Modulation of seminal fluid molecules by males and females

Gene regulation by mating depends on time, diet, and body region in female Aedes aegypti

Aedes aegypti is a major vector of several arboviruses that cause human mortality and morbidity. One method for controlling the spread of these viruses is to control mosquito reproduction. During mating, seminal fluid molecules and sperm are transferred and these stimuli influence female post-mating physiology and behavior. Yet, little is known about the mechanisms underlying these post-mating responses. To fill this gap, short-read RNA sequencing was used to identify differentially expressed genes between unmated (control) and mated females in the head/thorax (HT), abdomen (Ab) and the lower reproductive tract (LRT), of mosquitoes reared with 3% and 12% sucrose. The results revealed that at 3% sucrose, four, 408 and 415 significantly differential expressed genes (DEGs) were identified in the HT, Ab and LRT at six hours post mating (hpm). The number of DEGs dropped dramatically at 24 hpm with no DEGs in the HT, three in the Ab, and 112 in the LRT. In contrast, the number of DEGs was lower at 6 hpm than 24 hpm in the LRT at 12% sucrose. Comparing our results to a similar study which used 10% sucrose revealed evidence in support of condition-dependent regulation of gene expression by mating in this species. This study shows that mating-induced transcriptional changes depend on time point after mating, body region, and diet. Our results provide foundational knowledge for future functional analyses to identify genes and pathways involved in the post-mating behavioral and physiological changes of female mosquitoes.

Male condition and seminal fluid affect female host-marking behavior in the Mexican fruit fly

Mating and the transfer of seminal fluid components including male accessory glands (MAGs) proteins can affect oviposition behavior in insects. After oviposition, some species of fruit flies deposit a host-marking pheromone (HMP) on the fruit that discourages oviposition by other females of the same or different species or genus and reduces competition between larvae. However, we know very little about how mating, receiving seminal fluid, or male condition can affect female host marking behavior. Here, we tested how the physiological state of females (mated or unmated), the receipt of seminal fluid, and the condition of the male (wild or sterile) affect oviposition and host-marking behavior (HMB) in Anastrepha ludens (Diptera: Tephritidae). We also determined the efficiency of the host-marking pheromone from mated or unmated females in deterring oviposition. In a further examination of how seminal fluid may be affecting HMB we assessed if there were differences in the size of wild or sterile MAGs and the protein quantity transferred during mating. Our results indicate that receiving seminal fluid increased egg laying and increased time invested in host-marking (HM). Unmated females laid fewer eggs than mated females but invested the same amount of time in depositing host-marking pheromone, which had similar effectiveness in deterring oviposition as that of mated females. Females that mated with sterile males laid the same number of eggs as females that mated with wild males but spent less time depositing host-marking pheromone, which suggests that females detect the condition of the male and invest less in marking hosts. Finally, sterile males had larger accessory glands and transferred more MAGs proteins during mating compared to wild males. Seminal proteins could be manipulating HM behavior and female investment into their current reproductive effort. We are only beginning to understand how male condition and seminal fluid can affect female physiology and maternal investment in HMP.

Long-sperm precedence and other cryptic female choices in Drosophila melanogaster

Females that mate multiply make postmating choices about which sperm fertilize their eggs (cryptic female choice); however, the male characteristics they use to make such choices remain unclear. In this study, we sought to understand female sperm use patterns by evaluating whether Drosophila melanogaster females adjust sperm use (second male paternity) in response to four main factors: male genotype, male courtship effort, male pheromone alteration, and male postmating reproductive morphology. Our experiment was replicated across four different D. melanogaster lines, in a full factorial design, including a pheromone manipulation in which second males were perfumed to resemble heterospecific (D. yakuba) males. We found that females prefer longer sperm-regardless of mating order-in almost all contexts; this observed pattern of 'long-sperm precedence' is consistent with female postmating choice of high-fitness male traits. Nonetheless, we also found that this general preference can be plastically altered by females in response to effects including perfuming treatment; this differential female sperm use is between otherwise identical males, and therefore solely female-mediated. Furthermore, our finding that females exercise choice using diverse criteria suggests a possible mechanism for the maintenance of variation in sexually selected male traits.

Male-derived phospholipase A2 enhances WD46 expression and increases fertility in Ophraella communa

Successful bisexual reproduction requires interactions between males and females. Male-derived seminal fluid proteins (SFPs) transferred to females during mating profoundly affect females from pre- to post-mating, and the subsequent shift in female physiology enhances their fertility. SFPs have important evolutionary implications for the fitness of many insects. However, little is known about how females respond to male SFPs. In this study, we identified a male-derived SFP-phospholipase A2 (PLA2) in Ophraella communa. PLA2 is a vital enzyme in eicosanoid biosynthesis; however, it has not been identified as an insect SFP. We found that OcPLA2 is specifically expressed in males, especially in the male accessory glands (MAGs); it is transferred to the female during mating and functions as an SFP to enhance fertility. The expression of a female-derived gene encoding the WD repeat-containing protein 46 (WD46) was upregulated when OcPLA2 entered the female reproductive tract, and this contributed to female egg production by increasing triacylglycerol lipase (TGL) gene expression and the triglyceride (TG) content. This is the first study to identify PLA2 as an SFP in insects. Our findings also shed light on the regulatory role of OcPLA2 in beetle reproduction; the expression of OcPLA2 is initially correlated with female WD46 expression and later with the decline in TGL gene expression and the TG content. This represents a unique mechanism of reproductive regulation by an SFP.

Peroxiredoxin 1 transfer during mating protects eupyrene sperm against oxdative stress in Grapholita molesta

BACKGROUND

Each Grapholita molesta female only copulates once during its lifetime and thus must maintain the viability of stored eupyrene sperm for male reproductive success. The male ejaculate comprises abundant accessory gland proteins produced by the male accessory gland (AG), and many of which are major effectors for sperm storage and maintenance.

RESULTS

Here, we reported that an antioxidant protein, peroxiredoxin 1 (GmolPrx1), secreted by the male AG, is essential for protecting eupyrene sperm from oxidative stress and maintaining their quality during storage in the female bursa copulatrix (BC). Our data showed that GmolPrx1 is highly expressed in the AG of sexually mature males. The GmolPrx1 protein is localized to the cytoplasm of AG cells and delivered to the female BC during mating. Knockdown of GmolPrx1 strongly decreased the fertility of mated females. Additionally, we evaluated oxidative status in the spermatophore of females and found that the content of hydrogen peroxide increased significantly after mating with GmolPrx1 knockdown males. Finally, the quality assessment of eupyrene sperm demonstrated that the plasma membrane integrity, acrosome integrity, and DNA integrity were all severely impaired in the spermatophore of females after mating with GmolPrx1 knockdown males, which may contribute to the fertility decline in males.

CONCLUSION

Our current data demonstrated that activities of eupyrene sperm stored in females can be significantly impaired by enhanced oxidative stress through knocking down of GmolPrx1 in males. Our finding thus may further lay new foundations for the control of G. molesta through suppressing their populations by manipulating male reproductive genes. © 2023 Society of Chemical Industry.

The female Euscepes postfasciatus refractory period is induced by the male but length is determined by the female

Females of many animals mate multiple times during their lives (i.e., polyandry). The period between matings (mating interval) is called the refractory period (RP). In the West Indian sweet potato weevil (Euscepes postfasciatus), males use the ejaculate to induce the RP in females to prevent re-mating. By measuring the RP, a large variation of 1-49 days was observed. This variation may be due to the males (ejaculate quantity and quality) and females (ejaculate sensitivity/degradation ability and body size) and their interactions, but the exact mechanisms are currently unclear. Here, we investigated a tendency towards a particular female RP duration and the associated traits of males and females to test the following three factors responsible for variation in the length of the RP: male manipulation of ejaculate volume, individual differences in male ejaculation substances, and ejaculate sensitivity/degradation ability in females. We prepared virgin males and females to create mating pairs. The following day, another mate was introduced to the females, and the first RP was measured. The same procedure was used for measuring the second RP. The males were also provided with another female (second female), mated, and then the RP of the second female was measured. In addition, the relationship between the length of the RP and female fitness was investigated. The results showed that there was a significant positive correlation between the first and second RP in the focal females, while no significant correlation was observed between the RP of the first and second females induced by the same male. It was also found that the length of the RP did not affect female fitness. This indicated that the males did not adaptively manipulate ejaculation volume depending on the quality of the females, and variance in the length of the RP may be explained by variation in the female physiological ability against ejaculate.

Corazonin signaling modulates the synthetic activity of male accessory gland in Grapholita molesta

Although neuropeptide corazonin (Crz) has been identified in numerous insect species, the research about its function in regulation of reproduction is still in its infancy. Herein, we characterized the Crz (GmolCrz) and its receptor (GmolCrzR) to investigate their reproductive function in Grapholita molesta. Both molecular docking result and cell-based receptor activity assay showed that GmolCrz could interact with GmolCrzR. Additionally, spatial expression patterns of GmolCrz and GmolCrzR in males were evaluated. Knockdown of GmolCrz or GmolCrzR significantly lengthened copulation duration and decreased fertility in males. In these males, we found that the production of sperm was normal, while the content of accessory gland proteins (Acps) in the accessory gland (AG) was strongly diminished. Furthermore, knockdown of GmolCrz or GmolCrzR in males had no effect on sperm and Acps transfer to females. RNA-seq and gene expression analyses further confirmed that genes involved in serine-type endopeptidase activity were significantly downregulated in the AG upon GmolCrzR knockdown. Finally, sperm activation assays demonstrated that this process was disrupted in the spermatophore of females mated with GmolCrz or GmolCrzR knockdown males, which may cause the decreased fertility in males. Our findings provide new insights into the functions of Crz signaling in a Lepidopteran insect.

Effects of Larval Diet on the Male Reproductive Traits in the West Indian Sweet Potato Weevils Euscepes postfasciatus (Coleoptera: Curculionidae)

Simple Summary

In insects, it is known that the diet during the larval stage affects traits in the adult stage. However, it is still unclear how it affects reproductive traits such as ejaculation. The ejaculate contains many proteins and therefore requires much nutrition, so the larval diet strongly influences it. Males of the West Indian sweet potato weevil Euscepes postfasciatus use accessory gland substances to inhibit remating by females. Crossing experiments were conducted using lines reared on artificial diets or sweet potato tubers during the larval stage, and the refractory period was examined. The results showed that the larval stage diet had a significant effect on the refractory period of females. We also found one protein of approximately 15 kDa in size expressed only in the treatments reared on sweet potatoes. To our knowledge, this is the first study to show that larval diet qualitatively influences male ejaculate and female refractory period.

Abstract

Larval diet significantly affects adult traits, although less is known about how they affect reproductive traits. Males of West Indian sweet potato weevil Euscepes postfasciatus deliver a remating inhibitor along with sperm to their mates during mating, leading to a refractory period (the period before females mate again). Crossing experiments were conducted using lines reared on artificial diets, including sweet potato powder (AD) or sweet potato tubers (SP) during the larval stage, and the refractory period was examined. We also examined whether the larval diet qualitatively or quantitatively altered male ejaculate. The results showed that the refractory period was significantly longer in the SP treatment than in the AD treatment for males and females. There was no significant difference in ejaculate volume. However, the number of sperm in the testes-seminal vesicles complex was significantly higher in the SP treatment. Additionally, SDS-PAGE revealed that the ejaculate was qualitatively different depending on the larval diet, and one protein of approximately 15 kDa in size was expressed only in the SP treatments. Revealing how larval diet affects reproductive traits in adult males will help shed light on the diverse evolution of insect mating systems and reproductive behavior.

Effects of Mating on Gene Expression in Female Insects: Unifying the Field

Simple Summary

Insects play many important roles including in ecosystems, food production, pathogen transmission, and production of materials. As a result, humans are interested in understanding how to control insect population sizes for control, propagation, or conservation efforts. In many insect species, female reproductive output is promoted by mating and components of the ejaculate. Beyond just the impact of receiving sperm, mating and ejaculate components can result in increased rate of oocyte development, ovulation, and oviposition as well as other changes such as reduced mating receptivity. To understand how mating causes these changes, researchers have investigated changes in female gene expression that occur after mating. In this review, we summarize the current state of knowledge on mating-induced gene expression changes in female insects and the methods used for conducting such studies. We find that genes related to immune response, chemosensation, and metabolism are commonly regulated across species. We suggest future research paths to facilitate the comparison of studies on mating-regulated gene expression across insect species.

Abstract

There is intense interest in controlling insect reproductive output. In many insect species, reproductive output is profoundly influenced by mating, including the receipt of sperm and seminal fluid molecules, through physiological and behavior changes. To understand these changes, many researchers have investigated post-mating gene expression regulation. In this review, we synthesize information from studies both across and within different species about the impact of mating, or components of mating, on female gene expression patterns. We found that genes related to the roles of metabolism, immune-response, and chemosensation are regulated by mating across many different insect species. We highlight the few studies that have taken the important next step of examining the functional consequences of gene expression regulation which is crucial in order to understand the mechanisms underlying the mating-regulated control of female lifespan and reproduction and to make use of such knowledge to propagate or control insect populations. The potential of cross-study comparisons is diminished by different studies using different methods. Thus, we also include a consideration of how future studies could be designed to facilitate cross-study comparisons and a call for collaboration across researchers studying different insect species and different aspects of insect biology.

Testing potential mechanisms of conspecific sperm precedence in Drosophila pseudoobscura

Drosophila pseudoobscura females that co-occur with sister species D. persimilis show elevated fertilization by conspecific sperm when they mate with both a heterospecific and a conspecific male. This phenomenon, known as conspecific sperm precedence (CSP), has evolved as a mechanism to avoid maladaptive hybridization with D. persimilis. In this study, we assessed pericopulatory (during mating) and postcopulatory (after mating) traits in crosses with sympatric or allopatric D. pseudoobscura females and conspecific or heterospecific males to evaluate potential mechanisms of CSP in this system. We observed shorter copulation duration in crosses with sympatric females, but found no difference in quantity of sperm transferred or female reproductive tract toxicity between sympatry and allopatry. Our data show some support for the hypothesis that parasperm, a short, sterile sperm morph, can protect fertile eusperm from the D. pseudoobscura female reproductive tract, though it is unclear how this might affect patterns of sperm use in sympatry vs. allopatry. Overall, these results suggest that copulation duration could potentially contribute to the elevated CSP observed in sympatry.

Pronounced Postmating Response in the Drosophila Female Reproductive Tract Fluid Proteome

Fertility depends on the progression of complex and coordinated postmating processes within the extracellular environment of the female reproductive tract (FRT). Molecular interactions between ejaculate and FRT proteins regulate many of these processes, including sperm motility, migration, storage, and modification, along with concurrent changes in the female. Although extensive progress has been made in the proteomic characterization of the male-derived components of sperm and seminal fluid, investigations into the FRT have remained more limited. To achieve a comparable level of knowledge regarding female-derived proteins that comprise the reproductive environment, we utilized semiquantitative MS-based proteomics to study the composition of the FRT tissue and, separately, the luminal fluid, before and after mating in Drosophila melanogaster. Our approach leveraged whole-fly isotopic labeling to delineate female proteins from transferred male ejaculate proteins. Our results revealed several characteristics that distinguish the FRT fluid proteome from the FRT tissue proteome: (1) the fluid proteome is encoded by genes with higher overall levels of FRT gene expression and tissue specificity, including many genes with enriched expression in the fat body, (2) fluid-biased proteins are enriched for metabolic functions, and (3) the fluid exhibits pronounced postmating compositional changes. The dynamic mating-induced proteomic changes in the FRT fluid inform our understanding of secretory mechanisms of the FRT, serve as a foundation for establishing female contributions to the ejaculate-female interactions that regulate fertility, and highlight the importance of applying proteomic approaches to characterize the composition and dynamics of the FRT environment.

An inconvenient tooth: Evaluating female choice in multiple paternity using an evolutionarily and ecologically important vertebrate clade

Understanding mating systems is a pillar of behavioural ecology, placing the complex interactions between females and males into a reproductive context. The field of multiple paternity, the phenomenon whereby many sires contribute to an individual litter, has traditionally viewed females as passive players in a male–male competitive framework. With the emergence of feminist perspectives in ecological fields, novel alternative mechanisms and evolutionary theories across invertebrate and vertebrate taxa recognize females are active stakeholders in the reproductive process. Despite their evolutionary significance, ecological diversity and myriad reproductive modes, elasmobranch (sharks, skates and rays) research lags behind other fields regarding complex biological processes, such as multiple paternity which is often ascribed to convenience polyandry. Here, we layout hypotheses and resynthesize multiple paternity literature from a female and life history perspective to highlight how alternative mechanisms influence the predominance of multiple paternity across elasmobranchs. We draw upon parallels in other invertebrate and vertebrate taxa to demonstrate how female elasmobranchs can influence multiple paternity outcomes that benefit their reproductive success. Our article challenges dogma that has resulted from years of dismissing the female perspective as important and provides a framework for future advancement using more holistic approaches to studying mating systems.

The Drosophila seminal proteome and its role in postcopulatory sexual selection

Postcopulatory sexual selection (PCSS), comprised of sperm competition and cryptic female choice, has emerged as a widespread evolutionary force among polyandrous animals. There is abundant evidence that PCSS can shape the evolution of sperm. However, sperm are not the whole story: they are accompanied by seminal fluid substances that play many roles, including influencing PCSS. Foremost among seminal fluid models is Drosophila melanogaster, which displays ubiquitous polyandry, and exhibits intraspecific variation in a number of seminal fluid proteins (Sfps) that appear to modulate paternity share. Here, we first consolidate current information on the identities of D. melanogaster Sfps. Comparing between D. melanogaster and human seminal proteomes, we find evidence of similarities between many protein classes and individual proteins, including some D. melanogaster Sfp genes linked to PCSS, suggesting evolutionary conservation of broad-scale functions. We then review experimental evidence for the functions of D. melanogaster Sfps in PCSS and sexual conflict. We identify gaps in our current knowledge and areas for future research, including an enhanced identification of PCSS-related Sfps, their interactions with rival sperm and with females, the role of qualitative changes in Sfps and mechanisms of ejaculate tailoring. This article is part of the theme issue 'Fifty years of sperm competition'.

Copulation Song in Drosophila: Do Females Sing to Change Male Ejaculate Allocation and Incite Postcopulatory Mate Choice?

Drosophila males sing a courtship song to achieve copulations with females. Females were recently found to sing a distinct song during copulation, which depends on male seminal fluid transfer and delays female remating. Here, it is hypothesized that female copulation song is a signal directed at the copulating male and changes ejaculate allocation. This may alter female remating and sperm usage, and thereby affect postcopulatory mate choice. Mechanisms of how female copulation song is elicited, how males respond to copulation song, and how remating is modulated, are considered. The potential adaptive value of female signaling during copulation is discussed with reference to vertebrate copulation calls and their proposed function in eliciting mate guarding. Female copulation song may be widespread within the Drosophila genus. This newly discovered behavior opens many interesting avenues for future research, including investigation of how sexually dimorphic neuronal circuits mediate communication between nervous system and reproductive organs.

Males adjust their manipulation of female remating in response to sperm competition risk

To reduce the potential for sperm competition, male insects are thought to inhibit the post-mating reproductive behaviour of females through receptivity-inhibiting compounds transferred in the ejaculate. Selection is expected to favour phenotypic plasticity in male post-copulatory expenditure, with males investing strategically in response to their perceived risk of sperm competition. However, the impact that socially cued strategic allocation might have on female post-mating behaviour has rarely been assessed. Here, we varied male perception of sperm competition risk, both prior to and during mating, to determine if a male's competitive environment impacts the extent to which he manipulates female remating behaviour. We found that female Australian field crickets (Teleogryllus oceanicus) mated to males that were reared under sperm competition risk emerged from a shelter in search of male song sooner than did females mated to males reared without risk, but only when mating occurred in a risk-free environment. We also found that females reared in a silent environment where potential mates were scarce emerged from the shelter sooner than females exposed to male calls during development. Collectively, our findings suggest complex interacting effects of male and female sociosexual environments on female post-mating sexual receptivity.

Injection of seminal fluid into the hemocoel of honey bee queens (Apis mellifera) can stimulate post-mating changes

Honey bee queens undergo dramatic behavioral (e.g., reduced sexual receptivity), physiological (e.g., ovary activation, ovulation, and modulation of pheromone production) and transcriptional changes after they complete mating. To elucidate how queen post-mating changes are influenced by seminal fluid, the non-spermatozoa-containing component of semen, we injected queens with semen or seminal fluid alone. We assessed queen sexual receptivity (as measured by likelihood to take mating flights), ovary activation, worker retinue response (which is influenced by queen pheromone production), and transcriptional changes in queen abdominal fat body and brain tissues. Injection with either seminal fluid or semen resulted in decreased sexual receptivity, increased attractiveness of queens to workers, and altered expression of several genes that are also regulated by natural mating in queens. The post-mating and transcriptional changes of queens receiving seminal fluid were not significantly different from queens injected with semen, suggesting that components in seminal fluid, such as seminal fluid proteins, are largely responsible for stimulating post-mating changes in queens.

Introduction to “Reproduction: The Female Perspective from an Integrative and Comparative Framework”

This compendium is from a symposium about reproductive biology from the female perspective, but what do we mean by the female perspective? Most obviously, since all of our speakers, and most of our contributors, are female, one meaning is that the female perspective is the view of female scientists. Our diverse contributors are from a spectrum of academic ranks (post-docs to chaired professors) and study a range of animal taxa from insects to mammals. More importantly, we want to examine reproductive biology from the perspective of female organisms themselves. What happens when we examine social behavior, physiology, or ecology strictly from the viewpoint of females? In many cases, the female-centric perspective will alter our prior interpretations. For example, with deoxyribonucleic acid fingerprinting, differences between genetic and behavioral mating-systems became obvious. The scientific community came to realize that assessing parentage is the definitive way to categorize mating systems since using male-mating strategies resulted in flawed conclusions; in fact, the female selection of which sperm is involved in conception is more important in determining parentage than mating events per se. Perhaps parentage systems rather than mating systems would be more appropriate. This difference in interpretation relative to methodology exemplifies how behavioral ecology might change if we examine systems from the female perspective; similar changes may occur for other fields. Another example comes from studies of whole-organism performance. Here, jumping, running, and swimming have been measured in males, usually with the deliberate removal of females and the major facet of female physiology, that is, reproduction. However, female biology may actually set the limits of performance given the need to carry extra weight and the extensive changes in body shape required for reproduction. Female performance is a valuable area for research. In fact, novel insights into metabolic ceilings arose from examining energetics, including metabolic rates, during lactation. In the symposium and the associated papers, our contributors explored the various ways in which a female-focused framework shifts our research conclusions and programs. As a way forward, we also include a table of sex-neutral terminology to replace terms that are currently androcentric or value-laden.

Female copulation song is modulated by seminal fluid

In most animal species, males and females communicate during sexual behavior to negotiate reproductive investments. Pre-copulatory courtship may settle if copulation takes place, but often information exchange and decision-making continue beyond that point. Here, we show that female Drosophila sing by wing vibration in copula. This copulation song is distinct from male courtship song and requires neurons expressing the female sex determination factor DoublesexF. Copulation song depends on transfer of seminal fluid components of the male accessory gland. Hearing female copulation song increases the reproductive success of a male when he is challenged by competition, suggesting that auditory cues from the female modulate male ejaculate allocation. Our findings reveal an unexpected fine-tuning of reproductive decisions during a multimodal copulatory dialog. The discovery of a female-specific acoustic behavior sheds new light on Drosophila mating, sexual dimorphisms of neuronal circuits and the impact of seminal fluid molecules on nervous system and behavior.