Identification and comparative analysis of accessory gland proteins in Orthoptera

Comparative transcriptomics reveals the conservation and divergence of reproductive genes across three sympatric Tomicus bark beetles

Three tree-killing bark beetles belonging to the genus Tomicus, Tomicus yunnanensis, Tomicus brevipilosus and Tomicus minor (Coleoptera; Curculionidae, Scolytinae), are serious wood-borers with larvae feeding on the phloem tissues of Pinus yunnanensis. The three Tomicus beetles, in some cases, coexist in a same habitat, providing a best system for exploring the conservation and divergence of reproductive genes. Here, we applied comparative transcriptomics and molecular biology approaches to characterize reproductive-related genes in three sympatric Tomicus species. Illumina sequencing of female and male reproductive systems and residual bodies generated a large number of clean reads, representing 185,920,232 sequences in T. yunnanensis, 169,153,404 in T. brevipilosus and 178,493,176 in T. minor that were assembled into 32,802, 56,912 and 33,670 unigenes, respectively. The majority of the genes had detectable expression in reproductive tissues (FPKM >1), particularly those genes in T. brevipilosus accounting for 76.61 % of the total genes. From the transcriptomes, totally 838 genes encoding 463 detoxification enzymes, 339 chemosensory membrane proteins and 36 ionotropic glutamate receptors (iGluRs) were identified, including 622 reproductive tissue-expressed genes. Of these, members of carboxylesterases (COEs), ionotropic receptors (IRs), sensory neuron membrane proteins (SNMPs) and iGluRs were highly conserved in gene numbers and sequence identities across three Tomicus species. Further, expression profiling analyses revealed a number of genes expressed in reproductive tissues and the diverse expression characteristics in these beetles. The results provide evidence for the conservation and differences of reproductive genes among three sympatric closely related beetles, helping understand their different reproductive strategies and the maximization of the reproductive success.

Leucine aminopeptidase1 controls egg deposition and hatchability in male Aedes aegypti mosquitoes

Aedes aegypti are vectors for several arboviruses infecting hundreds of millions of people annually. Controlling mosquito populations by regulating their reproduction is a potential strategy to minimize viral transmission in the absence of effective antiviral therapies or vaccines. Here, we demonstrate that leucine aminopeptidase1 (LAP1), detected by a SWATH-MS-based proteomic screen of female spermathecae, is a crucial determinant in mosquito population expansion. Mitochondrial defects and aberrant autophagy of sperm in LAP1 mutant males (LAP1-/-), prepared using CRISPR/Cas9 system, result in a reduction of reproduction in wild-type females that mated with them. The fitness of LAP1-/- males is strong enough to efficiently transmit genetic changes to mosquito populations through a low number of hatchable offspring. Thus, LAP1-/- males represent an opportunity to suppress mosquito populations and further studies should be undertaken to characterize LAP1's suitability for gene drive usage.

Proteome Analysis of Male Accessory Gland Secretions in the Diamondback Moth, Plutella xylostella (Lepidoptera: Plutellidae)

In insects, male accessory gland proteins (ACPs) are important reproductive proteins secreted by male accessory glands (MAGs) of the internal male reproductive system. During mating, ACPs are transferred along with sperms inside female bodies and have a significant impact on the post-mating physiology changes of the females. Under sexual selection pressures, the ACPs exhibit remarkably rapid and divergent evolution and vary from species to species. The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a major insect pest of cruciferous vegetables worldwide. Mating has a profound impact on the females' behavior and physiology in this species. It is still unclear what the ACPs are in this species. In this study, two different proteomic methods were used to identify ACPs in P. xylostella. The proteins of MAGs were compared immediately before and after mating by using a tandem mass tags (TMT) quantitative proteomic analysis. The proteomes of copulatory bursas (CB) in mated females shortly after mating were also analyzed by the shotgun LC-MS/MS technique. In total, we identified 123 putative secreted ACPs. Comparing P. xylostella with other four insect ACPs, trypsins were the only ACPs detected in all insect species. We also identified some new insect ACPs, including proteins with chitin binding Peritrophin-A domain, PMP-22/ EMP/ MP20/ Claudin tight junction domain-containing protein, netrin-1, type II inositol 1,4,5-trisphosphate 5-phosphatase, two spaetzles, allatostatin-CC, and cuticular protein. This is the first time that ACPs have been identified and analyzed in P. xylostella. Our results have provided an important list of putative secreted ACPs, and have set the stage for further exploration of the functions of these putative proteins in P. xylostella reproduction.

Genomics and genome editing techniques of crickets, an emerging model insect for biology and food science

Most tools available for manipulating gene function in insects have been developed for holometabolous species. In contrast, functional genetics tools for the Hemimetabola are highly underdeveloped. This is a barrier both to understanding ancestral insect biology, and to optimizing contemporary study and manipulation of particular large hemimetabolous orders of crucial economic and agricultural importance like the Orthoptera. For orthopteran insects, including crickets, the rapid spread of next-generation sequencing technology has made transcriptome data available for a wide variety of species over the past decade. Furthermore, whole genome sequences of orthopteran insects with relatively large genome sizes are now available. With these new genome assemblies and the development of genome editing technologies such as the CRISPR-Cas9 system, it has become possible to create gene knock-out and knock-in strains in orthopteran insects. As a result, orthopteran species should become increasingly feasible for laboratory study not only in research fields that have traditionally used insects, but also in agricultural fields that use them as food and feed. In this review, we summarize these recent advances and their relevance to such applications.

Viviparity and habitat restrictions may influence the evolution of male reproductive genes in tsetse fly (Glossina) species

BACKGROUND

Glossina species (tsetse flies), the sole vectors of African trypanosomes, maintained along their long evolutionary history a unique reproductive strategy, adenotrophic viviparity. Viviparity reduces their reproductive rate and, as such, imposes strong selective pressures on males for reproductive success. These species live in sub-Saharan Africa, where the distributions of the main sub-genera Fusca, Morsitans, and Palpalis are restricted to forest, savannah, and riverine habitats, respectively. Here we aim at identifying the evolutionary patterns of the male reproductive genes of six species belonging to these three main sub-genera. We then interpreted the different patterns we found across the species in the light of viviparity and the specific habitat restrictions, which are known to shape reproductive behavior.

RESULTS

We used a comparative genomic approach to build consensus evolutionary trees that portray the selective pressure acting on the male reproductive genes in these lineages. Such trees reflect the long and divergent demographic history that led to an allopatric distribution of the Fusca, Morsitans, and Palpalis species groups. A dataset of over 1700 male reproductive genes remained conserved over the long evolutionary time scale (estimated at 26.7 million years) across the genomes of the six species. We suggest that this conservation may result from strong functional selective pressure on the male imposed by viviparity. It is noteworthy that more than half of these conserved genes are novel sequences that are unique to the Glossina genus and are candidates for selection in the different lineages.

CONCLUSIONS

Tsetse flies represent a model to interpret the evolution and differentiation of male reproductive biology under different, but complementary, perspectives. In the light of viviparity, we must take into account that these genes are constrained by a post-fertilization arena for genomic conflicts created by viviparity and absent in ovipositing species. This constraint implies a continuous antagonistic co-evolution between the parental genomes, thus accelerating inter-population post-zygotic isolation and, ultimately, favoring speciation. Ecological restrictions that affect reproductive behavior may further shape such antagonistic co-evolution.

Evolutionary dynamics of sex-biased genes expressed in cricket brains and gonads

Sex-biased gene expression, particularly sex-biased expression in the gonad, has been linked to rates of protein sequence evolution (nonsynonymous to synonymous substitutions, dN/dS) in animals. However, in insects, sex-biased expression studies remain centred on a few holometabolous species. Moreover, other major tissue types such as the brain remain underexplored. Here, we studied sex-biased gene expression and protein evolution in a hemimetabolous insect, the cricket Gryllus bimaculatus. We generated novel male and female RNA-seq data for two sexual tissue types, the gonad and somatic reproductive system, and for two core components of the nervous system, the brain and ventral nerve cord. From a genome-wide analysis, we report several core findings. Firstly, testis-biased genes had accelerated evolution, as compared to ovary-biased and unbiased genes, which was associated with positive selection events. Secondly, although sex-biased brain genes were much less common than for the gonad, they exhibited a striking tendency for rapid protein sequence evolution, an effect that was stronger for the female than male brain. Further, some sex-biased brain genes were linked to sexual functions and mating behaviours, which we suggest may have accelerated their evolution via sexual selection. Thirdly, a tendency for narrow cross-tissue expression breadth, suggesting low pleiotropy, was observed for sex-biased brain genes, suggesting relaxed purifying selection, which we speculate may allow enhanced freedom to evolve adaptive protein functional changes. The findings of rapid evolution of testis-biased genes and male and female-biased brain genes are discussed with respect to pleiotropy, positive selection and the mating biology of this cricket.

Combined transcriptomic, proteomic and genomic analysis identifies reproductive-related proteins and potential modulators of female behaviors in Spodoptera litura

The common cutworm, Spodoptera litura, is a polyandrous moth with high reproductive ability. Sexual reproduction is a unique strategy for survival and reproduction of population in this species. However, to date available information about its reproductive genes is rare. Here, we combined transcriptomics, genomics and proteomics approaches to characterize reproductive-related proteins in S. litura. Illumina sequencing in parallel with the reference genome led to the yields of 12,161 reproductive genes, representing 47.83% of genes annotated in the genome. Further, 524 genes of 19 specific gene families annotated in the genome were detected in reproductive tissues of both sexes, some of which exhibited sex-biased and/or tissue-enriched expression. Of these, manual efforts together with the transcriptome analyses re-annotated 54 odorant binding proteins (OBPs) and 23 chemosensory proteins (CSPs) with an increase of 18 OBPs and one CSP compared to those previously annotated in the genome. Interestingly, at least 35 OBPs and 22 CSPs were transcribed in at least one reproductive tissue, suggestive of their involvement in reproduction. Further proteomic analysis revealed 2381 common proteins between virgin and mated female reproductive systems, 79 of which were differentially expressed. More importantly, 74 proteins exclusive to mated females were identified as transferred relatives, coupled with their specific or high expression in male reproductive systems. Of the transferred proteins, several conserved protein classes across insects were observed including OBPs, serpins, trypsins and juvenile hormone-binding proteins. Our current study has extensively surveyed reproductive genes in S. litura with an emphasis on the roles of OBPs and CSPs in reproduction, and identifies potentially transferred proteins serving as modulators of female post-mating behaviors.

Decoding the Reproductive System of the Olive Fruit Fly, Bactrocera oleae

In most diploid organisms, mating is a prerequisite for reproduction and, thus, critical to the maintenance of their population and the perpetuation of the species. Besides the importance of understanding the fundamentals of reproduction, targeting the reproductive success of a pest insect is also a promising method for its control, as a possible manipulation of the reproductive system could affect its destructive activity. Here, we used an integrated approach for the elucidation of the reproductive system and mating procedures of the olive fruit fly, Bactrocera oleae. Initially, we performed a RNAseq analysis in reproductive tissues of virgin and mated insects. A comparison of the transcriptomes resulted in the identification of genes that are differentially expressed after mating. Functional annotation of the genes showed an alteration in the metabolic, catalytic, and cellular processes after mating. Moreover, a functional analysis through RNAi silencing of two differentially expressed genes, yellow-g and troponin C, resulted in a significantly reduced oviposition rate. This study provided a foundation for future investigations into the olive fruit fly's reproductive biology to the development of new exploitable tools for its control.

The male reproductive accessory glands of the blister beetle Meloe proscarabaeus Linnaeus, 1758 (Coleoptera: Meloidae): Anatomy and ultrastructure of the cantharidin-storing organs

Blister beetles owe their name to their ability to release cantharidin, a blistering terpene, the highest concentration of which is retained in male accessory glands. The anatomy and ultrastructure of the three pairs of male reproductive accessory glands and the glandular region of the two vasa deferentia of Meloe proscarabaeus were investigated using light, electron and ion beam microscopy. All of the mesodermal glands here analysed share a common structural organization with an outer muscular layer and an inner glandular epithelium facing a broad lumen in which the secretory products are released. Developed rough endoplasmic reticulum, Golgi systems, abundant mitochondria, numerous secretory vesicles and a microvillated apical membrane are commonly found in the cells of different glandular epithelia, suggesting that all accessory gland pairs as well as the vasa deferentia are involved in an active synthesis. Nevertheless, each pair of glands appears specialized in the production of a specific set of substances, as suggested by the peculiarities in cellular ultrastructure and by the different aspect of the secretions stored in their glandular lumen. The above cited features of male accessory glands of M. proscarabaeus are compared with those of other beetles and some hints on their potential role in producing and/or concentrating cantharidin are provided.

Transcriptome Analysis of Ophraella communa Male Reproductive Tract in Indirect Response to Elevated CO2 and Heat Wave

Increase in atmospheric CO₂ directly affects the insect physiology and behavior, and indirectly affects the herbivorous insects by affecting their hosts. The increase in atmospheric CO₂ is accompanied by an increase in temperature and heat waves. Ophraella communa LeSage is a natural enemy of Ambrosia artemisiifolia (common ragweed). The development and reproduction of this beetle is weakened upon eating common ragweed grown under stress conditions. As female behavior and physiology alter after mating, the reproductive tract of males is likely to modulate reproduction and development in this species. Herein, the transcriptional profiles of testes and accessory glands from male O. communa individuals feeding on common ragweed under conditions of high CO₂ concentration and heat waves and that grown under ambient CO₂ concentration were compared. Differentially expressed genes (DEGs) were identified between the same tissues from beetles fed on common ragweed grown under different stress conditions. There were 3, 2, 3, 1and 5 genes related to decomposition and transport of macromolecular substances, host location, stress response, reproduction, and poisonous food-utilization. No expected response was observed in the male reproductive tract, but some of the identified DEGs might control the development of the population. The results presented here should be helpful in guiding future studies on deciphering the indirect response of other organs to high CO₂ concentration and heat waves, as well as the functions of seminal fluid proteins in O. communa.

The Cricket Gryllus bimaculatus: Techniques for Quantitative and Functional Genetic Analyses of Cricket Biology

All extant species are an outcome of nature's "experiments" during evolution, and hence multiple species need to be studied and compared to gain a thorough understanding of evolutionary processes. The field of evolutionary developmental biology (evo-devo) aspires to expand the number of species studied, because most functional genetic studies in animals have been limited to a small number of "traditional" model organisms, many of which belong to the same phylum (Chordata). The phylum Arthropoda, and particularly its component class Insecta, possesses many important characteristics that are considered favorable and attractive for evo-devo research, including an astonishing diversity of extant species and a wide disparity in body plans. The development of the most thoroughly investigated insect genetic model system to date, the fruit fly Drosophila melanogaster (a holometabolous insect), appears highly derived with respect to other insects and indeed with respect to most arthropods. In comparison, crickets (a basally branching hemimetabolous insect lineage compared to the Holometabola) are thought to embody many developmental features that make them more representative of insects. Here we focus on crickets as emerging models to study problems in a wide range of biological areas and summarize the currently available molecular, genomic, forward and reverse genetic, imaging and computational tool kit that has been established or adapted for cricket research. With an emphasis on the cricket species Gryllus bimaculatus, we highlight recent efforts made by the scientific community in establishing this species as a laboratory model for cellular biology and developmental genetics. This broad toolkit has the potential to accelerate many traditional areas of cricket research, including studies of adaptation, evolution, neuroethology, physiology, endocrinology, regeneration, and reproductive behavior. It may also help to establish newer areas, for example, the use of crickets as animal infection model systems and human food sources.

Long-term interaction between Drosophila sperm and sex peptide is mediated by other seminal proteins that bind only transiently to sperm

Seminal fluid proteins elicit several post-mating physiological changes in mated Drosophila melanogaster females. Some of these changes persist for over a week after mating because the seminal protein that causes these changes, the Sex Peptide (SP), binds to sperm that are stored in the female reproductive tract. SP's sperm binding is mediated by a network of at least eight seminal proteins. We show here that some of these network proteins (CG1656, CG1652, CG9997 and Antares) bind to sperm within 2 h of mating, like SP. However, while SP remains bound to sperm at 4 days post-mating, none of the other network proteins are detectable at this time. We also observed that the same network proteins are detectable at 2 h post-mating in seminal receptacle tissue from which sperm have been removed, but are no longer detectable there by 4 days post-mating, suggesting short-term retention of these proteins in this female sperm storage organ. Our results suggest that these network proteins act transiently to facilitate the conditions for SP's binding to sperm, perhaps by modifying SP or the sperm surface, but are not part of a long-acting complex that stably attaches SP to sperm.

A targeted in situ hybridization screen identifies putative seminal fluid proteins in a simultaneously hermaphroditic flatworm

BACKGROUND

Along with sperm, in many taxa ejaculates also contain large numbers of seminal fluid proteins (SFPs). SFPs and sperm are transferred to the mating partner, where they are thought to play key roles in mediating post-mating sexual selection. They modulate the partner's behavior and physiology in ways that influence the reproductive success of both partners, thus potentially leading to sexual conflict. Despite the presumed general functional and evolutionary significance of SFPs, their identification and characterization has to date focused on just a few animal groups, predominantly insects and mammals. Moreover, until now seminal fluid profiling has mainly focused on species with separate sexes. Here we report a comprehensive screen for putative SFPs in the simultaneously hermaphroditic flatworm Macrostomum lignano.

RESULTS

Based on existing transcriptomic data, we selected 150 transcripts known to be (a) predominantly expressed in the tail region of the worms, where the seminal fluid-producing prostate gland cells are located, and (b) differentially expressed in social environments differing in sperm competition level, strongly implying that they represent a phenotypically plastic aspect of male reproductive allocation in this species. For these SFP candidates, we then performed whole-mount in situ hybridization (ISH) experiments to characterize tissue-specific expression. In total, we identified 98 transcripts that exhibited prostate-specific expression, 76 of which we found to be expressed exclusively in the prostate gland cells; additional sites of expression for the remaining 22 included the testis or other gland cells. Bioinformatics analyses of the prostate-limited candidates revealed that at least 64 are predicted to be secretory proteins, making these especially strong candidates to be SFPs that are transferred during copulation.

CONCLUSIONS

Our study represents a first comprehensive analysis using a combination of transcriptomic and ISH screen data to identify SFPs based on transcript expression in seminal fluid-producing tissues. We thereby extend the range of taxa for which seminal fluid has been characterized to a flatworm species with a sequenced genome and for which several methods such as antibody staining, transgenesis and RNA interference have been established. Our data provide a basis for testing the functional and evolutionary significance of SFPs.

Positive selection and comparative molecular evolution of reproductive proteins from New Zealand tree weta (Orthoptera, Hemideina)

Animal reproductive proteins, especially those in the seminal fluid, have been shown to have higher levels of divergence than non-reproductive proteins and are often evolving adaptively. Seminal fluid proteins have been implicated in the formation of reproductive barriers between diverging lineages, and hence represent interesting candidates underlying speciation. RNA-seq was used to generate the first male reproductive transcriptome for the New Zealand tree weta species Hemideina thoracica and H. crassidens. We identified 865 putative reproductive associated proteins across both species, encompassing a diverse range of functional classes. Candidate gene sequencing of nine genes across three Hemideina, and two Deinacrida species suggests that H. thoracica has the highest levels of intraspecific genetic diversity. Non-monophyly was observed in the majority of sequenced genes indicating that either gene flow may be occurring between the species, or that reciprocal monophyly at these loci has yet to be attained. Evidence for positive selection was found for one lectin-related reproductive protein, with an overall omega of 7.65 and one site in particular being under strong positive selection. This candidate gene represents the first step in the identification of proteins underlying the evolutionary basis of weta reproduction and speciation.

Sex-biased gene expression and sequence conservation in Atlantic and Pacific salmon lice (Lepeophtheirus salmonis)

BACKGROUND

Salmon lice, Lepeophtheirus salmonis (Copepoda: Caligidae), are highly important ectoparasites of farmed and wild salmonids, and cause multi-million dollar losses to the salmon aquaculture industry annually. Salmon lice display extensive sexual dimorphism in ontogeny, morphology, physiology, behavior, and more. Therefore, the identification of transcripts with differential expression between males and females (sex-biased transcripts) may help elucidate the relationship between sexual selection and sexually dimorphic characteristics.

RESULTS

Sex-biased transcripts were identified from transcriptome analyses of three L. salmonis populations, including both Atlantic and Pacific subspecies. A total of 35-43 % of all quality-filtered transcripts were sex-biased in L. salmonis, with male-biased transcripts exhibiting higher fold change than female-biased transcripts. For Gene Ontology and functional analyses, a consensus-based approach was used to identify concordantly differentially expressed sex-biased transcripts across the three populations. A total of 127 male-specific transcripts (i.e. those without detectable expression in any female) were identified, and were enriched with reproductive functions (e.g. seminal fluid and male accessory gland proteins). Other sex-biased transcripts involved in morphogenesis, feeding, energy generation, and sensory and immune system development and function were also identified. Interestingly, as observed in model systems, male-biased L. salmonis transcripts were more frequently without annotation compared to female-biased or unbiased transcripts, suggesting higher rates of sequence divergence in male-biased transcripts.

CONCLUSIONS

Transcriptome differences between male and female L. salmonis described here provide key insights into the molecular mechanisms controlling sexual dimorphism in L. salmonis. This analysis offers targets for parasite control and provides a foundation for further analyses exploring critical topics such as the interaction between sex and drug resistance, sex-specific factors in host-parasite relationships, and reproductive roles within L. salmonis.

Transcriptome analysis to identify genes for peptides and proteins involved in immunity and reproduction from male accessory glands and ejaculatory duct of Bactrocera dorsalis

In the male reproductive system of insects, the male accessory glands and ejaculatory duct (MAG/ED) are important organs and their primary function is to enhance the fertility of spermatozoa. Proteins secreted by the MAG/ED are also known to induce post-mating changes and immunity responses in the female insect. To understand the gene expression profile in the MAG/ED of the oriental fruit fly Bactrocera dorsalis (Hendel), that is an important pest in fruits, we performed an Illumina-based deep sequencing of mRNA. This yielded 54,577,630 clean reads corresponding to 4.91Gb total nucleotides that were assembled and clustered to 30,669 unigenes (average 645bp). Among them, 20,419 unigenes were functionally annotated to known proteins/peptides in Gene Orthology, Clusters of Orthologous Groups, Kyoto Encyclopedia of Genes and Genomes pathway databases. Typically, many genes were involved in immunity and these included microbial recognition proteins and antimicrobial peptides. Subsequently, the inducible expression of these immunity-related genes was confirmed by qRT-PCR analysis when insects were challenged with immunity-inducible factors, suggesting their function in guaranteeing fertilization success. Besides, we identified some important reproductive genes such as juvenile hormone- and ecdysteroid-related genes in this de novo assembly. In conclusion, this transcriptomic sequencing of B. dorsalis MAG/ED provides insights to facilitate further functional research of reproduction, immunity and molecular evolution of reproductive proteins in this important agricultural pest.

Females gain survival benefits from immune-boosting ejaculates

Females in many animal taxa incur significant costs from mating in the form of injury or infection, which can drastically reduce survival. Therefore, immune function during reproduction can be important in determining lifetime fitness. Trade-offs between reproduction and immunity have been extensively studied, yet a growing number of studies demonstrate that mated females have a stronger immune response than virgins. Here, we use the Texas field cricket, Gryllus texensis, to test multiple hypotheses proposed to explain this postmating increase in immune function. Using host-resistance tests, we found that courtship, copulation, and accessory fluids alone do not affect female immunity; rather, only females that acquire intact ejaculates containing testes-derived components exhibit significant increases in survival after exposure to bacterial pathogens. Our data suggest that male-derived components originating from an intact ejaculate and transferred to females during sex are required for the increased immune function characteristic of mated female crickets to occur.

Combining RNA-seq and proteomic profiling to identify seminal fluid proteins in the migratory grasshopper Melanoplus sanguinipes (F)

BACKGROUND

Seminal fluid proteins control many aspects of fertilization and in turn, they play a key role in post-mating sexual selection and possibly reproductive isolation. Because effective proteome profiling relies on the availability of high-quality DNA reference databases, our knowledge of these proteins is still largely limited to model organisms with ample genetic resources. New advances in sequencing technology allow for the rapid characterization of transcriptomes at low cost. By combining high throughput RNA-seq and shotgun proteomic profiling, we have characterized the seminal fluid proteins secreted by the primary male accessory gland of the migratory grasshopper (Melanoplus sanguinipes), one of the main agricultural pests in central North America.

RESULTS

Using RNA sequencing, we characterized the transcripts of ~ 8,100 genes expressed in the long hyaline tubules (LHT) of the accessory glands. Proteomic profiling identified 353 proteins expressed in the long hyaline tubules (LHT). Of special interest are seminal fluid proteins (SFPs), such as EJAC-SP, ACE and prostaglandin synthetases, which are known to regulate female oviposition in insects.

CONCLUSIONS

Our study provides new insights into the proteomic components of male ejaculate in Orthopterans, and highlights several important patterns. First, the presence of proteins that lack predicted classical secretory tags in accessory gland proteomes is common in male accessory glands. Second, the products of a few highly expressed genes dominate the accessory gland secretions. Third, accessory gland transcriptomes are enriched for novel transcripts. Fourth, there is conservation of SFPs' functional classes across distantly related taxonomic groups with very different life histories, mating systems and sperm transferring mechanisms. The identified SFPs may serve as targets of future efforts to develop species- specific genetic control strategies.

Proteome analysis of male accessory gland secretions in oriental fruit flies reveals juvenile hormone-binding protein, suggesting impact on female reproduction

In insects, the accessory gland proteins (Acps) secreted by male accessory glands (MAGs) account for the majority of seminal fluids proteins. Mixed with sperm, they are transferred to the female at mating and so impact reproduction. In this project, we identified 2,927 proteins in the MAG secretions of the oriental fruit fly Bactrocera dorsalis, an important agricultural pest worldwide, using LC-MS analysis, and all sequences containing open reading frames were analyzed using signalP. In total, 90 Acps were identified. About one third (26) of these 90 Acps had a specific functional description, while the other two thirds (64) had no functional description including dozens of new classes of proteins. Hence, several of these novel Acps were abundant in the MAG secretions, and we confirmed their MAG-specific expression by qPCR. Finally and interestingly, one of these novel proteins was functionally predicted as juvenile hormone-binding protein, suggesting the impact of Acps with reproductive events in the female. Our results will aid in the development of an experimental method to identify Acps in insects, and in turn this information with new Acps in B. dorsalis will pave the way of further exploration their function in reproduction and potential development as new insecticide targets.

What's in the Gift? Towards a Molecular Dissection of Nuptial Feeding in a Cricket

Nuptial gifts produced by males and transferred to females during copulation are common in insects. Yet, their precise composition and subsequent physiological effects on the female recipient remain unresolved. Male decorated crickets Gryllodes sigillatus transfer a spermatophore to the female during copulation that is composed of an edible gift, the spermatophylax, and the ampulla that contains the ejaculate. After transfer of the spermatophore, the female detaches the spermatophylax and starts to eat it while sperm from the ampulla are evacuated into the female reproductive tract. When the female has finished consuming the spermatophylax, she detaches the ampulla and terminates sperm transfer. Hence, one simple function of the spermatophylax is to ensure complete sperm transfer by distracting the female from prematurely removing the ampulla. However, the majority of orally active components of the spermatophylax itself and their subsequent effects on female behavior have not been identified. Here, we report the first analysis of the proteome of the G. sigillatus spermatophylax and the transcriptome of the male accessory glands that make these proteins. The accessory gland transcriptome was assembled into 17,691 transcripts whilst about 30 proteins were detected within the mature spermatophylax itself. Of these 30 proteins, 18 were encoded by accessory gland encoded messages. Most spermatophylax proteins show no similarity to proteins with known biological functions and are therefore largely novel. A spermatophylax protein shows similarity to protease inhibitors suggesting that it may protect the biologically active components from digestion within the gut of the female recipient. Another protein shares similarity with previously characterized insect polypeptide growth factors suggesting that it may play a role in altering female reproductive physiology concurrent with fertilization. Characterization of the spermatophylax proteome provides the first step in identifying the genes encoding these proteins in males and in understanding their biological functions in the female recipient.

Characterization of Melanoplus sanguinipes oviposition stimulating protein expression and re-examination of its potential role in stimulating oviposition

Melanoplussanguinipes oviposition stimulating protein (MsOSP) was characterized and its role in stimulating oviposition in virgin females was examined. A 967nt MsOSP mRNA sequence with homology to previously characterized N-terminal amino acid sequence data for MsOSP was identified in a RNAseq library generated from an mRNA pool from the long hyaline tubule (LHT) of the male accessory gland complex. This transcript contained a predicted 729nt open reading frame encoding the 242aa putative MsOSP protein and had the second highest read abundance in the library. The MsOSP transcript was detected exclusively in the LHT tissue of adult males and its abundance increased with time until 7 days post-eclosion. Western blot analysis using an anti-MsOSP antibody showed high levels of MsOSP protein in the LHT luminal secretions of virgin males and to a lesser degree was associated with the aedeagus and ejaculatory duct. MsOSP was shown to be a major protein component of the spermatophore packet transferred from the male to female during copulation. However, only minor amounts of MsOSP could be detected in the female bursa, spermatheca and oviduct. Intrahemocoelic injection of LHT luminal protein into mature virgin females stimulated oviposition in ∼ 65% of females. A similar but non-significant trend was observed upon injection of purified recombinant MsOSP protein, and immunoprecipitation of LHT protein with anti-MsOSP antibody led to abrogation of oviposition stimulation upon injection of mature virgin females. Despite the demonstration of stimulation of oviposition upon intrahemocoelic injection of LHT-derived-MsOSP into mature virgin females, the potential mode of action of MsOSP in this process remains to be determined. MsOSP cannot be detected in the tissues other than the bursa, spermatheca and oviduct of female grasshoppers and relatively large quantities of MsOSP are required to stimulate oviposition upon injection.

Identification and characterization of seminal fluid proteins in the Asian tiger mosquito, Aedes albopictus

The Asian tiger mosquito (Aedes albopictus) is an important vector for pathogens that affect human health, including the viruses that cause dengue and Chikungunya fevers. It is also one of the world's fastest-spreading invasive species. For these reasons, it is crucial to identify strategies for controlling the reproduction and spread of this mosquito. During mating, seminal fluid proteins (Sfps) are transferred from male mosquitoes to females, and these Sfps modulate female behavior and physiology in ways that influence reproduction. Despite the importance of Sfps on female reproductive behavior in mosquitoes and other insects, the identity of Sfps in Ae. albopictus has not previously been reported. We used transcriptomics and proteomics to identify 198 Sfps in Ae. albopictus. We discuss possible functions of these Sfps in relation to Ae. albopictus reproduction-related biology. We additionally compare the sequences of these Sfps with proteins (including reported Sfps) in several other species, including Ae. aegypti. While only 72 (36.4%) of Ae. albopictus Sfps have putative orthologs in Ae. aegypti, suggesting low conservation of the complement of Sfps in these species, we find no evidence for an elevated rate of evolution or positive selection in the Sfps that are shared between the two Aedes species, suggesting high sequence conservation of those shared Sfps. Our results provide a foundation for future studies to investigate the roles of individual Sfps on feeding and reproduction in this mosquito. Functional analysis of these Sfps could inform strategies for managing the rate of pathogen transmission by Ae. albopictus.

Role of sexual selection in speciation in Drosophila

The power of sexual selection to drive changes in the mate recognition system through divergence in sexually selected traits gives it the potential to be a potent force in speciation. To know how sexual selection can bring such type of divergence in the genus Drosophila, comparative studies based on intra- and inter-sexual selection are documented in this review. The studies provide evidence that both mate choice and male-male competition can cause selection of trait and preference which thereby leads to divergence among species. In the case of intrasexual selection, various kinds of signals play significant role in affecting the species mate recognition system and hence causing divergence between the species. However, intrasexual selection can bring the intraspecific divergence at the level of pre- and post-copulatory stage. This has been better explained through Hawaiian Drosophila which has been suggested a wonderful model system in explaining the events of speciation via sexual selection. This is due to their elaborate mating displays and some kind of ethological isolation persisting among them. Similarly, the genetic basis of sexually selected variations can provide yet another path in understanding the speciation genetics via sexual selection more closely.

Differential introgression in a mosaic hybrid zone reveals candidate barrier genes

Hybrid zones act as genomic sieves. Although globally advantageous alleles will spread throughout the zone and neutral alleles can be freely exchanged between species, introgression will be restricted for genes that contribute to reproductive barriers or local adaptation. Seminal fluid proteins (SFPs) are known to contribute to reproductive barriers in insects and have been proposed as candidate barrier genes in the hybridizing field crickets Gryllus pennsylvanicus and Gryllus firmus. Here, we have used 125 single nucleotide polymorphisms to characterize patterns of differential introgression and to identify genes that may contribute to prezygotic barriers between these species. Using a transcriptome scan of the male cricket accessory gland (the site of SFP synthesis), we identified genes with major allele frequency differences between the species. We then compared patterns of introgression for genes encoding SFPs with patterns for genes expressed in the same tissue that do not encode SFPs. We find no evidence that SFPs have reduced gene exchange across the cricket hybrid zone. However, a number of genes exhibit dramatically reduced introgression, and many of these genes encode proteins with functional roles consistent with known barriers.

Silencing of the Hsf gene, the transcriptional regulator of A. gambiae male accessory glands, inhibits the formation of the mating plug in mated females and disrupts their monogamous behaviour

Discovering the molecular factors that shape the mating behaviour and the fertility of the mosquito Anopheles gambiae, the principal vector of human malaria, is regarded as critical to better understand its reproductive success as well as for identifying new leads for malaria control measures. In A. gambiae mating induces complex behavioural and physiological changes in the females, including refractoriness to subsequent mating and induction of egg-laying. In other insects including Drosophila a group of proteins named Accessory gland proteins (Acps), produced by males and transferred with sperm to the female reproductive tract, have been implicated in this post-mating response. Although Acps represent a set of promising candidates for unravelling the mating physiology, their role in inducing behavioural changes in mated A. gambiae females remains largely unknown. In this work, we demonstrate that a down-regulation of a large fraction of Acp genes via silencing of the Acp regulating transcription factor Hsf, abolishes the formation of mating plug in mated females and fails to induce refractoriness of mated female to subsequent inseminations. A significant fraction of females mated to Hsf silenced males (66%) failed to receive the mating plug though seminal fluid had been transferred as documented by the presence of spermatozoa in the female sperm storage organ. Furthermore, nearly all females (95%) mated to HSF-silenced males were re-inseminated when exposed to males carrying EGPF marked sperm. Our findings provide evidence showing that Acp genes regulated by the transcription factor HSF play a key role in the function of the male accessory glands.

Tissue-specific transcriptomics in the field cricket Teleogryllus oceanicus

Field crickets (family Gryllidae) frequently are used in studies of behavioral genetics, sexual selection, and sexual conflict, but there have been no studies of transcriptomic differences among different tissue types. We evaluated transcriptome variation among testis, accessory gland, and the remaining whole-body preparations from males of the field cricket, Teleogryllus oceanicus. Non-normalized cDNA libraries from each tissue were sequenced on the Roche 454 platform, and a master assembly was constructed using testis, accessory gland, and whole-body preparations. A total of 940,200 reads were assembled into 41,962 contigs, to which 36,856 singletons (reads not assembled into a contig) were added to provide a total of 78,818 sequences used in annotation analysis. A total of 59,072 sequences (75%) were unique to one of the three tissues. Testis tissue had the greatest proportion of tissue-specific sequences (62.6%), followed by general body (56.43%) and accessory gland tissue (44.16%). We tested the hypothesis that tissues expressing gene products expected to evolve rapidly as a result of sexual selection—testis and accessory gland—would yield a smaller proportion of BLASTx matches to homologous genes in the model organism Drosophila melanogaster compared with whole-body tissue. Uniquely expressed sequences in both testis and accessory gland showed a significantly lower rate of matching to annotated D. melanogaster genes compared with those from general body tissue. These results correspond with empirical evidence that genes expressed in testis and accessory gland tissue are rapidly evolving targets of selection.

Sperm and seminal fluid proteomes of the field cricket Teleogryllus oceanicus: identification of novel proteins transferred to females at mating

Reproductive proteins are amongst the most evolutionarily divergent proteins known, and research on genetically well-characterized species suggests that postcopulatory sexual selection might be important in their evolution; however, we lack the taxonomic breadth of information on reproductive proteins that is required to determine the general importance of sexual selection for their evolution. We used transcriptome sequencing and proteomics to characterize the sperm and seminal fluid proteins of a cricket, Teleogryllus oceanicus, that has been widely used in the study of postcopulatory sexual selection. We identified 57 proteins from the sperm of these crickets. Many of these had predicted function in glycolysis and metabolism, or were structural, and had sequence similarity to sperm proteins found across taxa ranging from flies to humans. We identified 21 seminal fluid proteins, some of which resemble those found to be involved in postmating changes to female reproduction in other species. Some 27% of sperm proteins and 48% of seminal fluid proteins were of unknown function. The characterization of seminal fluid proteins in this species will allow us to explore their adaptive significance, and to contribute comparative data that will facilitate a general appreciation of the evolution of reproductive proteins within and among animal taxa.

Transcriptional profiles of mating-responsive genes from testes and male accessory glands of the Mediterranean fruit fly, Ceratitis capitata

BACKGROUND

Insect seminal fluid is a complex mixture of proteins, carbohydrates and lipids, produced in the male reproductive tract. This seminal fluid is transferred together with the spermatozoa during mating and induces post-mating changes in the female. Molecular characterization of seminal fluid proteins in the Mediterranean fruit fly, Ceratitis capitata, is limited, although studies suggest that some of these proteins are biologically active.

METHODOLOGY/PRINCIPAL FINDINGS

We report on the functional annotation of 5914 high quality expressed sequence tags (ESTs) from the testes and male accessory glands, to identify transcripts encoding putative secreted peptides that might elicit post-mating responses in females. The ESTs were assembled into 3344 contigs, of which over 33% produced no hits against the nr database, and thus may represent novel or rapidly evolving sequences. Extraction of the coding sequences resulted in a total of 3371 putative peptides. The annotated dataset is available as a hyperlinked spreadsheet. Four hundred peptides were identified with putative secretory activity, including odorant binding proteins, protease inhibitor domain-containing peptides, antigen 5 proteins, mucins, and immunity-related sequences. Quantitative RT-PCR-based analyses of a subset of putative secretory protein-encoding transcripts from accessory glands indicated changes in their abundance after one or more copulations when compared to virgin males of the same age. These changes in abundance, particularly evident after the third mating, may be related to the requirement to replenish proteins to be transferred to the female.

CONCLUSIONS/SIGNIFICANCE

We have developed the first large-scale dataset for novel studies on functions and processes associated with the reproductive biology of Ceratitis capitata. The identified genes may help study genome evolution, in light of the high adaptive potential of the medfly. In addition, studies of male recovery dynamics in terms of accessory gland gene expression profiles and correlated remating inhibition mechanisms may permit the improvement of pest management approaches.

Influence of the male ejaculate on post-mating prezygotic barriers in field crickets

Post-copulatory interactions between males and females involve highly coordinated, complex traits that are often rapidly evolving and divergent between species. Failure to produce and deposit eggs may be a common post-mating prezygotic barrier, yet little is known about what prevents the induction of egg-laying between species. The field crickets, Gryllus firmus and G. pennsylvanicus are isolated by a one-way reproductive incompatibility; G. pennsylvanicus males fail to fertilize G. firmus eggs or to induce normal egg-laying in G. firmus females. We use experimental crosses to elucidate the role of accessory gland-derived vs. testis-derived components of the G. firmus male ejaculate on egg-laying in conspecific and heterospecific crosses. Using surgical castrations to create ‘spermless’ males that transfer only seminal fluid proteins (SFPs) we test whether G. firmus male SFPs can induce egg-laying in conspecific crosses and rescue egg-laying in crosses between G. pennsylvanicus males and G. firmus females. We find G. firmus SFPs induce only a small short-term egg-laying response and that SFPs alone cannot explain the normal induction of egg-laying. Gryllus firmus SFPs also do not rescue the heterospecific cross. Testis-derived components, such as sperm or prostaglandins, most likely stimulate egg-laying or act as transporters for SFPs to targets in the female reproductive tract. These results highlight the utility of experimental approaches for investigating the phenotypes that act as barriers between species and suggest that future work on the molecular basis of the one-way incompatibility between G. firmus and G. pennsylvanicus should focus on divergent testis-derived compounds or proteins in addition to SFPs.

Regulation of Anopheles gambiae male accessory gland genes influences postmating response in female

In Drosophila, the accessory gland proteins (Acps) secreted from the male accessory glands (MAGs) and transferred along with sperm into the female reproductive tract have been implicated in triggering postmating behavioral changes, including refractoriness to subsequent mating and propensity to egg laying. Recently, Acps have been found also in Anopheles, suggesting similar functions. Understanding the mechanisms underlying transcriptional regulation of Acps and their functional role in modulating Anopheles postmating behavior may lead to the identification of novel vector control strategies to reduce mosquito populations. We identified heat-shock factor (HSF) binding sites within the Acp promoters of male Anopheles gambiae and discovered three distinct Hsf isoforms; one being significantly up-regulated in the MAGs after mating. Through genome-wide transcription analysis of Hsf-silenced males, we observed significant down-regulation in 50% of the Acp genes if compared to control males treated with a construct directed against an unrelated bacterial sequence. Treated males retained normal life span and reproductive behavior compared to control males. However, mated wild-type females showed a ∼46% reduction of egg deposition rate and a ∼23% reduction of hatching rate (∼58% combined reduction of progeny). Our results highlight an unsuspected role of HSF in regulating Acp transcription in A. gambiae and provide evidence that Acp down-regulation in males leads a significant reduction of progeny, thus opening new avenues toward the development of novel vector control strategies.

Post-mating prezygotic barriers to gene exchange between hybridizing field crickets

Studies of sexual selection in speciation have traditionally focused on mate preference, with less attention given to traits that act between copulation and fertilization. However, recent work suggests that post-mating prezygotic barriers may play an important role in speciation. Here, we evaluate the role of such barriers in the field crickets, Gryllus firmus and Gryllus pennsylvanicus. Gryllus pennsylvanicus females mated with G. firmus males produce viable, fertile offspring, but when housed with both species produce offspring sired primarily by conspecifics. We evaluate patterns of sperm utilization in doubly mated G. pennsylvanicus females and find no evidence for conspecific sperm precedence. The reciprocal cross (G. firmus female × G. pennsylvanicus male) produces no progeny. Absence of progeny reflects a barrier to fertilization rather than reduced sperm transfer, storage or motility. We propose a classification scheme for mechanisms underlying post-mating prezygotic barriers similar to that used for premating barriers.

Temporally variable selection on proteolysis-related reproductive tract proteins in Drosophila

In order to gain further insight into the processes underlying rapid reproductive protein evolution, we have conducted a population genetic survey of 44 reproductive tract-expressed proteases, protease inhibitors, and targets of proteolysis in Drosophila melanogaster and Drosophila simulans. Our findings suggest that positive selection on this group of genes is temporally heterogeneous, with different patterns of selection inferred using tests sensitive at different time scales. Such variation in the strength and targets of selection through time may be expected under models of sexual conflict and/or host-pathogen interaction. Moreover, available functional information concerning the genes that show evidence of selection suggests that both sexual selection and immune processes have been important in the evolutionary history of this group of molecules.

Identification of predicted seminal fluid proteins in Tribolium castaneum

In several insect species, seminal fluid proteins (SFPs) have been demonstrated to be key regulators of male and female fitness through their ability to alter female physiology and behaviour. Tribolium castaneum is an economically important pest species and a model system for sexual selection research, but little is known about SFPs in this insect. To create a foundation for the study of T. castaneum SFPs, we used mass spectrometry to identify putative SFPs by comparing proteins detected in the male reproductive glands with those found in the reproductive tracts of virgin and mated females. Fourteen putative SFPs, thirteen with male biased expression, were identified through this approach. We also used reverse transcription PCR (RT-PCR) to examine expression levels across different tissue types. We found strongly male-biased expression in 13 genes, nine of which were expressed only in male accessory gland tissue. This represents the first proteomic-based method of identifying putative SFPs in any coleopteran species, and is the first study in this species to identify putative SFPs that are likely transferred to the female. This work could lead to functional analyses of the role of SFPs in sexual selection, sexual conflict and potential control of a pest species.

Ultrastructural localization of basic proteins and carbohydrates in male accessory glands of two Triatoma species (Hemiptera, Reduviidae, Triatominae)

The male accessory glands in Triatoma are tubular and produce substances with some functions related to production of the spermatophore. In the current study, the cytochemistry of male accessory glands was evaluated in starved Triatoma brasiliensis and adult Triatoma melanica. The storage of carbohydrates and proteins in T. melanica male accessory glands occurs earlier than in T. brasiliensis. In addition, the occurrence of eletron-lucent granules without carbohydrates and proteins suggests that other substances are released by these glands, which may be used for lubrication of the male genitalia. Male T. brasiliensis has more intense secretory activity in the fifth day of adult life, which may indicate a higher reproductive capacity. The analysis of lipid production in male accessory glands can contribute to the knowledge of spermatophore formation in these species.

Seminal fluid affects sperm viability in a cricket

Recent studies have suggested that males may vary the quality of their ejaculates in response to sperm competition, although the mechanisms by which they do so remain unclear. The viability of sperm is an important aspect of ejaculate quality that determines competitive fertilization success in the field cricket Teleogryllus oceanicus. Using in vitro mixtures of sperm and seminal fluid from pairs of male crickets, we show that seminal fluid can affect the viability of sperm in this species. We found that males who invest greatly in the viability of their own sperm can enhance the viability of rival sperm, providing the opportunity for males to exploit the investments in sperm competition made by their rivals. Transitive effects of seminal fluids across the ejaculates of different males are expected to have important implications for the dynamics of male investments in sperm competition.

Towards a semen proteome of the dengue vector mosquito: protein identification and potential functions

Background

No commercially licensed vaccine or treatment is available for dengue fever, a potentially lethal infection that impacts millions of lives annually. New tools that target mosquito control may reduce vector populations and break the cycle of dengue transmission. Male mosquito seminal fluid proteins (Sfps) are one such target since these proteins, in aggregate, modulate the reproduction and feeding patterns of the dengue vector, Aedes aegypti. As an initial step in identifying new targets for dengue vector control, we sought to identify the suite of proteins that comprise the Ae. aegypti ejaculate and determine which are transferred to females during mating.

Methodology and Principal Findings

Using a stable-isotope labeling method coupled with proteomics to distinguish male- and female-derived proteins, we identified Sfps and sperm proteins transferred from males to females. Sfps were distinguished from sperm proteins by comparing the transferred proteins to sperm-enriched samples derived from testes and seminal vesicles. We identified 93 male-derived Sfps and 52 predicted sperm proteins that are transferred to females during mating. The Sfp protein classes we detected suggest roles in protein activation/inactivation, sperm utilization, and ecdysteroidogenesis. We also discovered that several predicted membrane-bound and intracellular proteins are transferred to females in the seminal fluids, supporting the hypothesis that Ae. aegypti Sfps are released from the accessory gland cells through apocrine secretion, as occurs in mammals. Many of the Ae. aegypti predicted sperm proteins were homologous to Drosophila melanogaster sperm proteins, suggesting conservation of their sperm-related function across Diptera.

Conclusion and Significance

This is the first study to directly identify Sfps transferred from male Ae. aegypti to females. Our data lay the groundwork for future functional analyses to identify individual seminal proteins that may trigger female post-mating changes (e.g., in feeding patterns and egg production). Therefore, identification of these proteins may lead to new approaches for manipulating the reproductive output and vectorial capacity of Ae. aegypti.

Dengue is a potentially lethal infection that impacts millions of humans annually. This disease is caused by viruses transmitted by infected female Aedes aegypti mosquitoes during blood feeding. No commercial vaccine or treatment is available for dengue infection. One way to break the disease transmission cycle is to develop new tools to reduce dengue vector populations. Seminal fluid proteins (Sfps) produced in the reproductive glands of male mosquitoes and transferred to females in the ejaculate during mating could be the target of such a tool. In related insects, Sfps modulate female reproduction and feeding patterns. Here we report 145 proteins that are transferred to females in the Ae. aegypti ejaculate. The proteins, which include Sfps and sperm proteins, fall into biochemical classes that suggest important potential roles in mated females. Of particular interest are proteins that could play roles in fertility and hormonal activity (including pathways involved in egg development and utilization of the blood meal). Our results lay important groundwork for new control strategies by identifying candidate proteins that may alter the reproductive biology or blood-feeding patterns of female Ae. aegypti and ultimately reduce the global burden of dengue.

Insect seminal fluid proteins: identification and function

Seminal fluid proteins (SFPs) produced in reproductive tract tissues of male insects and transferred to females during mating induce numerous physiological and behavioral postmating changes in females. These changes include decreasing receptivity to remating; affecting sperm storage parameters; increasing egg production; and modulating sperm competition, feeding behaviors, and mating plug formation. In addition, SFPs also have antimicrobial functions and induce expression of antimicrobial peptides in at least some insects. Here, we review recent identification of insect SFPs and discuss the multiple roles these proteins play in the postmating processes of female insects.

Combined EST and proteomic analysis identifies rapidly evolving seminal fluid proteins in Heliconius butterflies

Seminal fluid proteins (SFPs) directly influence a wide range of reproductive processes, including fertilization, sperm storage, egg production, and immune response. Like many other reproductive proteins, the molecular evolution of SFPs is generally characterized by rapid and frequently adaptive evolution. However, the evolutionary processes underlying this often-documented pattern have not yet been confidently determined. A robust understanding of the processes governing SFP evolution will ultimately require identifying SFPs and characterizing their evolution in many different taxa, often where only limited genomic resources are available. Here, we report the first comprehensive molecular genetic and evolutionary analysis of SFPs conducted in Lepidoptera (moths and butterflies). We have identified 51 novel SFPs from two species of Heliconius butterflies (Heliconius erato and Heliconius melpomene) by combining "indirect" bioinformatic and expression analyses of expressed sequence tags from male accessory gland and wing tissues with "direct" proteomic analyses of spermatophores. Proteomic analyses identified fewer SFPs than the indirect criteria but gave consistent results. Of 51 SFPs, 40 were identified in both species but fewer than half could be functionally annotated via similarity searches (Blast, IPRscan, etc.). The majority of annotated Heliconius SFPs were predicted to be chymotrypsins. Comparisons of Heliconius SFPs with those from fruit fly, mosquito, honeybee, and cricket suggest that gene turnover is high among these proteins and that SFPs are rarely conserved across insect orders. Pairwise estimates of evolutionary rates between SFPs and nonreproductive proteins show that, on average, Heliconius SFPs are evolving rapidly. At least one of these SFPs is evolving adaptively (dN/dS > 1), implicating a role for positive selection in this rapid evolution. This work establishes a strong precedent for future research on the causes and consequences of reproductive protein evolution in the Lepidoptera. Butterflies and moths have an extremely rich history of organismal research, which will provide an informative ecological context for further molecular evolutionary investigations.

Protease gene duplication and proteolytic activity in Drosophila female reproductive tracts

Secreted proteases play integral roles in sexual reproduction in a broad range of taxa. In the genetic model Drosophila melanogaster, these molecules are thought to process peptides and activate enzymes inside female reproductive tracts, mediating critical postmating responses. A recent study of female reproductive tract proteins in the cactophilic fruit fly Drosophila arizonae, identified pervasive, lineage-specific gene duplication amongst secreted proteases. Here, we compare the evolutionary dynamics, biochemical nature, and physiological significance of secreted female reproductive serine endoproteases between D. arizonae and its congener D. melanogaster. We show that D. arizonae lower female reproductive tract (LFRT) proteins are significantly enriched for recently duplicated secreted proteases, particularly serine endoproteases, relative to D. melanogaster. Isolated lumen from D. arizonae LFRTs, furthermore, exhibits significant trypsin-like and elastase-like serine endoprotease activity, whereas no such activity is seen in D. melanogaster. Finally, trypsin- and elastase-like activity in D. arizonae female reproductive tracts is negatively regulated by mating. We propose that the intense proteolytic environment of the D. arizonae female reproductive tract relates to the extraordinary reproductive physiology of this species and that ongoing gene duplication amongst these proteases is an evolutionary consequence of sexual conflict.

Seminal fluid protein depletion and replenishment in the fruit fly, Drosophila melanogaster: an ELISA-based method for tracking individual ejaculates

In many species, seminal fluid proteins (SFPs) affect female post-mating behavioral patterns, including sperm storage, egg laying, feeding, and remating. Yet, few studies have investigated the patterns of allocation, depletion, and replenishment of SFPs in male animals, despite the importance of these proteins to male and female reproductive success. To investigate such SFP dynamics, it is necessary to have a sensitive method for quantifying SFP levels in males and mated females. We developed such a method by adapting the enzyme-linked immunosorbent assay (ELISA) using anti-SFP antibodies. Here, we first use two Drosophila melanogaster SFPs (ovulin and sex peptide) to demonstrate that ELISAs provide accurate measures of SFP levels. We find that, consistent with previous data from Western blotting or immunofluorescence studies, levels of both ovulin and sex peptide decline in the mated female with time since mating, but they do so at different rates. We then use ELISAs to show that males become depleted of SFPs with repeated matings, but that previously mated males are able to transfer "virgin" levels of SFPs after 3 days of sexual inactivity. Finally, we demonstrate that ELISAs can detect SFPs from wild-caught D. melanogaster males and, thus, potentially can be used to track mating patterns in the wild. This method of measuring SFP dynamics can be used in a wide range of species to address questions related to male reproductive investment, female mating history, and variation in female post-mating behavioral changes.

Proteomic analysis of Drosophila mojavensis male accessory glands suggests novel classes of seminal fluid proteins

Fruit-flies of the genus Drosophila are characterized by overwhelming variation in fertilization traits such as copulatory plug formation, sperm storage organ use, and nutritional ejaculatory donation. Despite extensive research on the genetic model Drosophila melanogaster, little is known about the molecular underpinnings of these interspecific differences. This study employs a proteomic approach to pin-point candidate seminal fluid proteins in Drosophila mojavensis, a cactophilic fruit-fly that exhibits divergent reproductive biology when compared to D. melanogaster. We identify several classes of candidate seminal fluid proteins not previously documented in the D. melanogaster male ejaculate, including metabolic enzymes, nutrient transport proteins, and clotting factors. Conversely, we also define 29 SFPs that are conserved despite >40 million years of Drosophila evolution. We discuss our results in terms of universal processes in insect reproduction, as well as the specialized reproductive biology of D. mojavensis.

Battle and ballet: molecular interactions between the sexes in Drosophila

Varied and fascinating interactions occur between males and females to lead to the production of progeny. Interactions between the sexes continue even after the act of mating-but at the molecular and cellular level instead of between individual animals. Molecules transferred from males to females during mating (via the seminal fluid) exert potent effects on females' physiology and (at least in some animals) on behavior. Taking advantage of genetic, genomic, and biochemical tools for Drosophila, we investigate molecular interactions that underlie this form of chemical communication. Recent data show that molecules and cells from both sexes participate in this "ballet," facilitating the mutually beneficial outcome of increased progeny production. Examples to be presented include the storage and utilization of sperm in the mated female, and a proteolytic pathway that begins in the male but ends in the female and involves both male and female contributions. Despite the joint benefit of increased progeny production, the "interests" of the mating male can differ from those of his mate. Over evolutionary time this disconnect can, in theory, precipitate a "battle" between the sexes, potentially leading to the rapid sequence changes that have been observed for some seminal proteins across species.

Juvenile hormone regulation of male accessory gland activity in the red flour beetle, Tribolium castaneum

Male accessory gland proteins (Acps) act as key modulators of reproductive success in insects by influencing the female reproductive physiology and behavior. We used custom microarrays and identified 112 genes that were highly expressed in male accessory glands (MAG) in the red flour beetle, Tribolium castaneum. Out of these 112 identified genes, 59 of them contained sequences coding for signal peptide and cleavage site and the remaining 53 contained transmembrane domains. The expression of 14 of these genes in the MAG but not in other tissues of male or female was confirmed by quantitative real-time PCR. In virgin males, juvenile hormone (JH) levels increased from second day post adult emergence (PAE), remained high on third day PAE and declined on fourth day PAE. The ecdysteroid titers were high soon after adult emergence but declined to minimal levels from 1 to 5 days PAE. Feeding of juvenile hormone analog, hydroprene, but not the ecdysteroid analog, RH-2485, showed an increase in size of MAGs, as well as an increase in total RNA and protein content of MAG. Hydroprene treatment also increased the expression of Acp genes in the MAG. RNAi-mediated knock-down in the expression of JHAMT gene decreased the size of MAGs and expression of Acps. JH deficiency influenced male reproductive fitness as evidenced by a less vigor in mating behavior, poor sperm transfer, low egg and the progeny production by females mated with the JH deficient males. These data suggest a critical role for JH in the regulation of male reproduction especially through MAG secretions.

Detection of seminal fluid proteins in the bed bug, Cimex lectularius, using two-dimensional gel electrophoresis and mass spectrometry

The global increase of the human parasite, the common bed bug Cimex lectularius, calls for specific pest control target sites. The bed bug is also a model species for sexual conflict theory which suggests that seminal fluids may be highly diverse. The species has a highly unusual sperm biology and seminal proteins may have unique functions. One-dimensional PAGE gels showed 40-50% band sharing between C. lectularius and another cimicid species, Afrocimex constrictus. However, adult, sexually rested C. lectularius males were found to store 5-7 microg of seminal protein and with only 60 microg of protein we obtained informative 2-D PAGE gels. These showed 79% shared protein spots between 2 laboratory populations, and more than half of the shared protein spots were detected in the mated female. Further analysis using liquid chromatography electrospray ionization tandem mass spectrometry revealed that 26.5% of the proteins had matches among arthropods in databases and 14.5% matched Drosophila proteins. These included ubiquitous proteins but also those more closely associated with reproduction such as moj 29, ubiquitin, the stress-related elongation factor EF-1 alpha, a protein disulfide isomerase and an antioxidant, Peroxiredoxin 6.

Proteomics reveals novel Drosophila seminal fluid proteins transferred at mating

Across diverse taxa, seminal fluid proteins (Sfps) transferred at mating affect the reproductive success of both sexes. Such reproductive proteins often evolve under positive selection between species; because of this rapid divergence, Sfps are hypothesized to play a role in speciation by contributing to reproductive isolation between populations. In Drosophila, individual Sfps have been characterized and are known to alter male sperm competitive ability and female post-mating behavior, but a proteomic-scale view of the transferred Sfps has been missing. Here we describe a novel proteomic method that uses whole-organism isotopic labeling to detect transferred Sfps in mated female D. melanogaster. We identified 63 proteins, which were previously unknown to function in reproduction, and confirmed the transfer of dozens of predicted Sfps. Relative quantification of protein abundance revealed that several of these novel Sfps are abundant in seminal fluid. Positive selection and tandem gene duplication are the prevailing forces of Sfp evolution, and comparative proteomics with additional species revealed lineage-specific changes in seminal fluid content. We also report a proteomic-based gene discovery method that uncovered 19 previously unannotated genes in D. melanogaster. Our results demonstrate an experimental method to identify transferred proteins in any system that is amenable to isotopic labeling, and they underscore the power of combining proteomic and evolutionary analyses to shed light on the complex process of Drosophila reproduction.

EST analysis of male accessory glands from Heliconius butterflies with divergent mating systems

Background

Heliconius butterflies possess a remarkable diversity of phenotypes, physiologies, and behaviors that has long distinguished this genus as a focal taxon in ecological and evolutionary research. Recently Heliconius has also emerged as a model system for using genomic methods to investigate the causes and consequences of biological diversity. One notable aspect of Heliconius diversity is a dichotomy in mating systems which provides an unusual opportunity to investigate the relationship between sexual selection and the evolution of reproductive proteins. As a first step in pursuing this research, we report the generation and analysis of expressed sequence tags (ESTs) from the male accessory gland of H. erato and H. melpomene, species representative of the two mating systems present in the genus Heliconius.

Results

We successfully sequenced 933 ESTs clustering into 371 unigenes from H. erato and 1033 ESTs clustering into 340 unigenes from H. melpomene. Results from the two species were very similar. Approximately a third of the unigenes showed no significant BLAST similarity (E-value <10^-5) to sequences in GenBank's non-redundant databases, indicating that a large proportion of novel genes are expressed in Heliconius male accessory glands. In both species only a third of accessory gland unigenes were also found among genes expressed in wing tissue. About 25% of unigenes from both species encoded secreted proteins. This includes three groups of highly abundant unigenes encoding repetitive proteins considered to be candidate seminal fluid proteins; proteins encoded by one of these groups were detected in H. erato spermatophores.

Conclusion

This collection of ESTs will serve as the foundation for the future identification and evolutionary analysis of male reproductive proteins in Heliconius butterflies. These data also represent a significant advance in the rapidly growing collection of genomic resources available in Heliconius butterflies. As such, they substantially enhance this taxon as a model system for investigating questions of ecological, phenotypic, and genomic diversity.

Comparative proteomics reveals evidence for evolutionary diversification of rodent seminal fluid and its functional significance in sperm competition

During insemination, males of internally fertilizing species transfer a complex array of seminal fluid proteins to the female reproductive tract. These proteins can have profound effects on female reproductive physiology and behavior and are thought to mediate postcopulatory sexual selection and intersexual conflict. Such selection may cause seminal fluid to evolve rapidly, with potentially important consequences for speciation. Here we investigate the evolution of seminal fluid proteins in a major mammalian radiation, the muroid rodents, by quantifying diversity in seminal fluid proteome composition for the first time across a broad range of closely related species. Using comparative proteomics techniques to identify and cross-match proteins, we demonstrate that rodent seminal fluid is highly diverse at the level of both proteomes and individual proteins. The striking interspecific heterogeneity in seminal fluid composition revealed by our survey far exceeds that seen in a second proteome of comparable complexity, skeletal muscle, indicating that the complement of proteins expressed in seminal fluid may be subject to rapid diversification. We further show that orthologous seminal fluid proteins exhibit substantial interspecific variation in molecular mass. Because this variation cannot be attributed to differential glycosylation or radical differences in termination sites, it is strongly suggestive of rapid amino acid divergence. Sperm competition is implicated in generating such divergence for at least one major seminal fluid protein in our study, SVS II, which is responsible for copulatory plug formation via transglutaminase-catalyzed cross-linking after insemination. We show that the molecular mass of SVS II is positively correlated with relative testis size across species, which could be explained by selection for an increased number of cross-linking sites involved in the formation of the copulatory plug under sperm competition.