It is a matter of taste: chemical signals mediate nuptial gift acceptance in a neotropical spider

Behavioral Ecology doi:10.1093/beheco/arr209 Advance Access publication 8 December 2011 Original Article It is a matter of taste: chemical signals mediate nuptial gift acceptance in a neotropical spider Pedro Erê Disconzi Brum,a Luiz Ernesto Costa-Schmidt,b and Aldo Mellender de Araújoa Departamento de Genética, Universidade Federal do Rio Grande do Sul, Av. Bento Gonc xalves, 9500 Prédio 43323 - Sala 205, CEP 91501-970, Porto Alegre, RS, Brazil and bDepartamento de Ecologia, Universidade de São Paulo, Rua do Matão—Travessa 14, no 321—Sala 248, Cidade Universitária, CEP 05508-090, São Paulo—SP, Brazil a INTRODUCTION N uptial gifts are material donations transferred from a male to a female during courtship (Gwynne 2008). At least 2 nonexclusive hypotheses have been proposed to explain the evolution of gift-giving behavior (reviews in Vahed 1998, 2007 and Gwynne 2008). First, nuptial gifts could be interpreted in the light of a paternal investment hypothesis stating that the male provides a nutritional resource to a female that enhances her reproductive output (Simmons and Parker 1989). The second hypothesis links nuptial gifts to mating effort by proposing that nuptial gifts increase male reproductive success by attracting females, facilitating coupling, and/or maximizing ejaculate transfer (Thornhill 1976). Mating effort can be achieved by sensory exploitation mechanisms under which the evolution of such traits is the outcome of the exploitation of female preexisting preferences or biases favored by natural selection (i.e., the gustatory recognition of ‘‘food’’) in a sexually selected context (Ryan 1998). Gift-giving behavior is widespread among vertebrates and invertebrates but is particularly common in arthropods, in which males may donate food (i.e., food collected or captured by the male, glandular secretions, or specialized parts of the male’s body) (Vahed 1998, 2007; Gwynne 2008) and even nonnutritional products (Aisenberg et al. 2007). For spiders, the known cases of gift-giving behavior occur in 2 phylogenetically related families, Pisauridae (Austad and Thornhill 1986; Address correspondence to L.E. Costa-Schmidt. E-mail: luizernesto@ gmail.com. Received 13 July 2011; revised 1 November 2011; accepted 21 November 2011.
The Author 2011. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com Nitzsche 1988, 2011) and Trechaleidae (Costa-Schmidt et al. 2008; Lapinski and Tschapka 2009; Silva and Lise 2009), although a few other examples occur in Lycosidae (Aisenberg et al. 2007) and Theridiidae (Cobbold and Su 2010; Uetz et al. 2010). Nuptial gifts of pisaurids and trechaleids are composed of a prey item wrapped in silk, which is offered to the female during precopulatory courtship (Nitzsche 1988, 2011; CostaSchmidt et al. 2008). In both pisaurids and trechaleids, the nuptial gift has a white color and a round shape and is carried on the males’ chelicerae during mate search and courtship. For the trechaleid Paratrechalea ornata, nuptial gifts have a great influence in male mating success because males with prey are more likely to obtain copulations (Albo and Costa 2010), and in the populations studied by Costa-Schmidt et al. (2008), the female allows a male to start further courtship steps only after grabbing the gift. Experimental studies have already shown that nuptial gifts are an important component of male mating effort in spiders (Lang 1996; Stalhandske 2001; Bilde et al. 2007; Albo and Costa 2010). Moreover, nuptial gifts also seem to act on the female sensory system by exploiting their foraging motivation (Bilde et al. 2007), which can be interpreted as a reinforcing mechanism for mate acquisition. Little attention, however, has been given to the specific stimulus that triggers female acceptance of the nuptial gift both in spiders and in other arthropod groups. Female visual perception of the nuptial gift was already proposed for Pisaura mirabilis (Stalhandske 2002), but Nitzsche (2011) concluded that it is unlikely that visual information plays a major role in nuptial gift acceptance by that species, except at very close ranges. Additionally, chemical cues are important in a reproductive context for many spider species (Papke et al. 2001; Roberts and Uetz 2004; Schulz 2004; Gaskett 2007; Rypstra et al. 2009; Baruffaldi et al. Downloaded from https://academic.oup.com/beheco/article/23/2/442/246344 by guest on 05 June 2022 Nuptial gift offering is a courtship trait found among several insect orders and some spider families. Recent studies indicate that this gift-giving behavior in spiders represents the male mating effort acting on female receptivity through a mechanism of foraging motivation. However, little attention has been given to the sensory channels that are influencing female acceptance. To understand the role of these sensory channels in female perception of a nuptial gift, we focused on the nuptial gift of the neotropical spider Paratrechalea ornata (Araneae, Trechaleidae). The nuptial gift of this species is composed of a prey item wrapped in silk, and previous works suggest that visual and/or chemical cues may be involved in inducing female grasping behavior. We isolated sensory channels using mimetic nuptial gifts (artificial items) or by manipulating real nuptial gifts. Isolated visual signals were not responsible for female acceptance, whereas chemical signals found within the nuptial gift silk layer induced female acceptance. Our findings clearly indicate that a chemical signal located in the silk of the nuptial gift is the main attractant channel, and we formulated 2 hypotheses to explain the mechanisms of action in the female sensory system. We also discuss the consequences of such signaling over female acceptance. Key words: chemical communication, Paratrechalea, semiaquatic spider, sensory exploitation, sexual pheromone, sexual selection. [Behav Ecol 23:442–447 (2012)] Brum et al. • Nuptial gift chemical signals MATERIALS AND METHODS Collection and maintenance Paratrechalea ornata is a semiaquatic spider that occurs in northern Argentina, Paraguay, Uruguay, and southern Brazil (Carico 2005), usually inhabiting the riparian vegetation and rocks along streams and rivers. We collected juvenile Pa. ornata males and females from a single population located on the Pedra de Amolar River in Maquiné (lat 2932#20.52$S, long 5014#46.83$W), state of Rio Grande do Sul, southern Brazil. Each specimen was raised to adulthood in an individual vessel (65-mm diameter/ 85-mm height) with 1 cm of water at the bottom. We fed the spiders with one domestic fly (Musca domestica) twice a week. Only virgin spiders, at least 1 week old after their final molt, were used in the experiments. Females were fed 12 h before each trial to control for possible effects of starvation. Experimental procedures We conducted 4 independent experiments to investigate the female decision to accept a nuptial gift, exploring different sensory channels. We conducted the first experiment to evaluate the role of visual cues from the nuptial gifts during November and December 2006. The second experiment was concomitant with the first and evaluated if there were differences in silk composition between male dragline silk and nuptial gift silk. We conducted 2 other experiments to evaluate the role of chemical cues from the nuptial gifts between October 2010 and January 2011. All experiments were based on a similar protocol consisting of offering an item to the female with metal forceps, which was then advanced slowly toward her. Details on the types of items offered, and sample sizes for each experiment are presented below. For each experimental treatment, an exclusive pair of metal forceps was used. We categorized female grasping behavior into 1 of 2 categories: acceptance (A) and refusal (R). An item was considered accepted when a female grasped it with her chelicerae, even if she released the item just after biting it. We recorded a refusal when the female simply ignored the item after 2 consecutive offers. We obtained the nuptial gifts used as controls in the experiments described below from virgin males, and we did not use any male more than twice as a source of nuptial gifts. In all experiments, the order of the presentation of the experimental groups was chosen at random in each trial. Experiment 1: visual stimulus The goal of the first experiment was to test if females are able to distinguish an artificial gift from a natural nuptial gift based on a visual stimulus. We presented 20 females with an artificial gift (artificial gift treatment) and 20 females with a natural nuptial gift (control). The artificial gift was constructed of a rounded piece of cotton with the same shape, size, and color of a nuptial gift. If female grasping behavior is influenced by visual stimulus alone, we expected a similar frequency of acceptance between artificial gifts and nuptial gifts; otherwise, a chemical stimulus may be acting as the main communication channel for female grasping decisions. Experiment 2: silk composition The second experiment investigates the female ability to distinguish a male ‘‘ordinary silk’’ from a nuptial gift silk structurally through differences in chemical composition. Two types of silk treatments were randomly presented to 18 females. The same artificial gift core, consisting of a rounded piece of polystyrene with dimensions similar to those of a nuptial gift, was used with both groups. In the first treatment, we used a silk extracted from CO2-anesthetized Pa. ornata males by simply holding the male under a stereomicroscope and gently touching the artificial gift to the spinnerets. This process stimulates silk release by the male and was followed until the artificial gift was covered with a layer of what we called ordinary silk (AG 1 silk). The second treatment was prepared by removing the silk layer from a nuptial gift that was carefully dissected under a stereomicroscope. The silk layer was used to cover the artificial gift core (AG 1 NG silk). In the absence of differences in chemical composition between silk types, we expect that females will present the same frequency of grasping behavior for both silks. If a difference in grasping frequency occurs, we assumed that chemical signals found within the silk types are affecting the female grasping behavior. Experiment 3a: chemical stimulus In this experiment, we tested if female acceptance is based on chemical signals from the nuptial gift. We treated 2 groups of nuptial gifts with 1 of 2 solvents with different polarities (n ¼ 25 for each group): distilled water (NG 1 H2O), which dissolves polar substances, and ether (NG 1 Et), which dissolves apolar substances. In both experimental groups, we immersed nuptial gifts in the respective solvent bath for 2 min and left them to air dry for 3 min before each trial. Given the possibility that traces of the apolar solvent could remain on the nuptial gifts, thus affecting female response, we set up a control experiment using dead domestic flies. We treated the flies with the same protocol used for the ether baths (n ¼ 15) and compared female acceptance with nontreated flies (n ¼ 15). Because female response was identical between the ether-treated flies and the nontreated flies (93.33% acceptance in both groups), we concluded that the ether protocol did not influence female response, and we present only the data from the experimental group in the results. We compared the frequency of females that grabbed the nuptial gifts in each experimental group directly with a control group composed of untreated nuptial gifts (n ¼ 25). If chemical signs (be it polar or apolar) deposited by the males on the silk used to wrap the nuptial gifts stimulate female response, we predicted that the frequency of females grabbing the nuptial gifts would differ between the control and at least one of the experimental groups. Based on the semiaquatic habits of Pa. ornata, we also hypothesized that the apolar treatment (ether) would be the one to attenuate the nuptial gift chemical signal. Experiment 3b: transferring of the chemical stimulus We designed this experiment as a complement to the previous one. This experiment was also designed to test if female acceptance is based on chemical signals from the nuptial gift. This experiment allowed us to test whether the chemical cues are Downloaded from https://academic.oup.com/beheco/article/23/2/442/246344 by guest on 05 June 2022 2010; Xiao et al. 2010), and the silk layer covering the nuptial gift might contain chemical properties that stimulate or even induce female acceptance. Here, we investigated whether the female decision to accept nuptial gifts was mediated by visual or chemical signals, using Pa. ornata as a study model. Using a series of experiments, we isolated possible nuptial gift signaling channels and tested female responses toward isolated stimuli. Given that trechaleids belong to the Lycosoideae clade (Coddington 2005), which have well-developed vision (Foelix 2011), female acceptance may be mediated by visual stimulation. In fact, during a courtship step called hyperflexion, the male exposes the contrasting round, white nuptial gift held on his bright reddish chelicerae directly in the female’s line of sight (Costa-Schmidt et al. 2008). 443 Behavioral Ecology 444 Statistical analyses We used nonparametric tests for dependent samples: a McNemar test for comparisons involving 2 classes and a Cochran Q test for comparisons involving more than 2 classes. We performed all statistical analyses using the software package R (R Development Core Team 2009). RESULTS Experiment 1: visual stimulus The frequency of females that accepted the artificial gift treatment (30%) were considerably lower than the control treatment (80%) (McNemar chi-squared test: v2 ¼ 8.1, degrees of freedom [df] ¼ 1, P ¼ 0.004; Figure 1). All females that grasped the artificial gifts also grasped the nuptial gifts; 50% of the females only grasped the nuptial gifts, rejecting the artificial gifts, whereas 20% of the females did not grasp any item offered to them. Figure 1 Numbers of acceptances (solid bars) and refusals (open bars) of items offered to Paratrechalea ornata females in one experiment designed to test if female acceptance is based on visual cues from the NGs. NG: untreated nuptial gift (control group); AG: artificial gift. gifts (84%). These results indicate that the attractive chemical signal on the nuptial gift silk was attenuated by the apolar solvent, resulting in a lower frequency of acceptance by females in this experimental group (Cochran’s Q test: Q ¼ 8.93, df ¼ 2, P ¼ 0.011; Figure 3a). Experiment 3b: transferring of the chemical stimulus A high percentage of females accepted inedible items bathed in nuptial gift solution (72.2%), nuptial gift silk solution (66.7%), and prey solution (72.2%). In the control group, however, only 3 females (16.7%) accepted the inedible item. All treatments, therefore, were shown to induce females to accept gifts at a similar frequency, except for the control group, in which female acceptance was very low (Q ¼ 14.89, df ¼ 3, P ¼ 0.0019; Figure 3b). DISCUSSION Our results show that chemical cues found on nuptial gift silk of the spider Pa. ornata induce female grasping behavior. This finding represents one possible explanation for why Pa. ornata Experiment 2: chemical composition of the nuptial gift silk Artificial gifts wrapped with ordinary silk showed a lower frequency of grasping by females among the groups tested (Cochran’s Q test: Q ¼ 8.6, df ¼ 2, P ¼ 0.014; Figure 2). The female reactions to the nuptial gift and to the AG 1 NG silk were almost identical (72.2% and 77.8% of acceptance, respectively), except in the case of a single female that grasped the AG 1 NG silk and rejected the nuptial gift, whereas the AG 1 Silk treatment resulted in only 38.9% of acceptance (Figure 2). Experiment 3a: chemical stimulus Only 48% of the females accepted the nuptial gifts treated with ether, whereas a higher percentage of the females accepted the nuptial gifts treated with water (76%) and the untreated nuptial Figure 2 Numbers of acceptances (solid bars) and refusals (open bars) of items offered to Paratrechalea ornata females in one experiment designed to test if female acceptance is based on silk cues from the NGs. Control (NG): untreated nuptial gift; AG 1 silk: artificial gift covered with a silk layer extracted from anesthetized males; AG 1 NG silk: artificial gift covered with the silk layer removed from a nuptial gift. Downloaded from https://academic.oup.com/beheco/article/23/2/442/246344 by guest on 05 June 2022 located in the nuptial gift silk. We tested 18 females in the presence of an inedible item, that is, a rectangular piece of filter paper (9 3 3 mm) treated with 1 of 3 solutions (hereafter called ‘‘signal donors’’): nuptial gift solution, nuptial gift silk solution, or prey solution. We obtained the solutions containing the chemical cues of each signal donor after a 15 min ether bath inside a 0.5 ml tube with 0.3 ml of solvent. We chose the solvent to be used after the results obtained in the previous experiment (see RESULTS). For chemical signal transferring, we placed the inedible item for another 15 min inside the tube containing the solution after the removal of the signal donor. After this period, we left the item to dry out in the air for 5 min and then offered it to the female. The control group was composed of an inedible item treated only with ether following the same protocol described above. To test if a possible contamination of the nuptial gift silk by its inner content could influence female grasping behavior in the nuptial gift silk solution, we conducted an independent experiment (n ¼ 15) in which only a fraction of the inner content of nuptial gifts (i.e., prey or carrion) were carefully removed and treated following the same experimental protocol described above for chemical signal transfer. Because only one female accepted the item in this inner content group, we assume that the results obtained for the nuptial gift silk group were strictly related to the chemical information present on the silk layer and not influenced by a possible contamination of the wrapped prey. If chemical cues on the silk used to wrap the nuptial gift induce females to accept it, we expected that the acceptance frequency of inedible items bathed in nuptial gift solution and NG silk solution would be similar to the acceptance frequency of inedible items bathed in prey solution and higher than the control group. Brum et al. • Nuptial gift chemical signals males that previously failed to mate add more silk to the nuptial gift after being rejected by the female, thereby successfully mating in subsequent attempts (Albo and Costa 2010; Brum PED, personal observations). This behavior is also observed in another trechaleid (Lapinski and Tschapka 2009) and in Pi. mirabilis (Stalhandske 2002; Bilde et al. 2007). The additional silk probably increases the chemical signal within the gift, thus increasing its attractiveness to the female. Support for a visual signal inducing female grasping behavior exclusive to the nuptial gift was not found in our experiment, given the low acceptance of the artificial gift compared with the nuptial gift. However, due to our methodological design, we cannot rule out the possibility that visual signals play a significant role in nuptial gift acceptance. The short range of distances used for all trials may have stressed the effects of chemical signaling in preference to the visual effects. If the latter are present in the nuptial gifts, they could be more effective if an approaching male is too far from the female for chemical perception to occur but close enough to call her attention to the gift held in his chelicerae. Costa-Schmidt and Araújo (2008) investigated possible drivers of selective forces that could explain why the chelicerae of male Paratrechalea are larger and redder than those of females and concluded that this pattern is a trade-off between natural and sexual selection. Sexual selection would act on the male chelicerae by amplifying the visual information contained in the nuptial gift through morphological modifications of this structure (Costa-Schmidt and Araújo 2008). Further studies should investigate the possible influence of the morphology and color of the chelicerae on female visual acceptance and the visual ability of the female to perceive a nuptial gift at greater distances (for an experimental approach with Pi. mirabilis, see Nitzsche 2011). The second experiment furnishes evidence that nuptial gift silk has different properties from ordinary silk and that the male actively selects the type of silk to produce. These conclusions are consistent with the finding that artificial gifts wrapped with dragline silk directly extracted from the spinnerets of CO2-anesthetized Pa. ornata males are seldom accepted by females. Assuming that the silk types do not show significant differences in texture, differences in chemical properties remain as the source of the information involved in the female decision to grasp the nuptial gift. The results of experiment 3b give us support for the hypothesis of the existence of an attractive signal located on the silk used to wrap the prey. We suggest that the attractive signal is released on the silk threads either by an accessory gland not related to silk production and only active during nuptial gift construction or by silk glands connected to specific regions of the spinnerets that are used only during nuptial gift wrapping. In both cases, males would be able to actively add the attractive signal while wrapping the prey with silk. Therefore, it seems that the chemical signal contained in the nuptial gift silk is a sexual pheromone released by the males that stimulates female acceptance, which may increase male mating success (from now on referred to as the pheromone hypothesis). Evidence of the apolar nature of the attractive chemical signal confirms our prediction based on the semiaquatic habits of Pa. ornata. Given that the males wander in a permanently wet environment during mate searching, when they already hold a nuptial gift, it would be surprising to find a polar attractive chemical in the nuptial gift silk that would be removed by contact with water. Even with a significant reduction in the female acceptance frequency, 48% of the tested females grasped the nuptial gifts treated with ether. There are 2 nonmutually exclusive factors that could explain this result. First, our ether treatment may not have been capable of removing all of the attractive chemical components deposited on the silk. Second, other signaling components, such as visual cues, could account for part of the attractive signal or could act synergistically with the chemical signal to promote an enhanced female response (e.g., Hebets and Papaj 2005; Partan and Marler 2005). The prey item treatment resulted in similar acceptance compared with the nuptial gift treatments, indicating that chemical components found on the prey are also transferred using the same solvent (ether) and showing similar results. The similarity between the acceptance of the nuptial gift solution and prey solution treatments suggests the possibility that chemicals deposited in the nuptial gift silk are exploiting the female’s foraging motivation (the willingness of an individual to grasp and feed on an object). This pattern can be explained by 2 alternative hypotheses. First, the chemical signal found in the silk layer of nuptial gifts may have chemical components that resemble those found in the prey cuticle. Second, the nuptial gift signals differ from those found in the prey but elicit the same reaction from the female. In that sense, foraging motivation could be seen as an alternative hypothesis to the pheromone hypothesis presented above. Foraging motivation was previously proposed for Pi. mirabilis (Bilde et al. 2007) and was also supported for Downloaded from https://academic.oup.com/beheco/article/23/2/442/246344 by guest on 05 June 2022 Figure 3 Numbers of acceptances (solid bars) and refusals (open bars) of items offered to Paratrechalea ornata females in 2 experiments designed to test if female acceptance is based on chemical cues from the NGs. (A) Control (NG): untreated nuptial gift; NG 1 H2O: NG treated with water; NG 1 ether: NG treated with ether. (B) Control: inedible item treated with solvent (ether); Solution treatments: NG—inedible item treated with a solution of nuptial gift; Silk (NG)—inedible item treated with a solution of the external silk layer of the NG; Prey—inedible item treated with a solution of a domestic fly. 445 446 FUNDING Conselho Nacional de Desenvolvimento Cientı́fico e Tecnológico—Brazil (134081/2009-9 to P.E.D.B. and 141609/2003-6 to L.E.C.-S.); Fundac xão de Amparo à Pesquisa do Estado de São Paulo (09/52791-6 to L.E.C.-S.). We thank Lucas Caetano Silveira for field assistance, Luciana Baruffaldi for comments on the early experimental design, Paulo Oliveira, Glauco Machado, Greg Holwell, and an anonymous reviewer for comments on the manuscript. All animal collections complied with the current laws of the Brazilian government, represented by Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais RenovÃveis (IBAMA), which issued all the collection permits. REFERENCES Aisenberg A, Vieira C, Costa FG. 2007. Daring females, devoted males, and reversed sexual size dimorphism in the sand-dwelling spider Allocosa brasiliensis (Araneae, Trechaleidae). Behav Ecol Sociobiol. 62:29–35. Albo MJ, Costa FG. 2010. Nuptial gift-giving behaviour and male mating effort in the Neotropical spider Paratrechalea ornata (Trechaleidae). Anim Behav. 79:1031–1036. Andersen T, Bollerup K, Toft S, Bilde T. 2008. Why do males of the spider Pisaura mirabilis wrap their nuptial gifts in silk: female preference or male control? Ethology. 114:775–781. Austad SN, Thornhill R. 1986. Female reproductive variation in a nuptialfeeding spider, Pisaura mirabilis. Bull Br Arachnol Soc. 7:48–52. Baruffaldi L, Costa FG, Rodrı́guez A, González A. 2010. Chemical communication in Schizocosa malitiosa: evidence of a female contact sex pheromone and persistence in the field. J Chem Ecol. 36: 759–767. Bilde T, Tuni C, Elsayed R, Pekar S, Toft S. 2007. Nuptial gifts of male spiders: sensory exploitation of the female’s maternal care instinct or foraging motivation? Anim Behav. 73:267–273. Carico JE. 2005. Descriptions of two new spider genera of Trechaleidae (Araneae, Lycosoidea) from South America. J Arachnol. 33:797–812. Cobbold SM, Su Y. 2010. The host becomes dinner: possible use of Cyclosa as a nuptial gift by Argyrodes in a colonial web. J Arachnol. 38:132–134. Coddington JA. 2005. Phylogeny and classification. In: Ubick D, Paquin P, Cushing PE, Roth V, editors. Spiders of North America: an identification manual. New York: American Arachnological Society. p. 18–24. Costa-Schmidt LE, Araújo AM. 2008. Sexual dimorphism in chelicerae size in three species of nuptial gift spiders: a discussion of possible functions and driving selective forces. J Zool. 275:307–313. Costa-Schmidt LE, Carico JE, Araújo AM. 2008. Nuptial gifts and sexual behaviour in two species of spider (Araneae, Trechaleidae, Paratrechalea). Naturwissenschaften. 95:731–739. Foelix RF. 2011. The biology of spiders. 3rd ed. New York: Oxford University Press. Gaskett AC. 2007. Spider sex pheromones: emission, reception, structures, and functions. Biol Rev. 82:27–48. Gwynne DT. 2008. Sexual conflict over nuptial gift in insects. Annu Rev Entomol. 53:83–101. Hebets EA, Papaj DR. 2005. Complex signal function: developing a framework of testable hypotheses. Behav Ecol Sociobiol. 57:197–214. Huber BA. 1997. Evidence for gustatorial courtship in a haplogyne spider (Hedypsylus culicinus: Pholcidae: Araneae). Neth J Zool. 47:95–98. Kugimiya S, Nishida R, Sakuma M, Kuwahara Y. 2003. Nutritional phagostimulants function as male courtship pheromone in the German cockroach, Blattella germanica. Chemoecology. 13:169–175. Lang A. 1996. Silk investment in gifts by males of the nuptial feeding spider Pisaura mirabilis (Araneae: Pisauridae). Behaviour. 133:697–716. Lapinski W, Tschapka M. 2009. Erstnachweis von brautgeschenken bei Trachalea sp. (Trechaleidae, Araneae) in Costa Rica. Arachne. 14:4–13. Nitzsche ROM. 1988. ‘‘Brautgeschenk’’ und umspinnen der beute bei Pisaura mirabilis, Dolomedes fimbriatus und Thaumasia uncata (Arachnida, Araneida, Pisauridae). Verh Natwiss Ver Hambg. 30:353–393. Nitzsche ROM. 2011. Courtship, mating and agonistic behaviour in Pisaura mirabilis (Clerck, 1757). Bull Br Arachnol Soc. 15:93–120. Papke MD, Riechert SE, Schulz S. 2001. An airborne female pheromone associated with male attraction and courtship in a desert spider. Anim Behav. 61:877–886. Partan SR, Marler P. 2005. Issues in the classification of multimodal communication signals. Am Nat. 166:231–245. R Development Core Team. 2009. R: a language and environment for statistical computing [Internet]. Vienna (Austria): R Foundation for Statistical Computing [cited 2011 December 1]. Available from: http://www.R-project.org. Roberts JA, Uetz GW. 2004. Chemical signaling in a wolf spider: a test of ethospecies discrimination. J Chem Ecol. 30:1271–1284. Ryan MJ. 1998. Sexual selection, receiver biases and the evolution of sex differences. Science. 281:1999–2002. Rypstra AL, Schlosser AM, Sutton PL, Persons MH. 2009. Multimodal signalling: the relative importance of chemical and visual cues from females to the behaviour of male wolf spiders (Lycosidae). Anim Behav. 77:937–947. Downloaded from https://academic.oup.com/beheco/article/23/2/442/246344 by guest on 05 June 2022 other arachnids (Huber 1997) and insects (Sakaluk 2000; Kugimiya et al. 2003; Vahed 2007; Warwick et al. 2009). These results pose the question of why would Pa. ornata males invest time and energy to wrap the prey in silk with an attractive signal, when they could simply offer the prey without any silk. There are at least 2 possible and nonmutually exclusive hypotheses to explain this. Albo and Costa (2010) proposed that prey wrapped in silk increases control of Pa. ornata males over females prior to and during copulation, which corroborates with previous studies on Pi. mirabilis (Bilde et al. 2007; Andersen et al. 2008). According to these studies, males can achieve longer copulations and reduce the chance of having the nuptial gift stolen by the female prematurely. Moreover, although we were rearing individuals of Pa. ornata, we found that males can build low-quality nuptial gifts consisting of already digested prey or inedible items, like a seed wrapped in silk (as reported by Albo and Costa 2010). Digested prey wrapped in silk is readily accepted by females, but digested prey without silk is never grasped by females (Brum PED, unpublished data). Therefore, wrapping low-quality prey in silk with an attractive signal may be a male strategy to minimize the energy costs of the construction of a high-quality nuptial gift and maintain its attractiveness to females. In fact, only 6.7% of the females tested(1 female out of 15) accepted a filter paper disc bathed in extracts of a portion of the contents of a nuptial gift without its silk wrapping, whereas 72% accepted a filter paper disc treated with prey solution. This result suggests that the content of nuptial gifts may be of poorer quality than actual prey (e.g., has been fed on by the male). However, we remark that in situations where food is not a limiting factor (e.g., during seasons with high prey availability), males may choose to build nuptial gifts with highquality content (e.g., a ‘‘nonconsumed’’ prey). Further studies addressing the influence of the nutritional status of males on the nuptial gift composition and incorporating data from field observations are being conducted by our group and should provide insights into this question. In conclusion, our experiments elucidate an important aspect of the reproductive behavior of a gift-giving spider species by suggesting a causal function for nuptial gifts in inducing females to assume a courtship position (Costa-Schmidt et al. 2008). To our knowledge, this report is the first to show evidence for the existence of a chemical signal acting as the main attractant in the female acceptance of nuptial gifts in spiders. The chemical characterization of the nuptial gifts attractive signal is the next step that will allow further experimental investigations of sensory exploitation and the pheromone hypothesis. Behavioral Ecology Brum et al. • Nuptial gift chemical signals Uetz GW, McCrate A, Hieber CS. 2010. Stealing for love? Apparent nuptial gift behavior in a kleptoparasitic spider. J Arachnol. 38: 128–131. Vahed K. 1998. The function of nuptial feeding in insects: a review of empirical studies. Biol Rev. 73:43–78. Vahed K. 2007. All that glisters is not gold: sensory bias, sexual conflict and nuptial feeding in insects and spiders. Ethology. 113:105–127. Warwick S, Vahed K, Raubenheimer D, Simpson SJ. 2009. Free amino acids as phagostimulants in cricket nuptial gifts: support for the ‘Candymaker’ hypothesis. Biol Lett. 5:194–196. Xiao YH, Zhang JX, Li SQ. 2010. Male-specific (Z)-9-tricosene stimulates female mating behaviour in the spider Pholcus beijingensis. Proc R Soc B Biol Sci. 277:3009–3018. Downloaded from https://academic.oup.com/beheco/article/23/2/442/246344 by guest on 05 June 2022 Sakaluk SK. 2000. Sensory exploitation as an evolutionary origin to nuptial food gifts in insects. Proc R Soc B Biol Sci. 267:339–343. Schulz S. 2004. Semiochemistry of spiders. In: Cardé RT, Millar JG, editors. Advances of chemical ecology. Cambridge: Cambridge University Press. p. 100–150. Silva ELC, Lise AA. 2009. New record of nuptial gift observed in Trechalea amazonica (Araneae, Lycosoidea, Trechaleidae). Rev Peru Biol. 16:119–120. Simmons LW, Parker GA. 1989. Nuptial feeding in insects: mating effort versus paternal investment. Ethology. 81:332–343. Stalhandske P. 2001. Nuptial gift in the spider Pisaura mirabilis maintained by sexual selection. Behav Ecol. 12:691–697. Stalhandske P. 2002. Nuptial gifts of male spiders functions as sensory traps. Proc R Soc Lond B Biol Sci. 269:905–908. Thornhill R. 1976. Sexual selection and paternal investment in insects. Am Nat. 110:153–163. 447