A secondary sex trait under construction: age- and nutrition-related salivary gland development in a scorpionfly (Insecta: Mecoptera)

Males of Panorpa vulgaris Imhoff and Labram, 1836 (Insecta: Mecoptera) can apply three alternative mating tactics to gain access to female mating partners: (1) without nuptial feeding, (2) providing females with a dead arthropod or (3) producing salivary masses. Providing females with salivary masses during copulation leads to the highest reproductive success, as it results in longer mating durations relative to the other tactics. While the number of sperm transferred correlates with the duration of copulation, the sperm of different males are used according to the fair raffle model. Therefore, salivary mass production is an important fitness determining factor for males. In order to provide females with salivary masses, males must first produce and store saliva secretion inside their salivary glands. The present study was concerned with the development of male salivary glands (= production of saliva) in the course of time after adult emergence. We can show that saliva production did not start before adult emergence, that the state of development of salivary glands was affected by larval nutrition as well as by adult nutrition and, moreover, by age. Older individuals had developed glands of greater mass than had younger animals. After receiving a one‐time feeding immediately after eclosion salivary gland mass increased, while body mass decreased with age. Therefore, male P. vulgaris were able to enlarge the amount of their mating resources (= saliva) independently from external nutritional supply (after the initial feeding) and at the expense of losing weight. Possible reasons and functional explanations are discussed.     

Nuptial food gifts influence female egg production in the scorpionfly Panorpa cognata

Abstract.  1. Before copulation, male Panorpa cognata scorpionflies offer females a salivary secretion, which is consumed by the female during copulation. It has previously been demonstrated that this nuptial food gift functions as mating effort by increasing male attractiveness and by increasing ejaculate transfer during copulation.
2. In this study, the effect of saliva consumption on female reproductive output was investigated, and thus the possibility that nuptial food gifts also serve as paternal investment. The experimental design enabled the effect of nuptial gift consumption to be disentangled from other possible effects of multiple mating or increased copula duration.
3. The results showed that saliva consumption increases female egg production by on average 8% (4.5 eggs) per consumed salivary mass, whereas mean egg weight was not influenced.4. These results have important implications for the evolution and maintenance of both male nuptial gifts and female polyandry in this and other species.     

The function of nuptial feeding in insects: a review of empirical studies

Nuptial feeding encompasses any form of nutrient transfer from the male to the female during or directly after courtship and/or copulation. In insects, nuptial gifts may take the form of food captured or collected by the male, parts, or even the whole of the male's body, or glandular products of the male such as salivary secretions, external glandular secretions, the spermatophore and substances in the ejaculate. Over the past decade, there has been considerable debate over the current function of nuptial feeding in insects. This debate has centred on the issue of whether nuptial gifts function as paternal investment (i.e. function to increase the fitness and/or number of the gift-giving male's own offspring) or as mating effort (i.e. function to attract females, facilitate coupling, and/or to maximize ejaculate transfer), although the two hypotheses are not mutually exclusive. In the present article, evidence for the potential of nuptial gifts to function as either paternal investment, mating effort, or both is reviewed for each form of nuptial feeding in each insect taxon for which sufficient data are available. Empirical evidence suggests that many diverse forms of nuptial feeding in different insect taxa function, at least in part, as mating effort. For example, nuptial prey and salivary masses in the Mecoptera, regurgitated food in Drosophila (Diptera), hind-wing feeding in Cyphoderris (Orthoptera) and the secretion of the male's cephalic gland in Neopyrochroa (Coleoptera) and Zorotypus (Zoraptera) appear to function to entice females to copulate and/or to facilitate coupling. Nuptial prey and salivary masses in the Mecoptera also appear to function to maximize ejaculate transfer (which is also a form of mating effort), as do nuptial prey in Empis (Diptera), external glandular secretions in Oecanthus and Allonemobius (Orthoptera) and the spermatophylax in gryllids and tettigoniids (Orthoptera). Large spermatophores in, for example, the Lepidoptera and Coleoptera, also appear to be maintained by selection on the male to maximize ejaculate transfer and thereby counter the effects of sperm competition. In contrast to the large amount of evidence in support of the mating effort hypothesis, there is a relative lack of good evidence to support the paternal investment hypothesis. Certain studies have demonstrated an increase in the weight and/or number of eggs laid as a result of the receipt of larger gifts, or a greater number of gifts, in tettigoniids, gryllids, acridids, mantids, bruchid beetles, drosophilids and lepidopterans. However, virtually all of these studies (with the possible exception of studies of the spermatophylax in tettigoniids) have failed to control adequately for hormonal substances in the ejaculate that are known to affect female reproductive output. Furthermore, in at least four tettigoniids (but not in the case of two species), three lepidopterans, a drosophilid and probably also bruchid beetles and bittacids, evidence suggests that the male has a low probability of fertilising the eggs that stand to benefit from his nuptial gift nutrients. Therefore, the hypothesis that paternal investment might account for the function of nuptial gifts in general is not supported.     

Is diversification in male reproductive traits driven by evolutionary trade-offs between weapons and nuptial gifts?

Many male animals have evolved exaggerated traits that they use in combat with rival males to gain access to females and secure their reproductive success. But some male animals invest in nuptial gifts that gains them access to females. Both these reproductive strategies are costly in that resources are needed to produce the weapon or nuptial gift. In closely related species where both weapons and nuptial gifts are present, little is known about the potential evolutionary trade-off faced by males that have these traits. In this study, we use dobsonflies (order Megaloptera, family Corydalidae, subfamily Corydalinae) to examine the presence and absence of enlarged male weapons versus nuptial gifts within and among species. Many dobsonfly species are sexually dimorphic, and males possess extremely enlarged mandibles that they use in battles, whereas in other species, males produce large nuptial gifts that increase female fecundity. In our study, we show that male accessory gland size strongly correlates with nuptial gift size and that when male weapons are large, nuptial gifts are small and vice versa. We mapped weapons and nuptial gifts onto a phylogeny we constructed of 57 species of dobsonflies. Our among-species comparison shows that large nuptial gift production evolved in many species of dobsonfly but is absent from those with exaggerated weapons. This pattern supports the potential explanation that the trade-off in resource allocation between weapons and nuptial gifts is important in driving the diversity of male mating strategies seen in the dobsonflies, whereas reduced male–male competition in the species producing large spermatophores could be an alternative explanation on their loss of male weapons. Our results shed new light on the evolutionary interplay of multiple sexually selected traits in animals.     

Influence of Nutrition on Courtship and Mating in the Scorpionfly Panorpa cognata (Mecoptera, Insecta)

Scorpionflies have been used as model organisms for the study of alternative male mating tactics as well as sexual conflict and coercive mating. Here we describe the courtship and mating behaviour of the scorpionfly Panorpa cognata at different levels of nutrition. Alternative mating tactics in scorpionflies involve nuptial food gifts, and we expected an effect of nutrient availability and male individual condition on the relative frequency of these mating tactics. Subsequent to female attraction by means of male pheromonal emission (calling) and a conspicuous pairing prelude, the majority of matings were initiated by male secretion of one relatively large salivary mass on which females feed during copulation. Usually, males produced only a single salivary mass per mating, and the copulation was terminated after the female had consumed the salivary mass. Alternatively, in 40% of the copulations, males offered females a dead arthropod as nuptial gift. However, these matings were neither preceded by male calling nor by the pairing prelude. Copulations with no gifts were extremely rare, and forced copulations were absent. The manipulation of the clamp‐like notal organ used by male scorpionflies in coercive matings had no effect on the duration of copulation, suggesting that P. cognata males are not able to enforce longer matings. Copulations involving salivary mass gifts were significantly longer than copulations with prey provided as gifts. Although contrary to our expectations, nutrition had no effect on the relative frequency of the different male mating tactics, it had several effects on courtship and mating. First, well‐fed individuals copulated significantly more often, both with prey and salivary secretions, than individuals with limited nutrient resources available. This was true for both sexes, although the effect was stronger for males. Higher availability of nutrients decreased the time until male and female sexual maturity and increased male calling duration per day. Furthermore, high nutrient availability decreased the duration of the pairing prelude, and consequently pairs started copulating earlier at night in the high nutrient treatment.     

Preferred males are not always good providers: female choice and male investment in tree crickets

Female tree crickets (Oecanthus nigricornis) prefer large malesbut do not receive larger glandular courtship gifts from thesemales. This finding is puzzling from both the male and femaleperspectives, because females should prefer males providingmore direct benefits, and because males who provide larger giftsachieve higher insemination success. We tested for differencesin the quality of male secretions and found that larger malesprovided more proteinaceous food gifts than did rivals, whichcould explain why they are preferred by females. The preferencein turn could cause depletion of food gift reserves in favoredmales, because natural remating rates are high and because evena single feeding bout negatively affects glandular stores. Mostintriguingly, we showed that preferred males can adaptivelydecrease the size of courtship food-gifts provided (in orderto conserve gifts for future mating events) when they perceivethat the probability of multiple future mating opportunitiesis high. Thus, the elevated mating rates of preferred males(both before and after a focal mating event) could account forthe small size of their courtship food-gifts.     

Nuptial gift consumption influences female remating in a scorpionfly: male or female control of mating rate?

In the scorpionfly Panorpa cognata, males provide females with saliva secretions as nuptial food gifts. Consequently, females derive material benefits and possibly also genetic benefits from multiple matings. Females therefore generally should have a high motivation to remate. Males, on the other hand, do not share this interest, which will generate a sexual conflict over remating interval, possibly leading to male adaptations that prevent females from remating with other males. In this study, I found that mated females were less prone to copulate than virgin females, despite female benefits of multiple matings. Further, I found that the remating interval was significantly longer if the first copulation was long compared to shorter matings. This effect does not entirely depend on copulation duration per se, but on the amount of saliva, that a female is consuming during copulation. These results suggest a mating-induced refractory period and can be interpreted as male manipulation of female remating behaviour mediated through substances in the nuptial gift. Alternatively, receiving large nuptial gifts may decrease the prospective direct fitness benefits from further copulations, and thus change optimal female remating rate. Furthermore, gift size has been shown to correlate with male nutritional condition, which may be an indicator of male genetic quality. Females may therefore benefit indirectly by not remating following copulations involving large saliva gifts. In this scenario, female remating interval would be an effect of cryptic female choice.     

Mating tactic dependent sperm transfer rates in Panorpa similis (Mecoptera; Panorpidae): a case of female control?

Abstract 1. Male Panorpa scorpionflies offer salivary masses as nuptial gifts during copulation. Previous studies have shown that there is usually a strong correlation between the number or size of salivary masses provided and copulation duration. As a result of constant sperm transfer rates, copulation duration is the most important determinant of male fitness in these species. 2. Differences in copulation durations for gift‐giving and non‐gift‐giving males of the Caucasian scorpionfly Panorpa similis have been shown to be much smaller on average than those observed in other Panorpa species. In this study, we therefore focus on the number of sperm transferred in copulations of P. similis both with and without salivary masses. 3. We find that although the average copulation duration in the presence of nuptial gifts is only twice as long as the average copulation duration without nuptial gifts, gift‐giving males transfer almost 11 times more sperm during copulations than non‐gift‐giving males. This is as a result of substantially higher sperm transfer rates (sperm/minute) in copulations in which nuptial gifts are present. 4. Implications of this finding for the interpretation of the mating system of P. similis and the question of which sex controls sperm transfer rates are discussed.     

Diet affects female mating behaviour in a seed‐feeding beetle

In species where males provide nuptial gifts, females can improve their nutritional status and thus increase their fecundity by mating when in need of resources. However, mating can be costly, so females should only mate to acquire resources when the need for resources is large, such as when females are nutritionally‐deprived. Two populations of the seed‐feeding beetle Callosobruchus maculatus, a species that produces relatively large nuptial gifts, are used to test whether female nutritional status affects mating behaviour. Female access to water, sugar and yeast are manipulated and the fitness consequences of these manipulations are examined together with the effects of diet on the propensity of nonvirgin females to mate. Access to water has a small but significant effect on mass loss over time, lifespan and fecundity of females, relative to unfed controls. Access to sugar (dissolved in water) improves female fecundity and lifespan above that of hydrated females but access to yeast has no positive effects on female survival or reproduction. Diet has a large effect on both receptivity of nonvirgin females to a male and how quickly they accept that male. Unfed females are both more likely to mate, and accept a mate more quickly, than females provided access to water, which are more likely to mate and accept a mate more quickly than females provided with sugar. This rank order of behaviours matches the order predicted if females increase their mating rate when nutritionally deprived (i.e. it matches the effect of diet on female fitness). The results obtained also suggest that mate choice may be condition‐dependent: females from one population (Burkina Faso) show a preference for large males when well‐fed but not when unfed, although this result is not found in a second population (South India). It is concluded that nutritionally‐deprived females are more receptive to mates than are well‐fed females, consistent with the hypothesis that females ‘forage’ for nuptial gifts, or at least more willingly accept sperm in exchange for nuptial gifts, when they are nutritionally deprived.     

Nuptial gift in the spider Pisaura mirabilis maintained by sexual selection

The nuptial prey gift in the spider Pisaura mirabilis has been suggested to function as a male protection against sexual cannibalismduring courtship and mating. This hypothesis together withtwo alternatives—male mating effort and paternal investment hypotheses—were tested in a laboratory experiment withsexually inexperienced males and females. One group of malesoffered no gift to the female while three groups of males offeredsmall, medium, or large sized gifts, respectively. No malewas cannibalized among 82 trials. Aggression was observed onlyin encounters where a gift was presented. Males without a gift courted females, and 40% of these males managed to copulate,compared to 90% of males offering a gift. The copulation durationwas positively correlated with gift size. In general, the femaleterminated the copulation and ran away with the gift. The proportionof eggs fertilized increased with copulation time. Presenceor size of the nuptial gift did not affect female fecundityor spiderling size significantly. The results refute the hypothesesof sexual cannibalism and paternal investment. The nuptialgift represents a male mating effort; it entices the femaleto copulate, facilitates coupling during copulation, and byprolonging copulation it may increase the amount of sperm transferred.I conclude that the nuptial prey gift in Pisaura mirabilisis maintained by sexual selection.     

Limits to Nuptial Gift Production by Male Fireflies, Photinus ignitus

Males of diverse insect species provide females with nuptial gifts, and limits on males' ability to produce these gifts may influence courtship behavior and mating systems. In the firefly Photinus ignitus, males transfer a complex spermatophore to females during mating. We provided firefly males unlimited access to responsive females to examine whether spermatophore production limits male mating success. Male spermatophore mass decreased significantly across sequential matings, and the percentage of successful matings declined during the second half of each male's life span. Male body mass explained a significant proportion of variation in size of the first spermatophore produced by P. ignitus males, but this relationship disappeared with second spermatophores. This study indicates that males' ability to produce spermatophores declines over their lifetime and that limits on nuptial giftproduction can constrain male mating success in Photinus fireflies.     

Sex-specific response to nutrient limitation and its effects on female mating success in a gift-giving butterfly

Animals with complex life cycles respond to early food limitation by altering the way resources are allocated in the adult stage. Response to food limitation should differ between males and females, especially in organisms whose mating systems include nutritional nuptial gifts. In these organisms, males are predicted to keep their allocation to reproduction (sperm and nuptial gift production) constant, while females are predicted to sacrifice allocation to reproduction (egg production) since they can compensate by acquiring nuptial gifts when mating. In this study, we investigated how dietary nitrogen limitation during the larval stage affects sex-specific resource allocation in Pieris rapae butterflies. Also, we tested whether nutrient-limited females increased nuptial gift acquisition as a way to compensate for low allocation to reproduction. We found that as predicted females, but not males, sacrifice allocation to reproduction when larval dietary nitrogen is limited. However, females were unable to compensate for this low reproductive allocation by increasing their mating rate to acquire additional gifts. Females reared on low nitrogen diets also reduced wing coloration, a potential signal of female fecundity status. We suggest that female mating frequency is constrained by male mate choice based on females’ wing coloration. This study provides new insights into how larval dietary nitrogen, a key nutritional resource for all herbivores, alters male and female allocation to reproduction as well as to ornamentation.     

Structural evidence why males of Panorpa liui offer prey rather than salivary mass as their nuptial gift

Ma, N. and Hua, B. 2010. Structural evidence why males of Panorpa liui offer prey rather than salivary mass as their nuptial gift. —Acta Zoologica (Stockholm) 92 : 398–403. The scorpionflies are considered as ideal model animals for the study of mating systems in insects. The males generally offer both prey and salivary mass as nuptial gifts to the females during copulation. Our field observations show that Panorpa liui is peculiar because the males offer only prey rather than salivary secretions as nuptial gift. Through anatomical and histological examinations, the salivary glands of P. liui were found to be devoid of sexual dimorphism in Panorpa for the first time. Both the male and female P. liui bear simple salivary glands, which are only composed of a common duct and two short sac‐like glands. This is the first attempt to explore the relationship between the salivary glands and the mating tactics from the structural aspect in Panorpa, speculating that the simple structure of the male salivary glands in P. liui might be responsible for its failing to produce salivary mass as a nuptial gift during copulation. Compared with Boreidae, Meropidae, Bittacidae and Panorpidae, we presume that the absence of sexual dimorphism of the salivary glands might represent a plesiomorphy in P. liui. The origin and evolutionary process of the nuptial gift behaviour are tentatively speculated in Panorpa.     

Non-random Mating in the Dance Fly Empis borealis: The Importance of Male Choice

In the dance-fly Empis borealis (Diptera, Empididae), females form swarms to which males, carrying a nuptial gift, come for mating. We examined whether males or females were choosy and/or competed for mates. First, measurements of the size relationships between copulating males and females, nuptial gifts and the swarming females from different swarms were assessed. Second, male visiting time in differently sized female swarms was recorded. Larger (wing-length) females participated disproportionately in copulations in each swarm, but not for the population at large. Female mating status (virgin/non-virgin) or proximity to oviposition (egg size) did not influence the likelihood of copulation. No assortative mating pattern was found: male size and size of nuptial gift did not correlate with size of the mating female. The time spent by males in swarms increased with the number of females present and it took longer when males left a swarm without copulation than when doing so. Male visiting time per female was negatively correlated with number of females in swarms. Males more often left smaller than larger swarms without mating. We conclude that E. borealis males discriminate among females but find no evidence for male competition or for female choice. It is still a question to what degree females compete for males.     

Worthless and Nutritive Nuptial Gifts: Mating Duration,Sperm Stored and Potential Female Decisions in Spiders

In nuptial gift-giving species females sometimes select their potential mates based on the presence and size of the gift. But in some species, such as the Neotropical polyandrous spider Paratrechalea ornate male gifts vary in quality, from nutritive to worthless, and this male strategy can be in conflict with female nutritional benefits. In this species, males without gifts experience a reduction in mating success and duration, while males that offer worthless or genuine nutritive gifts mate with similar frequencies and durations. The female apparently controls the duration of copulation. Thus, there is scope for females to favour males offering gifts and further if these are nutritious, via post-copulatory processes. We first tested whether females differentially store sperm from males that offer the highest nutritional benefits by experimentally presenting females with males that offer either nutritive or worthless gifts (uninterrupted matings). Second, we carried out another set of experiments to examine whether females can select sperm based only on gift presence. This time we interrupted matings after the first pedipalp insertion, thus matching number of insertions and mating duration for males that: offered and did not offer gift. Our results showed that the amount of sperm stored is positive related to mating duration in all groups, except in matings with worthless gifts. Gift presence itself did not affect the sperm stored by females, while they store similar number of sperm in matings with males offering either nutritive or worthless gifts. We discuss whether females prefer males with gifts regardless, if content, because it represents an attractive and/or reliable signal. Or alternatively, they prefer nutritive nuptial gifts, as they are an important source of food supply and/or signal of male donor ability.     

The notal organ of the scorpionfly (Panorpa vulgaris): an adaptation to coerce mating duration

The notal organ in P. vulgaris (Insecta: Mecoptera) is a clamplikestructure on the dorsum of the middle of the male’s abdomenthat holds one of the female’s forewings throughout mating.Males often provide salivary masses as food to their mates duringmating, and a male’s ability to produce saliva dependsupon whether he has fed adequately before mating. To test thehypothesis that the evolutionary function of the notal organis to coerce longer matings than are in the interests of females,the notal organ and the amount of food males and females receivebefore mating were experimentally manipulated. In support ofthe hypothesis, copulation was reduced when the notal organwas made inoperative under the following four conditions: (1)female fed and male starved before mating, no saliva duringmating; (2) same as in condition 1 but with one salivary massduring mating; (3) both sexes starved before mating, no salivarymass during mating; and (4) both sexes fed before mating. However,when females were starved before mating and males were fed,resulting in multiple masses being provided during mating, thenotal organ had no effect on length of copulation, and thusthere was no sexual conflict over mating duration. In addition,the larger the female relative to her mate, the briefer thecopulation when the notal organ was operative, which suggeststhat a physical struggle between the male and female may occurduring sexual conflict about mating duration. This is one ofonly a few studies that provide evidence of adaptation to thedomain of sexual coercion. [Behav Ecol 1991;2:156–164]     

The evolution of sex differences in mate searching when females benefit: new theory and a comparative test

Sexual selection is thought to have led to searching as a profitable, but risky way of males obtaining mates. While there is great variation in which sex searches, previous theory has not considered search evolution when both males and females benefit from multiple mating. We present new theory and link it with data to bridge this gap. Two different search protocols exist between species in the bush-cricket genus Poecilimon (Orthoptera): females search for calling males, or males search for calling females. Poecilimon males also transfer a costly nuptial food gift to their mates during mating. We relate variations in searching protocols to variation in nuptial gift size among 32 Poecilimon taxa. As predicted, taxa where females search produce significantly larger nuptial gifts than those where males search. Our model and results show that search roles can reverse when multiple mating brings about sufficiently strong material benefits to females.     

Ejaculate size, second male size, and moderate polyandry increase female fecundity in a seed beetle

Several hypotheses have been proposed to explain the evolutionof polyandry in species that provide nuptial gifts. When nuptialgifts are in the form of nutritional elements in the ejaculateand ejaculate size is correlated with male body size, femalescan accrue both direct (nutritional) and indirect (genetic)benefits from multiple mating. We examined remating decisionsin females of the seed beetle Stator limbatus and, using pathanalysis, examined the effects of male body size on the sizeof his ejaculate, the amount of ejaculate that was successfullytransferred to females, and the overall effect of these variableson female fecundity. Larger males produced larger ejaculatesand consequently transferred a larger ejaculate to females,but the effects on female fecundity differed between the females'first and second mates. Both larger first and second males wereable to transfer more of their ejaculate to females than weresmaller males. Both the total amount of ejaculate transferredby these males and polyandry (number of matings) were positivelycorrelated to female fecundity independently of each other.However, larger second males were more successful at stimulatingfemale fecundity independently of how much ejaculate they transferred.We also provide evidence that females are choosy during theirsecond mating opportunity. Both female choosiness and higherfemale investment after mating with larger second males suggestthat females may benefit from both direct and indirect effectsfrom multiple mating. We also conclude that male body size isunder both directional fecundity selection and directional sexualselection.     

Weighing costs and benefits of mating in bushcrickets (Insecta: Orthoptera: Tettigoniidae), with an emphasis on nuptial gifts,protandry and mate density

ABSTRACT: Sexual selection is a major force driving evolution and is intertwined with ecological factors. Differential allocation of limited resources has a central role in the cost of reproduction. In this paper, I review the costs and benefits of mating in tettigoniids, focussing on nuptial gifts, their trade-off with male calling songs, protandry and how mate density influences mate choice. Tettigoniids have been widely used as model systems for studies of mating costs and benefits; they can provide useful general insights. The production and exchange of large nuptial gifts by males for mating is an important reproductive strategy in tettigoniids. As predicted by sexual selection theory spermatophylax size is condition dependent and is constrained by the need to invest in calling to attract mates also. Under some circumstances, females benefit directly from the nuptial gifts by an increase in reproductive output. However, compounds in the nuptial gift can also benefit the male by prolonging the period before the female remates. There is also a trade-off between adult male maturation and mating success. Where males mature before females (protandry) the level of protandry varies in the direction predicted by sperm competition theory; namely, early male maturation is correlated with a high level of first inseminations being reproductively successful. Lastly, mate density in bushcrickets is an important environmental factor influencing the behavioural decisions of individuals. Where mates are abundant, individuals are more choosey of mates; when they are scarce, individuals are less choosey. This review reinforces the view that tettigoniids provide excellent models to test and understand the economics of matings in both sexes.     

Unpredictable environments,nuptial gifts and the evolution of sexual size dimorphism in insects: an experiment

Many insects have a mating system where males transfer nutrients to females at mating, which are often referred to as ''nuptial gifts''. Among butterflies, some of the characteristic features of these species are polyandry (females mate multiple times), and relatively large male ejaculates. When males produce part of the resources used for offspring, the value of body size might then increase for males and decrease for females. The male/female size ratio is also observed to increase when the degree of polyandry and gift size increase. Butterfly species where gift-giving occurs are generally more variable in body size, suggesting that food quality/quantity fluctuates during juvenile stages. This will cause some males to have much to provide and some females to be in great need, and could be conducive to the evolution of a gift-giving mating system. In such a system, growing male and female juveniles should react differently to food shortage. Females should react by maturing at a smaller size since their own lack of reproductive resources can partly be compensated for by male contributions. Males have to pay the full cost of decreased reproduction if they mature at a small size, making it more important for males to keep on growing, even when growth is costly. An earlier experiment with the polyandrous and gift-giving butterfly, Pieris napi, supported this prediction. The pattern is expected to be absent or reversed for species with small nuptial gifts, where females do not benefit from mating repeatedly, and will thus be dependent on acquiring resources for reproduction on their own. To test this prediction, we report here on an experiment with the speckled wood butterfly, Pararge aegeria. We find that growth response correlates with mating system in the two above species, and we conclude that differences in environmental conditions between species may act as an important factor in the evolution of the mating system and sexual size dimorphism.