BACKGROUND
differences in the evolutionary interests between the sexes over maximizing reproductive success commonly lead to inter-sexual conflict  <cit> .
this conflict influences the opportunity, form and intensity of sexual selection that drives the evolution of traits that enhance mating success  <cit> .
traits that differ in optimum between males and females may include the number of mates, copulation duration, fertilization success as well as parental investment in offspring  <cit> .
male-male competition may be a particular strong driver of sexually antagonistic traits; thus to enhance their success in sperm competition, males may be under selection to manipulate females to mate at a suboptimal rate  <cit> .
in species where males provide females with a nuptial gift during mating, there is particular scope for males to manipulate females to acquire matings and prolong copulation to enhance their fertilization success  <cit> .
female choice for males with nuptial gifts could lead to the evolution of male "deception" by the use of token gifts.
for instance, males can decrease the costs of mating by re-using gifts or by offering worthless gifts  <cit> .
males of some dance flies  may deceive females by offering inadequate or false gifts  <cit> .
although males that offer inedible gifts run a higher risk of being rejected and may suffer from shorter matings compared to males offering edible gifts, the chance of acquiring an extra mating should make deception an attractive strategy for males.
hence, males of the dance fly rhamphomyia sulcata that use inedible token gifts to obtain mates are as successful as males offering small genuine gifts  <cit> .
in spiders, nuptial gifts in the form of prey are restricted to a few species from two families belonging to the superfamily lycosoidea: pisauridae and trechaleidae  <cit> .
in both families, the male courts the female by offering a prey wrapped in silk and mating occurs while the female consumes the gift  <cit> .
in the species pisaura mirabilis  the gift functions as a mating effort that increases male mating success  <cit> ; a similar function was recently suggested for the trechaleid spider, paratrechalea ornata  <cit> .
in both species, males can obtain mating without a gift, but male mating success increases dramatically when a gift is offered  <cit> .
in p. mirabilis, the male pushes up the female during mating and performs alternate pedipalp insertions into the female sperm storage organs placed ventrally on the abdomen.
after each insertion the male returns to a face-to-face position with the female, grabbing the gift in the chelicerae  <cit> .
females usually control mating duration and they often attempt to run away with the gift upon terminating the copulation  <cit> .
during each insertion the male and the female remain motionless.
however, if the female moves and attempts to terminate copulation, the male may perform "thanatosis" which is a "death feigning" behaviour  unique to this species.
the male ends the insertion and grasp the gift with his chelicerae.
the female moves away while holding the nuptial gift and the male is dragged along until the female stops.
subsequently he "revives" and resumes mating  <cit> .
thanatosis functions as a mating effort that increases the male's chances of completing or prolonging the copulation  <cit> .
silk wrapping facilitates male handling and control over the gift  <cit> , as it facilitates a stronger hold of the silk covered package, both with the chelicerae and the feet claws, compared to an unwrapped insect.
as a result, females are less likely to succeed in stealing a wrapped than an unwrapped gift  <cit> .
in addition, stålhandske  <cit>  showed that relatively brighter gifts, i.e.
gifts that were wrapped in plenty of white silk, were more attractive to females, suggesting an additional function of silk wrapping that directly influences mate choice.
the prey gift and silk wrapping thus provide males with opportunities to exploit female foraging preferences in a sexual context  <cit> .
male spiders have a unique opportunity for gift manipulation through the gift wrapping trait, for example by preventing female assessment of the gift content.
by disguising the gift content males may deceive females to copulate, while the female attempts to consume the gift.
in p. ornata, males were observed wrapping prey carrion and occasionally inedible items such as plant seeds  <cit> .
in p. mirabilis, males have been reported to carry gifts containing empty arthropod exoskeletons or plant parts  <cit> , gifts that are of no nutritional value.
dissection of  <dig> gifts carried by males in the field showed that 62% contained fresh prey, while the remaining 38% contained empty arthropod exoskeletons, i.e.
prey already sucked out probably by the male itself .
such evidence suggests that males of p. mirabilis may exploit the female's preference for prey gifts to gain a reproductive advantage without providing the nutritional benefit of fresh prey from which the gift-giving trait must ultimately have evolved  <cit> .
the costs of prey capture and gift construction may thus interact with male condition to favour the evolution of male deceit by donation of worthless gifts  <cit> .
here we tested male use of worthless gifts and investigated their effect on male and female reproductive success in a scandinavian population of p. mirabilis.
we explored how the gift content affects reproductive success in experimental trials where males offered either genuine prey gifts, worthless gifts, or no gift to females.
males are under strong selection to provide a gift  <cit> ; therefore, we expected males to offer a worthless  item if no prey is available.
males offering worthless gifts may initially be accepted by females, however during feeding the females should realize the low nutritional value of the gift and respond appropriately, e.g.
by interrupting the mating prematurely.
as a consequence, males would experience shorter matings, lower sperm transfer and ultimately lower reproductive success than males offering genuine gifts.
RESULTS
courtship and mating
in the worthless gift group ,  <dig> males  produced a worthless gift for courtship and  <dig> out of these mated, whereas the remaining  <dig> males  courted without a gift and only one mated .
comparing all treatment groups, males that offered a worthless gift  were equally successful in obtaining mating as those offering a genuine gift , whereas males with no gift  experienced significantly reduced mating success .
the total mating duration was significantly shorter for ng males compared with males that offered a gift .
although wg males experienced a 20% shorter mating duration compared with pg and fg males, this effect was not statistically significant .
insertion duration, which reflects the duration of actual sperm transfer, was significantly shorter for wg males compared with males offering genuine gifts, and shortest for males with no gift .
the number of pedipalp insertions followed a similar pattern .
male thanatosis and gift control
male death feigning  occurred in more than 50% of the trials in the pg and fg groups, with only one occurrence in the wg group and none in the ng group .
in the pg and fg groups, females terminated mating and retained the gift in all mating trials, in  <dig> out of  <dig> cases females and males were observed fighting over the gift.
in the wg group, all females that accepted the non-nutritive gift actively manipulated it, moving the item with the chelicerae and pedipalps in the same way as females from the pg and fg groups.
cotton balls were wet after handling, suggesting that the females had regurgitated digestive fluids on them in an attempt to feed on the gift.
we did not observe fights between males and females over the non-nutritive items.
worthless items and gift construction
in the wg group, the males preferred cotton balls over prey leftovers and flower heads .
two males wrapped and combined two items: one male combined a prey leftover and a flower head, while the other combined a prey leftover and a cotton ball.
to measure male silk investment in worthless gifts, we compared the duration of gift wrapping for wg and fg gifts.
males with worthless gifts spent less time on gift construction  than those with fly gifts   and showed a tendency to perform fewer wrapping bouts  than males with fly gifts  .
males with cotton ball gifts  performed a significantly lower number of wrapping bouts  compared to males with fly gifts  .
oviposition, spiderling emergence and female life span
we found no significant differences in the proportion of mated females that constructed an egg-sac among groups;  <dig>  pg females,  <dig>  fg females,  <dig>  wg females and  <dig>  ng females constructed an egg-sac .
the time until egg-sac hatching was similar among groups:  <dig>  days  in pg,  <dig>  days  in fg,  <dig>  days  in wg and  <dig>  days  in ng .
egg hatching success differed among groups, and was higher when females had received a gift  compared with no gift .
we found no significant differences in clutch-size or the number of spiderlings that emerged from the egg-sac among groups .
spiderling size differed among groups, the largest spiderlings appeared to be found in the wg group, however a significant treatment by clutch-size interaction and a significant positive co-variation between clutch size and spiderling size make a simple interpretation of these data difficult .
χ2group=  <dig>
χ2clutch-size =  <dig>
< <dig>
< <dig>
2
1
nsp = spiderlings sample size; nes= egg-sac sample size.
spiderling size was analyzed with glm with clutch size as covariate.
groups with the same letter were not significantly different .
mated females did not differ in adult lifespan among groups  days, fg females  <dig>   days, wg females  <dig>   days, and ng females  <dig>   days, n = 61).
discussion
we showed that p. mirabilis males that offered worthless gifts acquired similar copulation success as males offering genuine nutritional gifts.
in contrast, males with no gift experienced a significantly reduced mating success.
previous studies have demonstrated strong female preference for a prey gift , suggesting direct benefits to females of receiving a nuptial gift  <cit> .
together these findings support the hypothesis that strong selection on the nuptial gift-giving trait facilitates the evolution of male deception through donation of worthless gifts.
we suggest that the gift wrapping trait allows males to take advantage of the female preference for a gift by disguising the gift content, thus deceiving females into mating without acquiring a direct benefit.
probably gift wrapping was crucial for deceit to evolve, while gift wrapping itself evolved due to additional advantages to the male: it increases male control over the gift and mating  <cit> , and mating duration increases with the amount of silk invested in wrapping  <cit> .
male deceit may be costly for females if it results in a higher than optimal mating rate, without conferring females a direct benefit  <cit> .
if deception with worthless gifts is common , females should evolve the ability to discriminate nutritive and non-nutritive gifts and avoid mating with males offering worthless gifts.
indeed we found that females terminated copulations with males that offered worthless donations sooner than copulations with males offering genuine gifts.
this supports the hypothesis that the female can not evaluate the gift's value before having fed on it for some time.
males with worthless donations experienced shorter insertion duration and thus had less time to transfer sperm.
this reveals a cost of deception for males, as shorter copulations and reduced sperm transfer disadvantages males in sperm competition  <cit> .
females that received a worthless gift did not retain the gift post-mating while they always retained genuine prey gifts, indicating that the nutritional value of the gift was actually revealed to the female during gift consumption and mating.
female preference for a genuine prey gift combined with her control over mating duration therefore counteracts male deception.
however, males appear to hold the upper hand in the co-evolutionary cycle, since deception is only discovered after the copulation is initiated.
males offering worthless gifts were less likely to feign dead , which is puzzling, as thanatosis functions as a male mating effort  <cit> .
however, males often feign death if the female attempts to steal the gift without mating  <cit> .
as the females did not try to run away with the worthless gifts, there was less scope for males to use thanatosis to prolong the copulation.
we did not detect strong negative effects of worthless donations on female reproductive fitness.
females receiving no gift, however, experienced reduced egg hatching success.
this may suggest that successful sperm transfer  is tightly coupled to whether the female receives a gift or not, but not to actual gift content .
males that mated without a gift experienced shorter copulations and fewer pedipalp insertions, indeed indicating that the gift facilitates sperm transfer, at least through its effect on mating duration.
this produces a strong incentive on males to present any type of gift rather than no gift.
while copulation is possible without a gift, the short mating and insertion durations make mating without a gift unsuccessful.
to some extent this also holds for mating with worthless gifts.
we found an effect of gift type on spiderling size, though not in the direction expected if worthless gifts had negative effects on spiderling size.
instead, females receiving protein gifts which were presumably of the highest nutritional quality produced the smallest spiderlings; this effect was partly explained by the positive co-variation between clutch size and spiderlings size.
positive nutrient effects of the gift might be revealed in female adult life span  <cit> , however, female longevity was similar among groups.
overall we found no indication of a cost of worthless donations on female reproductive fitness.
as females in our study received only a single gift, it is possible that the small amount of nutrients obtained through one gift is insufficient to detect an effect of nuptial gift quality on female fitness traits.
pisaura mirabilis females are polyandrous  <cit> , and may thus benefit from receiving multiple nuptial gifts.
nuptial feeding may be particularly beneficial for females in poor feeding condition, and such females would benefit from the ability to choose males with a nutritive gift  <cit> .
the cost for females of receiving worthless gifts is expected to vary with natural mating rates and to be high under poor foraging conditions.
among the non-nutritive items, males showed preference for using the cotton ball rather than the other inedible items as a nuptial gift.
since the cotton ball visually appears to resemble a silk wrapped gift, it is possible that males took advantage of this characteristic.
the preference may be for both colour  and shape : stålhandske  <cit>  showed increased female preference the whiter the gift, and andersen et al.
<cit>  showed male preference for a round gift compared with an elongate one, probably because the latter mechanically inhibited his access to the female's genitalia.
these features suggest that nuptial gift-giving spiders may be more restricted in the availability and suitability of worthless items to use as gifts compared to, for example, the empidid dance flies .
empidid dance flies offer a variety of token gifts that are not disguised, for example seed tufts, leaves, or small twigs, these gifts should be less costly to acquire than those of spiders, as they do not require prey capture and gift construction  <cit> .
in contrast, spider males are more conservative, they wrap insect exoskeletons which could be prey remains and only occasionally use plant material to construct gifts.
hence, even worthless donations are costly for the male to produce as they require investment in silk and time for gift production.
indeed gift production was shown to be costly, as p. mirabilis males in poor condition are constrained in their ability to construct nuptial gifts  <cit> .
CONCLUSIONS
there are large benefits to males of achieving a mating with a worthless donation, favouring male deception and the evolution of worthless gifts.
however, the potential disadvantage in sperm competition through shorter copulations effected by the females coupled with costs of gift construction counteracts deceit.
this may explain the maintenance of both mating tactics in the population and the prevalence of matings with genuine gifts.

 differences in the evolutionary interests between the sexes over maximizing reproductive success commonly lead to inter-sexual conflict. this conflict influences the opportunity, form and intensity of sexual selection that drives the evolution of traits that enhance mating success. traits that differ in optimum between males and females may include the number of mates, copulation duration, fertilization success as well as parental investment in offspring. male-male competition may be a particular strong driver of sexually antagonistic traits; thus to enhance their success in sperm competition, males may be under selection to manipulate females to mate at a suboptimal rate. in species where males provide females with a nuptial gift during mating, there is particular scope for males to manipulate females to acquire matings and prolong copulation to enhance their fertilization success. female choice for males with nuptial gifts could lead to the evolution of male "deception" by the use of token gifts. for instance, males can decrease the costs of mating by re-using gifts or by offering worthless gifts. males of some dance flies may deceive females by offering inadequate or false gifts. although males that offer inedible gifts run a higher risk of being rejected and may suffer from shorter matings compared to males offering edible gifts, the chance of acquiring an extra mating should make deception an attractive strategy for males. hence, males of the dance fly rhamphomyia sulcata that use inedible token gifts to obtain mates are as successful as males offering small genuine gifts. in spiders, nuptial gifts in the form of prey are restricted to a few species from two families belonging to the superfamily lycosoidea: pisauridae and trechaleidae. in both families, the male courts the female by offering a prey wrapped in silk and mating occurs while the female consumes the gift. in the species pisaura mirabilis the gift functions as a mating effort that increases male mating success; a similar function was recently suggested for the trechaleid spider, paratrechalea ornata. in both species, males can obtain mating without a gift, but male mating success increases dramatically when a gift is offered. in p. mirabilis, the male pushes up the female during mating and performs alternate pedipalp insertions into the female sperm storage organs placed ventrally on the abdomen. after each insertion the male returns to a face-to-face position with the female, grabbing the gift in the chelicerae. females usually control mating duration and they often attempt to run away with the gift upon terminating the copulation. during each insertion the male and the female remain motionless. however, if the female moves and attempts to terminate copulation, the male may perform "thanatosis" which is a "death feigning" behaviour unique to this species. the male ends the insertion and grasp the gift with his chelicerae. the female moves away while holding the nuptial gift and the male is dragged along until the female stops. subsequently he "revives" and resumes mating. thanatosis functions as a mating effort that increases the male's chances of completing or prolonging the copulation. silk wrapping facilitates male handling and control over the gift, as it facilitates a stronger hold of the silk covered package, both with the chelicerae and the feet claws, compared to an unwrapped insect. as a result, females are less likely to succeed in stealing a wrapped than an unwrapped gift. in addition, stålhandske showed that relatively brighter gifts, i.e. gifts that were wrapped in plenty of white silk, were more attractive to females, suggesting an additional function of silk wrapping that directly influences mate choice. the prey gift and silk wrapping thus provide males with opportunities to exploit female foraging preferences in a sexual context. male spiders have a unique opportunity for gift manipulation through the gift wrapping trait, for example by preventing female assessment of the gift content. by disguising the gift content males may deceive females to copulate, while the female attempts to consume the gift. in p. ornata, males were observed wrapping prey carrion and occasionally inedible items such as plant seeds. in p. mirabilis, males have been reported to carry gifts containing empty arthropod exoskeletons or plant parts, gifts that are of no nutritional value. dissection of gifts carried by males in the field showed that 62% contained fresh prey, while the remaining 38% contained empty arthropod exoskeletons, i.e. prey already sucked out probably by the male itself. such evidence suggests that males of p. mirabilis may exploit the female's preference for prey gifts to gain a reproductive advantage without providing the nutritional benefit of fresh prey from which the gift-giving trait must ultimately have evolved. the costs of prey capture and gift construction may thus interact with male condition to favour the evolution of male deceit by donation of worthless gifts. here we tested male use of worthless gifts and investigated their effect on male and female reproductive success in a scandinavian population of p. mirabilis. we explored how the gift content affects reproductive success in experimental trials where males offered either genuine prey gifts, worthless gifts, or no gift to females. males are under strong selection to provide a gift; therefore, we expected males to offer a worthless item if no prey is available. males offering worthless gifts may initially be accepted by females, however during feeding the females should realize the low nutritional value of the gift and respond appropriately, e.g. by interrupting the mating prematurely. as a consequence, males would experience shorter matings, lower sperm transfer and ultimately lower reproductive success than males offering genuine gifts.  courtship and mating in the worthless gift group, males produced a worthless gift for courtship and out of these mated, whereas the remaining males courted without a gift and only one mated. comparing all treatment groups, males that offered a worthless gift were equally successful in obtaining mating as those offering a genuine gift, whereas males with no gift experienced significantly reduced mating success. the total mating duration was significantly shorter for ng males compared with males that offered a gift. although wg males experienced a 20% shorter mating duration compared with pg and fg males, this effect was not statistically significant. insertion duration, which reflects the duration of actual sperm transfer, was significantly shorter for wg males compared with males offering genuine gifts, and shortest for males with no gift. the number of pedipalp insertions followed a similar pattern. male thanatosis and gift control male death feigning occurred in more than 50% of the trials in the pg and fg groups, with only one occurrence in the wg group and none in the ng group. in the pg and fg groups, females terminated mating and retained the gift in all mating trials, in out of cases females and males were observed fighting over the gift. in the wg group, all females that accepted the non-nutritive gift actively manipulated it, moving the item with the chelicerae and pedipalps in the same way as females from the pg and fg groups. cotton balls were wet after handling, suggesting that the females had regurgitated digestive fluids on them in an attempt to feed on the gift. we did not observe fights between males and females over the non-nutritive items. worthless items and gift construction in the wg group, the males preferred cotton balls over prey leftovers and flower heads. two males wrapped and combined two items: one male combined a prey leftover and a flower head, while the other combined a prey leftover and a cotton ball. to measure male silk investment in worthless gifts, we compared the duration of gift wrapping for wg and fg gifts. males with worthless gifts spent less time on gift construction than those with fly gifts and showed a tendency to perform fewer wrapping bouts than males with fly gifts. males with cotton ball gifts performed a significantly lower number of wrapping bouts compared to males with fly gifts. oviposition, spiderling emergence and female life span we found no significant differences in the proportion of mated females that constructed an egg-sac among groups; pg females, fg females, wg females and ng females constructed an egg-sac. the time until egg-sac hatching was similar among groups: days in pg, days in fg, days in wg and days in ng. egg hatching success differed among groups, and was higher when females had received a gift compared with no gift. we found no significant differences in clutch-size or the number of spiderlings that emerged from the egg-sac among groups. spiderling size differed among groups, the largest spiderlings appeared to be found in the wg group, however a significant treatment by clutch-size interaction and a significant positive co-variation between clutch size and spiderling size make a simple interpretation of these data difficult. χ2group= χ2clutch-size = < < 2 1 nsp = spiderlings sample size; nes= egg-sac sample size. spiderling size was analyzed with glm with clutch size as covariate. groups with the same letter were not significantly different. mated females did not differ in adult lifespan among groups days, fg females days, wg females days, and ng females days, n = 61). discussion we showed that p. mirabilis males that offered worthless gifts acquired similar copulation success as males offering genuine nutritional gifts. in contrast, males with no gift experienced a significantly reduced mating success. previous studies have demonstrated strong female preference for a prey gift, suggesting direct benefits to females of receiving a nuptial gift. together these findings support the hypothesis that strong selection on the nuptial gift-giving trait facilitates the evolution of male deception through donation of worthless gifts. we suggest that the gift wrapping trait allows males to take advantage of the female preference for a gift by disguising the gift content, thus deceiving females into mating without acquiring a direct benefit. probably gift wrapping was crucial for deceit to evolve, while gift wrapping itself evolved due to additional advantages to the male: it increases male control over the gift and mating, and mating duration increases with the amount of silk invested in wrapping. male deceit may be costly for females if it results in a higher than optimal mating rate, without conferring females a direct benefit. if deception with worthless gifts is common, females should evolve the ability to discriminate nutritive and non-nutritive gifts and avoid mating with males offering worthless gifts. indeed we found that females terminated copulations with males that offered worthless donations sooner than copulations with males offering genuine gifts. this supports the hypothesis that the female can not evaluate the gift's value before having fed on it for some time. males with worthless donations experienced shorter insertion duration and thus had less time to transfer sperm. this reveals a cost of deception for males, as shorter copulations and reduced sperm transfer disadvantages males in sperm competition. females that received a worthless gift did not retain the gift post-mating while they always retained genuine prey gifts, indicating that the nutritional value of the gift was actually revealed to the female during gift consumption and mating. female preference for a genuine prey gift combined with her control over mating duration therefore counteracts male deception. however, males appear to hold the upper hand in the co-evolutionary cycle, since deception is only discovered after the copulation is initiated. males offering worthless gifts were less likely to feign dead, which is puzzling, as thanatosis functions as a male mating effort. however, males often feign death if the female attempts to steal the gift without mating. as the females did not try to run away with the worthless gifts, there was less scope for males to use thanatosis to prolong the copulation. we did not detect strong negative effects of worthless donations on female reproductive fitness. females receiving no gift, however, experienced reduced egg hatching success. this may suggest that successful sperm transfer is tightly coupled to whether the female receives a gift or not, but not to actual gift content. males that mated without a gift experienced shorter copulations and fewer pedipalp insertions, indeed indicating that the gift facilitates sperm transfer, at least through its effect on mating duration. this produces a strong incentive on males to present any type of gift rather than no gift. while copulation is possible without a gift, the short mating and insertion durations make mating without a gift unsuccessful. to some extent this also holds for mating with worthless gifts. we found an effect of gift type on spiderling size, though not in the direction expected if worthless gifts had negative effects on spiderling size. instead, females receiving protein gifts which were presumably of the highest nutritional quality produced the smallest spiderlings; this effect was partly explained by the positive co-variation between clutch size and spiderlings size. positive nutrient effects of the gift might be revealed in female adult life span, however, female longevity was similar among groups. overall we found no indication of a cost of worthless donations on female reproductive fitness. as females in our study received only a single gift, it is possible that the small amount of nutrients obtained through one gift is insufficient to detect an effect of nuptial gift quality on female fitness traits. pisaura mirabilis females are polyandrous, and may thus benefit from receiving multiple nuptial gifts. nuptial feeding may be particularly beneficial for females in poor feeding condition, and such females would benefit from the ability to choose males with a nutritive gift. the cost for females of receiving worthless gifts is expected to vary with natural mating rates and to be high under poor foraging conditions. among the non-nutritive items, males showed preference for using the cotton ball rather than the other inedible items as a nuptial gift. since the cotton ball visually appears to resemble a silk wrapped gift, it is possible that males took advantage of this characteristic. the preference may be for both colour and shape: stålhandske showed increased female preference the whiter the gift, and andersen et al. showed male preference for a round gift compared with an elongate one, probably because the latter mechanically inhibited his access to the female's genitalia. these features suggest that nuptial gift-giving spiders may be more restricted in the availability and suitability of worthless items to use as gifts compared to, for example, the empidid dance flies. empidid dance flies offer a variety of token gifts that are not disguised, for example seed tufts, leaves, or small twigs, these gifts should be less costly to acquire than those of spiders, as they do not require prey capture and gift construction. in contrast, spider males are more conservative, they wrap insect exoskeletons which could be prey remains and only occasionally use plant material to construct gifts. hence, even worthless donations are costly for the male to produce as they require investment in silk and time for gift production. indeed gift production was shown to be costly, as p. mirabilis males in poor condition are constrained in their ability to construct nuptial gifts.  there are large benefits to males of achieving a mating with a worthless donation, favouring male deception and the evolution of worthless gifts. however, the potential disadvantage in sperm competition through shorter copulations effected by the females coupled with costs of gift construction counteracts deceit. this may explain the maintenance of both mating tactics in the population and the prevalence of matings with genuine gifts. 
in nuptial gift-giving species, benefits of acquiring a mate may select for male deception by donation of worthless gifts. the results suggest that strong selection on the nuptial gift-giving trait facilitates male deception by donation of worthless gifts. female preference for a genuine prey gift combined with control over mating duration, however, counteracts the male deception. we investigated the effect of worthless gifts on mating success in the spider pisaura mirabilis. males usually offer an insect prey wrapped in silk; however, worthless gifts containing inedible items are reported. we tested male mating success in the following experimental groups: protein enriched fly gift, regular fly gift, worthless gift, or no gift. males that offered worthless gifts acquired similar mating success as males offering nutritional gifts, while males with no gift experienced reduced mating success. females terminated matings faster when males offered worthless donations; this demonstrate a cost of deception for the males as shorter matings lead to reduced sperm transfer and thus give the deceiving males a disadvantage in sperm competition. we propose that the gift wrapping trait allows males to exploit female foraging preference by disguising the gift content thus deceiving females into mating without acquiring direct benefits.
 in nuptial gift-giving species, benefits of acquiring a mate may select for male deception by donation of worthless gifts. we investigated the effect of worthless gifts on mating success in the spider pisaura mirabilis. males usually offer an insect prey wrapped in silk; however, worthless gifts containing inedible items are reported. we tested male mating success in the following experimental groups: protein enriched fly gift, regular fly gift, worthless gift, or no gift.  males that offered worthless gifts acquired similar mating success as males offering nutritional gifts, while males with no gift experienced reduced mating success. the results suggest that strong selection on the nuptial gift-giving trait facilitates male deception by donation of worthless gifts. females terminated matings faster when males offered worthless donations; this demonstrate a cost of deception for the males as shorter matings lead to reduced sperm transfer and thus give the deceiving males a disadvantage in sperm competition.  we propose that the gift wrapping trait allows males to exploit female foraging preference by disguising the gift content thus deceiving females into mating without acquiring direct benefits. female preference for a genuine prey gift combined with control over mating duration, however, counteracts the male deception. 