Genital Coupling Research Articles

Pair formation in Enchenopa treehoppers (Hemiptera: Membracidae) involves complex male–female duetting, and three stages of female mate choice

Abstract We explore the complexity of the signal repertoire and sequences of behavioural interactions involved in pair formation in Enchenopa binotata treehoppers, which communicate via plant-borne vibrational signals, and whose pair formation involves prolonged male-female duetting interactions. We recorded these interactions using laser vibrometry and video assays. In males, we report two phases of signalling: a searching phase in which males use a basic repertoire to solicit engagement from females; and a more complex phase incorporating additional signal types and elements males used once engaged by females. In females, we report a novel three-stage process of selective cooperation with males, as well as a novel signal type that was necessary but not sufficient for copulation to occur. These three stages include active duetting with a male that was necessary for him to locate and mount females; the novel signal that females produce after continued mounted duetting that prompts the male to attempt genital coupling; and the female actively allowing coupling. We discuss implications of our observations for these insects’ cognitive abilities in terms of the memory and selective attention required to sustain signalling interactions and proceed along the decision-making stages of mate choice. Using attention to detail as an aid to discovery, we aim to promote research on how such animals express such capabilities.

Genital coupling and copulatory wounding in the Drosophila rufa species complex: comparison with the D. auraria species complex (Diptera: Drosophilidae)

Abstract In sexually reproducing animals, genital morphology is usually divergent among closely related species, which can lead to a mismatch of genital coupling (i.e. mechanical isolation). The montium species group of the subgenus Sophophora is the largest clade in Drosophila and is a useful model in which to study the evolution of genital morphology. This group includes a pair of sister clades, i.e. the Drosophila auraria and Drosophila rufa species complexes. The former includes four species with overlapping distributions, and the latter consists of five species that are almost allopatric. The previous study on the D. auraria complex suggested genital co-evolution between sexes (female structures accepting for or protecting from male structures). To test the generality, we analysed the D. rufa complex and three outgroup species. In the D. rufa complex, we detected genital structures corresponding between sexes, and copulatory wounds with species-specific positions. Given that approximately the same number of evolutionary changes in the genital traits were detected in both sexes of the two clades, we conclude that selection pressure to avoid interspecific mating (reproductive character displacement) is not a prerequisite for rapid genital co-evolution.

Subcortical life, evolution of flattened body, and constrained mating posture in the earwig Platylabia major (Insecta: Dermaptera: "Anisolabididae").

Many animals take advantage of the shaded, humid, and protected environments in subcortical spaces, i.e., thin spaces under the loosened bark of dead trees. Permanent inhabitants of subcortical spaces often show specialized morphologies, such as a miniaturized or dorsoventrally flattened body. However, the evolutionary consequences of these specialized morphologies on behavioral, ecological, and life-history traits have been little studied. We studied the mating biology and anatomy of Platylabia major (usually placed in the family Anisolabididae), which is an obligate inhabitant of subcortical spaces with a paper-like flattened body, and compared them with those of two thicker, spongiphorid earwigs, Nesogaster amoenus and Paralabellula curvicauda. Mating trials in various settings showed that Pl. major requires thin spaces sandwiched by two planes to accomplish genital coupling and insemination. In contrast, the thicker species, although also frequently found in subcortical spaces, could mate on a single horizontal plane due to the ability of the male to twist its abdomen through approximately 180°. Examination by micro-computed tomography and a reagent-based clearing technique revealed no substantive differences in the configuration of mid-abdominal musculature between the species. The dorsal and lateral muscles of Pl. major, which are almost parallel to the antero-posterior body axis for accommodation within the thin abdomen, seemed incapable of producing the power to twist the abdomen. The abdominal musculature conforms to a simple pattern in both male and female earwigs, which is repeated in each of the pregenital segments. We conclude that small differences in the range of motion of each abdominal segment can result in large differences in possible mating postures and positions. Surgical experiments also demonstrated that both right and left penises of Pl. major are competent and used for insemination with no lateral bias, as in most other earwigs with twin penises studied to date.

Genital coupling and copulatory wounding in the interspecific mating of theDrosophila aurariaspecies complex (Diptera: Drosophilidae)

AbstractStructural matching of genitalia between sexes of the same species would guarantee a stable mating posture and tight genital coupling that minimizes the reproductive cost in females. Interspecific mating might cause mismatches in genital structures between sexes, leading to an unstable mating posture, abnormal genital coupling, enhanced risk of wounding to the genitalia, and reduced mating duration. In this study, copulation duration, mating posture, genital coupling and copulatory wounding were analysed in reciprocal combinations of interspecific mating between Drosophila auraria and Drosophila triauraria and between Drosophila biauraria and Drosophila subauraria. Interspecific mating exhibited a large variation in copulation duration, and copulatory wounds were produced in females at positions that lacked the corresponding fold structures, although the frequency of copulatory wounds was sometimes lower than in intraspecific mating. The angle of the aedeagus insertion during mating and positions of the copulatory wounds after interspecific mating were as expected from the male species, suggesting that males attempt to tighten genital coupling and stabilize copulation using the genitalia regardless of the female species. As in other groups of Drosophila studied to date, the species-specific structures in female genitalia contact the conspecific male organs during copulation, and the results suggest that they might have functions related to sexual conflict or sexual selection.

MicroCT analysis unveils the role of inflatable female genitalia and male tibial complex in the genital coupling in the spider genus Aysha (Anyphaenidae, Araneae).

Sperm transfer in spiders is achieved by copulatory organs on the male pedipalps (i.e., copulatory bulbs), which can be simple or a complex set of sclerites and membranes. During copulation, these sclerites can be used to anchor in corresponding structures in the female genitalia by means of hydraulic pressure. In the most diverse group of Entelegynae spiders, the retrolateral tibial apophysis clade, the female role in the coupling of genitalia is considered rather passive, as conformational changes of the female genital plate (i.e., the epigyne) during copulation are scarce. Here, we reconstruct the genital mechanics of two closely related species belonging to the Aysha prospera group (Anyphaenidae) that bear a membranous, wrinkled epigyne and male pedipalps with complex tibial structures. By using microcomputed tomography dataof a cryofixed mating pair, we reveal that most of the epigyne remains greatly inflated during genital coupling, and that the male tibial structures are coupled to the epigyne by the inflation of a tibial hematodocha. We propose that a turgent female vulva is a prerequisite for the genital coupling, which could implicate a female control device, and that the structures from the male copulatory bulb have been functionally replaced by tibial structures in these species. Furthermore, we show that the conspicuous median apophysis is maintained in spite of being functionally redundant, posing a puzzling situation.

Genital coupling and copulatory wounding in the Drosophila auraria species complex (Diptera: Drosophilidae)

Abstract Animal genitalia have changed substantially and rapidly during evolution, and functionally interacting anatomical structures complementarily match between the sexes. Several hypotheses have been proposed to explain how such structure-matching evolved. A test of these hypotheses would require a detailed analysis of male and female genitalia among closely related species and a comparison of the functional aspects of the interacting structures between the sexes. Therefore, here we document genital coupling and copulatory wounds in the four species of the Drosophila auraria complex. The position of the protrusion of the median gonocoxite of males relative to the female terminalia differed among the species, which may reflect differences in protrusion morphology. Species-specific female structures were discovered on the membrane between the genitalia and analia and on the vaginal wall. The former makes contact with the protrusion, and the latter makes contact with appendages of the aedeagus. Copulatory wounds, which are produced during copulation, were seen at three locations on females: depressions near the genital orifice, the membrane between the genitalia and analia, and the vaginal wall. Some of the copulatory wounds were located at sites that could potentially make contact with the species-specific structures that we identified. We speculate that the female structures that differ between species of the D. auraria complex evolved in concert with the genitalia of male conspecifics.

The Importance of Biosemiotics for Morphology

Morphology and its relevance for systematics is a promising field for the application of biosemiotic principles in scientific practice. Genital coupling in spiders involves very complex interactions between the male and female genital structures. As exemplified by two spider species, Nephila clavipes and Nephila pilipes ssp. fenestrata, from a biosemiotic point of view the microstructures of the male bulb’s embolus and the corresponding female epigynal and vulval parts form the morphological zone of an intraspecific communication and sign-interpreting process that is one of the prerequisites for sperm transfer. Hence these morphological elements are of high taxonomic value, as they play an essential role in mating and fertilization and consequently in establishing and preserving a reproductive community. Morphology clearly benefits from a biosemiotic approach, as biosemiotics helps to sort out species-specific morphological characters and to avoid problematic typological interpretations.

Copulatory mechanics in the wolf spider Agalenocosa pirity reveals a hidden diversity of locking systems in Lycosidae (Araneae).

Genital traits are among the fastest to evolve, and the processes that drive their evolution are intensively studied. Spiders are characterized by complex genitalia, but the functional role of the different structures during genital coupling is largely unknown. Members of one of the largest spider groups, the retrolateral tibial apophysis (RTA) clade, are characterized by a RTA on the male palp, which is thought to play a crucial role during genital coupling. However, the RTA was lost in several families including the species-rich wolf spiders (Lycosidae) leading to the hypothesis that the genital coupling is achieved by alternative mechanisms. Here, we investigate the genital interactions during copulation in the wolf spider Agalenocosa pirity (Zoicinae) on cryofixed mating pairs using electron, optical and X-ray microscopy and compare our findings with other lycosids and entelegyne spiders. We found an unprecedented coupling mechanism for lycosid spiders involving the palea and a membranous cuticle folding adjacent to the epigynal plate. Additionally, we show an uncommon coupling between the median apophysis and the contralateral genital opening, and confirmed that the terminal apophysis acts as functional conductor, as previously hypothesized for males of Zoicinae. Phylogenetic mapping of RTA indicated that the basal tibial process found in Agalenocosa is a secondary acquisition rather than a modified RTA.

Genital coupling, morphology and evolution of male holding structures in Cicadinae (Hemiptera: Cicadidae)

Abstract Male and female genitalia include some of the most complex and morphologically diverse structures in Metazoa. Ornamentations in genitalia have been studied in several groups, and a variety of functional roles have been proposed. Although complex features of the genitalia have been observed in internal genitalia in cicadas, their functions have not yet been elucidated. These ornamentations, together with precopulatory sexual selection, make cicadas good models for evolutionary studies on genital coupling. We explore the structural interaction of male and female genitalia in Guyalna bonaerensis (Berg) (Cicadinae) and the morphology of male ornamentations in Cicadinae generally. We group these ornamentations into two traits according to their inferred function: anchoring or gripping. We analyse the theca and vesica of 24 species and perform ancestral trait reconstruction under maximum likelihood and stochastic mapping on a Bayesian tree. Ornamentations of the male vesica and the female seminal ampoule possibly ensure male attachment by working as an active lock to avoid the premature termination of intercourse. These ornamentations emerged independently in different lineages in Cicadinae, reinforcing the suggestion that they are important adaptations to achieve complete copulation. Our results foster questions for the field of sexual selection and associated mechanisms shaping the evolution of male and female genitalia.

Nuptial feeding and genital coupling of Neopanorpa scorpionflies (Insecta: Mecoptera: Panorpidae) with notal organs of various lengths

Neopanorpa, the second largest genus in Panorpidae, is mainly characterized by the well-developed notal organ on male tergum III. However, it remains largely unknown how the length of the notal organ influences the nuptial feeding behaviour of Neopanorpa. Here, we investigated the nuptial feeding by comparing the morphology of mating-related structures and the genital coupling of a) Neopanorpa lui Chou & Ran, 1981 with a weakly-developed notal organ, b) N. carpenteri Cheng, 1957 with a medium-sized notal organ, and c) N. longiprocessa Hua & Chou, 1997 with an extremely elongated notal organ. The couples of N. lui and N. carpenteri maintain an intermittent mouth-to-mouth mode but do not exchange any edible food. After that the males secrete a salivary mass onto the surface as a nuptial gift, which is distinctly larger in N. carpenteri than in N. lui. Correspondingly, the male salivary glands are more developed in N. carpenteri than in N. lui. Males of N. longiprocessa bear very short salivary glands corresponding to a coercive mating tactic. The genital couplings are similar among the three species of Neopanorpa. The paired hypovalves of males are used to control the cerci of females. The prominent basal processes of male gonostyli grasp the posterior portion of the female medigynium across the intersegmental membrane. The male aedeagus physically couples with the female medigynium to ensure the male phallotreme to connect to the female copulatory pore. The influence of the notal organ length on the nuptial feeding behaviour of Neopanorpa is briefly discussed.

Optimal ultra-short copulation duration in a sexually cannibalistic spider

Sexual conflict has been shown to shape many behaviors in the reproductive context, such as the duration of copulation, across a broad taxonomic range. In spiders, copulation duration is one of the most variable reproductive traits, ranging from seconds to hours. Some species in the araneid genus Argiope exhibit very short copulations of a few seconds per pedipalp insertion. This has been hypothesized to be the result of cannibalistic females imposing selection on males to escape the attack by reducing insertion duration to a minimum. However, copulation duration is positively correlated with the number of sperm transferred and fertilization success in many species. Thus, given the tradeoff between sperm transfer and the risk of being cannibalized, males may optimize the duration of copulation to maximize lifetime reproductive success. Here we test whether males in the orb-weaver Argiope aurantia, which exhibits the shortest copulation in any spider and rivals the honey bee for shortest copulation reported for any arthropod with internal genital coupling, are optimizing the insertion duration of the first pedipalp to maximize the number of sperm transferred and eggs fertilized. We analyzed total sperm transferred to the female, and male fertilization success as a function of the first insertion’s duration, using data collected in previous staged-mating experiments and determined optimal copulations of 3–4 s, which is close to the averages of the source populations. Thus, we present evidence for sexual cannibalism as a driver of the extremely short copulations in A. aurantia. Females and males often conflict over mating frequency. In spiders, both sexes have paired reproductive organs and can remain half virgin if only one of the two possible copulations are completed. In the orb-weaver Argiope aurantia, males place mating plugs and females almost always immediately attack males in copula, probably to prevent them from achieving both copulations and to be able to upgrade to a second mate. We find an optimal duration of 3–4 s for males to terminate copulation, which reduces the risk of being killed, while at the same time maximizing sperm transfer and fertilization success because copulation duration is positively related to the number of sperm transferred and allows males to achieve the second copulation. The optimal duration detected here is very close to average copulation durations in nature. Hence, we document the adaptive value of the shortest copulation known for any spider.

Fitness advantages of the biased use of paired laterally symmetrical penises in an insect.

The evolution of laterality, that is the biased use of laterally paired, morphologically symmetrical organs, has attracted the interest of researchers from a variety of disciplines. It is, however, difficult to quantify the fitness benefits of laterality because many organs, such as human hands, possess multimodal functions. Males of the earwig Labidura riparia (Insecta: Dermaptera: Labiduridae) have morphologically similar laterally paired penises, only one of which is used for inseminating the female during a single copulation bout, and thus provide a rare opportunity to address how selection pressure may shape the evolution of population-level laterality. Our population studies revealed that in 10 populations, located at 2.23-43.3° north, the right penis is predominantly used for copulating (88.6%). A damaged penis was found in 23% of rare left-handers, suggesting that the left penis can function as a spare when the right one is damaged. By pairing L.riparia females with surgically manipulated males, we found that males forced to use the right penis outperformed left-handed males in copulation (the probability of establishing genital coupling during the 1-hr observation period: odds ratio [OR] of 3.50) and insemination (probability of transferring a detectable amount of sperm: OR of 2.94). This right-handed advantage may be due to the coiled morphology of the sperm storage organ with a right-facing opening. Thus, female genital morphology may play a significant role in the evolution of handedness and may have acted as a driving force to reduce penis number in related taxa.

Digest: The importance of genital morphology inDrosophilacopulation*

Drosophila is a common model organism in the study of reproductive isolation. In their 2018 work, Tanaka etal. used introgression to substitute D. mauritiana genomic segments into a D. simulans genetic background, creating lines with modified genital structures. These changes were found to significantly alter the copulation duration and motility of mating pairs by influencing genital coupling.

Knockdown of rotund gene through larval RNA interference affects genital and elytral morphology in the ground beetle Carabus maiyasanus (Coleoptera: Carabidae)

AbstractInterspecific variation in genital morphology contributes to prezygotic reproductive isolation in many insect species. However, developmental genes affecting genital morphology are poorly understood. We undertook larval RNA interference (RNAi) experiments with rotund (rn) gene in the ground beetle Carabus (Ohomopterus) maiyasanus to examine the knockdown effects of this gene on genital development. We injected double‐stranded RNA (dsRNA) into third instar larvae of C. maiyasanus. The injection of rn dsRNA resulted in the absence or deformation of the copulatory piece in the male genitalia, which is a characteristic part playing a role in species‐specific genital coupling between the sexes. In addition, the rn dsRNA injection resulted in shortened elytra in both sexes, which is related to the known role of rn in forewing formation in Drosophila. Our study suggests that rn plays a previously underappreciated role in male genital development and potentially contributes to genital diversity in this beetle group.

An innovative ovipositor for niche exploitation impacts genital coevolution between sexes in a fruit-damaging Drosophila.

Limited attention has been given to ecological factors influencing the coevolution of male and female genitalia. The innovative ovipositor of Drosophila suzukii, an invading fruit pest, represents an appealing case to document this phenomenon. The serrated saw-like ovipositor is used to pierce the hard skin of ripening fruits that are not used by other fruit flies that prefer soft decaying fruits. Here, we highlight another function of the ovipositor related to its involvement in genital coupling during copulation. We compared the morphology and coupling of male and female genitalia in this species to its sibling species, Drosophila subpulchrella, and to an outgroup species, Drosophila biarmipes These comparisons and a surgical manipulation indicated that the shape of male genitalia in D. suzukii has had to be adjusted to ensure tight coupling, despite having to abandon the use of a hook-like structure, paramere, because of the more linearly elongated ovipositor. This phenomenon demonstrates that ecological niche exploitation can directly affect the mechanics of genital coupling and potentially cause incompatibility among divergent forms. This model case provides new insights towards elucidating the importance of the dual functions of ovipositors in other insect species that potentially induce genital coevolution and ecological speciation.

Mechanical incompatibility caused by modifications of multiple male genital structures using genomic introgression inDrosophila*

Mechanical incompatibility of male and female genitalia is common in animals with internal fertilization. However, our knowledge regarding the precise mechanisms is limited. One key question regards the susceptibility of the match between male and female genitalia to morphological modification. To address this issue, we generated six different second-chromosome introgression lines possessing partially Drosophila mauritiana-like genital morphology in multiple structures in D. simulans background. Three of the six introgression males showed elevated mobility at some stages during copulation with D. simulans females; this was assumed to be an indication of genital mismatch. Notably, one of the introgression males with D. mauritiana-like enlarged anal plates showed occasional leakage of adhesive ejaculate on the body surface when mated with pure D. simulans females, suggesting apparent structural incompatibility in genital coupling. These observations suggested that both sexual and natural selection shape the anal plate morphology, highlighting the role of this structure as an important component of mechanical isolation. Partial replacement (introgression) by a sibling species genome can induce perturbations in genital coupling mechanics, suggesting that genital compatibility can be susceptible to subtle genomic changes at the early stages of divergence in these species.

Microsurgical manipulation reveals pre-copulatory function of key genital sclerites.

The copulatory organs of male insects are generally complex, species-specific arrangements of hardened sclerotized plates bound together by flexible, less sclerotized cuticle. Their extensive morphological diversification is a recurrent pattern in the evolutionary radiation of animals, yet a clear consensus as to what selection pressures drive this divergence is still to emerge. In part, this stems from the fact that the function of individual sclerites that integrate to form the aedeagus are poorly understood. In insects, the male copulatory organ is often bounded by two lateral parameres tipped with setae. In a number of species, these have been observed to brush against the terminal abdominal sclerites of the female, suggesting a role in pre- and/or post-copulatory female choice. However, in the absence of experimental manipulation, their function remains elusive. Here, we used microsurgery to reduce paramere length and show that males with one or both paramere tips removed were less likely to achieve genital coupling than sham-operated male control groups. Where treatment males did achieve copulation, surgical removal of the paramere tip(s) had no detectable effect on copulation duration or on the outcome of sperm competition. Surgical manipulation of the end-plate, a genital sclerite that covers the ostium of the median lobe (the non-intromittent section of the aedeagus), resulted in near-complete failure of males to achieve copulation. Our experimental manipulations show that the parameres and end-plate function during pre-copulatory sexual interactions and thus most likely evolved in response to sexual selection occurring prior to insemination.

A fresh look over the genital morphology of Triaenonychoides (Opiliones: Laniatores: Triaenonychidae) unravelling for the first time the functional morphology of male genitalia

Harvestmen penises are intromittent structures surprisingly complex and diverse, making it difficult to imagine that the sole function of the penis is sperm transfer. Knowledge of penis morphology in harvestmen is largely derived from taxonomic works. Therefore, we have a considerable amount of information regarding genital structures, but relatively little is known about their movements and functions. Yet, in the case female genitalia, there is an even deeper gap on the understanding of the morphology and its functional features. Female genitalia are commonly neglected due to the assumption that they are not a valuable source of information for taxonomy. In this scenario of fragmented morphological knowledge, complete and accurate descriptions of male and female genitalia are highly desirable, and are essential to understanding the functional morphology of copulatory organs in Phalangida. Our study improves upon the original genitalia descriptions (ovipositor and penis) for two Chilean Triaenonychidae species (Triaenonychoides cekalovici and Triaenonychoides breviops) and provides corrections to several original mistakes and misinterpretation. In addition, we report here that T. cekalovici was described based on the morphology of an everted penis, illustrate and compare penises in the resting and everted state, and describe for the first time the mechanical eversion of the penis' glans. Through mechanical system the muscular penis type can execute a remarkably complicated movement resulting in eversion of the glans. The contraction of the muscle connected to the rounded basis of the ventral plate (via the tendon) is responsible for the ventral scrolling of the ventral plate and this in turn triggers the eversion of the capsula interna. We predict that this elongation is necessary during genital coupling, for positioning the stylus closer to the seminal receptacles area. Depositing the sperm closer to the seminal receptacles can be a decisive advantage, considering that in harvestmen the spermatozoa are immobile. We also suggest that this process of glans' muscular mechanical eversion could be widespread among Triaenonychidae and that the knowledge of functional morphology is relevant for taxonomic purposes, as this is probably not the only case of taxonomic description based on an everted genitalia.

Evolution of external female genital mutilation: why do males harm their mates?

Sperm competition may select for male reproductive traits that influence female mating or oviposition rate. These traits may induce fitness costs to the female; however, they may be costly for the males as well as any decrease in female fitness also affects male fitness. Male adaptations to sperm competition manipulate females by altering not only female behaviour or physiology, but also female morphology. In orb-weaving spiders, mating may entail mutilation of external structures of the female genitalia, which prevents genital coupling with subsequent males. Here, we present a game theoretical model showing that external female genital mutilation is favoured even under relatively high costs of mutilation, and that it is favoured by a high number of mate encounters per female and last-male sperm precedence.

Drosophila pachea asymmetric lobes are part of a grasping device and stabilize one-sided mating.

BackgroundMultiple animal species exhibit morphological asymmetries in male genitalia. In insects, left-right genital asymmetries evolved many times independently and have been proposed to appear in response to changes in mating position. However, little is known about the relationship between mating position and the interaction of male and female genitalia during mating, and functional analyses of asymmetric morphologies in genitalia are virtually non-existent. We investigated the relationship between mating position, asymmetric genital morphology and genital coupling in the fruit fly Drosophila pachea, in which males possess an asymmetric pair of external genital lobes and mate in an unusual right-sided position on top of the female.ResultsWe examined D. pachea copulation by video recording and by scanning electron microscopy of genital complexes. We observed that the interlocking of male and female genital organs in D. pachea is remarkably different from genital coupling in the well-studied D. melanogaster. In D. pachea, the female oviscapt valves are asymmetrically twisted during copulation. The male’s asymmetric lobes tightly grasp the female’s abdomen in an asymmetric ‘locking’ position, with the left and right lobes contacting different female structures. The male anal plates, which grasp the female genitalia in D. melanogaster, do not contact the female in D. pachea. Experimental lobe amputation by micro-surgery and laser-ablation of lobe bristles led to aberrant coupling of genitalia and variable mating positions, in which the male was tilted towards the right side of the female.ConclusionWe describe, for the first time, how the mating position depends on coupling of male and female genitalia in a species with asymmetric genitalia and one-sided mating position. Our results show that D. pachea asymmetric epandrial lobes do not act as a compensatory mechanism for the change from symmetric to one-sided mating position that occurred during evolution of D. pachea’s ancestors, but as holding devices with distinct specialized functions on the left and right sides.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0747-4) contains supplementary material, which is available to authorized users.