Male mating history and female fecundity in the Lepidoptera: do male virgins make better partners?

Synthesis of sexual selection: a systematic map of meta-analyses with bibliometric analysis

Sexual selection has been a popular subject within evolutionary biology because of its central role in explaining odd and counterintuitive traits observed in nature. Consequently, the literature associated with this field of study became vast. Meta-analytical studies attempting to draw inferences from this literature have now accumulated, varying in scope and quality, thus calling for a synthesis of these syntheses. We conducted a systematic literature search to create a systematic map with a report appraisal of meta-analyses on topics associated with sexual selection, aiming to identify the conceptual and methodological gaps in this secondary literature. We also conducted bibliometric analyses to explore whether these gaps are associated with the gender and origin of the authors of these meta-analyses. We included 152 meta-analytical studies in our systematic map. We found that most meta-analyses focused on males and on certain animal groups (e.g. birds), indicating severe sex and taxonomic biases. The topics in these studies varied greatly, from proximate (e.g. relationship of ornaments with other traits) to ultimate questions (e.g. formal estimates of sexual selection strength), although the former were more common. We also observed several common methodological issues in these studies, such as lack of detailed information regarding searches, screening, and analyses, which ultimately impairs the reliability of many of these meta-analyses. In addition, most of the meta-analyses' authors were men affiliated to institutions from developed countries, pointing to both gender and geographical authorship biases. Most importantly, we found that certain authorship aspects were associated with conceptual and methodological issues in meta-analytical studies. Many of our findings might simply reflect patterns in the current state of the primary literature and academia, suggesting that our study can serve as an indicator of issues within the field of sexual selection at large. Based on our findings, we provide both conceptual and analytical recommendations to improve future studies in the field of sexual selection.

Interaction between females and males grapevine moth Lobesia botrana modifies further mating preference

During reproduction, females may boost their fitness by being selective based on direct material benefits provided by the males, such as nuptial gifts. In Lepidoptera, male provides a spermatophore containing nutrients. However, virgin males produce a bigger spermatophore, containing spermatozoa and nutrients, allowing higher female fertility. Lepidoptera females that could detect the sexual status of males may thus prefer a male without previous mating experience (i.e. a virgin male). This mate selection could be achieved by the use of chemical indices, such as sexual pheromones and cuticular compounds, known to be possibly exchanged during reproduction, and which can be indicators of a previous mating experience and known to be possibly sources of information exchanged. In this study, we experimentally presented Lobesia botrana virgin males with females in order for them to be exposed to females' natural sexual pheromones or cuticular compounds. 12 or 48 h after the exposure of males to either females' sexual pheromones or cuticular compounds, these males were confronted to naïve females, which have a choice between them or a virgin non-exposed males. We highlighted that, despite producing a spermatophore of similar volume, all exposed virgin males were less likely to mate with females 12 h after exposure, while after 48 h of exposure this is only the case for virgin males exposed to sexual pheromones. L. botrana females may thus discriminate male sexual experience based on chemical cues (either from cues transferred directly from females to males, or from changes in the cuticular or pheromone males' profile) indicating past mating experiences. Mating duration was longer for males exposed to sexual pheromones after 12 h only, and for males exposed to cuticular compounds after 48 h only. Pheromones signal might be more persistent over time and seems to more easily gather information for males. The physiological reasoning behind this result still needs to be investigated.

Male nutritional status does not impact the reproductive potential of female Cnaphalocrocis medinalis moths under conditions of nutrient shortage

In addition to sperm, some accessory substances transferred to females during copulation act as nuptial gifts by passing on valuable nutrients in many insect species. The nutritional status of the males can thus have a great effect on the mating behavior, fecundity and even the longevity of females. However, little is known about the effect of male nutritional status on the female reproductive traits in migratory insect species, particularly when females experience nutrient shortage and have to choose between reproduction and migration. Here, Cnaphalocrocis medinalis, a migratory rice pest in Asia, was studied to explore this issue. Our results showed that in male moths fed with honey solution, their gonads had higher energy content than gonads of starved males, resulting in increased energy content of the bursa copulatrix of females after mating with fed males. Such females showed increased mating frequency, fecundity and longevity compared to females mating with starved males, indicating that male moths deliver nuptial gifts to females and improve their reproductive performance. However, when females were starved, only about 45% mated, with just a single copulation, regardless of male nutritional status. Starved females showed lower fecundity, and a longer pre-oviposition period (indicating a greater propensity to migrate), compared to fed females. However, copulation still significantly extended their longevity. These results suggest that starved females invest in migration to escape deteriorating habitats, rather than investing the nuptial gift to increased fecundity. Our results further our understanding of the reproductive adaptability of migratory insects under conditions of food stress.

Timing of Pubertal Development and Midlife Blood Pressure in Men and Women: A Mendelian Randomization Study

INTRODUCTION

Observational studies suggest earlier puberty is associated with higher adulthood blood pressure (BP), but these findings have not been replicated using Mendelian randomization (MR). We examined this question sex-specifically using larger genome-wide association studies (GWAS) with more extensive measures of pubertal timing.

METHODS

We obtained genetic instruments proxying pubertal maturation (age at menarche [AAM] or voice breaking [AVB]) from the largest published GWAS. We applied them to summary sex-specific genetic associations with systolic and diastolic BP z-scores, and self-reported hypertension in women (n = 194 174) and men (n = 167 020) from the UK Biobank, using inverse-variance weighted meta-analysis. We conducted sensitivity analyses using other MR methods, including multivariable MR adjusted for childhood obesity proxied by body mass index (BMI). We used late pubertal growth as a validation outcome.

RESULTS

AAM (beta per 1-year later = -0.030 [95% confidence interval, -0.055 to -0.005] and AVB (beta -0.058 [95% CI, -0.100 to -0.015]) were inversely associated with systolic BP independent of childhood BMI, as were diastolic BP (-0.035 [95% CI, -0.060 to -0.009] for AAM and -0.046 [95% CI, -0.089 to -0.004] for AVB) and self-reported hypertension (odds ratio 0.89 [95% CI, 0.84-0.95] for AAM and 0.87 [95% CI, 0.79-0.96] for AVB). AAM and AVB were positively associated with late pubertal growth, as expected. The results were robust to sensitivity analysis using other MR methods.

CONCLUSION

Timing of pubertal maturation was associated with adulthood BP independent of childhood BMI, highlighting the role of pubertal maturation timing in midlife BP.

Fighting over defense chemicals disrupts mating behavior

Studies on intraspecific contest behavior predominantly focus on contests between individuals of the same sex, however contest behavior is also expected to occur between individuals of the opposite sex including possible mates. Here we investigate potential trade-offs between mating and fighting behavior in the turnip sawfly (Athalia rosae). Adults of this species collect chemical defense compounds (clerodanoids) directly from plants but also indirectly by nibbling on conspecifics that have already obtained clerodanoids, a highly aggressive behavioral interaction. An A. rosae individual without clerodanoids may therefore be the potential mate or attacker of an individual of the opposite sex that has gained clerodanoids. To test the effect of clerodanoids on agonistic and mating behavior we paired females and males with or without clerodanoid access in a two-way factorial design. We show that asymmetrical clerodanoid acquisition between female-male pairs causes an increase in agonistic nibbling behavior, irrespective of sex, and moreover that conflict between individuals delays mating behavior. Our study highlights the importance of investigating agonistic intersex interactions, which can occur when adults are able to acquire valuable non-reproductive resources from a potential partner.

Successive matings affect copulatory courtship but not sperm transfer in a spider model

Previous studies have reported that males augment their reproductive success by increasing the number of females with which they copulate, and that such copulations are not energetically demanding in terms of trivial sperm production costs. However, we now know that males do pay reproductive costs. As males mate successively, a reduction in the performance of copulatory behaviours would be expected, as well as in the number of sperm transferred. Here we compared the duration of courtship, mating and post-insemination phase, the number of genital and non-genital copulatory courtship occurrences, and the number of sperm transferred in successive matings in Holocnemus pluchei spider males. As matings increased in males, there was no effect on the duration of courtship, mating or post-insemination phase. Interestingly, genital copulatory courtship varied in successive copulations depending on male size, but there was no change in the number of sperm transferred. In addition, the occurrence of non-genital copulatory courtship decreased along successive copulations. The negative effects of successive matings on copulatory courtship indicate that these behaviours are costly for males, except for the number of sperm transferred. Our research lays the foundation for future studies on male costs as a function of mating history in spiders.

Atypical functioning of female genitalia explains monandry in a butterfly

Monandrous species are rare in nature, especially in animals where males transfer nutrients to females in the ejaculate. The proximate mechanisms responsible for monandry are poorly studied. In butterflies and moths, the male transfers a nutritious spermatophore into the corpus bursae (CB) of the female. The CB is a multifunctional organ that digests the spermatophore and has partial control of the post-mating sexual receptivity of the female. The spermatophore distends the CB and the post-mating sexual receptivity of the female is inversely proportional to the degree of distension. The CB of many butterfly species has a muscular sheath whose contractions mechanically contribute to digest the spermatophore. As the contents of the CB are absorbed, the degree of distension decreases and the female recovers receptivity. We studied the monandrous butterfly Leptophobia aripa (Boisduval, 1836) (Pieridae) and found that females do not digest the spermatophores. We investigated the structure of the CB and found that a muscular sheath is absent, indicating that in this butterfly females lack the necessary "apparatus" for the mechanical digestion of the spermatophore. We propose that female monandry in this species is result of its incapability to mechanically digest the spermatophore, which results in a constant degree of CB distension after mating and, thus, in the maintenance of the sexually unreceptive state of females. Hypotheses on the evolution of this mechanism are discussed.

Sperm depletion in relation to developmental nutrition and genotype in Drosophila melanogaster

Nutrient limitation during development can restrict the ability of adults to invest in costly fitness traits, and genotypes can vary in their sensitivity to developmental nutrition. However, little is known about how genotype and nutrition affect male ability to maintain ejaculate allocation and achieve fertilization across successive matings. Using 17 isogenic lines of Drosophila melanogaster, we investigated how variation in developmental nutrition affects males' abilities to mate, transfer sperm, and sire offspring when presented with successive virgin females. We found that, with each successive mating, males required longer to initiate copulation, transferred fewer sperm, and sired fewer offspring. Males reared on a low-nutrient diet transferred fewer sperm than those reared on nutritionally superior diets, but the rate at which males depleted their sperm, as well as their reproductive performance, was largely independent of diet. Genotype and the genotype × diet interaction explained little of the variation in these male reproductive traits. Our results show that sperm depletion can occur rapidly and impose substantial fitness costs for D. melanogaster males across multiple genotypes and developmental environments.

Disentangling the effects of male age and mating history: Contrasting effects of mating history on precopulatory mating behavior and paternity success

Many studies ask whether young or older males are better at acquiring mates. Even so, how age affects reproductive success is still poorly understood because male age and mating history are confounded in most studies: older males usually have more mating experience. To what extent does mating history rather than age explain variation in male mating success? And how do mating history and male age determine paternity when there is also postcopulatory sexual selection? Here, we experimentally manipulated the mating history of old and young males in the eastern mosquitofish (Gambusia holbrooki). We then recorded male mating behavior and share of paternity (1259 offspring from 232 potential sires) when they competed for mates and fertilizations. Old males, and males with no mating experience, spent significantly more time approaching females, and attempting to mate, than did young males and those with greater mating experience. Male age and mating history interacted to affect paternity: old males benefited from having previous mating experience, but young males did not. Our results highlight that the age-related changes in male reproductive traits and in paternity that have been described in many taxa may be partly attributable to male mating history and not simply to age itself.

Effects of operational sex ratio, mating age, and male mating history on mating and reproductive behavior in Grapholita molesta

The short-lived polygamous moth Grapholita molesta (Busck) is an important fruit pest worldwide. Trapping males by synthetic female sex pheromones is not an effective reproductive control strategy. It is important to improve this technology by understanding the mating system of G. molesta. This study investigated mating opportunities and fertile egg production by altering the operational sex ratio, mating age, and male mating history in repeated single mating and multiple mating in the two sexes. Our results showed that the mating and reproductive parameters of virgin males were affected by the number and age of virgin females. Males preferred a female number ≤three-fifths of the male number or ≤2-day-old females, while they discriminated against a female number ≥three times of the male number or ≥5-day-old females. On the other hand, the mating and reproductive parameters of virgin females were affected by repeated single mating and especially multiple mating under different male mating histories. Females preferred once-mated males and discriminated against virgin males. These results indicated that mating systems including more and older virgin females for virgin males and different virgin males for virgin females may be suitable for suppressing G. molesta populations. Hence, these results revealed that preventing mating of virgin adults by synthetic female sex pheromones should be most effective in controlling G. molesta.

Does recent experience affect large male advantage in a sequentially-mating fish?

In many mating systems, large male body size is associated with dominance in direct contests with rivals and females may exhibit preference for larger males. As such, body size is often positively associated with mating success. However, mating experience can influence the potential advantage of large body size through alterations in behaviour and depletion of sperm reserves. In Japanese medaka (Oryzias latipes), males mate with many females each day, and larger males mate more frequently than smaller males. In an observational experiment, we tested the following alternate predictions: (1) recent mating experience may enhance mating success through a carry-over effect of prior mating, whereby small experienced males gain an advantage over large inexperienced rivals in mating contests; or (2) recent mating experience decreases mating success through a reduction in fertilization due to sperm limitation, effectively dampening the large-male advantage against a small inexperienced rival. We examined the interactive effect of size and recent experience on mating behaviour and success. While mating contests were monopolized by large males, recent experience enhanced mating success, especially in small male winners. Experienced males courted more readily than those without recent experience, suggesting that recent prior mating enhances this behaviour. Furthermore, males who had copulated recently did not exhibit sperm depletion when in the presence of a competitor, nor did female behaviour indicate a preference for inexperienced males. This suggests that males can use sexual experience to increase their reproductive success in future mating situations, which may influence the action of sexual selection and alternative tactics in shaping mating systems.

Food Limitation but Not Enhanced Rates of Ejaculate Production Imposes Reproductive and Survival Costs to Male Crickets

Estimating costs of ejaculate production is challenging. Metabolic investment in ejaculates may come at the expense of other physiological functions and may negatively affect future reproduction and/or survival. These trade-offs are especially likely to occur under constrained resource pools (e.g., poor nutrition). Here, we investigated costs of ejaculate production via trade-offs in the field cricket Gryllus bimaculatus. We experimentally increased rates of ejaculate production, while keeping an unmanipulated group, in adult males kept at high and low feeding regimes and tested the effects of our treatments on (i) somatic maintenance (i.e., changes in male body mass), (ii) future reproduction (i.e., the likelihood of producing a spermatophore and the viability of its sperm), and (iii) lifetime survival and longevity. We predicted investment in ejaculates to impinge upon all measured responses, especially in low-fed individuals. Instead, we only found negative effects of food limitation, suggesting low or undetectable costs of spermatophore production. High mating rates may select for males to maximize their capacity of ejaculate production, making ejaculate traits less prone to trade-offs with other fitness-related life history traits. Nevertheless, males were impaired due to nutrient deficiency in producing viable ejaculates, suggesting condition-dependent costs for ejaculate production.

Delayed Mating with Multiple Partners Decreases Indexes of Mating in Female and Male Spodoptera litura (Lepidoptera: Noctuidae)

Delayed mating is an effective strategy that can decrease the fecundity of a pest by reducing the time that females have to mate. This disruption does not completely inhibit mating and may lead to multiple matings. The effects of delayed mating with multiple partners on different indexes of mating in female and male Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) were determined in this study. The delay in mating significantly decreased the number of matings and the mating success of both sexes and the male contribution to reproduction. Compared with the effect on female fecundity, the delayed mating with multiple partners had a greater effect on the male mate contribution to fecundity. The longevity of females and males increased significantly with a 72 h delay in mating. Linear regression analysis showed negative relationships between delayed mating and fecundity and number of matings in both sexes. Thus, delayed mating with multiple partners can disrupt the mating and reproductive potential of S. litura.

An experimental test of the role of male mating history on paternal effects in the livebearer fish Gambusia holbrooki

Studies often show that paternal age affects offspring fitness. However, such effects could be due either to age, or to a male's previous mating effort (which is necessarily confounded with age). We experimentally tested whether differences in the mating history of old males affect offspring performance in the mosquitofish Gambusia holbrooki. Upon maturation, males were housed for a duration of the natural field-breeding season (23 weeks) either with mating access to females (lifetime-mating), or with visual but no physical access to females (no-mating). We then paired these males with a female to test whether male mating history had a significant effect on their mate's breeding success or offspring performance. The daughters, but not the sons, of 'no-mating' treatment males matured significantly sooner, and at a significantly smaller size, than those of 'lifetime-mating' treatment males. There was, however, no effect of male mating history on their daughters' initial fecundity, or on proxy measures of their sons' reproductive success. These results, when combined with earlier studies showing effects of male mating history on sperm quality, growth and immunity, suggest that variation in paternal effects currently attributed to male age could partly arise because older males have usually mated more often than younger males.

Parental breeding age effects on descendants' longevity interact over 2 generations in matrilines and patrilines

Individuals within populations vary enormously in mortality risk and longevity, but the causes of this variation remain poorly understood. A potentially important and phylogenetically widespread source of such variation is maternal age at breeding, which typically has negative effects on offspring longevity. Here, we show that paternal age can affect offspring longevity as strongly as maternal age does and that breeding age effects can interact over 2 generations in both matrilines and patrilines. We manipulated maternal and paternal ages at breeding over 2 generations in the neriid fly Telostylinus angusticollis. To determine whether breeding age effects can be modulated by the environment, we also manipulated larval diet and male competitive environment in the first generation. We found separate and interactive effects of parental and grand-parental ages at breeding on descendants' mortality rate and life span in both matrilines and patrilines. These breeding age effects were not modulated by grand-parental larval diet quality or competitive environment. Our findings suggest that variation in maternal and paternal ages at breeding could contribute substantially to intrapopulation variation in mortality and longevity.

Biparental mealybugs may be more promiscuous than we thought

Knowledge on the reproductive biology of target insect pest is essential for the effective implementation of pheromone-based pest management tactics. In mealybugs, the second largest family of scale insects, the existence of female multiple mating was recently suggested. In this study, we aimed at testing how general is this behavior in mealybugs, by investigating polygyny and polyandry in two cosmopolitan pest mealybugs, Planococcus citri and Pseudococcus calceolariae. Males of these species were able to mate an average of 11.9 and 13.3 females, respectively, during their lifespan. The number of fertilized females per male decreased with male age/mating history for both mealybugs. We found no differences in female fecundity and fertility, when fertilized by males with different mating history. When we used male age as a proxy of mating history, we observed a significant negative effect on female fecundity. The females of both species remained receptive after first copula and eventually mated multiple times. The percentage of remated females of P. citri decreased linearly with time since first copula, with some maintaining receptivity up to 24 h. Males showed no preference between virgin and mated females, in static-air olfactometer tests. We found no benefit of female multiple mating in relation to fecundity. In biparental mealybugs, the mating system of males is possibly scramble competition polygyny; and that of females is possibly polyandry, with female receptivity restricted to a relatively short period. We discuss the practical implications of the results for pest management.

Mating experience affects male mating success, but not female fecundity in the wolf spider Pardosa pseudoannulata (Araneae: Lycosidae)

In a mating system in which females are monandrous and males are polygynous, females may incur a risk by mating with males with possible sperm depletion following consecutive matings. Here, we examined the effects of male mating history on male mating success and female reproductive fitness in the wolf spider Pardosa pseudoannulata by performing mating trials and sperm counting experiments. Results showed that male mating history had a significant negative impact on subsequent copulation success but had little effect on courtship duration and courtship intensity. In addition, neither male courtship intensity nor morphological measurements of males and females had significant effects on male mating success. Furthermore, male mating history had no obvious impact on the fecundity of inseminated females, with no significant differences observed in the oviposition rate of females, the numbers and the carapace width of the second-instar spiderlings between treatments. Results showed that the number of sperm decreased significantly after mating but could be replenished, with no significant differences observed between groups in which males had rested for 7 d. These findings suggest that polygynous male spiders may recharge their sperm during the mating season, but how females differentiate the mating status of males remains unknown.

Successive matings produce opposite patterns on ejaculate volume and spermatozoa number in an ancient arthropod model with indirect sperm transfer

The production of spermatophore and ejaculate is energetically expensive for males. High mating rates may accelerate sperm depletion and progressively decrease the size of the ejaculates. Sperm competition can shape spermatozoon numbers according to different signals and cues such as number of potential rivals or female mating status. Factors influencing patterns of sperm allocation have been neglected in terrestrial arthropods that transfer sperm indirectly using a complex sclerotized spermatophore deposited on the soil. We used the Neotropical scorpion Bothriurus bonariensis (C.L. Koch, 1842) to examine ejaculate volume, spermatozoon number, and spermatophore’s trunk length along three successive matings and their relationship with body size of males. Males mated and deposited a pre-insemination spermatophore every 10 days. Ejaculate volume and trunk length decreased, whereas spermatozoon number increased over matings. Male body size positively influenced ejaculate volume and trunk length interacted with mating event. High mating rates may decrease ejaculate volume. Sperm competition may produce increased spermatozoon number. Ejaculates are more energetically expensive than spermatozoa and larger males may better face the energetic requirements. Larger spermatophore trunks contain bigger ejaculate volume in the first two mating events, but this relationship disappears at the third mating event. Our discussion focuses on the factors responsible for the observed patterns.

Male mating and female postmating performances in cotton mealybug (Hemiptera: Pseudococcidae): effects of female density

For insects, female density is closely related to reproductive output. However, little is known about the effects of female density on male mating and female postmating performances. Here, we explored the effects of female density in cotton mealybug, Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae), an invasive, rapidly spreading pest in Asia damaging multiple crops and horticultural plants. Using USB digital microscopes, we investigated the frequency, duration, and intervals of mating for males that were individually supplied with 1, 5, 10, and 15 females. We also evaluated the reproduction of mated females and the sex ratio of their offspring. As the female density increased, males mated with more females while substantially shortening mating intervals. Mating occurred actively at the densities of 10 and 15 females, where males mated four times on average, and some mated 6-9 times. However, mating duration and the observed reproductive parameters of females (preoviposition period, overall period from formation of ovisacs to female death, fecundity, and offspring sex ratio) did not differ significantly with female density. A weak trade-off existed between males' mating frequency and longevity, but there was no relationship between females' fecundity and longevity. In conclusion, despite their short lifespan, P. solenopsis males have a high mating capacity, and their mating frequency and intervals can be significantly affected by female density. In contrast, female density has little influence on females' postmating performance. Our findings indicate the significance of the reproductive biology and life history strategies for rapid establishment and population development of mealybugs in newly invaded regions.

Strategic adjustment of copulatory plug size in a nematode

Copulatory plugs (CP) are substances produced during copulation that block the genital openings of the female. In several species of Nematoda, males produce CP that are thought to impede female remating and thus sperm competition. The relatively large size of the CP in several nematodes, and its evolutionary loss in self-fertilizing populations of Caenorhabditis elegans, suggests that CP are costly to produce. If CP production is costly, the application of basic concepts of strategic ejaculation theory suggests a modulated allocation of CP in response to sperm competition risk. This hypothesis led us to predict that males perceiving a higher risk of sperm competition will produce larger CP. We tested these ideas with the entomopathogenic, gonochoristic nematode Rhabditis regina. Our first experiment provides evidence suggesting that production of CP is costly, because the size of CP is negatively affected by stressful conditions (high population density, small male adult size, and suboptimal food type). The results of our second experiment support the prediction that males adjust the size of CP to sperm competition risk: the average size of CP increased as the number of males competing for one female increased. Overall, our study supports the idea that in R. regina the production of CP is costly for males and that the size of the CP produced is influenced by sperm competition risk.

Mating experience influences mate choice and reproductive output in an aphidophagous ladybird, Menochilus sexmaculatus

Information about mating status can be used to decide about whether to invest resources in mating with a particular partner. In the present study, we evaluated mate choice in relation to the mating experience of males and females of Menochilus sexmaculatus. We subjected both unmated and multiply mated males and females to different mate choice trials. The mating experience of the adults includes unmated, once-mated, twice-mated and multiply mated. The mate choice trials revealed that unmated adults were preferred over mated adults by both unmated and multiply mated partners. This preference for unmated partners also had consequences for mating behaviour and reproductive output. Unmated and multiply mated females commenced mating with unmated males earlier. In addition, unmated and multiply mated males invested more time in copula with unmated females. Moreover, females mated with unmated males were more fecund than those mated with previously mated males. This suggests that mating experience of mates may influence mating and reproductive behaviour in this species.

Proximity of signallers can maintain sexual signal variation under stabilizing selection

How sexual communication systems can evolve under stabilizing selection is still a paradox in evolutionary biology. In moths, females emit a species-specific sex pheromone, consisting of a blend of biochemically related components, to which males are attracted. Although males appear to exert strong stabilizing selection on female pheromone, these blends seem to have evolved rapidly, as evidenced by ~120,000 moth species. Here we propose and test a “proximity model” wherein two females that vary in their relative attractiveness to males, can both benefit from calling in close proximity to each other. In a field study, we show that (1) artificially selected unattractive females can achieve mating rates comparable to attractive females if they signal in close proximity to attractive females, and (2) attractive females benefit from higher mating rates when signalling in close proximity to unattractive females. We propose that frequency-dependent behavioural and spatial interactions can sustain signal variation within populations even when these signals are under stabilizing selection.

Variation in the benefits of multiple mating on female fertility in wild stalk-eyed flies

Polyandry, female mating with multiple males, is widespread across many taxa and almost ubiquitous in insects. This conflicts with the traditional idea that females are constrained by their comparatively large investment in each offspring, and so should only need to mate once or a few times. Females may need to mate multiply to gain sufficient sperm supplies to maintain their fertility, especially in species in which male promiscuity results in division of their ejaculate among many females. Here, we take a novel approach, utilizing wild-caught individuals to explore how natural variation among females and males influences fertility gains for females. We studied this in the Malaysian stalk-eyed fly species Teleopsis dalmanni. After an additional mating, females benefit from greatly increased fertility (proportion fertile eggs). Gains from multiple mating are not uniform across females; they are greatest when females have high fecundity or low fertility. Fertility gains also vary spatially, as we find an additional strong effect of the stream from which females were collected. Responses were unaffected by male mating history (males kept with females or in male-only groups). Recent male mating may be of lesser importance because males in many species, including T. dalmanni, partition their ejaculate to maintain their fertility over many matings. This study highlights the importance of complementing laboratory studies with data on wild-caught populations, where there is considerable heterogeneity between individuals. Future research should focus on environmental, demographic and genetic factors that are likely to significantly influence variation in individual female fecundity and fertility.

Effect of male mating history and age on remating by female European corn borer

If mating with an inferior male has high fitness costs, females may try to avoid mating with these males. Alternatively, females may accept an inferior male to ensure they have obtained at least one mate, and/or to avoid the costs of resisting these males. We hypothesized that females compensate for mating with an inferior male by remating. We tested this hypothesis by measuring remating propensity in females that had mated with an old, multiply-mated male, a 9-day-old virgin male, or a young, virgin male. Females were more likely to remate when they had mated with multiply-mated males than when they had mated with a 9-day-old or young virgin male. We discuss the observed mating behavior by females in terms of sexual selection for multiple mating.

Concurrent modulation of neuronal and behavioural olfactory responses to sex and host plant cues in a male moth

Mating has profound effects on animal physiology and behaviour, not only in females but also in males, which we show here for olfactory responses. In cotton leafworm moths, Spodoptera littoralis, odour-mediated attraction to sex pheromone and plant volatiles are modulated after mating, producing a behavioural response that matches the physiological condition of the male insect. Unmated males are attracted by upwind flight to sex pheromone released by calling females, as well as to volatiles of lilac flowers and green leaves of the host plant cotton, signalling adult food and mating sites, respectively. Mating temporarily abolishes male attraction to females and host plant odour, but does not diminish attraction to flowers. This behavioural modulation is correlated with a response modulation in the olfactory system, as shown by electro-physiological recordings from antennae and by functional imaging of the antennal lobe, using natural odours and synthetic compounds. An effect of mating on the olfactory responses to pheromone and cotton plant volatiles but not to lilac flowers indicates the presence of functionally independent neural circuits within the olfactory system. Our results indicate that these circuits interconnect and weigh perception of social and habitat odour signals to generate appropriate behavioural responses according to mating state.

Rival male chemical cues evoke changes in male pre- and post-copulatory investment in a flour beetle

Males can gather information on the risk and intensity of sperm competition from their social environment. Recent studies have implicated chemosensory cues, for instance cuticular hydrocarbons (CHCs) in insects, as a key source of this information. Here, using the broad-horned flour beetle (Gnatocerus cornutus), we investigated the importance of contact-derived rival male CHCs in informing male perception of sperm competition risk and intensity. We experimentally perfumed virgin females with male CHCs via direct intersexual contact and measured male pre- and post-copulatory investment in response to this manipulation. Using chemical analysis, we verified that this treatment engendered changes to perfumed female CHC profiles, but did not make perfumed females "smell" mated. Despite this, males responded to these chemical changes. Males increased courtship effort under low levels of perceived competition (from 1-3 rivals), but significantly decreased courtship effort as perceived competition rose (from 3-5 rivals). Furthermore, our measurement of ejaculate investment showed that males allocated significantly more sperm to perfumed females than to control females. Together, these results suggest that changes in female chemical profile elicited by contact with rival males do not provide males with information on female mating status, but rather inform males of the presence of rivals within the population and thus provide a means for males to indirectly assess the risk of sperm competition.

Association between changes in reproductive activity and D-glucose metabolism in the tephritid fruit fly, Bactrocera dorsalis (Hendel)

Reproduction is an important life process in insects; however, few studies have attempted to demonstrate the association between reproductive activity and energy metabolism. To address this problem, we focused on the reproductive changes in Bactrocera dorsalis males. We analyzed B. dorsalis male gene expression profiles during mating (DM), 3 h after mating (A3HM) and 12 h after mating (A12HM). Gene annotation and pathway analyses of differentially expressed genes show that galactose metabolism and the starch and sucrose metabolism pathway activities were significantly higher in A12HM group. Moreover, the maltase D gene was the most strongly up-regulated gene. The D-glucose levels were significantly higher in A12HM group. Maltase D expression level was significantly higher in males reared with sucrose. Body weights of the males reared with D-glucose and sucrose were significantly higher than those of the males reared with yeast extract. We observed more mated males from the groups fed sucrose and D-glucose than from those fed yeast extract. The D-glucose levels in individual males were highest at 18:00 h, when flies exhibit the most active mating behavior. This study shows that the maltase D gene and D-glucose are the critical gene and substrate, respectively, in male B. dorsalis mating process.

The influence of male ejaculate quantity on female fitness: a meta-analysis

Although the primary function of mating is gamete transfer, male ejaculates contain numerous other substances that are produced by accessory glands and transferred to females during mating. Studies with several model organisms have shown that these substances can exert diverse behavioural and physiological effects on females, including altered longevity and reproductive output, yet a comprehensive synthesis across taxa is lacking. Here we use a meta-analytic approach to synthesize quantitatively extensive experimental work examining how male ejaculate quantity affects different components of female fitness. We summarize effect sizes for female fecundity (partial and lifetime) and longevity from 84 studies conducted on 70 arthropod species that yielded a total of 130 comparisons of female fecundity and 61 comparisons of female longevity. In response to greater amounts of ejaculate, arthropod females demonstrate enhanced fecundity (both partial and lifetime) but reduced longevity, particularly for Diptera and Lepidoptera. Across taxa, multiply mated females show particularly large fecundity increases compared to singly mated females, indicating that single matings do not maximize female fitness. This fecundity increase is balanced by a slight negative effect on lifespan, with females that received more ejaculate through polyandrous matings showing greater reductions in lifespan compared with females that have mated repeatedly with the same male. We found no significant effect size differences for either female fecundity or longevity between taxa that transfer sperm packaged into spermatophores compared to taxa that transfer ejaculates containing free sperm. Furthermore, females that received relatively larger or more spermatophores demonstrated greater lifetime fecundity, indicating that these seminal nuptial gifts provide females with a net fitness benefit. These results contribute to our understanding of the evolutionary origin and maintenance of non-sperm ejaculate components, and provide insight into female mate choice and optimal mating patterns.

The evolution of a female genital trait widely distributed in the Lepidoptera: comparative evidence for an effect of sexual coevolution

BACKGROUND

Sexual coevolution is considered responsible for the evolution of many male genital traits, but its effect on female genital morphology is poorly understood. In many lepidopterans, females become temporarily unreceptive after mating and the length of this refractory period is inversely related to the amount of spermatophore remaining in their genital tracts. Sperm competition can select for males that delay female remating by transferring spermatophores with thick spermatophore envelopes that take more time to be broken. These envelopes could select for signa, sclerotized sharp structures located within the female genital tract, that are used for breaking spermatophores. Thus, this hypothesis predicts that thick spermatophore envelopes and signa evolve in polyandrous species, and that these adaptations are lost when monandry evolves subsequently. Here we test the expected associations between female mating pattern and presence/absence of signa, and review the scant information available on the thickness of spermatophore envelopes.

METHODOLOGY/PRINCIPAL FINDINGS

We made a literature review and found information on female mating pattern (monandry/polyandry), presence/absence of signa and phylogenetic position for 37 taxa. We built a phylogenetic supertree for these taxa, mapped both traits on it, and tested for the predicted association by using Pagel's test for correlated evolution. We found that, as predicted by our hypothesis, monandry evolved eight times and in five of them signa were lost; preliminary evidence suggests that at least in two of the three exceptions males imposed monandry on females by means of specially thick spermatophore envelopes. Previously published data on six genera of Papilionidae is in agreement with the predicted associations between mating pattern and the characteristics of spermatophore envelopes and signa.

CONCLUSIONS/SIGNIFICANCE

Our results support the hypothesis that signa are a product of sexually antagonistic coevolution with spermatophore envelopes.

Use of quality control charts for detection of outliers and temporal trends in cumulative meta-analysis

Cumulative meta-analysis (CMA) aims to aggregate accumulating evidence. Essentially a visual tool, CMA should be supplemented by formal statistical methods for assessment of the significance of the accumulating evidence, and for detection of temporal trends in effect sizes. These methods should also take into account multiple testing inherent in CMA. We review the existing methods for detection of temporal trends in effect sizes and suggest a new approach, namely the use of standard quality control (QC) charts, in particular X charts and CUSUM charts, to detect possible outliers and trends over time. We discuss the application of the QC charts to four popular measures of effect size: the odds ratios, the relative risks, the correlation coefficients and the standardized mean differences. Applications of QC charts are illustrated by three meta-analysis examples from medicine, ecology and evolutionary biology. Copyright © 2011 John Wiley & Sons, Ltd.

Male mating history and body size influence female fecundity and longevity of the dengue vector Aedes aegypti

Male reproductive success is dependent on insemination success and reproductive output. During mating, male mosquitoes transfer not just sperm, but also seminal fluid proteins that may have profound effects on mated female biology and behavior. In this study, we investigated the role of male body size and mating history on semen depletion, female longevity, and reproductive success in Aedes aegypti L. Small and large males were mated in rapid succession with up to five females. Our results indicate that large males had greater mating capacity than small males. A reduction in fecundity by >50% was observed in females that were fourth to mate with small males in comparison with females that mated earlier in sequence. For females mated to large males, this reduction became evident for females that mated fifth in sequence. No loss of fertility (measured as hatch rate) was observed in females that were third-fifth in mating sequence compared with females mated to virgin males. When females were maintained on a low-quality (5% sucrose) diet, those mated to virgin males had a greater longevity compared with females mated third in sequence. We conclude that small males experience more rapid seminal depletion than large males, and discuss the role of semen depletion in the mated female. Our results contribute toward a better understanding of the complexity of Ae. aegypti mating biology and provide refined estimates of mating capacity for genetic control efforts.