Reproductive skew drives patterns of sexual dimorphism in sponge-dwelling snapping shrimps

Sexual dimorphism is typically a result of strong sexual selection on male traits used in male–male competition and subsequent female choice. However, in social species where reproduction is monopolized by one or a few individuals in a group, selection on secondary sexual characteristics may be strong in both sexes. Indeed, sexual dimorphism is reduced in many cooperatively breeding vertebrates and eusocial insects with totipotent workers, presumably because of increased selection on female traits. Here, we examined the relationship between sexual dimorphism and sociality in eight species of Synalpheus snapping shrimps that vary in social structure and degree of reproductive skew. In species where reproduction was shared more equitably, most members of both sexes were physiologically capable of breeding. However, in species where reproduction was monopolized by a single individual, a large proportion of females—but not males—were reproductively inactive, suggesting stronger reproductive suppression and conflict among females. Moreover, as skew increased across species, proportional size of the major chela—the primary antagonistic weapon in snapping shrimps—increased among females and sexual dimorphism in major chela size declined. Thus, as reproductive skew increases among Synalpheus, female–female competition over reproduction appears to increase, resulting in decreased sexual dimorphism in weapon size.     

The past,present and future of reproductive skew theory and experiments

A major evolutionary question is how reproductive sharing arises in cooperatively breeding species despite the inherent reproductive conflicts in social groups. Reproductive skew theory offers one potential solution: each group member gains or is allotted inclusive fitness equal to or exceeding their expectation from reproducing on their own. Unfortunately, a multitude of skew models with conflicting predictions has led to confusion in both testing and evaluating skew theory. The confusion arises partly because one set of models (the ‘transactional’ type) answer the ultimate evolutionary question of what ranges of reproductive skew can yield fitness‐enhancing solutions for all group members. The second set of models (‘compromise’) give an evolutionarily proximate, game‐theoretic evolutionarily stable state (ESS) solution that determines reproductive shares based on relative competitive abilities. However, several predictions arising from compromise models require a linear payoff to increased competition and do not hold with non‐linear payoffs. Given that for most species it may be very difficult or impossible to determine the true relationship between effort devoted to competition and reproductive share gained, compromise models are much less predictive than previously appreciated. Almost all skew models make one quantitative prediction (e.g. realized skew must fall within ranges predicted by transactional models), and two qualitative predictions (e.g. variation in relatedness or competitive ability across groups affects skew). A thorough review of the data finds that these three predictions are relatively rarely supported. As a general rule, therefore, the evolution of cooperative breeding appears not to be dependent on the ability of group members to monitor relatedness or competitive ability in order to adjust their behaviour dynamically to gain reproductive share. Although reproductive skew theory fails to predict within‐group dynamics consistently, it does better at predicting quantitative differences in skew across populations or species. This suggests that kin selection can play a significant role in the evolution of sociality. To advance our understanding of reproductive skew will require focusing on a broader array of factors, such as the frequency of mistaken identity, delayed fitness payoffs, and selection pressures arising from across‐group competition. We furthermore suggest a novel approach to investigate the sharing of reproduction that focuses on the underlying genetics of skew. A quantitative genetics approach allows the partitioning of variance in reproductive share itself or that of traits closely associated with skew into genetic and non‐genetic sources. Thus, we can determine the heritability of reproductive share and infer whether it actually is the focus of natural selection. We view the ‘animal model’ as the most promising empirical method where the genetics of reproductive share can be directly analyzed in wild populations. In the quest to assess whether skew theory can provide a framework for understanding the evolution of sociality, quantitative genetics will be a central tool in future research.     

Reproductive skew, costs, and benefits of cooperative breeding in female wood mice (Apodemus sylvaticus)

Two current models seek to explain reproduction of subordinatesin social groups: incentives given by dominants for peacefullyremaining in the group (reproductive skew model) or incompletecontrol by dominants. These models make different predictionsconcerning genetic relatedness between individuals for thedistribution of reproduction and the stability of cooperativebreeding associations. To test these models and to furtherexplore the relationships between reproductive skew, geneticrelatedness, and investment of each participant, we performedbehavioral observations of female wood mice (Apodemus sylvaticus)raising pups communally. Our results do not support previousmodels. Differences in lifetime reproductive success were significantlygreater within mother—daughter pairs than within pairsof sisters or unrelated females. Subordinate females of eitherbreeding unit did not differ in their direct reproduction.Calculations of inclusive fitness based on our results leadto the following predictions: (1) Communal nests should occuronly when ecological circumstances prevent solitary breeding.(2) Subordinate females gain the highest inclusive fitnessjoining their mothers; they also show the highest nursing investment.(3) Mothers should accept daughters, who have no opportunityfor solitary breeding. (4) Dominant sisters and unrelated femalesshould reject subordinate females because cooperative breedingreduces their reproductive success. However, breeding unitsof dominant sisters and unrelated females nevertheless occurand can be explained by our finding that such females significantlyreduce nursing time, which may help them save energy for futurebreeding cycles. Our data demonstrate that both genetic relatednessand investment skew are important in the complex evolutionof reproductive skew in cooperative breeding.     

Parentage analysis of Ansell's mole‐rat family groups indicates a high reproductive skew despite relatively relaxed ecological constraints on dispersal

To better understand evolutionary pathways leading to eusociality, interspecific comparisons are needed, which would use a common axis, such as that of reproductive skew, to array species. African mole‐rats (Bathyergidae, Rodentia) provide an outstanding model of social evolution because of a wide range of social organizations within a single family; however, their reproductive skew is difficult to estimate, due to their cryptic lifestyle. A maximum skew could theoretically be reached in groups where reproduction is monopolized by a stable breeding pair, but the value could be decreased by breeding‐male and breeding‐female turnover, shared reproduction and extra‐group mating. The frequency of such events should be higher in species or populations inhabiting mesic environments with relaxed ecological constraints on dispersal. To test this prediction, we studied patterns of parentage and relatedness within 16 groups of Ansell's mole‐rat (Fukomys anselli) in mesic miombo woodland. Contrary to expectation, there was no shared reproduction (more than one breeder of a particular sex) within the studied groups, and proportion of immigrants and offspring not assigned to current breeding males was low. The within‐group parentage and relatedness patterns observed resemble arid populations of ‘eusocial’ Fukomys damarensis, rather than a mesic population of ‘social’ Cryptomys hottentotus. As a possible explanation, we propose that the extent ecological conditions affect reproductive skew may be markedly affected by life history and natural history traits of the particular species and genera.     

Female eviction, abortion, and infanticide in banded mongooses (Mungos mungo): implications for social control of reproduction and synchronized parturition

Most cooperatively breeding species exhibit high reproductiveskew, where reproduction within the social group is monopolizedby a dominant pair. In many of these species, social controlof reproduction is the mechanism driving reproductive skew:individuals within the social group actively reduce the reproductivesuccess of others. In species where females do not suppressconception in other females, alternative routes to skewing thesocial group's reproductive output include inducing abortionin rivals, evicting them, or killing their young. This studyexamines instances of female eviction, abortion, and infanticidein a cooperatively breeding species with low preparturitionreproductive skew, the banded mongoose (Mungos mungo). Althoughinstances of these behaviors are rare in this species, aspectsof their occurrence have implications for social control ofreproduction. Abortion can be induced by the stress of beingevicted. The readmittance of females that abort suggests thatreducing communal litter size is a possible selective pressurefor eviction. This is supported by the occurrence of evictionevents in groups with relatively high numbers of reproductivefemales and by the eviction of young reproductive females. Thetiming of abortion events suggests that synchronization of parturitionwith other females in the group is a major selective pressure.Infanticide could represent the selective pressure for synchronizedparturition. Alternatively, synchronization may minimize competitiveasymmetry between pups born to different females. This paperalso describes incidences where a female aborts or gives birthto her litter over different days in order to synchronize parturition:behavior previously unrecorded in mammals.     

Effects of within‐colony competition on body size asymmetries and reproductive skew in a social spider

Reproductive partitioning is a key component of social organization in groups of cooperative organisms. In colonies of permanently social spiders of the genus Stegodyphus less than half of the females reproduce, while all females, including nonreproducers, perform suicidal allo‐maternal care. Some theoretical models suggest that reproductive skew is a result of contest competition within colonies, leading to size hierarchies where only the largest females become reproducers. We investigated the effect of competition on within‐group body size variation over six months in S. dumicola, by manipulating food level and colony size. We found no evidence that competition leads to increased size asymmetry within colonies, suggesting that contest competition may not be the proximate explanation for reproductive skew. Within‐colony body size variation was high already in the juvenile stage, and did not increase over the course of the experiment, suggesting that body size variation is shaped at an early stage. This might facilitate task specialization within colonies and ensure colony‐level reproductive output by early allocation of reproductive roles. We suggest that reproductive skew in social spiders may be an adaptation to sociality selected through inclusive fitness benefits of allo‐maternal care as well as colony‐level benefits maximizing colony survival and production.     

Female dominance status and fecal corticoids in a cooperative breeder with low reproductive skew: ring-tailed lemurs (Lemur catta)

Many studies have shown that low dominance status within a social group is associated with elevated glucocorticoid hormone production, a common index of physiological stress. However, the reverse may be true among cooperatively breeding female mammals with high reproductive skew; that is, high dominance status is associated with elevated glucocorticoid levels. Elevated glucocorticoid levels in these dominant females may be a product of their being the only breeder within a group or may result from other challenges associated with high status. To test this difference, we studied fecal corticoid levels in cooperative breeding females with low reproductive skew (i.e., where reproduction is not limited to dominant group members): ring-tailed lemurs (Lemur catta). We collected behavioral and fecal corticoid data from 39 ring-tailed lemur females from eight groups across three sites. In seven of the eight groups, either one or both of the two most dominant females (ranks 1 and 2) exhibited the highest fecal corticoid levels in the groups. The best predictor of corticoid levels in high-ranking females was the proportion of aggressive agonistic interactions they initiated. For the lower-ranking females the best predictors of elevated corticoid levels were being the recipient of aggressive attacks and being relatively close to one's nearest neighbors. These results differ from many studies of caged male mammals where subordinate individuals often exhibit the highest glucocorticoid levels of a group. Furthermore, the results indicate that reproduction itself is not the primary reason for higher glucocorticoid levels among dominant cooperative-breeding females, but that some other factor must account for these elevated levels.     

Life history of breeding partners alters age‐related changes of reproductive traits in a natural population of blue tits

Reproductive senescence, an intra‐individual decline in reproductive function with age, is widespread, but proximate factors determining its rate remain largely unknown. Most studies of reproductive senescence focus on females, leaving senescence in male function and its implications for female function largely understudied. We constructed linear mixed models to explore the interactive effects of paternal and maternal age and a life‐history trait (i.e. age at first reproduction) on four fitness components (i.e. laying date, clutch size, number of fledglings and number of recruits) measured in a wild, breeding population of blue tits Cyanistes caeruleus ogliastrae where individual breeding success has been followed for over 30 years (our dataset spanned 29 years). Previous studies have shown that, across female lifespan, laying date decreases and subsequently increases; earlier laying dates result in higher fitness because hatchlings have greater access to a seasonal food source. Our analyses reveal that females that initiate reproduction early in life show a greater delay in laying date with old age. In addition to delayed laying dates, older females lay smaller clutches. However, the magnitude of female age effects was influenced by the age at first reproduction of their breeding partners. Senescence of laying date and clutch size was reduced when females mated with males that reproduced early in life compared to males that delayed reproduction. We confirmed that both laying date and clutch size were significantly correlated with reproductive fitness suggesting that these dynamics early in the breeding cycle can have long‐term consequences. These complex phenotypic interactions shed light on the proximate mechanisms underlying reproductive senescence in nature and highlight the potential importance of cross‐sex age by life‐history interactions.     

Group size and composition influence male and female reproductive success in black howler monkeys (Alouatta pigra)

It has been argued that grouping patterns might influence the reproductive performance of individuals. Increasing group size results in greater travel costs and competition over depletable food resources, which could lead to reduced individual reproductive success. However, in groups with an increasing number of males, female reproductive success is predicted to augment because larger male groups might better protect immatures from infanticidal attacks. In contrast, male reproductive success is predicted to decrease with number of males in a group because fertilization cannot be shared between males. In this paper, we test these predictions on the Mesoamerican black howler monkey (Alouatta pigra) with data on group size and composition for 120 groups from eight populations of black howler monkeys existing in eight protected forests in Mexico and Guatemala. Male and female reproductive success were calculated as a deviation of the observed number of infants (or immatures) from the expected number of infants (or immatures), relative to the number of males and females in a group. Results indicate that both male and female reproductive success decreased with group size. Male reproductive success decreased with an increasing number of males in a group and with increasing proportion of males relative to females in a group. Decreased female reproductive success was associated with increasing number of females in a group, and female reproductive success had a tendency to increase with increasing number of males in a group. These results suggest that in black howler monkeys, living in larger groups might negatively affect the reproductive success of each member. Our findings are similar to those reported for a population of a sister species, Alouatta palliata, living in larger groups.     

The costs of egg production and incubation in great tits (Parus major).

The costs of egg production and incubation may have a crucial effect on avian reproductive decisions, such as clutch size and the timing of reproduction. We carried out a brood-size enlargement experiment on the great tit (Parus major), in which the birds had to lay and incubate extra eggs (full costs), only incubate extra eggs (free eggs) or did not pay any extra cost (free chicks) in obtaining a larger brood. We used female fitness (half the recruits produced plus female survival) as a fitness measure because it is the female which pays the costs of egg production and incubation, and because clutch size is under female control. Female fitness decreased with increasing costs (fitness of free chicks females is higher than that of free eggs females which is higher than that of full costs females). These fitness differences were due to differences in female survival rather than in the number of recruits produced. This is the first time that the costs of egg production and incubation have been estimated using such a complete fitness measure, including, as our measure does, the local survival to the following year of both the female and her offspring. Our results emphasize that reproductive decisions cannot be understood without taking egg production and incubation costs into account.     

Strategic female reproductive investment in response to male attractiveness in birds

Life-history theory predicts that individuals should adjust their reproductive effort according to the expected fitness returns on investment. Because sexually selected male traits should provide honest information about male genetic or phenotypic quality, females may invest more when paired with attractive males. However, there is substantial disagreement in the literature whether such differential allocation is a general pattern. Using a comparative meta-regression approach, we show that female birds generally invest more into reproduction when paired with attractive males, both in terms of egg size and number as well as food provisioning. However, whereas females of species with bi-parental care tend to primarily increase the number of eggs when paired with attractive males, females of species with female-only care produce larger, but not more, eggs. These patterns may reflect adaptive differences in female allocation strategies arising from variation in the signal content of sexually selected male traits between systems of parental care. In contrast to reproductive effort, female allocation of immune-stimulants, anti-oxidants and androgens to the egg yolk was not consistently increased when mated to attractive males, which probably reflects the context-dependent costs and benefits of those yolk compounds to females and offspring.     

Mechanistic and experimental analysis of condition and reproduction in a polymorphic lizard

Abstract The importance of genetic and environmental variation in condition in shaping evolutionary trade‐offs have recently been subject to much theoretical discussion, but is very difficult to investigate empirically in most field‐based systems. We present the results from mechanistic experimental manipulations of reproductive investment and condition in two female colour morphs (‘orange’ and ‘yellow’) of side‐blotched lizards (Uta stansburiana). We investigated the interactions between throat colour morphs, condition, local social environment and female survival using path‐analysis. Using follice‐ablation experiments, we show that large clutch size has a negative effect on field survival among yellow females, and that this effect is partly mediated by immunosuppressive effects of large clutches. In orange females these effects were less pronounced, and there was a negative survival effect of strong antibody responses. Hence, we experimentally confirmed our previous findings of correlational selection between female morphotype and immunocompetence, an important condition trait. Manipulation of corticosterone revealed multiple (‘pleiotropic’) direct and indirect effects of this hormone on both condition and reproductive traits. We argue that interaction effects (e.g. between local environments and genotypes) could explain a substantial fraction of variation in condition and reproduction in natural populations. Increased attention to such interaction effects and their fitness consequences will provide novel insights in field studies of selection and reproductive allocation.     

Survival costs of reproduction predict age-dependent variation in maternal investment

Life-history theory predicts that older females will increase reproductive effort through increased fecundity. Unless offspring survival is density dependent or female size constrains offspring size, theory does not predict variation in offspring size. However, empirical data suggest that females of differing age or condition produce offspring of different sizes. We used a dynamic state-variable model to determine when variable offspring sizes can be explained by an interaction between female age, female state and survival costs of reproduction. We found that when costs depend on fecundity, young females with surplus state increase offspring size and reduce number to minimize fitness penalties. When costs depend on total reproductive effort, only older females increase offspring size. Young females produce small offspring, because decreasing offspring size is less expensive than number, as fitness from offspring investment is nonlinear. Finally, allocation patterns are relatively stable when older females are better at acquiring food and are therefore in better condition. Our approach revealed an interaction between female state, age and survival costs, providing a novel explanation for observed variation in reproductive traits.     

Maternal influences on brood sex ratios: an experimental study in tree swallows

When the reproductive value of sons and daughters differ, parents are expected to adjust the sex ratio of their offspring to produce more of the sex that provides greater fitness returns. The body condition of females or environmental factors, such as food abundance and mate quality, may influence these expected fitness returns. In a previous study of tree swallows (Tachycineta bicolor), we found that females produced more sons in their broods when they were in better body condition (mass corrected for size). We tested this relationship by experimentally clipping some flight feathers to reduce female body condition. As predicted, we found that females with clipped feathers had a lower proportion of sons in their broods and poorer body condition. However, female body condition alone was not a significant predictor of brood sex ratio in our experiment. We suggest that brood sex ratio is causally related to some other factor that covaries with body condition, most likely the foraging ability of females. The hypothesis that brood sex ratios are influenced by individual differences in female foraging ability is supported by a high repeatability of brood sex ratio for individual females. Thus, maternal effects may have a strong influence on the sex ratios of offspring.     

Cichlids do not adjust reproductive skew to the availability of independent breeding options

Helpers in cooperatively breeding species forego all or partof their reproduction when remaining at home and assisting breedersto raise offspring. Different models of reproductive skew generatealternative predictions about the share of reproduction unrelatedsubordinates will get depending on the degree of ecologicalconstraints. Concession models predict a larger share when independentbreeding options are good, whereas restraint and tug-of-warmodels predict no effects on reproductive skew. We tested thesepredictions by determining the share of reproduction by unrelatedmale and female helpers in the Lake Tanganyika cichlid Neolamprologuspulcher depending on experimentally manipulated possibilitiesfor helper dispersal and independent breeding and dependingon helper size and sex. We created 32 breeding groups in thelaboratory, consisting of two breeders and two helpers each,where only the helpers had access to a nearby dispersal compartmentwith (treatment) or without (control) breeding substrate, usinga repeated measures design. We determined the paternity andmaternity of 1185 offspring from 47 broods using five to nineDNA microsatellite loci and found that: (1) helpers participatedin reproduction equally across the treatments, (2) large malehelpers were significantly more likely to reproduce than smallhelpers, and (3) male helpers engaged in significantly morereproduction than female helpers. Interestingly, in four broods,extragroup helper males had fertilized part of the brood. Nohelper evictions from the group after helper reproduction wereobserved. Our results suggest that tug-of-war models based oncompetition over reproduction within groups describe best thereproductive skew observed in our study system. Female breedersproduced larger clutches in the treatment compared to the controlsituation when the large helpers were males. This suggests thatmale breeder-male helper reproductive conflicts may be alleviatedby females producing larger clutches with helpers around.     

Unpredictable food supply modifies costs of reproduction and hampers individual optimization

Investment into the current reproductive attempt is thought to be at the expense of survival and/or future reproduction. Individuals are therefore expected to adjust their decisions to their physiological state and predictable aspects of environmental quality. The main predictions of the individual optimization hypothesis for bird clutch sizes are: (1) an increase in the number of recruits with an increasing number of eggs in natural broods, with no corresponding impairment of parental survival or future reproduction, and (2) a decrease in the fitness of parents in response to both negative and positive brood size manipulation, as a result of a low number of recruits, poor future reproduction of parents, or both. We analysed environmental influences on costs and optimization of reproduction on 6 years of natural and experimentally manipulated broods in a Central European population of the collared flycatcher. Based on dramatic differences in caterpillar availability, we classified breeding seasons as average and rich food years. The categorization was substantiated by the majority of present and future fitness components of adults and offspring. Neither observational nor experimental data supported the individual optimization hypothesis, in contrast to a Scandinavian population of the species. The quality of fledglings deteriorated, and the number of recruits did not increase with natural clutch size. Manipulation revealed significant costs of reproduction to female parents in terms of future reproductive potential. However, the influence of manipulation on recruitment was linear, with no significant polynomial effect. The number of recruits increased with manipulation in rich food years and tended to decrease in average years, so control broods did not recruit more young than manipulated broods in any of the year types. This indicates that females did not optimize their clutch size, and that they generally laid fewer eggs than optimal in rich food years. Mean yearly clutch size did not follow food availability, which suggests that females cannot predict food supply of the brood-rearing period at the beginning of the season. This lack of information on future food conditions seems to prevent them from accurately estimating their optimal clutch size for each season. Our results suggest that individual optimization may not be a general pattern even within a species, and alternative mechanisms are needed to explain clutch size variation.     

Transactional skew and assured fitness return models fail to predict patterns of cooperation in wasps

Cooperative breeders often exhibit reproductive skew, where dominant individuals reproduce more than subordinates. Two approaches derived from Hamilton's inclusive fitness model predict when subordinate behavior is favored over living solitarily. The assured fitness return (AFR) model predicts that subordinates help when they are highly likely to gain immediate indirect fitness. Transactional skew models predict dominants and subordinates "agree" on a level of reproductive skew that induces subordinates to join groups. We show the AFR model to be a special case of transactional skew models that assumes no direct reproduction by subordinates. We use data from 11 populations of four wasp species (Polistes, Liostenogaster) as a test of whether transactional frameworks suffice to predict when subordinate behavior should be observed in general and the specific level of skew observed in cooperative groups. The general prediction is supported; in 10 of 11 cases, transactional models correctly predict presence or absence of cooperation. In contrast, the specific prediction is not consistent with the data. Where cooperation occurs, the model accurately predicts highly biased reproductive skew between full sisters. However, the model also predicts that distantly related or unrelated females should cooperate with low skew. This prediction fails: cooperation with high skew is the observed norm. Neither the generalized transactional model nor the special-case AFR model can explain this significant feature of wasp sociobiology. Alternative, nontransactional hypotheses such as parental manipulation and kin recognition errors are discussed.     

Sociality, mating system and reproductive skew in marmots: evidence and hypotheses

Marmot species exhibit a great diversity of social structure, mating systems and reproductive skew. In particular, among the social species (i.e. all except Marmota monax), the yellow-bellied marmot appears quite different from the others. The yellow-bellied marmot is primarily polygynous with an intermediate level of sociality and low reproductive skew among females. In contrast, all other social marmot species are mainly monogamous, highly social and with marked reproductive skew among females. To understand the evolution of this difference in reproductive skew, I examined four possible explanations identified from reproductive skew theory. From the literature, I then reviewed evidence to investigate if marmot species differ in: (1) the ability of dominants to control the reproduction of subordinates; (2) the degree of relatedness between group members; (3) the benefit for subordinates of remaining in the social group; and (4) the benefit for dominants of retaining subordinates. I found that the optimal skew hypothesis may apply for both sets of species. I suggest that yellow-bellied marmot females may benefit from retaining subordinate females and in return have to concede them reproduction. On the contrary, monogamous marmot species may gain by suppressing the reproduction of subordinate females to maximise the efficiency of social thermoregulation, even at the risk of departure of subordinate females from the family group. Finally, I discuss scenarios for the simultaneous evolution of sociality, monogamy and reproductive skew in marmots.     

Effects of food restriction across stages of juvenile and early adult development on body weight,survival and adult life history

Organisms have to allocate limited resources among multiple life‐history traits, which can result in physiological trade‐offs, and variation in environmental conditions experienced during ontogeny can influence reproduction later in life. Food restriction may lead to an adaptive reallocation of the limited resources among traits as a phenotypically plastic adjustment, or it can act as an overall constraint with detrimental effects throughout reproductive life. In this study, we investigated experimentally the effects of food restriction during different stages of the juvenile and early adult development on body weight, survival and reproductive success in females and males of the European earwig Forficula auricularia. Individuals either received limited or unlimited access to food across three different stages of development (fully crossed) allowing us to identify sensitive periods during development and to test both additive and interactive effects of food limitation across stages on development and reproduction. Food restriction during the early and late juvenile stage had additive negative effects on juvenile survival and adult body weight. With regard to reproductive success of females which produce up to two clutches in their lifetime, restriction specifically in the late juvenile stage led to smaller first and second clutch size, lower probability of second clutch production and reduced hatching success in the second clutch. Reproductive success of females was not significantly affected when their male mates experienced food restriction during their development. Our findings in general support the ‘silver‐spoon’ hypothesis in that food restriction during juvenile development poses constraints on development and reproduction throughout life.     

Female Gryllus vocalis Field Crickets Gain Diminishing Returns from Increasing Numbers of Matings

Although female insects generally gain reproductive benefits from mating frequently, females do not mate unlimited numbers of times. This study asks whether the limit on female mating rate is imposed by trade‐offs between reproduction and survival. Female Gryllus vocalis were given the opportunity to mate 5, 10, or 15 times with novel males, and the effects on daily fecundity (egg production), fertility (proportion of eggs that were fertilized), and female post‐experimental longevity were measured. Females that mated 10 times laid more eggs and had a higher proportion of fertile eggs than females that mated 5 times. However, females that mated 15 times did not lay significantly more eggs or have a higher proportion of fertile eggs than females that mated 10 times. Although number of matings did not affect the date that females laid their last egg, mating more times was associated with a prolonged period of laying fertile eggs. Number of matings did not affect female post‐experimental longevity. Thus, there was no trade‐off between female reproductive effort and survival, even when females mated very large numbers of times. When females were allowed to mate ad libitum, the average number of times that females mated was greater than the number of times that confers maximal fitness. The lack of cost to mating explains why females might be willing to mate beyond the point of diminishing reproductive returns.