Starving infecund widow spiders maintain sexual attractiveness and trade off safety for enhanced prey capture

Starving animals must balance their resources between immediate survival and future reproduction. False widow spiders, Steatoda grossa, inhabit indoor settings with scarce prey. Here, we investigated the effects of lengthy starvation on the physiology, web architecture, sexual signaling, and reproductive success of S. grossa females. Compared to well-fed females, starving females (1) lost body mass faster, (2) had lower survival, (3) produced more silk for prey capture than for safety, and (4) deposited less contact pheromone components on their webs but accelerated their hydrolysis to mate-attractant components. As starving females became infecund - but still attracted and copulated with males - they misguided males that would gain reproductive fitness by selecting fecund females. Whether starving females store sperm and potentially regain fecundity upon feeding is still unknown. Our study shows how prey shortage shapes sexual signaling, predation, and reproductive behavior of S. grossa females that seem to engage in deceptive signaling.

Drosophila oocyte proteome composition covaries with female mating status

Oocyte composition can directly influence offspring fitness, particularly in oviparous species such as most insects, where it is the primary form of parental investment. Oocyte production is also energetically costly, dependent on female condition and responsive to external cues. Here, we investigated whether mating influences mature oocyte composition in Drosophila melanogaster using a quantitative proteomic approach. Our analyses robustly identified 4,485 oocyte proteins and revealed that stage-14 oocytes from mated females differed significantly in protein composition relative to oocytes from unmated females. Proteins forming a highly interconnected network enriched for translational machinery and transmembrane proteins were increased in oocytes from mated females, including calcium binding and transport proteins. This mating-induced modulation of oocyte maturation was also significantly associated with proteome changes that are known to be triggered by egg activation. We propose that these compositional changes are likely to have fitness consequences and adaptive implications given the importance of oocyte protein composition, rather than active gene expression, to the maternal-to-zygotic transition and early embryogenesis.

Molecular characterization of firefly nuptial gifts: a multi-omics approach sheds light on postcopulatory sexual selection

Postcopulatory sexual selection is recognized as a key driver of reproductive trait evolution, including the machinery required to produce endogenous nuptial gifts. Despite the importance of such gifts, the molecular composition of the non-gametic components of male ejaculates and their interactions with female reproductive tracts remain poorly understood. During mating, male Photinus fireflies transfer to females a spermatophore gift manufactured by multiple reproductive glands. Here we combined transcriptomics of both male and female reproductive glands with proteomics and metabolomics to better understand the synthesis, composition and fate of the spermatophore in the common Eastern firefly, Photinus pyralis. Our transcriptome of male glands revealed up-regulation of proteases that may enhance male fertilization success and activate female immune response. Using bottom-up proteomics we identified 208 functionally annotated proteins that males transfer to the female in their spermatophore. Targeted metabolomic analysis also provided the first evidence that Photinus nuptial gifts contain lucibufagin, a firefly defensive toxin. The reproductive tracts of female fireflies showed increased gene expression for several proteases that may be involved in egg production. This study offers new insights into the molecular composition of male spermatophores, and extends our understanding of how nuptial gifts may mediate postcopulatory interactions between the sexes.

Sclerotised spines in the female bursa associated with male's spermatophore production in cantharidin-producing false blister beetles

Cantharidin is a defence chemical synthesised in only two beetle families Meloidae and Oedemeridae. In Meloidae, cantharidin is used as a defence chemical in eggs. However, in Oedemeridae the function of cantharidin remains unclear. Based on morphological comparison of female internal reproductive organs in 39 species of Oedemeridae, we found that some species have sclerotised spines in the bursa copulatrix (bursal spines), while others have no such spines. Molecular phylogenetic trees inferred from mitochondrial 16S and nuclear 28S rRNA gene sequences suggested multiple evolutionary origins of bursal spines from an ancestor without spines. In the species which lacked spines, males transferred small amounts of ejaculates to females; however, in species with spines, males transferred large spermatophores. Deposited spermatophores gradually disappeared in the bursa, probably owing to absorption. To compare the amounts of cantharidin in eggs laid by species with and without bursal spines, we constructed a new bioassay system using the small beetle Mecynotarsus tenuipes from the family Anthicidae. M. tenuipes individuals were attracted to droplets of cantharidin/acetone solution, and the level of attraction increased with cantharidin concentration. This bioassay demonstrated that the eggs of Nacerdes caudata and N. katoi, both of which species have conspicuous bursal spines, contain more cantharidin than the eggs of N. waterhousei, which lacks spines. In the former species, males transfer large spermatophores to the female, and spermatophores are eventually broken down and digested within the female's spiny bursa. Thus, females with bursal spines may be able to provide more cantharidin to their eggs.

Sexual dimorphism, mating systems, and nuptial gifts in two Asian fireflies (Coleoptera: Lampyridae)

Many insect taxa show conspicuous sexual dimorphism in which females lack functional wings and are therefore incapable of flight. In fireflies, this loss of female flight is correlated with male production of spermatophore nuptial gifts, with species with flightless females also lacking gift production. In this study we further examined the relationship between sexual dimorphism and nuptial gifts by examining the reproductive ecology of two Asian fireflies, the sexually monomorphic Aquatica ficta (Luciolinae) and dimorphic Pyrocoelia pectoralis (Lampyrinae). We describe the reproductive anatomy of P. pectoralis males and females, and the time course of A. ficta spermatophore transfer. Through a series of mating experiments, we determined the effect of the number of matings on female fecundity, egg hatching success and female lifespan. The spermatophore-producing A. ficta was found to be monandrous, and female lifespan doubled as a result of that single mating. P. pectoralis was found to lack spermatophores but females were polyandrous and fecundity and egg hatching success both increased with additional matings. These results contradict patterns known from North American firefly species and provide insight into the role of male-derived substances in mating systems.

Effects of male ejaculate on female reproductive output and longevity in Photinus fireflies

In many insects, nuptial gifts in the form of spermatophores have been shown to increase female fecundity and to contribute to female somatic maintenance. Examining how variation in male spermatophore size affects female fitness components can provide insight into the evolution of nuptial gifts, as well as insight into potential conflicts between the sexes. Here we present an experimental study on the firefly Photinus obscurellus LeConte, 1851 in which we altered spermatophore size by manipulating male mating history and examined effects on female offspring production and longevity. Females were randomly allocated to one of two mating treatments in which they mated once with a male producing either a large or a small spermatophore. We found that male spermatophore size had no significant effect on lifetime fecundity or daily reproductive rates of female P. obscurellus, but females that received a larger spermatophore showed a tendency toward longer postmating life spans. These results suggest a direct benefit to females from nuptial gifts and also reveal the potential for synergistic effects on multiple facets of female fitness.

Determinants of reproductive success across sequential episodes of sexual selection in a firefly

Because females often mate with multiple males, it is critical to expand our view of sexual selection to encompass pre-, peri- and post-copulatory episodes to understand how selection drives trait evolution. In Photinus fireflies, females preferentially respond to males based on their bioluminescent courtship signals, but previous work has shown that male paternity success is negatively correlated with flash attractiveness. Here, we experimentally manipulated both the attractiveness of the courtship signal visible to female Photinus greeni fireflies before mating and male nuptial gift size to determine how these traits might each influence mate acceptance and paternity share. We also measured pericopulatory behaviours to examine their influence on male reproductive success. Firefly males with larger spermatophores experienced dual benefits in terms of both higher mate acceptance and increased paternity share. We found no effect of courtship signal attractiveness or pericopulatory behaviour on male reproductive success. Taken together with previous results, this suggests a possible trade-off for males between producing an attractive courtship signal and investing in nuptial gifts. By integrating multiple episodes of sexual selection, this study extends our understanding of sexual selection in Photinus fireflies and provides insight into the evolution of male traits in other polyandrous species.

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.

Correlated evolution of female neoteny and flightlessness with male spermatophore production in fireflies (Coleoptera: Lampyridae)

The beetle family Lampyridae (fireflies) encompasses ∼100 genera worldwide with considerable diversity in life histories and signaling modes. Some lampyrid males use reproductive accessory glands to produce spermatophores, which have been shown to increase female lifetime fecundity. Sexual dimorphism in the form of neotenic and flightless females is also common in this family. A major goal of this study was to test a hypothesized link between female flight ability and male spermatophore production. We examined macroevolutionary patterns to test for correlated evolution among different levels of female neoteny (and associated loss of flight ability), male accessory gland number (and associated spermatophore production), and sexual signaling mode. Trait reconstruction on a molecular phylogeny indicated that flying females and spermatophores were ancestral traits and that female neoteny increased monotonically and led to flightlessness within multiple lineages. In addition, male spermatophore production was lost multiple times. Our evolutionary trait analysis revealed significant correlations between increased female neoteny and male accessory gland number, as well as between flightlessness and spermatophore loss. In addition, female flightlessness was positively correlated with the use of glows as female sexual signal. Transition probability analysis supported an evolutionary sequence of female flightlessness evolving first, followed by loss of male spermatophores. These results contribute to understanding how spermatophores have evolved and how this important class of seminal nuptial gifts is linked to other traits, providing new insights into sexual selection and life-history evolution.

The production and transfer of spermatophores in three Asian species of Luciola fireflies

During mating, many male insects transfer sperm packaged within a spermatophore that is produced by reproductive accessory glands. While spermatophores have been documented in some North American fireflies (Coleoptera: Lampyridae), little is known concerning either production or transfer of spermatophores in the aquatic Luciola fireflies widespread throughout Asia. We investigated this process in Japanese Luciola lateralis and L. cruciata by feeding males rhodamine B, a fluorescent dye known to stain spermatophore precursors. We then mated males with virgin females, and dissected pairs at various timepoints after mating. In both of these Luciola species, spermatophores were produced by three pairs of male accessory glands and were transferred to females during the second stage of copulation. Male spermatophores were highly fluorescent, and were covered by a thin outer sheath; a narrow tube leading from an internal sperm-containing sac fit precisely into the female spermathecal duct, presumably for sperm delivery. Both L. lateralis and L. cruciata females have a spherical spermatheca as well as a highly extensible gland where spermatophore breakdown commences by 24h post-mating. Similar reproductive anatomy was observed for both sexes in Luciola ficta from Taiwan. These results suggest that nuptial gifts may play an important role in many firefly-mating systems.

Flash signal evolution, mate choice, and predation in fireflies

Many key advances in our understanding of firefly biology and signaling have been made over the past two decades. Here we review this recent research, which includes new phylogenetic results that shed light on the evolution of courtship signal diversity within the family Lampyridae, new insights into firefly flash control, and the discovery of firefly nuptial gifts. We present a comprehensive overview of sexual selection in lampyrids, including evidence from Photinus fireflies that females choose their mates on the basis of male flash signals, and discuss the importance of examining both precopulatory and postcopulatory sexual selection in this group. Finally, we review recent findings on firefly chemical defenses, and discuss their implications for flash signal evolution in response to generalist predators as well as specialist predatory fireflies. This review provides new insight into how firefly flash signals have been shaped by the dual evolutionary processes of sexual selection (mate choice) and natural selection (predation), and proposes several exciting directions for future research.

Male courtship attractiveness and paternity success in Photinus greeni fireflies

Although female mate choice and male sperm competition have separately attracted much attention, few studies have addressed how precopulatory and postcopulatory episodes of sexual selection might interact to drive the evolution of male traits. In Photinus fireflies, females preferentially respond to males based on their bioluminescent courtship signals, and females gain direct benefits through male nuptial gifts acquired during multiple matings over several nights. We experimentally manipulated matings of P. greeni fireflies to test the hypothesis that postcopulatory paternity success might be biased toward males that are more attractive during courtship interactions. We first measured male courtship attractiveness to individual females using field behavioral assays. Females were then assigned to two double-mating treatments: (1) least attractive second male-females were first mated with their most attractive male, followed by their least attractive male, or (2) most attractive second male-females mated with males in reverse order. Larval offspring produced by each female following these double matings were genotyped using random amplified polymorphic DNA (RAPD) markers, and male paternity was determined. Contrary to prediction, firefly males that were more attractive to females based on their bioluminescent courtship displays subsequently showed significantly lower paternity, reflecting possible male trade-offs or sexual conflict. Differences in male paternity were not related to male body condition, testes or accessory gland mass, or to variation in female spermathecal size. Additionally, this study suggests that changes in phenotypic selection gradients may occur during different reproductive stages. These results indicate that it is crucial for future studies on sexual selection in polyandrous species to integrate both precopulatory and postcopulatory episodes to fully understand the evolution of male traits.

Transfer and fate of seminal fluid molecules in the beetle, Diaprepes abbreviatus: implications for the reproductive biology of a pest species

Molecules transferred from males to females via seminal fluids are important to the study of insect reproduction because they affect female physiology, reproductive behavior, and longevity. These molecules (seminal fluid molecules or SFMs) interest applied entomologists because of their potential use in insect control. SFMs are also interesting because of their relatively rapid evolution and important role in post-mating sexual selection. We studied SFMs in Diaprepes abbreviatus, a major pest of numerous plant species of economic importance. Using radiolabeled-methionine (35S), we found that D. abbreviatus males synthesized proteins de novo in their reproductive tissues after mating. Males that were fed radiolabeled methionine transferred radioactivity to females beginning within the first 10 min of mating. Male-derived substances are absorbed from the female's reproductive tract into the hemolymph and circulated throughout the body, but are found primarily in the eggs and ovaries. As a result, SFMs may be a useful means of both horizontal (to mates) and vertical transfer (to offspring) of control agents between conspecifics.

Sperm storage and viability in Photinus fireflies

In many species females mate with and store sperm from multiple males, and some female insects have evolved multiple compartments for sperm storage. Sperm storage and sperm viability were investigated in two firefly species, Photinus greeni and P. ignitus, which differ in the morphology of the female reproductive tract. Although the primary spermatheca is similar in both species, P. greeni females have an additional, conspicuous outpocketing within the bursa copulatrix whose potential role in sperm storage was investigated in this study. An assay that distinguishes between live and dead sperm was used to examine sperm viability in male seminal vesicles and sperm storage sites within the female reproductive tract. For both Photinus species, sperm from male seminal vesicles showed significantly higher viability compared to sperm from the primary spermatheca of single mated females. In single mated P. greeni females, sperm taken from the channel outpocketing (secondary spermatheca) showed significantly higher viability compared to sperm from the primary spermatheca. This sperm viability difference was not evident in double mated females. There were no significant differences between P. greeni and P. ignitus females in the viability of sperm from the primary spermatheca. These studies contribute to our understanding of post-mating processes that may influence paternity success, and suggest that sexual conflict over control of fertilizations may occur in multiply mated firefly females.

Males influence maternal effects that promote sexual selection: a quantitative genetic experiment with dung beetles Onthophagus taurus

Recently, doubt has been cast on studies supporting good genes sexual selection by the suggestion that observed genetic benefits for offspring may be confounded by differential maternal allocation. In traditional analyses, observed genetic sire effects on offspring phenotype may result from females allocating more resources to the offspring of attractive males. However, maternal effects such as differential allocation may represent a mechanism promoting genetic sire effects, rather than an alternative to them. Here we report results from an experiment on the horned dung beetle Onthophagus taurus, in which we directly compare genetic sire effects with maternal effects that are dependent on sire phenotype. We found strong evidence that mothers provide more resources to offspring when mated with large-horned males. There were significant heritabilities for both horn length and body size, but when differential maternal effects were controlled, the observed estimates of genetic variance were greatly reduced. Our experiment provides evidence that differential maternal effects may amplify genetic effects on offspring traits that are closely related to fitness. Thus, our results may partly explain the relatively high coefficients of additive genetic variation observed in fitness-related traits and provide empirical support for the theoretical argument that maternal effects can play an important role in evolution.

The potential for incorporation of male derived proteins into developing eggs in the leafhopper Bothrogonia ferruginea

The leafhoppers, Bothrogonia ferruginea (Homoptera: Cicadellidae), eclose to adults in summer with immature reproductive organs. The adults live for 10 months including a hibernation of 4 months. Overwintered females mate multiply in spring. Eggs develop rapidly and are laid continuously in this mating period. Males produce sperm-bundles in which sperm are attached in a row to a rope-like hyaline material, and transfer them to the female via a large spermatophore that is placed in her bursa copulatrix. After mating, sperm are separated and removed to a spermatheca for storage prior to fertilization, but the sperm-binding material (trypsin degradable proteins) and the spermatophore disappear in the bursa and an enlarged portion of the genital duct. An injection of rhodamine B-dyed proteins into the female bursa with a microsyringe results in the production of intensely fluorescent eggs developing in the ovaries. This suggests that females could incorporate proteinaceous material derived from male spermatophores and/or sperm-binding material into their oocytes.

Patterns of divergence in the effects of mating on female reproductive performance in flour beetles

Sexual selection can lead to rapid divergence in reproductive characters. Recent studies have indicated that postmating events, such as sperm precedence, may play a key role in speciation. Here, we stress that other components of postmating sexual selection may be involved in the evolution of reproductive isolation. One of these is the reproductive investment made by females after mating (i.e., differential allocation). We performed an experiment designed to assess genetic divergence in the effects of mating on female reproductive performance in flour beetles, Tribolium castaneum. Females were mated to males of three different wild-type genotypes at two different frequencies, in all possible reciprocal combinations. Male genotype affected all aspects of female reproduction, through its effects on female longevity, total offspring production, reproductive rate, mating rate, and fertility. Moreover, male and female genotype interacted in their effects on offspring production and reproductive rate. We use the pattern of these interactions to discuss the evolutionary process of divergence and suggest that the pattern is most consistent with that expected if divergence was driven by sexually antagonistic coevolution. In particular, the fact that females exhibited a relatively weak response to males with which they were coevolved suggests that females have evolved resistance to male gonadotropic signals/stimuli.

The evolution of polyandry: multiple mating and female fitness in insects

Theory suggests that male fitness generally increases steadily with mating rate, while one or a few matings are sufficient for females to maximize their reproductive success. Contrary to these predictions, however, females of the majority of insects mate multiply. We performed a meta-analysis of 122 experimental studies addressing the direct effects of multiple mating on female fitness in insects. Our results clearly show that females gain directly from multiple matings in terms of increased lifetime offspring production. Despite a negative effect of remating on female longevity in species without nuptial feeding, the positive effects (increased egg production rate and fertility) more than outweigh this negative effect for moderate mating rates. The average direct net fitness gain of multiple mating was as high as 30-70%. Therefore, the evolutionary maintenance of polyandry in insects can be understood solely in terms of direct effects. However, our results also strongly support the existence of an intermediate optimal female mating rate, beyond which a further elevated mating rate is deleterious. The existence of such optima implies that sexual conflict over the mating rate should be very common in insects, and that sexually antagonistic coevolution plays a key role in the evolution of mating systems and of many reproductive traits. We discuss the origin and maintenance of nuptial feeing in the light of our findings, and suggest that elaborate and nutritional ejaculates may be the result of sexually antagonistic coevolution. Future research should aim at gaining a quantitative understanding of the evolution of female mating rates. Copyright 2000 The Association for the Study of Animal Behaviour.

Hexameric storage proteins during metamorphosis and egg production in the diamondback moth, Plutella xylostella (Lepidoptera)

As in many Lepidoptera, Plutella xylostella adults do not feed on protein and females must use accumulated reserves to supply vitellogenin synthesis. Storage proteins were quantified in females and males from the late larval stage through day 4 of adult life. The level of storage protein peaked in the early pupal stage, with females having about twice as much as males. In males, the level fell through pupal development and dropped to a trace by one day after eclosion. In females, level of storage proteins fell until eclosion, and then rose dramatically within four hours after the molt to about 2/3 of the original peak level. This post-eclosion increase, which has not been reported previously in insects, suggests that adult females synthesize hexamerins to resequester amino acids. Subsequently, the level of storage proteins fell as vitellogenin appeared and eggs were laid. The ability to synthesize and sequester amino acids as storage proteins during the adult stage has wide-ranging implication for protein management in insects, particularly those that are long-lived and have flexible schedules of reproduction.

Sperm storage by females of the polyandrous noctuid moth Heliothis virescens

Female tobacco budworm moths, Heliothis virescens, generally mate with more than one male, receiving from each mate both fertilizing sperm (eupyrene) and nonfertilizing anucleate sperm (apyrene), which is thought to play a role in sperm competition. One male typically gains sperm precedence, but it is not consistently the last or the first male to mate. I investigated the mechanism of this variable pattern of paternity by examining the patterns of storage of both types of sperm in the female's spermatheca as a function of multiple mating and male phenotype. The number of stored apyrene sperm varied with mating history, being greatest in twice-mated females and least in females mated to one nonvirgin male. In contrast, only one ejaculate's worth of eupyrene sperm was stored regardless of female mating history (once or twice mated). Thus, while they store two complements of apyrene sperm, twice-mated females apparently store only one ejaculate's worth of eupyrene sperm. This biased pattern of sperm storage may contribute to the variable pattern of paternity observed in this species. Eupyrene sperm storage also correlated positively with female size, male age and spermatophore size. Finally, a new sperm storage site was identified and described. It is a bulged region in the seminal duct. Copyright 2000 The Association for the Study of Animal Behaviour.