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Additions to Wikipedia page https://en.wikipedia.org/wiki/Nuptial_gift

Other research suggests that sensory bias is not the main contributing force behind gift selection in P. mirabilis. Interestingly, females did not preferentially select unwrapped gifts over wrapped gifts.

Additionally, Prokop found that female mate choice is dependent on nuptial gifts rather than female reproductive status as an unmated or mated individual. This effect demonstrates sexual selection's ability to make one sex more discriminatory than the other, since females may negatively impact their output of offspring by refusing mating events with males that do not offer gifts.

One of the more recently identified costs to males is reduced running speed due to gift-carrying. This cost may be exacerbated in areas of high predation.

In bell crickets, nuptial gifts may be necessary to avoid injury or death by cannibalizing females. This additional benefit allows gift-giving males to surpass the fitness of other males. In this way, females are exploiting the inherent sexual dimorphism of their species.

Typically, females control the duration and volume of sperm transfer throughout the mating process. Research has suggested that the gifts presented by males temporarily obstruct the female's capacity to manage the copulation event.

It may be possible the females are using age and gift quality as a proxy for mates with good genes as their offspring are likely to have high relative fitness.

However, some studies have shown that male spiders rarely cheat in nature. Cogent reasons for this disparate behavior are being explored. It is possible there are confounding factors which do not account for ecological implications.

The eggs of female spiders who receive nuptial gifts may hatch at a higher rate than those without nuptial gifts.

However, this may in part be due to an experimental bias due to the ease of rearing it for experiments. Other taxa may commonly exhibit gift-giving behavior. Thus, more research is required to evaluate the scope of nuptial gifts in arachnid taxa.

Final paper STARTS HERE

The Evolution of Nuptial Gifts in Arthropods

1. Introduction

Nuptial gifts are generally defined as gifts, such as food, nutrient-rich spermatophores, and other items which a female may find valuable, given to a mate in the context of reproduction in order to secure and prolong a mating event (Kuriwada and Kasuya 2012; Wedell and Ritchie 2004). The gift occupies the female while the male copulates, thus allowing more sperm to fertilize her eggs (Stålhandske 2001). Nuptial gifts rarely occur in vertebrates and are widespread amongst invertebrates (LeBas and Hockham 2005). In particular, arthropods tend to be the most studied, perhaps due to their sheer volume. Current research is focused on the importance of three hypotheses of sexual selection: good genes, sensory bias, and direct benefits. There are differences in nuptial gifts across taxa and these differences may be explained by combinations of these hypotheses.

2. Sexual Selection

Sexual selection can be seen in animals where there is a greater variance in the reproductive success of one sex in comparison to the other sex. Nuptial gifts involve both intersexual and intrasexual selection. Males are indirectly competing with each other to mate with females by furnishing her with impressive gifts. This creates intrasexual conflict and one can infer how an arms race might be initiated. Meanwhile, there is also intersexual conflict due to the asymmetric nature of the exchange of nuptial gifts. The females seek lavish gifts, while the males must sacrifice resources in order to obtain them. We expect to find an equilibrium between the cost of the gift and the benefit to the male’s fitness, as conflict theory might predict.

3. Why Should Females Accept Gifts?

Although many reasons for the exchange can be postulated and supported by evidence, it is not entirely clear why the female should accept the gifts. Among competing hypotheses, there are many different conclusions about the effect of the gift on the fitness of the female. In Pisaura mirabilis, a gift-giving spider, it has been shown that males may receive a net benefit in fitness as a result of nuptial gifts. However, in P. mirabilis and bell crickets, females may not necessarily receive any benefit to their own fitness (Stålhandske 2001; Kuriwada and Kasuya 2012). This is in striking contrast to the common perception of both sexes being beneficiaries of nuptial gifts. Other research indicates the eggs of female spiders who receive nuptial gifts hatch at a higher rate than those without nuptial gifts (Ghislandi et al., 2014). Nuptial gifts seem to be integral to male spiders acquiring mating events independent of female mating status (Prokop 2006). Virgin females tend to choose mates who provided nuptial gifts over those who do not, even though it may negatively impact their output of offspring if they can’t find another mate (Prokop 2006). This effect demonstrates sexual selection’s ability to make one sex more discriminatory than the other.

3.1 Direct Benefits

Nuptial gifts are a classic example of direct benefits as they provide immediate benefits to the recipient. However, these benefits are relatively minimal compared to the benefits the male receives in achieving a mating event. Therefore, it has been proposed that it is unlikely for females to gain a benefit due to a single gift alone. Instead, it is probable that the polyandrous female achieves a net benefit over the course of many matings and, by extension, many nuptial gifts (Ghislandi et al., 2014). A female who is less likely to retain the gift will be at a disadvantage over the course of many subsequent matings. As such, the females stand to gain more by accepting gifts prior to mating to ensure complete transfer. Female preference for nuptial gifts may not be able to explain this effect in its entirety because sperm competition occurs after the copulation event (Sakaluk 2000).

3.2 Good Genes

The cost of nuptial gifts requires males to expend energy which weakened males cannot afford. This sets up an opportunity for females to choose mates based on the presence and/or quality of the gift since these traits should correlate with higher fitness. In spite of this, recent research suggests that this is unlikely in P. mirabilis. Since their gifts are often wrapped in silk, the quality cannot be readily assessed (Ghislandi et al., 2014). Although the good genes hypothesis may not necessarily be supported in spiders, it can be a powerful explanation in other taxa of arthropods. In particular, bush crickets also present nuptial gifts to their mates, often in the form of a spermatophore. Female bush crickets have been shown to preferentially mate with males who present higher quality gifts (Wedell and Ritchie 2004). Nonetheless, this seems to correlate with age so it is not clear if the females are selecting for young males or for the quality of the gifts (Wedell and Ritchie 2004).

3.3 Sensory Bias

Sensory bias may be persistent in the selection of nuptial gifts. Often times this bias is related to food items which have no context in the realm of mating, but it can also be applied to other nuptial gifts which don’t provide nutritional value (Sakaluk 2000). Food items exploit the female’s desire to feed. It is especially important for a female to obtain nutrition throughout the mating process as she diverts resources towards reproduction. In many arthropods, such as spiders and bush crickets, the female controls the duration and volume of sperm transfer throughout the mating process. This asymmetric relationship gives rise to conflict which males seek to exploit. It has been suggested that the gifts presented by males temporarily obstruct the female’s capacity to manage the copulation event (Sakaluk 2000). Other evidence indicates sensory bias is not the main contributing factor to nuptial gifts in P. mirabilis, as females did not preferentially select unwrapped gifts over wrapped gifts (Ghislandi et al., 2014).

4. Why Should Males Give Gifts?

Another fundamental question which should be asked is: why should males provide nuptial gifts in the first place? A study measuring running speed of male spiders carrying gifts found that gift carrying adversely affected speed, which is disadvantageous if predation is high (Prokop and Maxwell 2012). Males enhance their fitness by affecting the female in various ways as outlined by the three aforementioned hypotheses. In some taxa where sexual cannibalism occurs, such as bell crickets, gift-giving confers an additional advantage. Research suggests that males offer the gift as a preventative measure to guard against cannibalizing females (Kuriwada and Kasuya 2012). Due to enhanced survivability after an encounter with a cannibalizing female, males who offer gifts will outcompete males who do not. In this way, females are exploiting the sexual dimorphism in their own species, rather than sensory bias initiated by males (Prokop 2006). Unlike in bell crickets, it appears P. mirabilis females do not cannibalize males (Stålhandske 2001).

5. Conflict

Due to the asymmetric nature of the female-male relationships, conflict often arises. Each individual is looking to maximize their own fitness, but this may come at the cost of the fitness of the other sex. We must evaluate the selection pressures, such as resource constraints, between the two sexes. One of the primary examples of conflict due to nuptial gift-giving occurs due to the evolution of deception.

5.1 Cheating

The inherent burden of nuptial gifts on the male sex forces selection to act on the behavior of gift-giving itself. It is reasonable to predict that “cheaters” might arise in a population of gift-givers. These cheaters would seek to exploit a female’s initial acuity (or lack thereof) of the quality of nuptial gifts. One might expect that females tend to prefer gifts which are of higher nutritional value, such as large prey items or large spermatophores. While the latter might be true in bush crickets, it is not a certain conclusion in other taxa. In particular, P. mirabilis tends to wrap its gifts in silk, which prevents the female from detecting its contents (Ghislandi et al., 2014). This sets up an opportunity for males to offer low-cost gifts. As an unintentional consequence, the female receives very little benefit from the gift. The male is purely seeking to increase his own fitness by minimizing costs and maximizing benefits. However, this also places selection pressure upon the females. As a result, males who cheat may not have prolonged mating events. Instead, they obtain many chances to mate (Ghislandi et al., 2014). Contrasting this research, some studies have shown that male spiders rarely cheat in nature (Prokop and Maxwell 2012).

Cheating also appears to be prevalent in the dance fly Rhamphomyia sulcata. Unlike P. mirabilis, which seals its worthless gifts inside silk, the dance fly presents its gift for the female to view. It has been proposed that species of gift-giving animals are susceptible to cheaters, which may become an evolutionarily stable strategy (LeBas and Hockham 2005). This evidence supports the view that cheating can be beneficial under specific conditions (LeBas and Hockham 2005). However, cheating could be ineffective in the long run as the females evolve in response to male deception.

6. Conclusion

Despite all of the evidence and explanatory power of the hypotheses of nuptial gifts, there is more research to be done. In particular, much of the current effort focuses on behavioral observations, in contrast to genetic analysis. It may be possible that in some taxa there is no apparent reason for the female to accept gifts, even if there was once an evolutionary advantage for doing so. Instead, it’s possible that the trait for giving gifts and the preference for giving gifts are under linkage disequilibrium. For example, if a female is more likely to select a gift-giving mate, she likely received the preference for the trait from her mother. By extension, if her mother had this preference, her father likely gave a gift to her mother. In this way the traits may be linked.

It has been demonstrated that nuptial gift strategies are varied across taxa. Further investigations into other taxa of arthropods may necessitate more research as different behaviors are observed. Currently, P. mirabilis is the prime candidate due to the ease of rearing it in captivity for experiments (Prokop and Maxwell 2012). Other methods may allow us to observe taxa for which we have little data. This would broaden our understanding of the phenomenon and give us more explanatory power when applying our knowledge to newly documented species.

Literature Cited

Ghislandi P.G., M.J. Albo, C. Tuni, & T. Bilde (2014). Evolution of deceit by worthless donations in a nuptial gift-giving spider. Current Zoology 60(1):43-51.

Kuriwada T., Kasuya E. (2012). Nuptial gifts protect male bell crickets from female aggressive behavior. Behavioral Ecology 23(2):302-306. (doi:10.1093/beheco/arr186)

LeBas N.R., Hockham L.R. (2005). An Invasion of Cheats: The Evolution of Worthless Nuptial Gifts. Current Biology 15(1):64-67. (doi:10.1016/j.cub.2004.12.043)

Prokop P. (2006). Insemination does not affect female mate choice in a nuptial feeding spider., Italian Journal of Zoology 73(3):197-201. (doi:10.1080/11250000600727741) Prokop P., Maxwell M.R. (2012). Gift carrying in the spider Pisaura mirabilis: nuptial gift contents in nature and effects on male running speed and fighting success. Animal Behaviour 83(6): 1395-1399. (doi:10.1016/j.anbehav.2012.03.007)

Sakaluk S.K. (2000). Sensory exploitation as an evolutionary origin to nuptial food gifts in insects. Proc. R. Soc. Lond. B. 267:339-343. (doi:10.1098/rspb.2000.1006)

Stålhandske P. (2001). Nuptial gift in the spider Pisaura mirabilis maintained by sexual selection. Behavioral Ecology 12(6):691-697. (doi:10.1093/beheco/12.6.691)

Wedell N., Ritchie M.G. (2004). Male age, mating status and nuptial gift quality in a bushcricket. Animal Behavior 67(6):1059-1065. (doi:10.1016/j.anbehav.2003.10.007)

Suggestions https://en.wikipedia.org/wiki/Nuptial_gift

1. Stålhandske's research suggests female spiders receiving gifts don't receive an increase in fitness due to the gifts, unlike other research. This should be mentioned as it's worth outlining all of the current research. 2. Discuss research which shows female mate choice is dependent on nuptial gifts independent of female reproductive status (virgin vs mated). This reflects the importance of the gift while noting other factors may not be as important. 3. Discuss the additional benefit of protection from cannibalizing females in species such as the bell cricket.

Sentence: Additionally, female mate choice is dependent on nuptial gifts rather than female reproductive status as a mated or unmated individual.

Reference: Prokop P. (2006). Insemination does not affect female mate choice in a nuptial feeding spider. Italian Journal of Zoology, 73(3), 197-201. (doi:10.1080/11250000600727741)

Annotated Bibliography Topic: How did nuptial gifts evolve in arthropods? Does this strategy benefit males and females equally?

1) Ghislandi P.G., Albo M.J., Tuni C., & Bilde T. (2014). Evolution of deceit by worthless donations in a nuptial gift-giving spider. Current Zoology, 60(1), 43-51.

The authors intend on addressing how deceit could evolve to be an evolutionary stable strategy in spiders which offer nuptial gifts in order to copulate. They suggest that deceit is a viable strategy due to its rarity, among other factors. By looking at deceit in nuptial gifts, it is possible to gain a better understanding of the origins of this trait. The authors are affiliated with the Department of Bioscience at Aarhus University in Denmark.

2) Stålhandske P. (2001). Nuptial gift in the spider Pisaura mirabilis maintained by sexual selection. Behavioral Ecology, 12(6), 691-697. (doi:10.1093/beheco/12.6.691)

The research evaluates the potential mechanism underlying the evolution of nuptial gifts and whether it affects the fitness of male or female spiders. It concludes that males increase their fitness, but females don’t show any increased fitness based on gifts alone. This position provides a contrast to other research, which suggest both females and males benefit from nuptial gift-giving. The author is affiliated with the Department of Zoology at the University of Gothenburg in Sweden.

3) LeBas N.R., Hockham L.R. (2005). An Invasion of Cheats: The Evolution of Worthless Nuptial Gifts. Current Biology, 15(1), 64-67. (doi:10.1016/j.cub.2004.12.043)

The main purpose of this work is to examine deception in males of species which provide nuptial gifts. The author argues that current models inadequately describe how cheating could evolve in species where copulation rate is enhanced by nuptial gift-giving. Although this research focuses on flies, it’s possible it will provide insight into the mechanisms of the evolution of nuptial gifts, especially when compared with similar experiments in spiders. The authors are affiliated with the Department of Environmental and Evolutionary Biology at the University of St. Andrews in the United Kingdom.

4) Kuriwada T., Kasuya E. (2012). Nuptial gifts protect male bell crickets from female aggressive behavior. Behavioral Ecology, 23(2), 302-306. (doi:10.1093/beheco/arr186)

Here the researchers investigate nuptial gifts as an adaptation and whether or not they present an advantage to females. The authors conclude that gift-giving protects males from females, which should increase the fitness of males which offer nuptial gifts. The crickets offer secretions as gifts, which contrasts to the methods employed by spiders, but the underlying reason to do so is similar. The authors are affiliated with the Department of Biology at Kyushu University in Japan.

5) Prokop P. (2006). Insemination does not affect female mate choice in a nuptial feeding spider. Italian Journal of Zoology, 73(3), 197-201. (doi:10.1080/11250000600727741)

The mission of this research is to compare female mate choice based on her mating status. Generally, virgin females did not allow males without gifts to copulate, which suggests that the nuptial gift is essential to the fitness of the male spiders. Although this research aims to test a hypothesis independent of the evolution of nuptial gifts, instead focusing on female response, its conclusion provides insight into the mechanism of its evolution. The author is affiliated with the Department of Biology at the University of Trnava and Institute of Zoology in Slovakia.