Search

Sperm competition drives traits that enhance fertilization success. The amount of sperm transferred relative to competitors is key for attaining paternity. Female reproductive morphology and male mating order may also influence fertilization, however the outcome for sperm precedence under intense sperm competition remains poorly understood. In the polyandrous spider Pisaura mirabilis, males offer nuptial gifts which prolong copulation and increase sperm transfer, factors proposed to alter sperm precedence patterns under strong sperm competition. First, we assessed the degree of female polyandry by genotyping wild broods. A conservative analysis identified up to four sires, with a mean of two sires per brood, consistent with an optimal mating female rate. Then we asked whether intense sperm competition shifts sperm precedence patterns from first male priority, as expected from female morphology, to last male advantage. We varied sexual selection intensity experimentally and determined competitive fertilization outcome by genotyping broods. In double matings, one male monopolised paternity regardless of mating order. A mating order effect with first male priority was revealed when females were mated to four males, however this effect disappeared when females were mated to six males, probably due to increased sperm mixing. The proportion of males that successfully sired offspring drastically decreased with the number of competitors. Longer copulations translated into higher paternity shares independently of mating order, reinforcing the advantage of traits that prolong copulation duration under intense competition, such as the nuptial gift. Sperm competition intensity enhances the impact of competitive sexual traits and imposes multiple effects on paternity. [ABSTRACT FROM AUTHOR]

Abstract: The expression of alternative reproductive tactics can be plastic and occur simultaneously depending on cues that vary spatially or temporally. For example, variation in resources and sexual selection intensity is expected to influence the pay‐off of each tactic and shape the decision of which tactic to employ. Males of the nuptial gift‐giving spider Pisaura mirabilis can adopt three tactics: offering a genuine prey gift, a ‘worthless’ non‐nutritious gift or no gift. We hypothesized that resources and/or male body condition, and mating opportunity and sexual selection intensity, vary over the course of the mating season to shape the co‐existence of alternative traits. We measured these variables in the field over two seasons, to investigate the predictions that as the mating season progresses, (i) males become more likely to employ a gift‐giving tactic, and (ii) the likelihood of switching from worthless to genuine gifts increases. Prey availability increased over the season and co‐varied with the propensity of males to employ the gift‐giving tactic, but we found no support for condition‐dependent gift giving. Males responded to an increase in female availability by increasing their mating effort (gift production). Furthermore, the frequency of genuine gift use increased with sexual selection intensity, consistent with the assumption that sperm competition intensity increases with time. Our results suggest that the frequency of alternative tactics is shaped by seasonal changes in ecological factors and sexual selection. This leads to relaxed selection for the gift‐giving tactic early in the season when females are less choosy and resources more scarce, and increased selection for genuine gifts later in the season driven by mating opportunity and risk of sperm competition. [ABSTRACT FROM AUTHOR]

The interplay between pre- and postmating responses to intrasexual competition remains enigmatic. Sperm competition models often assume a trade-off between pre- and postmating traits that enhance mate acquisition and fertilization success, respectively. However, when males court females through food donations (i.e., nuptial gifts), pre- and postmating responses may be aligned, as nuptial gifts have the dual function of facilitating both mate acquisition and sperm transfer. In the spider Pisaura mirabilis, nuptial gifts consist of silk-wrapped prey. We tested whether males respond to a competitor by altering: 1) premating investment in the gift, 2) postmating sperm investment, and 3) whether pre- and postmating responses are coupled and respond to competition in the same direction or not. Under competition risk males silk-wrapped their gifts for significantly shorter time and transferred less sperm to females, pointing to a reduction of both pre- and postmating responses. Because silk is not a target of female choice, reducing gift construction may speed up mate acquisition. In accordance with models of sperm allocation, perceived high levels of competition and/or sperm priority patterns may explain the reduced patterns of sperm transfer found in our study. Overall, our findings suggest that in competitive environments pre- and postmating traits are coupled and respond in the same direction. [ABSTRACT FROM AUTHOR]

Males of the nursery web spider Pisaura mirabilis usually offer an insect prey wrapped in white silk as a nuptial gift to facilitate copulation. Males exploit female foraging preferences in a sexual context as females feed on the gift during copulation. It is possible for males to copulate without a gift, however strong female preference for the gift leads to dramatically higher mating success for gift-giving males. Females are polyandrous, and gift-giving males achieve higher mating success, longer copulations, and increased sperm transfer that confer advantages in sperm competition. Intriguingly, field studies show that approximately one third of males carry a worthless gift consisting of dry and empty insect exoskeletons or plant fragments wrapped in white silk. Silk wrapping disguises gift content and females are able to disclose gift content only after accepting and feeding on the gift, meanwhile males succeed in transferring sperm. The evolution of deceit by worthless gift donation may be favoured by strong intra-sexual competition and costs of gift-construction including prey capture, lost foraging opportunities and investment in silk wrapping. Females that receive empty worthless gifts terminate copulation sooner, which reduces sperm transfer and likely disadvantages males in sperm competition. The gift-giving trait may thus become a target of sexually antagonistic co-evolution, where deceit by worthless gifts leads to female resistance to the trait. We discuss factors such as female mating rate and intensity of sperm competition that may shape the evolution of male deception, and how ecological factors may influence the evolution and maintenance of worthless gifts as an evolutionarily stable alternative mating strategy by frequency dependent selection. [ABSTRACT FROM AUTHOR]

Polyandrous females may gain genetic benefits for their offspring through postmating sexual selection. To facilitate postcopulatory choice for males of superior genetic quality females are expected to bias precopulatory mate choice towards novel males (i.e. genetically novel sources). Preference for novel partners is also expected to maximize male lifetime reproductive success by allowing males to increase the number of mates. We investigated male and female preference for novel or former mating partners in the spider Pisaura mirabilis by offering females novel males (polyandry) or the same male (monogamy). Precopulatory (mate acceptance) and prefertilization (latency to copulation, mating interruption and copulation duration) behaviours were compared between the two treatments. Males provide females with a nuptial prey gift during courtship. Because of the direct benefit associated with nuptial feeding, females should accept males indiscriminately and exert preference only at the prefertilization level. We found that monogamous females remated more readily than polyandrous females, suggesting less resistance to remating with the same male than with novel mates. No differences in female prefertilization responses were found. Lack of preference for novel mates may suggest that direct selection exerted by the nuptial gift rather than indirect selection for genetic benefits is a more likely driver of female remating propensity. Females were nevertheless resistant to remating, suggesting a trade-off between direct benefits and costs of remating. We found no effect of mate novelty on male mating behaviour, indicating either lack of discriminatory ability or that risk of sperm competition creates paternity benefits from remating with the same female. [ABSTRACT FROM AUTHOR]

Nuptial feeding can evolve as sensory traps where the male exploits the female''s foraging motivation in a sexual context. The nuptial prey gift of the nursery-web spider Pisaura mirabilis is wrapped in white silk, and it has been suggested that males initially exploit the maternal care instinct by producing a nuptial gift that resembles the female''s eggsac. In mating experiments we examined whether males exploit the female''s foraging motivation or the female''s maternal care instinct. We carried out a gift-switching experiment, where males presented an eggsac, a wrapped fly or an unwrapped fly as nuptial gifts. Females fed on eggsacs as well as on prey gifts. Mating success was similar for males with both wrapped and unwrapped gifts, indicating that wrapping per se does not increase male mating success. In a food manipulation experiment, we investigated the effect of the female''s hunger level on male mating success. Hungry females were more likely to accept a gift and copulate; hence the female''s hunger state is decisive for male mating success. Our results strongly suggest that the female''s foraging motivation is the true context for the maintenance of the nuptial gift. [Copyright &y& Elsevier]

1. Sexual conflict, which results from the divergence of genetic interests between males and females, is predicted to affect multiple behavioural, physiological, and morphological traits. 2. Sexual conflict over mating may interact with population density to produce predictable changes in resource allocation into inter-sexual armament. 3. In the spider Stegodyphus lineatus, males fight with females over re-mating. The outcome of the fight is influenced by the cephalothorax size of the contestants. The investment in armament – the cephalothorax, may be traded-off against investment in abdomen, which is a trait that affects survival and fecundity. Pay-offs may depend on population density. Both sexes are expected to adjust resource allocation into different body parts accordingly. 4. Males had increased cephalothorax/body size ratio in low densities where probability of finding another receptive female is low and females had increased cephalothorax/body size ratio in high densities where cumulative costs of multiple mating are high. 5. The results support the theoretical conjecture that population density affects resource allocation into inter-sexual armament and call for further research on the interaction between sexual selection and population density. [ABSTRACT FROM AUTHOR]

Female-biased sexual size dimorphism (SSD) is found in many organisms yet is poorly understood. Spiders in general, and web-building species in particular, typically have strongly female-biased SSD. We investigated the causes of SSD in the web-building spider Stegodyphus lineatus. Females are slightly, but significantly, larger than males. Large females are more fecund but the selection pressures on male body size are not clear. Males were introduced on to the webs of virgin and mated females and we also conducted competition experiments between males. Large males did not have longer copulations, nor did they mate more successfully with virgin females than small males did; however, they were more successful with previously mated females and remated more often. They also won more fights, and were more successful at obtaining prey from the female''s web. Indiscriminate mating by virgin females, however, conferred a fitness advantage on early maturing males. We suggest that the female''s mating strategy selects for protandry, which results in female-biased SSD, despite the selection for large body size in males. Indiscriminate mating by females and a trade-off between time to maturation and male body size may be important in understanding the evolution of female-biased SSD. [Copyright &y& Elsevier]

Polyandrous females are expected to discriminate among males through postcopulatory cryptic mate choice. Yet, there is surprisingly little unequivocal evidence for female-mediated cryptic sperm choice. In species in which nuptial gifts facilitate mating, females may gain indirect benefits through preferential storage of sperm from gift-giving males if the gift signals male quality. We tested this hypothesis in the spider Pisaura mirabilis by quantifying the number of sperm stored in response to copulation with males with or without a nuptial gift, while experimentally controlling copulation duration. We further assessed the effect of gift presence and copulation duration on egg-hatching success in matings with uninterrupted copulations with gift-giving males. We show that females mated to gift-giving males stored more sperm and experienced 17% higher egg-hatching success, compared with those mated to no-gift males, despite matched copulation durations. Uninterrupted copulations resulted in both increased sperm storage and egg-hatching success. Our study confirms the prediction that the nuptial gift as a male signal is under positive sexual selection by females through cryptic sperm storage. In addition, the gift facilitates longer copulations and increased sperm transfer providing two different types of advantage to gift-giving in males. [ABSTRACT FROM AUTHOR]