Live for the moment—Adaptations in the male genital system of a sexually cannibalistic spider (Theridiidae, Araneae)

Monogyny in spiders culminates in extreme traits, like dramatic male self-sacrifice and emasculation of the male by the female during copulation. Here we show that monogynous males can be highly adapted for this fatal sexual behaviour. Dwarf males of the one-palped theridiid spider Tidarren argo, which are cannibalised immediately after the insertion of their single copulatory organ, stop spermiogenesis when reaching adulthood. Their testes atrophy, which might economise the energy expenditures of these males. We also found that the amount of seminal fluid produced is stored in an enlarged seminal vesicle until the single sperm induction takes place. The volume of the seminal vesicle is similar to the sperm droplet taken up into the copulatory organ (palpal organ). Sperm uptake takes much longer than in related species most likely due to the large amount of seminal fluid. As shown by histological observations males are able to fill one of the paired female sperm storage organs during copulation thereby presumably impeding subsequent charging by rival males.     

Frequent Failure of Male Monopolization Strategies as a Cost of Female Choice in the Black Widow Spider Latrodectus tredecimguttatus

In many mating systems, males strive for securing paternity through monopolizing females. As male monopolization attempts often contradict female interests, this conflict may fuel an evolutionary arms race. In the widow spider genus Latrodectus, females are commonly polyandrous, whereas males are monogynous, hence restricted to mate with a single female, making paternity protection particularly important. Potential mating plugs (specialized embolus sclerites of male copulatory organs) have been discovered in the complex female genital tracts of several Latrodectus species. In this study, we investigated mating strategies in the Mediterranean black widow spider Latrodectus tredecimguttatus and tested the adaptive value of female attacks against male monopolization efforts. In a double mating experiment, we manipulated the number of insertions (=copulations) for first and second males to assess female behaviour and male embolus sclerite placement success. Our results indicate that first males′ embolus sclerites inside the females′ sperm stores physically block sclerites of subsequent males. While female attacks did not affect the deposition of potential mating plugs, they significantly reduced copulation duration. Irrespective of female aggression, male sclerite placement failure occurred frequently, but large males were more successful than smaller competitors. We suggest that the complex genital morphology in both sexes may have co‐evolved antagonistically and female morphology could serve to favour large males for fertilization.     

Mate plugging via genital mutilation in nephilid spiders: an evolutionary hypothesis

Nephilid spiders are known for gigantic females and tiny males. Such extreme sexual dimorphism and male-biased sex ratios result in fierce male–male competition for mates. Intense sperm competition may be responsible for behaviors such as mate guarding, mate binding, opportunistic mating, genital mutilation, mating plugs and male castration (eunuchs). We studied the mating biology of two phylogenetically, behaviorally and morphologically distinct south-east Asian nephilid spider species ( Herennia multipuncta, Nephila pilipes ) in nature and in the laboratory. Specifically, we established the frequencies and effectiveness of plugging (a plug is part of the male copulatory organ), and tested for male and female copulatory organ reuse. Both in nature and in the laboratory, plug frequencies were higher in H. multipuncta (75–80% females plugged) compared with N. pilipes (45–47.4%), but the differences were not significant. Plugs were single and effective (no remating) in H. multipuncta but multiple and ineffective (remating possible) in N. pilipes . In Herennia , the males plugged when the female was aggressive and in Nephila plugging was more likely when mating with previously mated and larger females. Further differences in sexual biology are complete palpal removal and higher sexual aggressiveness in Herennia (sexual cannibalism recorded for the first time), and mate binding in Nephila . Thus, we propose the following evolutionary hypothesis: nephilid plugging was ancestrally successful and enabled males to monopolize females, but plugging became ineffective in the phylogenetically derived Nephila . If the evolution of nephilid sexual mechanisms is driven by sexual conflict, then the male mechanism to monopolize females prevailed in a part of the phylogeny, but the female resistance to evade monopolization ultimately won the arms race.     

Complex genital system of a haplogyne spider (Arachnida, Araneae, Tetrablemmidae) indicates internal fertilization and full female control over transferred sperm

The female genital organs of the tetrablemmid Indicoblemma lannaianum are astonishingly complex. The copulatory orifice lies anterior to the opening of the uterus externus and leads into a narrow insertion duct that ends in a genital cavity. The genital cavity continues laterally in paired tube-like copulatory ducts, which lead into paired, large, sac-like receptacula. Each receptaculum has a sclerotized pore plate with associated gland cells. Paired small fertilization ducts originate in the receptacula and take their curved course inside the copulatory ducts. The fertilization ducts end in slit-like openings in the sclerotized posterior walls of the copulatory ducts. Huge masses of secretions forming large balls are detectable in the female receptacula. An important function of these secretory balls seems to be the encapsulation of spermatozoa in discrete packages in order to avoid the mixing of sperm from different males. In this way, sperm competition may be completely prevented or at least severely limited. Females seem to have full control over transferred sperm and be able to express preference for spermatozoa of certain males. The lumen of the sperm containing secretory balls is connected with the fertilization duct. Activated spermatozoa are only found in the uterus internus of females, which is an indication of internal fertilization. The sperm cells in the uterus internus are characterized by an extensive cytoplasm and an elongated, cone-shaped nucleus. The male genital system of I. lannaianum consists of thick testes and thin convoluted vasa deferentia that open into the wide ductus ejaculatorius. The voluminous globular palpal bulb is filled with seminal fluid consisting of a globular secretion in which only a few spermatozoa are embedded. The spermatozoa are encapsulated by a sheath produced in the genital system. The secretions in females may at least partly consist of male secretions that could be involved in the building of the secretory balls or play a role in sperm activation. The male secretions could also afford nutriments to the spermatozoa.     

Ultrastructure of spermatozoa of orsolobidae (Haplogynae,Araneae) with implications on the evolution of sperm transfer forms in Dysderoidea

Haplogynae are highly diverse with respect to the primary male genital system and sperm characteristics. Additionally, all sperm transfer forms (STF) known for spiders are present. Besides individually transferred sperm (cleistospermia), sperm are transferred as conjugates, both primary (synspermia) and secondary sperm conjugates (coenospermia, rouleaux) occur. Nevertheless, the ultrastructure of spermatozoa and STF are described for few Haplogynae and often only one representative species was studied, resulting in a superficial insight in the evolution of these traits. To elucidate the evolution of STF within Haplogynae we investigated representatives of four genera of the dysderoid family Orsolobidae. Our data show the presence of synspermia (Orsolobus, Osornolobus, Hickmanolobus, and Tasmanoonops) and also cleistospermia (Osornolobus). The occurrence of different STF within one family or even genus has not been described for any other spider taxon so far. Moreover, the synspermia of species of Tasmanoonops and Hickmanolobus were not covered by a secretion sheath suggesting a previously unknown strategy of transferring sperm that is possibly related to sperm residency time or female triggered processes after copulation. Based on serial ultrathin sectioning and subsequent 3D‐reconstruction, we obtained detailed measurements revealing remarkable size differences of STF. To evaluate the previously suggested correlation with the most distal region of the spermophor inside the embolus (intromittent part of the copulatory organ) we measured the diameter of the spermophor using micro‐computed X‐ray tomography data to obtain corresponding morphometric parameters. Based on these data only two species show similarity in STF and spermophor diameter. J. Morphol. 275:1238–1257, 2014. © 2014 Wiley Periodicals, Inc.     

Broken Copulatory Organs are Low-Cost Adaptations to Sperm Competition in Redback Spiders

In some spiders, a discrete portion of the male's copulatory organ (the apical sclerite) breaks off during copulation and remains in the female's reproductive tract. Apical sclerites may prevent insemination by rivals (sperm competition), stimulate females to favourably bias paternity (cryptic choice) or breakage may reflect sexual conflict over copulation duration with little direct effect on paternity. It has been assumed that any benefits of organ breakage are balanced by a large cost (male sterility) in species where males could otherwise mate multiply, but this has never been experimentally tested. We examined these ideas in the Australian redback spider (Latrodectus hasselti Thorell 1870, Araneae: Theridiidae), a species where males are functionally sterile after one normal mating. We experimentally removed sclerites and found males were able to mate, had similar copulation durations and transferred similar numbers of sperm as males with intact sclerites. Benefits of organ breakage were examined by forcing intact, rival males to inseminate the same or opposite reproductive tracts (female have paired, independent tracts in this taxon) and assessing paternity as a function of sclerite location. As predicted, apical sclerites were typically deposited at the entrance to the female's sperm storage organ, where they could physically block insemination by rivals. First male precedence was common when males inseminated the same tract and deposited sclerites at the entrance to the spermatheca, but not when sclerites were found elsewhere in the tract, or when rivals inseminated opposite tracts (where physically blocking rivals was impossible). Our data show that, in redbacks, copulatory organ breakage is not a side‐effect of sexual conflict, is unlikely to be a cue for cryptic female choice, but allows males to avoid sperm competition. Moreover, copulatory organ damage can have minimal reproductive cost for males, so assumptions of sterility after organ breakage are unjustified without supporting data.     

A non-sperm transferring genital trait under sexual selection: an experimental approach

Male genitalia are among the fastest evolving morphological characters, and at a general level sexual selection seems to be involved. But experimental determination of the functions of many remarkable genitalic elaborations is very rare. Here we present the first study to address experimentally the adaptive function of a male genital structure that is not involved in sperm transfer. Females of the orb-weaving spider Argiope bruennichi are sexually cannibalistic and polyandrous. The male increases his paternity by obstructing the female's insemination duct with a fragment of his complex genitalia (embolus tip). We manipulated males by detaching another species-specific structure, the median apophysis spur, and found that the spur promotes breakage of the embolus tip inside the female duct, but does not affect the probability and duration of copulation. These data are novel in that they suggest that a genitalic structure which does not transfer sperm nevertheless evolved in the context of sperm competition.     

Sperm dumping in a haplogyne spider

The present study shows that females of Silhouettella loricatula (Arachnida: Araneae: Oonopidae) manage to process sperm in an unusual and previously unknown way. The male ejaculate consisting of spermatozoa and globular secretion is enclosed in a secretory sac. This may avoid the mixing of sperm from different males and at least severely limit sperm competition. The process of sperm enclosure occurs within the female's sperm storage site (receptaculum) as the ejaculate is not surrounded by a sac inside the male's sperm-transferring organs (palpal bulbs). The secretion forming the sac is produced by glands adjoining the receptaculum. The possibility that globular secretions in the male palpal bulbs partly contribute to the sac cannot be ruled out completely. It is suggested that in S. loricatula , the main function of sperm enclosure in a sac is enabling females to dump the ejaculate of a male. The present study represents the first report on sperm dumping in the family Oonopidae. During five first and three second copulations in the laboratory, the dumping of a sac was observed. One dumped sac was sectioned and contained spermatozoa. Two couples were flash-fixed with liquid nitrogen early during copulation, which revealed the mechanism of the sac dumping. By muscle contractions, the receptaculum is bent backwards and the sac moved into the genital opening. The actual sac dumping occurs most probably in cooperation with the male, which moves his pedipalps rhythmically during the entire copulation. Extensions and furrows on the emboli suggest that they may additionally be used as copulatory courtship devices. The enclosure of sperm from the current male in secretion takes place during or immediately following copulation as all mated females sacrificed after copulation had a new sac containing spermatozoa in the receptaculum. Dumping sperm of a previous male during the next copulation may allow females to bias sperm precedence.     

numb, a gene required in determination of cell fate during sensory organ formation in Drosophila embryos

Neurons and support cells of each sensory organ in Drosophila embryos are most likely derived from a single precursor cell. This cell lineage is affected in numb mutants. Morphological alterations of sensory structures, as well as changes in the number of cells expressing cell type-specific markers, indicate that sensory neurons in numb mutant embryos are transformed into lineage-related nonneuronal support cells. Thus the numb gene controls the fate of progeny derived from sensory organ precursors. The numb gene has been isolated by the plasmid rescue method. The structure of its predicted product is discussed.     

Cryptic female choice via sperm dumping favours male copulatory courtship in a spider

Males of many animals perform ‘copulatory courtship’ during copulation, but the possible reproductive significance of this behaviour has seldom been investigated. In some animals, including the spider Physocyclus globosus (Pholcidae), the female discards sperm during or immediately following some copulations. In this study, we determined which of several variables associated with copulation correlated with paternity success in P. globosus when two males mate with a single female. Then, by determining which of these variables also correlated with sperm dumping, we inferred which variables may affect paternity via the mechanism of sperm dumping. Male abdomen vibration (a copulatory courtship behaviour) and male genitalic squeezing both correlated with both paternity and sperm dumping; so, these traits may be favoured by biased sperm dumping. Biased sperm dumping may also be the mechanism by which possible cryptic female choice favours another male trait that was the subject of a previous study, responsiveness to female stridulation.     

Two distinctly different sperm storage organs in female Dysdera erythrina (Araneae: Dysderidae)

The haplogyne spider D. erythrina possesses two distinctly different sperm storage organs: a bilobed anterior spermatheca and a large, sac-like posterior diverticulum. The glandular equipment of both storage types is markedly different: the glandular tissue of the spermatheca is composed of complicated glandular units comprising a cuticular ductule and three canal cells (class 3 cells) whereas the glandular tissue of the posterior diverticulum is composed of simple gland cells that discharge their product through the cuticle (class 1 cells). Thus, the glandular products produced differ, leading to different storage conditions for the spermatozoa from copulation to egg laying. It is suggested that multiple organ types have evolved to facilitate specialization in short-term and long-term storage and to allow (posterior diverticulum) or prevent (spermatheca) males from accessing previously stored sperm.     

Ultrastructural analysis of the functional copulatory organ of the male rotifer,Asplanchna brightwelli

The male rotifer copulatory organ is composed of a urethral canal extending from the tip of the copulatory organ internally to a layer of microvilli. The microvilli project from two different cell types, referred to as the internal and peripheral microvillar cells according to their location. At this microvillar junction a second canal, the vas deferens, continues posteriorly and enters the sperm duct region of the testis. The channel of the vas deferens is formed from the inner wall of three separate cells; the cap, intermediate and basal cells. Peripheral to these cells and parallel to them for their entire length, cross sections of seven prostate gland cells can be observed. Anteriorly, these gland cells are connected to the basal end of the microvillar layer via a short neck region, through which glandular secretion occurs only during copulation. The mechanism of secretion appears to be a form of exocytosis whereby the secretory granule membrane fuses with the cell plasmalemma so that rupturing at the point of fusion will release the granule content into the neck region. The prostate gland cells contain an abundance of autophagic vacuoles while most of the other cells of the copulatory organ contain primary lysosomes and cytolosomes. These organelles may be associated with the aging process in rotifers, or, as in the case of the prostate gland-autophagic vacuoles, with a fast organelle turnover during secretion.     

Female wolf spiders exert cryptic control drastically reducing ejaculate size

Sexes' roles in post‐copulatory processes have important effects on individual fitness and are promising to study in species showing complex mating behaviours. In the spider Schizocosa malitiosa, males perform two different copulatory patterns, pattern 1 includes 80% of total pedipalp insertions and pattern 2 includes 20%. Both patterns produce similar number of offspring, but pattern 1 induces higher female reluctance to remating than pattern 2. We hypothesised that the complex copulatory patterns are linked to post‐copulatory sexual selection, affecting males' sperm transfer and the resulting sperm storage by females. First, we examined amounts of sperm in males and live females from uninterrupted (pattern 1 + 2) and interrupted matings (pattern 1, pattern 2). Second, in order to disentangle male and female actions, we induced males to mate with dead females and examined amounts of sperm. Males transfer in total 71% of the sperm available in their pedipalps, being higher but not significant in pattern 1 than in pattern 2. Females drastically reduced the amount of sperm stored in their spermathecae and such control is stronger in pattern 1 compared to pattern 2 matings. We propose that cryptic female control is a main factor driving males to strengthen sperm transfer. Active female reduction in ejaculate most probably diminished her reluctance to remate.     

A cholinergic-regulated circuit coordinates the maintenance and bi-stable states of a sensory-motor behavior during Caenorhabditis elegans male copulation

Penetration of a male copulatory organ into a suitable mate is a conserved and necessary behavioral step for most terrestrial matings; however, the detailed molecular and cellular mechanisms for this distinct social interaction have not been elucidated in any animal. During mating, the Caenorhabditis elegans male cloaca is maintained over the hermaphrodite's vulva as he attempts to insert his copulatory spicules. Rhythmic spicule thrusts cease when insertion is sensed. Circuit components consisting of sensory/motor neurons and sex muscles for these steps have been previously identified, but it was unclear how their outputs are integrated to generate a coordinated behavior pattern. Here, we show that cholinergic signaling between the cloacal sensory/motor neurons and the posterior sex muscles sustains genital contact between the sexes. Simultaneously, via gap junctions, signaling from these muscles is transmitted to the spicule muscles, thus coupling repeated spicule thrusts with vulval contact. To transit from rhythmic to sustained muscle contraction during penetration, the SPC sensory-motor neurons integrate the signal of spicule's position in the vulva with inputs from the hook and cloacal sensilla. The UNC-103 K(+) channel maintains a high excitability threshold in the circuit, so that sustained spicule muscle contraction is not stimulated by fewer inputs. We demonstrate that coordination of sensory inputs and motor outputs used to initiate, maintain, self-monitor, and complete an innate behavior is accomplished via the coupling of a few circuit components.     

粉尘螨生殖系统超微结构的透射电镜观察

本研究主要采用透射电镜观察粉尘螨Dermatophagoides farinae (Hughes)生殖系统超微结构。粉尘螨雄性生殖系统是由精巢、 输 精管、 附腺、 射精管、 交配器官及附属交配器官组成。精巢内可同时有精子发育各阶段的细胞。精子无核膜、 核染色质聚集成束、 线 粒体缺乏典型的嵴、 胞质内有平行排列的电子致密薄片等为其特征性结构。雌性生殖系统由交合囊、 交合囊管、 储精囊、 囊导管、 卵 巢、 输卵管、 子宫及产卵管构成。卵巢内可见含多个细胞核的中央细胞, 其周为卵母细胞等生殖细胞。该研究丰富了对粉尘螨生殖系统 结构的认识。     

The retrolateral tibial apophysis in spiders—shaped by sexual selection?

The functional significance of the retrolateral tibial apophysis (rta) on the male pedipalps in four spider species with different mating positions is investigated with the help of histological serial sections prepared after freeze-fixing copulating pairs with liquid nitrogen. The results of this study, as well as most data in previous works, suggest that the rta is mostly used to fix the male pedipalp to the female epigyne in order to ensure the intromission of the sperm transferring embolus. This is in accordance with the female choice hypothesis on genitalia which predicts that species-specific genital structures should directly or indirectly contact the female during copulation and thus be shaped by sexual selection.     

Patterns of Sperm Transfer in the Golden Orb‐Weaver Nephila edulis

Sperm competition studies typically identify copulation duration as an important predictor of paternity as it may determine the quantity of sperm transferred and thus paternity success. This study explores the relationship between copulation duration, male body size, male age and sperm transfer in the golden orb‐weaving spider, Nephila edulis. Paternity in this species is strongly associated with the relative frequency and duration of copulation, which is also influenced by male size. We determined the number of sperm transferred during copulation, by performing sperm counts in both the male copulatory organs (palps) and female sperm receptacle (spermatheca) of recently mated pairs. The total number of sperm recorded (the sum in the male palps and female spermathecae) was greater for younger males than older males, but did not vary with male body size. In general, younger males transferred more sperm and a greater proportion of their sperm supplies than older males and, among these younger males, larger individuals transferred more sperm. However, there were no significant size effects for older males. More sperm was transferred with longer copulations, but in contrast with previous studies, we found that larger males copulated for longer. The rate of sperm transferred was negatively correlated with the duration of copulation, suggesting that the variation in copulation duration in N. edulis may represent strategic investment by males to alter patterns of paternity, in addition to transferring additional sperm.     

Relationship between pre‐ and post‐copulatory traits in Salvator rufescens (Squamata: Teiidae)

Understanding pre‐ and post‐copulatory mechanisms of sexual selection can provide insights into the evolution of male reproductive strategies. The phenotype‐linked fertility hypothesis postulates that male sperm quality and secondary sexual characteristics will positively co‐vary, whereas the sperm competition hypothesis predicts a negative association between those traits. Male reproductive traits often show variation throughout the reproductive period, suggesting that the relationship between pre‐ and post‐copulatory sexual selection may vary temporally. Here, we evaluated the relationship between secondary sexual character and sperm traits and its temporal variation in Salvator rufescens, a south American lizard. We observed a negative relationship between jaw muscle and principal piece length of sperm and a variation in the relationship between pre‐ and post‐copulatory traits throughout the reproductive period. Collectively, our results evidenced a trade‐off between pre‐ and post‐copulatory traits and a strong seasonal flexibility of male reproductive strategies in this lizard species.     

Female genital system of the folding-trapdoor spider Antrodiaetus unicolor (Hentz, 1842) (Antrodiaetidae, Araneae): ultrastructural study of form and function with notes on reproductive biology of spiders

The genitalia of the female folding-trapdoor spider Antrodiaetus unicolor are characterized by two pairs of spermathecae that are arranged in a single row and connected to the roof of the bursa copulatrix. Each single spermatheca is divided into three main parts: stalk, bowl, and bulb, which are surrounded by the spermathecal gland. The epithelium of the spermathecal gland is underlain by a muscle meshwork and consists of different types of cells partly belonging to glandular cell units (Class 3 gland cells) that extend into pores in the cuticle of the stalk and bowl. Interestingly, the bulb lacks glandular pores and is characterized by a weakly sclerotized cuticle. This peculiarly structured bulb probably plays an important role in the discharge of the sperm mass. It is suggested that by contraction of the muscle layer the sperm mass may be squeezed out, when the bulb invaginates and expands into the spermathecal lumen, pushing the sperm to the uterus lumen. Each glandular unit consists of usually one or two central secretory cells that are for the most part surrounded by a connecting cell that again is surrounded by a canal cell. The canal cell, finally, is separated from the other epithelial cells (intercalary cells) located between the glandular units by several thin sheath cells that form the outer enveloping layer of the unit. The secretions are released through a cuticular duct that originates proximally between the apical part of the connecting cell and the apical microvilli of the secretory cells and runs into a pore of the spermathecal cuticle. The glandular products of the Class 3 gland cells likely contribute to the conditions allowing long-term storage of the spermatozoa in this species. Details regarding the ovary, the uterus internus, and the uterus externus are reported. Most of the secretion that composes the chorion of the egg is produced in the ovary. Glandular cell units observed in the uterus externus differ structurally from those in the spermathecae and likely play a different role. Finally, we briefly discuss our results on the female genitalia of A. unicolor in the light of knowledge about the reproductive biology of spiders.