–female contexts. These signaling behaviors have been described as either aggression or courtship according to the context observed. We tested the possibility of dual functions by comparing the relationship between behaviors and outcome of male–male contests (winner/loser) and male–female mating encounters (mating success). Frequency, rate, and mean duration of signaling behaviors did not vary with outcome of male–male contests, which appears instead to be based upon relative size and body mass. Winners of contests had significantly greater body mass than losers, and greater mass relative to opponents was significantly associated with probability of winning. Overall, signaling rates were much higher in male–female interactions than in male–male contests and were higher for males that successfully mated than for those that did not mate. Mean duration of some male displays was also greater for males that successfully mated. However, male size was not associated with probability of mating. Taken together, results suggest an intersexual selection context for the current function of male signals in these wolf spiders and that increased display vigor is associated with male mating success.     

Kinship and food availability influence cannibalism tendency in early-instar wolf spiders (Araneae: Lycosidae)

For potentially cannibalistic animals such as spiders, the ability to recognize and avoid kin and/or preferentially cannibalize non-relatives would permit exploiting conspecifics as prey while minimizing loss of inclusive fitness. We investigated the effects of relatedness and availability of alternative food on cannibalism tendency in pairs of juvenile Hogna helluo (Walckenaer), a North American wolf spider (Araneae: Lycosidae). For second-instar spiderlings (dispersing stage), cannibalism was more likely among pairs of non-sibs than pairs of sibs and, interestingly, was also more likely when other prey were available. We found no evidence of increased cannibalism in pairings involving broods of greatest average size disparity, indicating that size differences are unlikely to explain differences in cannibalism tendency. Additionally, the relative number of deaths from cannibalism or other causes did not increase with increasing risk of starvation. For third-instar spiderlings, which had lived independently of their mother and sibs following dispersal, cannibalism rates were very high in all treatments and there were no significant effects of relatedness or food availability. Our results suggest that spiders with predominantly solitary lifestyles may bias cannibalism toward non-kin during the juvenile associative period, and that this effect is lost in the subsequent instar. Results are discussed in the context of several potential mechanisms that might result in differential cannibalism.Communicated by M. Elgar     

Limb regeneration and subsequent asymmetry in a male secondary sexual character influences sexual selection in wolf spiders

Males of the brush-legged wolf spider Schizocosa ocreata (Hentz) have conspicuously decorated forelegs used in courtship and agonistic displays. Approximately one in five juvenile males has a missing or regenerating foreleg, and regeneration of a leg lost during development usually results in the absence of a decorative tuft on that leg. The subsequent asymmetry in this male secondary character significantly decreases success in both courtship of females and male-male agonistic interactions. Experimental removal of tufts from one leg of previously successful symmetric males produces similar results. As a test for concomitant behavioral effects, female spiders were shown video images of a courting male with symmetric tufts and the same video image altered to have asymmetric tufts. Female receptivity to the asymmetric video image was lower. In contrast to fluctuating asymmetry resulting from developmental instability, leg tuft asymmetry in S. ocreata most likely arises from a single event during ontogeny – possibly leg loss from an aggressive or predator encounter  – and may serve as a quality indicator in female mate choice. Received: 27 July 1995/ Accepted after revision: 19 November 1995     

Determinants of paternity success in the spider Pholcus phalangioides (Pholcidae: Araneae): the role of male and female mating behaviour

In double mating experiments, we examined whether and to what extent various male and female behavioural traits influence the course of mating and fertilization success in the cellar spider. In males, we focussed on pre-copulatory behaviour and on the rhythmic twisting movements that the male performs with his pedipalps during copulation. In females, we investigated remating decisions and the effect of female termination of copulation. Second males fertilized a high proportion of the eggs (P ₂: median 89%) despite much shorter second matings, with high variation in relative paternity success. The number of pedipalp movements (PPMs) of either male was a better predictor of paternity than copulation duration. Our results suggest that in second matings, PPMs help to remove sperm from previous males, whereas in first matings a high number of PPMs enhances fertilization success, either due to numerical sperm competition or cryptic female choice. Furthermore, we found a negative male age effect on paternity in second matings, implying that age-related deterioration of spermatozoa may promote variation in fertilization success. Female receptivity decreased significantly in second matings; only 70% of the females remated. Females that accepted a second copulation were found to terminate these much earlier and with higher probability than first matings. This suggests that the intensity of conflict between the sexes is higher in second matings. Increased intensity of sexual conflict may be responsible for stronger selection on male traits, as pre-copulatory behaviour and age only affected male copulatory performance and paternity in second matings. Electronic Publication     

Sexual signalling and viability in a wolf spider (Hygrolycosa rubrofasciata): measurements under laboratory and field conditions

This study examined the crucial prediction of the conditional-handicap theory, the relationship between male sexual trait size and male viability, in the wolf spider Hygrolycosa rubrofasciata. In this species, males court females by drumming dry leaves with their abdomen, and males with the highest drumming rate enjoy highest mating success. We determined male drumming rate, body mass, and mobility, which reflects mate-searching activity, in relation to male survival. Because it is often difficult to know how results obtained from laboratory studies reflect the natural world, particularly when the measured variable is survival, we repeated our study in both laboratory and field conditions. Males drumming at the highest rate survived better than males drumming at a lower rate in both laboratory and field conditions. These results are in accordance with the predictions of conditional-handicap models of sexual selection. Survival was independent of male body mass and there was no significant correlation between male drumming activity and body mass. However, large males moved further than smaller males, and males moving longer distances lost less mass than those moving shorter distances. These results suggest that, moving, and consequently mate-searching activity, may be a condition-dependent trait and that there may be a advantage for large males in mate searching. Received: 22 October 1998 / Received in revised form: 28 January 1999 / Accepted: 14 February 1999     

Factors influencing cannibalism in the wolf spider Pardosa agrestis (Araneae, Lycosidae)

Cannibalistic tendencies are well known in spiders and may be a significant factor influencing population size. The wolf spider, Pardosa agrestis, is the dominant non-web-building spider in a wide range of central European agricultural habitats. Preliminary field observations indicated an extended reproductive period, which results in a very wide size distribution of juvenile instars. We hypothesised that if cannibalism is enhanced by differences in size, especially during periods when prey is scarce, these populations might be susceptible to cannibalism in an ecologically significant way. Laboratory studies were conducted on juvenile P. agrestis in arenas. We analysed the following specific aspects of cannibalism: (1) the effect of the weight ratio between the opponents; (2) the effect of weight per se, and (3) the role of hunger level in determining cannibalistic tendencies of spiders. The role of weight and hunger were analysed in separate experiments, in both cases by controlling for the other variable. The results showed that cannibalism was strongly positively correlated with both weight ratio and hunger, but absolute size/age of an individual could not predict the occurrence of a cannibalistic event. These experiments generated the plausible hypothesis that cannibalism might be an important phenomenon in the regulation of real populations, which should be tested specifically in future field experiments. Received: 15 December 1997 / Accepted after revision: 10 October 1998     

Effects of male dominance and courtship display on female choice in the ring-necked pheasant

Male traits and behaviours acting in mate choice and intrasexual competition are expected to be congruent. When studying their evolution, this often makes it difficult to differentiate between these two components of sexual selection. Studies are therefore needed on mate choice in conjunction with the role of displays and dominance. We present the results from two experiments conducted to investigate the effects of male dominance and courtship displays on female choice in the ring-necked pheasant, Phasianus colchicus, controlling for differences in morphological male traits. We found: (1) different courtship behaviours had different effects on female choice: females were mainly attracted by the feeding courtship behaviour, while another courtship display (the lateral display) was effective in producing the copulation-acceptance response by the females; (2) subordinate males performed the courtship behaviour before females less frequently than dominant males, and females reinforced intrasexual selection by choosing dominant males, and (3) subordinate males in visual contact with a dominant became less attractive to females. The results support the idea (armament-ornament model) that female pheasants may benefit from using traits selected in male-male competition as clues for mate choice. Received: 23 October 1997 / Accepted after revision: 7 October 1998     

Immune function, dominance and mating success in drumming male wolf spiders Hygrolycosa rubrofasciata

In this study, we provide a piece of experimental evidence that immune function is related to dominance and mating success in wild caught male wolf spiders, Hygrolycosa rubrofasciata. In the mating season, H. rubrofasciata males are actively searching for receptive females, and while searching males often engage in agonistic behavior (i.e., agonistic drumming signals, chases, and fights) with each other. The present results demonstrate that dominant males had higher lytic activities in their hemolymph than subordinates. Lytic activity estimates the concentration of antimicrobial peptides with lysozyme-like activity in hemolymph, which have been shown to play an important role in defense against bacteria, viruses, and fungi. Dominants also had higher courtship drumming rates than subordinates. Moreover, winners in mating competition had higher lytic activities than losers, but this was measured nonindependently of dominance status. Among males with mating failure, there was a moderate negative correlation between encapsulation rate and courtship drumming rate, suggesting that low quality males might not be able to bear the immunological costs of courtship behavior. These results suggest that females might gain immunological benefits by preferring vigorous males.     

Prior encounters with the opposite sex affect male and female mating behavior in a wolf spider (Araneae,Lycosidae)

Mate availability can vary widely in nature depending upon population density and sex ratio and can affect the ability of individuals to be selective in mate choice. We tested the effects of prior encounters with the opposite sex (i.e., exposure to the opposite sex either with or without mating) on subsequent mating behavior in two experiments that manipulated mate availability for both males and females in the wolf spider, Hogna helluo. The probability of mating in the experimental trial depended upon whether the prior encounter involved mating or not, and males and females responded in opposite directions. Exposure without mating resulted in a higher subsequent frequency of mating for females and a lower subsequent frequency of mating for males, while prior mating experience resulted in a lower frequency of female remating and a higher frequency of male remating. Prior exposure without mating did not affect female aggression. However, mated females engaged in precopulatory cannibalism more frequently than virgins. Mated males escaped postcopulatory cannibalism more frequently than virgins. Our results show that males respond to exposure without mating in the expected manner. However, prior mating (1 week earlier) had unexpected effects on males, which may be due to mated males being of higher quality. There were little or no effects of the size of the prior exposure individual or mate on subsequent mating behaviors. Further research is needed to determine why different species use different degrees of prior information in mate choice.     

Preference for male traits in female wolf spiders varies with the choice of available males,female age and reproductive state

Individual variation in female preference for male traits may influence mate choice, especially if benefits and costs of choosiness vary with the range of available males or reproductive timing. We examined variation in female preference for male leg tuft size in Schizocosa ocreata (Hentz) wolf spiders with video playback. Dichotomous (simultaneous) choice test experiments included all possible combinations of four stimuli (i.e., modified versions of the same video male stimulus): average tuft size (control), reduced (−25%), enlarged (+25%), and no tufts (removed). Females exhibited a directional preference for larger tuft size independent of the nature of the choice (except for reduced tufts vs no tufts where no difference was seen). Female preference in the short term (over a period of 4 days) was also highly repeatable for control vs reduced tufts, but not for control vs enlarged tufts. Responses of females in ‘no-choice’ presentations of a single (control) male stimulus varied with age post-maturity; females were less receptive in weeks 1 and 2, highly receptive at week 3, and less thereafter. Mated females were least receptive and most aggressive towards a male stimulus. Females offered choices repeatedly at different ages post-maturity consistently preferred the control male vs reduced tufts over all 3 weeks but varied in their preference for enlarged tufts vs control male. In the first 2 weeks, females preferred the enlarged tuft male stimulus, but showed no preference by the third week. Females tested in week 4 showed no preference in either choice. Results suggest that the potential interaction between female preference for male traits and female reproductive timing may be a critical consideration in mate choice.     

Sexual selection in the northern pintail (Anas acuta): the importance of female choice versus male-male competition in the evolution of sexually-selected traits

We experimentally studied the relative importance of plumage, dominance status, and courtship behavior in determining male pairing success in the northern pintail Anas acuta and assessed whether these traits function in female choice, male-male competition or both. In an experiment (experiment IA) that eliminated the confounding effects of male-male competition and social courtship, females chose males with pure white breasts and colorful scapular feathers. When the same group of birds were free to interact (experiment 1B), male behavior was more important: females chose males that courted them intensely and were attentive to them, although preferred males again had whiter breasts and more colorful scapulars. In a second experiment (experiment 2), testing the effect of age on pairing success, females showed a significant preference for 2-year-old males over yearlings: 2-year-old males courted more and were more attentive to the female than yearlings; they were also more colorful than yearlings in a number of plumage measurements. Although males (in both experiments 1B and 2) were aggressive to one another while courting the female and dominant males were sometimes able to exclude subordinates from social courtship, contrary to expectation, we found no relationship between initial dominance rank and pairing success or dominance rank and age. In addition, dominance was not correlated with any of the morphological traits measured. Once chosen, however, subordinate males typically initiated fights with the higher-ranked male(s) and quickly achieved dominance. These results suggest that (1) females choose males based on a suite of morphological and behavioral characteristics, (2) male dominance relationships do not constrain active female choice, (3) a male's position in a dominance hierarchy is largely a result rather than a cause of female choice, and (4) female choice plays a more significant role than male-male competition in the evolution of several secondary sexual traits in male northern pintails.     

Environmental chemical cues associated with prey and subsequent prey preference in the wolf spider Hogna carolinensis Hentz (Araneae,Lycosidae)

The purpose of this study was to determine if environmental chemical cues associated with prey can affect subsequent prey choice in wolf spiderlings (Hogna carolinensis). After emergence from the egg sac, three groups of 10 spiderlings were each fed for one-week on one of three naturally-occurring prey species: group 1 fed on nymphs of the field cricket Gryllus pennsylvanicus; group 2 (house cricket, Acheta domesticus); group 3 (mole cricket, Gryllotalpa hexadactyla). They were then tested for subsequent prey preference in choice tests conducted in a plastic arena. Each spiderlings was presented simultaneously with one individual of each prey species in a randomized design. Spiderlings exhibited a significant first preference for the original diet. Thus, experience with certain foods (environmental chemical cues) encountered by newly hatched spiderlings can affect subsequent prey preference in this species.     

Factors influencing sexual cannibalism and its benefit to fecundity and offspring survival in the wolf spider Pardosa pseudoannulata (Araneae: Lycosidae)

Sexual cannibalism is hypothesized to have evolved as a way to obtain a high-quality meal, as an extreme mate choice or as a consequence of female aggressive spillover. Here, we examined underlying factors likely to influence sexual cannibalism in the wolf spider Pardosa pseudoannulata (Bösenberg & Strand, 1906) from China, including mating status, female egg-laid status, female hunger level, female adult age and mate size dimorphism. The results showed that about 10 % of P. pseudoannulata virgin females cannibalized the approaching males before mating and that 28 % of P. pseudoannulata virgin females immediately cannibalized the males after mating. No incidents of sexual cannibalism during copulation were observed. Before mating, previously mated females and starved females tended to engage in significantly higher rates of attacks compared to virgin and well-fed females. Females that had laid egg sacs tended to engage in a significantly higher rate of attacks and sexual cannibalism than virgin females before mating. Regardless of pre- or post-mating, there was a strong positive relationship between mate size dimorphism and the occurrence of sexual cannibalism. We also tested the effects of sexual cannibalism on the fecundity of cannibalistic females and the survival of their offspring. Our results indicated that sexual cannibalism affected positively the offspring survival of cannibalistic females, but not fecundity. Our findings support the hypothesis that sexual cannibalism has evolved as an adaptive component of female foraging strategy and that it benefits offspring survival as a result of paternal investment.     

Sexual dimorphism in amphipods: the role of male posterior gnathopods revealed in Gammarus pulex

In the mate-guarding amphipod, Gammarus pulex, the enlarged male posterior gnathopods have been variously suggested to function to grasp and subdue the female, to be used as weapons in fights between males, to signal to the female the male presence and stimulate moult accelaration, egg development or egg extrusion. These hypotheses were tested in a series of experiments, the results of which reveal an unexpected function. Ablation of the posterior gnathopods of males showed that they were neither necessary for, nor advantageous in, establishment and/or maintenance of precopula mate guarding, with or without competition with intact males. Furthermore, these appendages do not function to advance female moult, or stimulate egg development or extrusion. However, only males with intact posterior gnathopods were able to copulate. We also show that females require a full copulation of several bouts to extrude eggs. We conclude that the function of the posterior gnathopods is to facilitate copulation and suggest future studies focus on the selective pressures acting on copulating males.     

Female distribution affects mate searching and sexual selection in male northern water snakes (Nerodia sipedon)

Mating systems and sexual selection are assumed to be affected by the distribution of critical resources. We use observations of 312 mating aggregations to compare mate-searching success of male northern water snakes (Nerodia sipedon) in two marshes in which differences in mating substrate availability resulted in more than fourfold differences in female dispersion. Reproductive males had significantly larger home ranges where females were dispersed than where females were clumped. The number of females encountered by males increased significantly with male home range size where females were dispersed, and decreased significantly where females were clumped. Where females were clumped, males were more likely to encounter other males when they located females. We found no evidence in either population that mate searching was energetically expensive or that males with relatively more energy had larger home ranges. However, males with greater fat reserves at the start of the season participated in more mating aggregations when females were dispersed, suggesting that fat reserves could affect a male’s willingness to attempt mating or to persist in aggregations. When females were dispersed there was weak stabilizing selection acting to maintain male body size (β=–0.14), but strong directional selection favoring larger (β=0.50) and fatter (β=0.37) males. Over 7 years, the intensity of selection favoring larger males varied substantially (β=0.14–1.15), but that variation was not related to variation in the operational sex ratio. We found no evidence of directional selection on either body size (β=0.05) or fat reserves (β=0.10) of males when females were spatially clumped. Overall, the distribution of females had a pronounced effect on male behavior, on the factors that affected male success in locating females, and probably on the extent of sperm competition once females had been located. Received: 23 November 1998 / Received in revised form: 9 August 1999 / Accepted: 18 August 1999     

Independent effects of male and female density on sexual harassment, female fitness, and male competition for mates in the western mosquitofish Gambusia affinis

Operational sex ratio (the ratio of sexually active males to fertilizable females) has a major influence on male competition for mates and male–female interactions. The contributions of male and female density per se to mating system dynamics, however, are rarely examined, and the fitness consequences are often inferred rather than quantified. Male mosquitofish (Gambusia affinis) compete aggressively and frequently harass females for copulations, a behavior thought to reduce female fitness. Female fitness can also be reduced by increases in female density, which may affect food availability, cannibalism rates, and chemical interactions between females. I manipulated male and female densities of G. affinis to measure their effects on male–male aggression, male harassment toward females, and female fitness. I found that males chased rivals more often and attempted fewer copulations when female density decreased, but surprisingly male density had no significant effect on the frequency of these male behaviors. In contrast, males’ agonistic displays toward other males increased with male density, but display behavior was unaffected by female density. These results suggest that male and female density do not always contribute equally or at all to the patterns of behavior we observe. Female fitness declined as female density increased, the opposite pattern expected if male harassment is costly to females. This suggests that a strong, negative effect of female density overwhelmed any potential costs of male harassment. Sources of female density dependence and the consequences of changes in male and female density to patterns of male behavior are discussed.     

Sex differences in olfactory communication in a primate, the moustached tamarin, Saguinus mystax (Callitrichinae)

This study examines the hypothesis that sexual selection has shaped patterns of olfactory communication in wild moustached tamarins, Saguinus mystax. Do sex differences exist in frequencies and in the intensity of scent marking, in the use of different scent-marking types, and in behavioural responses to scent marks? Scent marking (anogenital, suprapubic, sternal) and behavioural responses (sniffing and overmarking) were recorded in four groups (ten adult and subadult males, seven adult and subadult females in all groups combined) in north-eastern Peru. Frequencies and intensity of scent marking were significantly higher in female tamarins. Males and females did not differ in the use of anogenital marking, but suprapubic marking was employed significantly more often by females. Only 10% of scent marks were monitored by another group member, and only 5% were overmarked by another group member. Most sniffing of scent marks was done by males, and males sniffed at marks produced by females significantly more often than at marks produced by males. Both sexes overmarked scent marks with similar frequency, but females overmarked scent marks produced by males significantly more often than those produced by females. An increase in frequencies of scent marking was observed in two females of one group after the death of the reproducing female, but frequencies of scent marking remained the same in the males of this group. The female-biased rates of scent marking are consistent with predictions made by sexual selection theory for species with substantial male care for offspring and strong reproductive competition between females. However, a decisive test of the proposed role of sexual selection will only be possible with more field data on patterns of olfactory communication in other callitrichine species.     

Daring females,devoted males,and reversed sexual size dimorphism in the sand-dwelling spider <Emphasis Type="Italic">Allocosa brasiliensis</Emphasis> (Araneae,Lycosidae)

Sexual selection theory predicts that a higher investment in offspring will turn females into the selective sex, while males will compete for accessing and courting them. However, there are exceptions to the rule. When males present a high reproductive investment, sex roles can reverse from typical patterns, turning males into the choosy sex, while females locate males and initiate courtship. In many spiders, males are smaller than females, wandering in search of sedentary females and maximizing the number of copulations. In the present study, we present findings on the sand-dwelling wolf spider, Allocosa brasiliensis, evidencing a reversal in typical courtship roles reported for the first time in spiders. Males were bigger than females. Females located males and initiated courtship. Copulation always occurred in male burrows and took place mainly in long burrows. Males donated their burrows to the females after copulation, closing the entrance before leaving with female cooperation from inside. Males would provide females with a secure place for ovipositing, being exposed to predation and diminishing their future mating possibilities until constructing a new burrow. The cost of vacating the burrow and losing the refuge in an unpredictable habitat, such as sand dunes, would explain the courtship roles reversal in this spider species. Results turn A. brasiliensis as a promising model for discussing the determinants of sex roles and the pressures that drive their evolution and maintenance. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Sexual cohabitation as mate-guarding in the leaf-curling spider Phonognatha graeffei Keyserling (Araneoidea, Araneae)

The leaf-curling spider Phonognatha graeffei incorporates a twisted leaf into the central hub of its orb-web that is used as a retreat. This species is unusual among orb-weaving spiders because males cohabit in the leaf retreat with both immature and mature females, mating with the former shortly after the female molts. Cohabitation appears to be a form of mate-guarding because cohabiting males respond agonistically to rival males that venture onto the web, and their behaviour depends upon the reproductive status of the female; males defending immature females are more aggressive than those defending virgin, adult females. Males copulate with previously mated females for significantly longer than with virgin females. Females may cannibalise cohabiting males, which occurs independently of whether the female has been deprived of food. Females that cannibalise a single male do not have a higher fecundity than non-cannibalistic females. Received: 2 February 1996 / Accepted after revision: 27 October 1996