Ultrastructure of the Accessory Glands in Female Genitalia ofPholcus phalangioides(Fuesslin, 1775) (Pholcidae; Araneae)

Copulatory behaviour and genital mechanics suggest sperm allocation by a non-intromittent sclerite in a pholcid spider

The male genitalia of pholcid spiders, which is one of the most species-rich spider families, are characterized by a procursus, which is a morphologically diverse projection of the copulatory organ. It has been shown that the procursus interacts with the female genitalia during copulation. Here, we investigate the function of the procursus in Gertschiola neuquena, a species belonging to the early branched and understudied subfamily Ninetinae, using behavioural and morphological data. Although many aspects of the copulatory behaviour of G. neuquena follow the general pattern described for the family, males use only one pedipalp during each copulation. Based on our micro-CT analysis of cryofixed mating pairs using virgin females, we can show that the long and filiform procursus is inserted deeply into the unpaired convoluted female spermatheca, and the intromittent sclerite, the embolus, is rather short and stout only reaching the most distal part of the female sperm storage organ. Histological data revealed that sperm are present in the most proximal part of the spermatheca, suggesting that the procursus is used to allocate sperm deeply into the female sperm storage organ. This represents the first case of a replacement of the sperm allocation function of the intromittent sclerite in spiders.

Post-ejaculatory modifications to sperm (PEMS)

Mammalian sperm must spend a minimum period of time within a female reproductive tract to achieve the capacity to fertilize oocytes. This phenomenon, termed sperm 'capacitation', was discovered nearly seven decades ago and opened a window into the complexities of sperm-female interaction. Capacitation is most commonly used to refer to a specific combination of processes that are believed to be widespread in mammals and includes modifications to the sperm plasma membrane, elevation of intracellular cyclic AMP levels, induction of protein tyrosine phosphorylation, increased intracellular Ca2+ levels, hyperactivation of motility, and, eventually, the acrosome reaction. Capacitation is only one example of post-ejaculatory modifications to sperm (PEMS) that are widespread throughout the animal kingdom. Although PEMS are less well studied in non-mammalian taxa, they likely represent the rule rather than the exception in species with internal fertilization. These PEMS are diverse in form and collectively represent the outcome of selection fashioning complex maturational trajectories of sperm that include multiple, sequential phenotypes that are specialized for stage-specific functionality within the female. In many cases, PEMS are critical for sperm to migrate successfully through the female reproductive tract, survive a protracted period of storage, reach the site of fertilization and/or achieve the capacity to fertilize eggs. We predict that PEMS will exhibit widespread phenotypic plasticity mediated by sperm-female interactions. The successful execution of PEMS thus has important implications for variation in fitness and the operation of post-copulatory sexual selection. Furthermore, it may provide a widespread mechanism of reproductive isolation and the maintenance of species boundaries. Despite their possible ubiquity and importance, the investigation of PEMS has been largely descriptive, lacking any phylogenetic consideration with regard to divergence, and there have been no theoretical or empirical investigations of their evolutionary significance. Here, we (i) clarify PEMS-related nomenclature; (ii) address the evolutionary origin, maintenance and divergence in PEMS in the context of the protracted life history of sperm and the complex, selective environment of the female reproductive tract; (iii) describe taxonomically widespread types of PEMS: sperm activation, chemotaxis and the dissociation of sperm conjugates; (iv) review the occurence of PEMS throughout the animal kingdom; (v) consider alternative hypotheses for the adaptive value of PEMS; (vi) speculate on the evolutionary implications of PEMS for genomic architecture, sexual selection, and reproductive isolation; and (vii) suggest fruitful directions for future functional and evolutionary analyses of PEMS.

Sperm dynamics in spiders (Araneae): ultrastructural analysis of the sperm activation process in the garden spider Argiope bruennichi (Scopoli, 1772)

Storage of sperm inside the female genital tract is an integral phase of reproduction in many animal species. The sperm storage site constitutes the arena for sperm activation, sperm competition and female sperm choice. Consequently, to understand animal mating systems information on the processes that occur from sperm transfer to fertilization is required. Here, we focus on sperm activation in spiders. Male spiders produce sperm whose cell components are coiled within the sperm cell and that are surrounded by a proteinaceous sheath. These inactive and encapsulated sperm are transferred to the female spermathecae where they are stored for later fertilization. We analyzed the ultrastructural changes of sperm cells during residency time in the female genital system of the orb-web spider Argiope bruennichi. We found three clearly distinguishable sperm conditions: encapsulated sperm (secretion sheath present), decapsulated (secretion sheath absent) and uncoiled sperm (cell components uncoiled, presumably activated). After insemination, sperm remain in the encapsulated condition for several days and become decapsulated after variable periods of time. A variable portion of the decapsulated sperm transforms rapidly to the uncoiled condition resulting in a simultaneous occurrence of decapsulated and uncoiled sperm. After oviposition, only decapsulated and uncoiled sperm are left in the spermathecae, strongly suggesting that the activation process is not reversible. Furthermore, we found four different types of secretion in the spermathecae which might play a role in the decapsulation and activation process.

Functional genital morphology of armored spiders (Arachnida: Araneae: Tetrablemmidae)

This study describes the female genitalia of the tetrablemmid spiders Brignoliella acuminata, Monoblemma muchmorei, Caraimatta sbordonii, Tetrablemma magister, and Ablemma unicornis by means of serial semi-thin sections and scanning electron microscopy and compares the results with previous findings on Indicoblemma lannaianum. Furthermore, the male palps and chelicerae are briefly described. The general vulval organization of females is complex and shows similarities in all of the investigated species. The copulatory orifice is situated near the posterior margin of the pulmonary plate. The opening of the uterus externus lies between the pulmonary and the postgenital plate. Paired copulatory ducts lead to sac-like receptacula. Except for A. unicornis, the male emboli of all investigated species are elongated and thread-like. However, they are too short to reach the receptacula. Hence, the spermatozoa have to be deposited inside the copulatory ducts. The same situation was also found in I. lannaianum. Females of this species store sperm encapsulated in secretory balls in their receptacula. The secretion is produced by glands adjoining the receptacula. The presence of paired fertilization ducts and spermatozoa in the uterus internus suggested that fertilization takes place internally in I. lannaianum. Secretory balls in the receptacula are found in all of the investigated species in this study, showing that sperm are stored in the same way. The place of fertilization may also be identical since dark particles, presumably spermatozoa, are located in the uterus internus of all investigated species except for T. magister. However, fertilization ducts are only found in B. acuminata and M. muchmorei. A sclerotized central process with attached muscles is present in A. unicornis, M. muchmorei, C. sbordonii and T. magister. Only in A. unicornis does the central process show an internal lumen and hold spermatozoa. In the other species, it could be used to lock the uterus during copulation in order to prevent sperm from getting into it as suggested for certain oonopid species. The uterus externus of all investigated species shows a sclerotized dorsal fold with attached muscles, previously described as "inner vulval plate." Contractions of the muscles lead to a widening of the dorsal fold, thus creating enough space for the large oocytes to pass the narrow uterus externus. The males of all investigated species have apophyses on their chelicerae. At least in B. acuminata and A. unicornis, where females have paired grooves on the preanal plate, these apophyses allow males to grasp the female during copulation as described for I. lannaianum.

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.

Silhouettella loricatula (Arachnida, Araneae, Oonopidae): A Haplogyne spider with complex female genitalia

The female genital system of the oonopid Silhouettella loricatula is astonishingly complex. The genital opening is situated medially and leads into an oval receptaculum that is heavily sclerotized except for the ventral half of the posterior wall that appears chitinized only. A large striking sclerite lying in the posterior wall of the uterus externus is attached anteriorly to the receptaculum and continues dorsally into a globular appendix that bears a furrow. The uterus externus shows a peculiar modification in its anterior wall: a paddle-like sclerite with a nail-like posterior process. This sclerite lies opposite to the furrow proceeding in the globular appendix and may serve females to lock the uterus externus by muscle contractions. Massive muscles connect the sclerite with the anterior scutum of the opisthosoma and with two other sclerites that are attached to the receptaculum and serve as attachments for further muscles. Gland cells extend around a pore field of the receptaculum. They produce secretion that encloses spermatozoa in a discrete package (secretory sac) inside the receptaculum. In this way, the mixing of sperm from different males and thus sperm competition may be severely limited or completely prevented. During a copulation in the laboratory the ejection of a secretory sac that most probably contained spermatozoa was observed, indicating sperm dumping in S. loricatula. The ejection of the secretory sac may be caused by female muscle contractions or by male pedipalp movements. The majority of the investigated females have microorganisms in the receptacula that could represent symbionts or infectious agents. The microorganisms can be identified partly as bacteria. They are enclosed in secretion and are always found in the same position inside the receptaculum.

The male genital system of the cellar spider Pholcus phalangioides (Fuesslin, 1775) (Pholcidae, Araneae): development of spermatozoa and seminal secretion

BACKGROUND

Most arthropods pass through several molting stages (instars) before reaching sexual maturity. In spiders, very little is known about the male genital system, its development and seminal secretions. For example, it is unknown whether spermatozoa exist prior to-, or only after the final molt. Likewise, it is unclear whether sperm are produced throughout male adulthood or only once in a lifetime, as is whether seminal secretions contain factors capable of manipulating female behavior. In order to shed light on these aspects of the reproductive biology of spiders, we investigated the male genital system of the common cellar spider Pholcus phalangioides, with special emphasis on its development and seminal secretions.

RESULTS

Testes already display all stages of spermatogenesis in subadult males (about four weeks before the final molt). Their vasa deferentia possess proximally a very voluminous lumen containing dense seminal fluid and few spermatozoa, whereas the distal part is seemingly devoid of contents. Spermatoza of P. phalangioides are typical cleistospermia with individual secretion sheaths. In male stages approximately two weeks prior to the final molt, the lumina of the testes are wider and filled with a dense secretion. The wide, proximal portion of the vasa deferentia is filled with secretion and a large number of spermatozoa, and the narrow distal part also contains secretion. In adult males, the wide lumina of the testes are packed with spermatozoa and secretions. The latter are produced by the somatic cells that bear microvilli and contain many vesicles. The lumina of the vasa deferentia are narrow and filled with spermatozoa and secretions. We could identify a dense matrix of secretion consisting of mucosubstances and at least three types of secretion droplets, likely consisting of proteinaceous substances.

CONCLUSION

This study reveals that spermatogenesis begins weeks before maturity and takes place continuously in the long-lived males of P. phalangioides. Possible functions of the various types of secretion in the seminal fluid and previously investigated female secretions are discussed in the light of sexual selection.

Female genital system of the folding-trapdoor spiderAntrodiaetus 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.

Genital structures in the entelegyne widow spiderLatrodectus revivensis (Arachnida; Araneae; Theridiidae) indicate a low ability for cryptic female choice by sperm manipulation

The female genital structures of the entelegyne spider Latrodectus revivensis are described using semithin sections and scanning electron microscopy. Apart from the tactile hairs overhanging the opening of the atrium, the contact zones of the female epigynum are devoid of any sensilla, indicating that the female does not discriminate in favor or against males due to their genital size or stimulation through copulatory courtship. The dumb-bell shape and the spatial separation of the entrance and the exit of the paired spermathecae suggest that they are functionally of the conduit type. Not described for other entelegyne spiders so far, the small fertilization ducts originating from the spermathecae of each side lead to a common fertilization duct that connects the spermathecae to the uterus externus. During oviposition, it is most likely that spermatozoa are indiscriminately sucked out of the spermathecal lumina by the low pressure produced by the contraction of the muscle extending from the epigynal plate to the common fertilization duct. As no greater amounts of secretion are produced by the female during oviposition, and no activated sperm are present within the female genital tract, the secretion produced by the spermathecal epithelium does not serve in displacement or (selective) activation of spermatozoa. These findings suggest that female L. revivensis are not able to exert cryptic female choice by selectively choosing spermatozoa of certain males.

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.

Wise, winsome, or weird? Mechanisms of sperm storage in female animals

Female sperm storage is an integral part of the reproductive pattern of many species. In the female, sperm become sequestered in specialized storage organs or reservoirs, where they may remain for several days, weeks, months, or years before being used to fertilize eggs. Several different but interrelated mechanisms are used by animals to target the sperm to the portion of the female genital tract adapted for sperm storage. Both males and females influence this process. This review describes themes among the mechanisms and molecules necessary for sperm to become efficiently stored in females and the roles that the female storage organs play in the nourishment, protection, and release of stored sperm.