Sex allocation in a simultaneously hermaphroditic marine shrimp

Two fundamental questions dealing with simultaneous hermaphrodites are how resources are optimally allocated to the male and female function and what conditions determine shifts in optimal sex allocation with age or size. In this study, I explored multiple factors that theoretically affect fitness gain curves (that depict the relationship between sex-specific investment and fitness gains) to predict and test the overall and size-dependent sex allocation in a simultaneously hermaphroditic brooding shrimp with an early male phase. In Lysmata wurdemanni, sperm competition is absent as hermaphrodites reproducing in the female role invariably mated only once with a single other shrimp. Shrimps acting as females preferred small over large shrimps as male mating partners, male mating ability was greater for small compared to large hermaphrodites, and adolescent males were predominant in the population during the breeding season. In addition, brooding constraints were not severe and varied linearly with body size whereas the ability to acquire resources increased markedly with body size. Using sex allocation theory as a framework, the findings above permitted to infer the shape of the male and female fitness gain curves for the hermaphrodites. The absence of sperm competition and the almost unconstrained brooding capacity imply that both curves saturate, however the male curve levels off much more quickly than the female curve with increasing level of investment. In turn, the predominance of adolescent males in the population implies that the absolute gain of the female curve is greater than that of the male curve. Last, the size-dependent female preference and male mating ability of hermaphrodites determines that the absolute gain of the male curve is greater for small than for large hermaphrodites. Taking into consideration the inferred shape of the fitness gain curves, two predictions with respect to the optimal sex allocation were formulated. First, overall sex allocation should be female biased; it permits hermaphrodites to profit from the female function that provides a greater fitness return than the male function. Second, sex allocation should be size-dependent with smaller hermaphrodites allocating more than proportionally resources to male reproduction than larger ones. This size-dependent sex allocation permits hermaphrodites to profit from male mating opportunities that are the greatest at small body sizes. Size-dependent sex allocation is also expected because the male fitness gain curve decelerates more quickly than the female gain curve and experiments indicated that resources are greater for large than small hermaphrodites. These two predictions were tested when determining the sex allocation of hermaphrodites by dissecting their gonad and quantifying ovaries versus testes mass. Supporting the predictions above, hermaphrodites allocated, on average, 118 times more to the female than to the male gonad and the proportion of resources devoted to male function was higher in small than in large hermaphrodites. A trade-off between male and female allocation is assumed by theory but no negative correlation between male and female reproductive investment was observed. In L. wurdemanni, the relationship between sex-specific investment and fitness changes during ontogeny in a way that is consistent with an adjustment of sex allocation to improve size-specific reproductive success.     

Plasticity in sex allocation in the plant Mercurialis annua is greater for hermaphrodites sampled from dimorphic than from monomorphic populations

Plants are notoriously variable in gender, ranging in sex allocation from purely male through hermaphrodite to purely female. This variation can have both a genetic and an adaptive plastic component. In gynodioecious species, where females co‐occur with hermaphrodites, hermaphrodites tend to shift their allocation towards greater maleness when growing under low‐resource conditions, either as a result of hermaphrodites shifting away from an expensive female function, or because of enhanced siring advantages in the presence of females. Similarly, in the androdioecious plant Mercurialis annua, where hermaphrodites co‐exist with males, hermaphrodites also tend to enhance their relative male allocation under low‐resource conditions. Here, we ask whether this response differs between hermaphrodites that have been evolving in the presence of males, in a situation analogous to that supposed for gynodioecious populations, vs. those that have been evolving in their absence. We grew hermaphrodites of M. annua from populations in which males were either present or absent under different levels of nutrient availability and compared their reaction norms. We found that, overall, hermaphrodites from populations with males tended to be more female than those from populations lacking males. Importantly, hermaphrodites' investment in pollen and seed production was more plastic when they came from populations with males than without them, reducing their pollen production at low resource availability and increasing their seed production at high resource availability. These results are consistent with the hypothesis that plasticity in sex allocation is enhanced in hermaphrodites that have likely been exposed to variation in mating opportunities due to fluctuations in the frequency of co‐occurring males.     

Sexual Selection in the Water Spider: Female Choice and Male–Male Competition

The water spider Argyroneta aquatica is the only spider spending its whole life under water, and one of the few spider species in which males are larger than females. Previous studies indicated that males can cannibalize females, which is uncommon among spiders. Here we aimed to further test for a potential influence of sexual selection on male body size. We examined the importance of female choice by testing whether females prefer the larger of two simultaneously presented males as mating partners. Further, we examined the influence of male–male competition by comparing the fighting behaviour between large and small males when alone or when together with a female, and we determined the outcome of fights. We found that females approach and choose large males as mating partners, despite the risk of male cannibalism. Additionally, males intensively compete for females, and large males clearly win against smaller ones. Hence sexual selection seems to be important for the evolution of the peculiar sexual size dimorphism of water spiders, as large size is beneficial for males in both the intra‐ and intersexual context. Previous studies have suggested an important role of natural selection in the sex‐specific body size of water spiders, but natural and sexual selection mechanisms apparently work in the same direction, favouring large male size.     

Influences of sex, size, and symmetry on ejaculate expenditure in a moth

Although sperm fundamentally function to fertilize eggs, forcesarising from both sexes select for optimal ejaculate composition.Sperm competition is one recognized agent in the evolution ofsperm and ejaculate structure. Few studies, however, have examinedhow female factors influence ejaculate structure, despite somebehavioral evidence for male mate choice. Male Plodia interpunctella(Lepidoptera, Pyralidae) accrue all resources for reproductionas larvae. Adults emerge with a limited sperm complement andare therefore under intense selection to optimize gamete allocation.I detected no effect of male body weight on ejaculate size.However, female reproductive potential (ovary masses) was dictatedby body weight In addition, heavier females had greater spermathecalvolumes, but there was no such relationship with bursal size.Finally, heavier females showed a higher mating frequency. Ifound that mating males were sensitive to female size and producedlarger ejaculates when mating with heavier females. Males mayejaculate more sperm into larger females either because it paysthem to "spend" more reproductive resources on matings thatprovide greater reproductive potential, or because heavier (longerlived and more attractive) females mate more frequently andhave larger spermathecal volumes. Alternatively, females maycontrol spermatophore formation and "accept" an appropriateejaculate to maximize fertility. Males may therefore be alsoselected to ejaculate more sperm into larger females to counteractgreater risks of sperm competition associated with heavier females.There was no association between male or female femur asymmetryand ejaculate size. P.interpunctella may be selected to exercisemodulation of ejaculate size because males invest paternally,sperm for the single reproductive episode are limited, and femalefecundity and mating pattern vary between individuals and areassociated with body weight. More obvious variability in malereproductive behavior and choice may therefore be paralleledat the cryptic gametic level by plasticity in ejaculate allocation.     

Seasonal Variation in Mate Choice of Photinus ignitus Fireflies

Mate choice by either sex may vary with changes in the associated costs and benefits, determined by factors such as the availability of potential mates and variation in mate quality. We examined seasonal variation in operational sex ratio, courtship behavior, spermatophore mass, egg count, and the relationship between morphological traits and mating success in Photinus ignitus fireflies to determine if mate choice in either sex varied with the availability and relative reproductive investment of fertilizable females and sexually active males. Successfully mating males had larger lanterns than unsuccessful males when the operational sex ratio was male‐biased. In addition, female responsiveness to male signals increased as the number of courting males decreased, and male spermatophore mass decreased with body size across the mating season. Successfully mating females had larger body mass than unsuccessful females. Female body mass predicted egg count and female rejection by males increased as the season progressed and female size decreased. These results suggest that both male and female P. ignitus exhibit mate choice, and that such choice is influenced by seasonal variation in the abundance and quality of potential mates.     

The effect of size and sex ratio experiences on reproductive competition in Nicrophorus vespilloides burying beetles in the wild

Male parents face a choice: should they invest more in caring for offspring or in attempting to mate with other females? The most profitable course depends on the intensity of competition for mates, which is likely to vary with the population sex ratio. However, the balance of pay‐offs may vary among individual males depending on their competitive prowess or attractiveness. We tested the prediction that sex ratio and size of the resource holding male provide cues regarding the level of mating competition prior to breeding and therefore influence the duration of a male's biparental caring in association with a female. Male burying beetles, Nicrophorus vespilloides were reared, post‐eclosion, in groups that differed in sex ratio. Experimental males were subsequently translocated to the wild, provided with a breeding resource (carcass) and filmed. We found no evidence that sex ratio cues prior to breeding affected future parental care behaviour but males that experienced male‐biased sex ratios took longer to attract wild mating partners. Smaller males attracted a higher proportion of females than did larger males, securing significantly more monogamous breeding associations as a result. Smaller males thus avoided competitive male–male encounters more often than larger males. This has potential benefits for their female partners who avoid both intrasexual competition and direct costs of higher mating frequency associated with competing males.     

Conflict over multiple-partner mating between males and females of the polygynandrous common lizards

The optimal number of mate partners for females rarely coincides with that for males, leading to a potential sexual conflict over multiple-partner mating. This suggests that the population sex ratio may affect multiple-partner mating and thus multiple paternity. We investigate the relationship between multiple paternity and the population sex ratio in the polygynandrous common lizard (Lacerta vivipara). In six populations the adult sex ratio was biased toward males, and in another six populations the adult sex ratio was biased toward females, the latter corresponding to the average adult sex ratio encountered in natural populations. In males the frequency and the degree of polygyny were lower in male-biased populations, as expected if competition among males determines polygyny. In females the frequency of polyandry was not different between treatments, and polyandrous females produced larger clutches, suggesting that polyandry might be adaptive. However, in male-biased populations females suffered from reduced reproductive success compared to female-biased populations, and the number of mate partners increased with female body size in polyandrous females. Polyandrous females of male-biased populations showed disproportionately more mating scars, indicating that polyandrous females of male-biased populations had more interactions with males and suggesting that the degree of multiple paternity is controlled by male sexual harassment. Our results thus imply that polyandry may be hierarchically controlled, with females controlling when to mate with multiple partners and male sexual harassment being a proximate determinant of the degree of multiple paternity. The results are also consistent with a sexual conflict in which male behaviors are harmful to females.     

The effect of hunger on mating behaviour and sexual selection for male body size in Gerris buenoi

The set of mating behaviours expressed by an individual may depend upon the state of that individual and local environmental conditions. Understanding how these factors affect mating behaviours may elucidate how a mating system operates, and its consequences for the form and strength of sexual selection. We conducted two experiments on the water striderGerris buenoi to (1) determine the effect of hunger on the mating behaviour of both sexes and (2) examine female choice for large males. In our first experiment, we manipulated hunger (20 h starvation) in both sexes and recorded mating, male harassment, copulation duration and guarding duration. We predicted that hunger would increase female reluctance to mate because mating conflicts with foraging. Female hunger (20 h starvation) decreased mating rate by two-thirds but had no significant effect on male mating behaviour. In a second experiment, we examined the effect of female hunger, and resulting reluctance, on sexual selection for large male size. Hungry females (5 h starvation) were placed with two fed males (one large, one small) and we recorded male premating and mating behaviours. We observed significant large-male mating advantage when females were hungry, but not when satiated. Mating efforts (harassment, premating struggles) were similar for both male phenotypes in both female hunger treatments, suggesting that the mating advantage of large males resulted from increased reluctance of hungry females to mate. Neither male body size nor female hunger explained a significant amount of variation in copulation duration or guarding duration. We discuss our results in light of two competing hypotheses for female choice (active and passive) on male body size and suggest that passive choice for large males acts in this system. Copyright 2002 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour     

Factors influencing mate choice in Euschistus conspersus Uhler (Heteroptera: Pentatomidae)

The patterns of mating and possible factors influencing mate choice in the consperse stink bug, Euschistus conspersus Uhler, were studied in a series of laboratory experiments. Males were found to transfer a significant percentage of their body mass during the initial mating. Mating was also found to reduce male longevity by 37.8% but had no significant effect on female longevity or fecundity. There was no evidence of male or female choice based on weight of potential mating partners. There was assortative mating based on experience, however, with males mating preferentially with virgin females and females preferring mated males when given the choice. The implications of these findings within the mating dynamics of this aggregating species are discussed.     

Female American mink, Mustela vison, mate multiply in a free-choice environment

Like most solitary carnivores, the home ranges of male American mink overlap with those of several females, but each female typically shares its range with only a single male. Nevertheless, female mink produce multiply sired litters. Unusually among mammals, the physiological characteristics of female American mink make them highly suited to multiple paternity, suggesting that polyandry in the species may result from female behaviour rather than from coercion by males. In a free-choice experiment on captive-bred animals, all female mink mated multiply, with seven of the eight mating with all three available partners. Since females sometimes resisted copulations, multiple mating in this species may result from their behaviour rather than male coercion. Females visited males nonrandomly, but visiting patterns did not predict mating patterns, suggesting disparate social and mating preferences. There was no evidence for precopulatory female choice, since the allocation of copulations among available males did not deviate significantly from the expected distribution. Females mated multiply only around the predicted times of ovulation, contrary to the expectation that they should be more selective at times of peak fertility. Larger males copulated for longer in total: copulation duration is probably under male control, suggesting that larger males could influence mating duration, perhaps increasing their share of paternity by greater sperm transfer. Our observations suggest that in wild populations, mating patterns could be influenced by female preference for multiple partners.     

SIZE,SYMMETRY, AND SEXUAL SELECTION IN THE HOUSEFLY,MUSCA DOMESTICA

Relationships between measures of body size, asymmetry, courtship effort, and mating success were investigated in the housefly, Musca domestica (Diptera: Muscidae). A previous study indicated that both male and female flies with low fluctuating asymmetry enjoyed enhanced mating success. The aim of our investigations was to determine whether the greater success of symmetrical males is due to variation in male mating effort or to female choice and whether males exhibited mate choice. However, our study found directional rather than fluctuating asymmetry with both male and female flies having, on average, longer left wings than right. Also, asymmetry was not related to mating success in either sex. Rather, both males and females appeared to exhibit choice on the basis of the size of potential mates, with males preferring females with long bodies and females preferring heavy males. Possible benefits from choice of large mates are discussed. The initial mating strikes (in which the male leaps onto the back of the female) did not appear to be targeted according to female morphology, and their frequency did not vary according to male morphology. This indicates that mate choice by both sexes according to size probably occurs during the later stages of courtship, when the flies are in intimate contact. Possible reasons for the absence of choice according to asymmetry are discussed.     

Seeking a Sex‐Specific Coolidge Effect in a Simultaneous Hermaphrodite

In polygamous mating systems, a capability to discriminate against familiar mates may be beneficial to both sexes. Polyandrous females, for instance, may enhance the odds of finding sires with optimal genetic compatibility or high genetic quality by mating with multiple different males; polygynous males, in addition, may more efficiently invest their limited ejaculates across multiple (rather than single) females. The Coolidge effect facilitates this kind of mate discrimination, as sexual motivation declines across consecutive copulations with a familiar partner but resurrects with a novel mate. In simultaneous hermaphrodites, we expect the Coolidge effect to show sex role‐dependent patterns and vary with previous sex‐specific mating activity. Using the promiscuous hermaphroditic sea slug Chelidonura sandrana, we investigated (1) whether sexual motivation indeed declines when repeatedly exposed to familiar partners, (2) whether the Coolidge effect occurs in a sex‐specific manner and (3) whether ejaculation is strategic with respect to partner familiarity. We found neither mating latency, nor penis intromission duration, mating propensity or the frequency of sex role alternations to vary significantly with treatments. Furthermore, slugs did not donate larger ejaculates to novel than to familiar partners. Partner novelty thus elicited no detectable response in sexual motivation or mating effort in C. sandrana. We suggest that the sea slugs' promiscuous mating system in often large mating aggregations makes mate discrimination based on novelty obsolete in comparison with more relevant criteria such as partner body size or mating history.     

Mutual mate choice in a female-dominant and sexually monomorphic primate

Sexual dimorphism is common in polygynous species, where intrasexual competition is often thought to drive the evolution of large male body size, and in turn, male behavioral dominance over females. In Madagascar, the entire lemur radiation, which embraces diverse mating systems, lacks sexual dimorphism and exhibits frequent female dominance over males. The evolution of such morphological and behavioral peculiarities, often referred to as "the lemur syndrome," has proven difficult to understand. Among other hypotheses, a potential role of intersexual selection has been repeatedly proposed but hardly ever tested. Here, we investigate whether female choice favors small and compliant males, and whether male choice favors large females in captive gray mouse lemurs (Microcebus murinus). Detailed analysis of a combination of behavioral observations and hormonal data available for both sexes shows that (1) females accept more matings from males with higher fighting abilities, (2) males adjust their investment in intrasexual competition to female fertility, and (3) both male and female strategies are weakly influenced by the body mass of potential partners, in directions contradicting our predictions. These results do not suggest a prominent role of intersexual selection in the evolution and maintenance of the lemur syndrome but rather point to alternative mechanisms relating to male-male competition, specifically highlighting an absence of relationship between male body mass and fighting ability. Finally, our findings add to the growing body of evidence suggesting flexible sex roles, by showing the expression of mutual mate choice in a female-dominant, sexually monomorphic and promiscuous primate.     

In hot pursuit: fluctuating mating system and sexual selection in sand lizards

A changing climate is expected to have profound effects on many aspects of ectotherm biology. We report on a decade-long study of free-ranging sand lizards (Lacerta agilis), exposed to an increasing mean mating season temperature and with known operational sex ratios. We assessed year-to-year variation in sexual selection on body size and postcopulatory sperm competition and cryptic female choice. Higher temperature was not linked to strength of sexual selection on body mass, but operational sex ratio (more males) did increase the strength of sexual selection on body size. Elevated temperature increased mating rate and number of sires per clutch with positive effects on offspring fitness. In years when the "quality" of a female's partners was more variable (in standard errors of a male sexual ornament), clutches showed less multiple paternity. This agrees with prior laboratory trials in which females exercised stronger cryptic female choice when male quality varied more. An increased number of sires contributing to within-clutch paternity decreased the risk of having malformed offspring. Ultimately, such variation may contribute to highly dynamic and shifting selection mosaics in the wild, with potential implications for the evolutionary ecology of mating systems and population responses to rapidly changing environmental conditions.     

Sex-role reversal revisited: choosy females and ornamented, competitive males in a pipefish

In the pipefish Syngnathus typhle sex roles are reversed, thatis, females compete more intensely than males over mates. However,competition over mates among individuals of one sex does notnecessarily prevent members of that same sex from being choosy,and choosiness in the other sex does not prevent competitionwithin it. In an experiment we allowed a female pipefish tochoose freely between two males, after which we released themales and let the three interact. Comparisons with earlier resultsshow that both sexes courted partners and competed with consexuals.However, females courted more often than did males, and courtshipwas more frequent in treatments involving large individualsthan in treatments with small individuals. Males competed amongthemselves for access to mates but for a shorter duration thanfemales in the same situation. Males displayed an ornament towardsfemales but not to males during mating competition. Females,however, used their ornament in both contexts. Females did notalways mate with the male of their previously made choice, whichwe interpret as females being constrained by male-male competition,male motivation to mate, or both. Thus, in this sex-role reversedspecies, mate choice in the more competitive sex may be circumventedand even overruled by mate competition and mating willingnessin the least competitive sex. Hence, sex roles should not beconsidered as sexes being either choosy or competitive but ratherthat males and females may exhibit different combinations ofchoice and competition.     

Relatively large males lower reproductive success in female zebrafish

Females can adjust their reproductive effort in relation to their partner’s perceived fitness value. In zebrafish (Danio rerio), large males are typically preferred mating partners. However, females have been observed to reduce their reproductive output with exceptionally large males but it remains unknown whether it is due to sexual harassment or aggressive behavior to establish and maintain dominance. Here, we study the association between relative male size, sexual harassment and dominance behavior, female stress status (stress behaviors and whole-body cortisol concentration), and reproductive success during a 4 day spawning trial. We found female cortisol to correlate negatively with female body size and positively with female dominance behavior. However, male and female behavior as well as female cortisol level were not related to relative male size. Females mating with relatively large males produced more and most of their eggs during the first spawning day, while females with smaller males produced few eggs during the first day but then increased egg production. Despite females produced more eggs when mating with relatively larger males, their eggs had substantially lower fertilization rates compared to females mating with relatively smaller males. Hence, overall, the reproductive fitness was lowest when females mated with a relatively large male. These findings could help to explain the maintenance of male size variation under natural conditions.     

Does sexual experience affect the strength of male mate choice for high‐quality females in Drosophila melanogaster?

Although females are traditionally thought of as the choosy sex, there is increasing evidence in many species that males will preferentially court or mate with certain females over others when given a choice. In the fruit fly, Drosophila melanogaster, males discriminate between potential mating partners based on a number of female traits, including species, mating history, age, and condition. Interestingly, many of these male preferences are affected by the male''s previous sexual experiences, such that males increase courtship toward types of females that they have previously mated with and decrease courtship toward types of females that have previously rejected them. D. melanogaster males also show courtship and mating preferences for larger females over smaller females, likely because larger females have higher fecundity. It is unknown, however, whether this preference shows behavioral plasticity based on the male''s sexual history as we see for other male preferences. Here, we manipulate the sexual experience of D. melanogaster males and test whether this manipulation has any effect on the strength of male mate choice for large females. We find that sexually inexperienced males have a robust courtship preference for large females that is unaffected by previous experience mating with, or being rejected by, females of differing sizes. Given that female body size is one of the most common targets of male mate choice across insect species, our experiments with D. melanogaster may provide insight into how these preferences develop and evolve.     

Sex allocation predicts mating rate in a simultaneous hermaphrodite

Sexual selection theory for separate-sexed animals predicts that the sexes differ in the benefit they can obtain from multiple mating. Conventional sex roles assume that the relationship between the number of mates and the fitness of an individual is steeper in males compared with females. Under these conditions, males are expected to be more eager to mate, whereas females are expected to be choosier. Here we hypothesize that the sex allocation, i.e. the reproductive investment devoted to the male versus female function, can be an important predictor of the mating strategy in simultaneous hermaphrodites. We argue that within-species variation in sex allocation can cause differences in the proportional fitness gain derived through each sex function. Individuals should therefore adjust their mating strategy in a way that is more beneficial to the sex function that is relatively more pronounced. To test this, we experimentally manipulated the sex allocation in a simultaneously hermaphroditic flatworm and investigated whether this affects the mating behaviour. The results demonstrate that individuals with a more male-biased sex allocation (i.e. relatively large testes and small ovaries) are more eager to mate compared with individuals with a more female-biased sex allocation (i.e. relatively small testes and large ovaries). We argue that this pattern is comparable to conventional gender roles in separate-sexed organisms.     

Sexual Competition,Coercive Mating and Mate Assessment in the One‐Sided Livebearer,Jenynsia multidentata: Are They Predictive of Sexual Dimorphism?

We investigated the mechanisms of sexual selection operating on body size in the one‐sided livebearer (Jenynsia multidentata), a small fish characterized by male dwarfism. Mating in the one‐sided livebearer is coercive: males approach females from behind and try to thrust their copulatory organ at the female genital pore. Females counter males' mating attempts by either swimming away or attacking them. We tested the hypothesis that the components of sexual selection favouring small size in males (sexual coercion) were more effective than those favouring a large size (male competition and mate choice). When alone, small males had a significantly higher success in their mating attempts than large males. The proportion of successful attempts was also positively correlated with female size. When two males competed for the same female, the large male had a significant mating advantage over the small one. With a 1 : 1 sex ratio, the large‐male mating advantage vanished because each male tended to follow a different female. Large males, however, preferentially defended large females, thus compelling small males to engage with smaller, less fecund females. Males did not discriminate between gravid and non‐gravid females, but preferred mating with larger females. This preference disappeared when males were much smaller than the female, probably in relation to the risk for the male of being eaten or injured by the female. In a choice chamber, male‐deprived females that had their sperm storage depleted remained close to males and showed a preference for large individuals, a behaviour not observed in non‐deprived females. Nonetheless, when placed with males in the same aquarium, all females showed avoidance and aggression. Struggling may represent a way by which the female assesses the skill and endurance of males.     

Mating frequency and resource allocation to male and female function in the simultaneous hermaphrodite land snail Arianta arbustorum

Sex allocation theory predicts that mating frequency and long‐term sperm storage affect the relative allocation to male and female function in simultaneous hermaphrodites. We examined the effect of mating frequency on male and female reproductive output (number of sperm delivered and eggs deposited) and on the resources allocated to the male and female function (dry mass, nitrogen and carbon contents of spermatophores and eggs) in individuals of the simultaneous hermaphrodite land snail Arianta arbustorum. Similar numbers of sperm were delivered in successive copulations. Consequently, the total number of sperm transferred increased with increasing number of copulations. In contrast, the total number of eggs produced was not influenced by the number of copulations. Energy allocation to gamete production expressed as dry mass, nitrogen or carbon content was highly female‐biased (>95% in all estimates). With increasing number of copulations the relative nitrogen allocation to the male function increased from 1.7% (one copulation) to 4.7% (three copulations), but the overall reproductive allocation remained highly female‐biased. At the individual level, we did not find any trade‐off between male and female reproductive function. In contrast, there was a significant positive correlation between the resources allocated to the male and female function. Snails that delivered many sperm also produced a large number of eggs. This finding contradicts current theory of sex allocation in simultaneous hermaphrodites.