Spermiophagy by the spermathecal epithelium of the salamander Eurycea cirrigera

Long-term sperm storage in eusocial Hymenoptera

In internally fertilizing species, sperm transfer is not always immediately followed by egg fertilization, and female sperm storage (FSS) may occur. FSS is a phenomenon in which females store sperm in a specialized organ for periods lasting from a few hours to several years, depending on the species. Eusocial hymenopterans (ants, social bees, and social wasps) hold the record for FSS duration. In these species, mating takes place during a single nuptial flight that occurs early in adult life for both sexes; they never mate again. Males die quickly after copulation but survive posthumously as sperm stored in their mates' spermathecae. Reproductive females, also known as queens, have a much longer life expectancy, up to 20 years in some species. Here, we review what is currently known about the molecular adaptations underlying the remarkable FSS capacities in eusocial hymenopterans. Because sperm quality is crucial to the reproductive success of both sexes, we also discuss the mechanisms involved in sperm storage and preservation in the male seminal vesicles prior to ejaculation. Finally, we propose future research directions that should broaden our understanding of this unique biological phenomenon.

in vivo cellular evidence of autophagic associated spermiophagy within the principal cells during sperm storage in epididymis of the turtle

The epididymis plays a significant role as a quality control organ for long-term sperm storage, maturation, and fertilizing ability and perform filtration function to eliminate abnormal or residual spermatozoa by phagocytosis. However, the role of autophagy in spermiophagy during sperm storage in turtle epididymis still needs to be studied. In this study, we reported in vivo spermiophagy via the cellular evidence of lysosome engulfment and autophagy within the principal cells during sperm storage in the turtle epididymis. Using immunofluorescence, Lysosome associated membrane protein-1 (LAMP1) and microtubule-associate protein light chain 3 (LC3) showed strong immunosignals within the apical cytoplasm of epididymal epithelia during hibernation than non-hibernation. Co-immunolabeling of LAMP1 and LC3 was strong around the phagocytosed spermatozoa in the epididymal epithelia and protein signaling of LAMP1 and LC3 was confirmed by western blotting. During hibernation, ultrastructure showed epididymal principal cells were involved in spermiophagy and characterized by the membrane’s concentric layers around phagocytosed segments of spermatozoa, degenerative changes in the sperm head and lysosome direct attachment, and with the existence of cellular components related to autophagy (autophagosome, autolysosome). In conclusion, spermiophagy occurs by lysosomal engulfment and autophagic activity within the principal cells of the turtle epididymis during sperm storage.

Proteinaceous sperm motility inhibitory factor from the female Indian garden lizard Calotes versicolor

Female sperm storage is an intriguing adaptation exhibited by a wide array of both vertebrates and invertebrates. The mechanisms underlying female sperm storage have remained elusive. Using the Indian garden lizard Calotes versicolor as a model organism, we investigated the role of low and high molecular weight factors in this phenomenon. Previously, we demonstrated three distinct phases of the reproductive cycle in this animal with live, motile spermatozoa recovered from the uterovaginal region during the reproductive phase. In the present study, we analysed the uterovaginal contents using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and identified an abundant protein band corresponding to ~55 kDa regardless of the phase of the reproductive cycle. Analysis of the purified protein by liquid chromatography-tandem mass spectrometry suggested a unique protein without any homology to the National Center for Biotechnology Information database. Exogenous addition of this protein to washed spermatozoa derived from the epididymis reversibly inhibited sperm motility in a concentration- and time-dependent manner, suggesting it plays a key role in sperm storage. These studies are likely to offer new avenues to unravel the secrets of female sperm storage seen across the animal taxa and may have novel applications not only in reproductive biology, but also in general cell storage and preserving endangered animal species.

Ultrastructural Features of Sperm Storage Tubules in the Oviduct of the Indian Garden Lizard, Calotes Versicolor

This study provides the first description of the ultrastructural features of sperm storage tubules (SSTs) in the uterovaginal region of the oviduct of the Indian garden lizard, Calotes versicolor. Abundant spermatozoa along with copious secretory material were found in the lumen of the SSTs. These secretory granules appeared similar in electron density to those found in the epithelial cells lining the SSTs indicating their similar origin. The close physical proximity of sperm with these granules suggests an intimate association between the two. The present study is also the first report of recovery of motile sperm from the flushings of SSTs in C. versicolor. The density of sperm found in the flushings varied, being most abundant during the reproductive phase and minimum/absent during the regressive phase. Understanding the microenvironment of the SSTs, the nature of the secretory granules and their interaction with sperm can guide us in unraveling the biology of oviductal sperm storage.

Influence of Macrophages on the Rooster Spermatozoa Quality

The goal of this study was to evaluate the occurrence of macrophages in rooster semen and to investigate their impact on the spermatozoa quality. Ross 308 breeder males (n = 30) with no evidence of genital tract infections were used to determine the concentration of macrophages using fluorescently conjugated acetylated low-density lipoprotein (AcLDL). Subsequently, the roosters were divided into two groups on the basis of semen macrophage concentration, and semen quality was compared in two heterospermic samples. We applied computer-assisted semen analysis (CASA) system to determine motility parameters. Fluorescence microscopy and flow cytometry were used to evaluate occurrence of apoptotic and dead spermatozoa. Spermatozoa fertility potential was examined after intravaginal artificial insemination of hens. Eighteen roosters (control group) contained 0.2-3% of macrophages within spermatozoa population and ten roosters (macrophage group) had 10-15% of macrophages. Males from macrophage group had lower (p < 0.05) motility parameters (total and progressive movement, velocity curved line) and increased concentration of dead spermatozoa detected by flow cytometry and fluorescence microscopy (p < 0.001 and p ˂ 0.05, respectively). Differences (p < 0.05) between fluorescent microscopy and flow cytometry in results on spermatozoa apoptosis and viability were observed. No significant difference was found between groups in fertility of spermatozoa. In conclusion, the higher presence of macrophages in rooster semen may have a negative effect on some parameters of rooster spermatozoa evaluated in vitro. Furthermore, our study suggests that flow cytometry allows more precise examination of spermatozoa viability and apoptosis in a very short time compared with the fluorescent microscopy.

Spermiophagy in the male reproductive tract of some passerine birds

In order to elucidate the locus and means of spermiophagy in passerine birds, we examined histologically the entire male reproductive tract of sexually mature birds of three passerine species with different forms of sperm competition, namely, the alpine accentor (Prunella collaris), the redflanked bush robin (Tarsiger cyanurus), and the Bengalese finch (Lonchura striata var. domestica). Spermiophagy occurred consistently and frequently in the epithelial layer of the seminal glomera and ejaculatory duct in each species, which were regularly identified by non-ciliated epithelial cells. The epithelial spermiophagy was occasional or infrequent in other portions of the seminal tract, and spermiophagy by macrophages was uncommon throughout the tract. Quantitative data in the seminal glomera and ejaculatory duct gave no clear answer concerning a possible relationship between the epithelial spermiophagy and different levels of sperm competition among these passerine species. In conclusion, the epithelial lining of the terminal region of the seminal tract is the main site for spermiophagy in the male reproductive tract of these passerine species, which activity serves to maintain the quality of semen by eliminating infertile spermatozoa as well as sperm remaining at the end of the breeding season.

Cloacal morphology in Bolitoglossa nicefori (Caudata: Plethodontidae): Variation during the reproductive cycle

Male and female plethodontid salamanders have specialized cloacal glands associated with the reproductive activity. The reproductive cycle in Bolitoglossa nicefori is characterized by males that are potentially reproductive throughout the year, and females that are reproductive only for a few months. To determine whether morphological and histochemical variation occur in cloacal structures related to reproductive activity, the cloacal region of male and female specimens of B. nicefori was studied in different stages of their annual reproductive cycle using light microscopy and compared with features reported in other plethodontid salamanders. The main anatomy and histology of the male and female cloacal regions of B. nicefori are similar to those of other salamanders; however, in comparison to other Bolitoglossa previously studied, B. nicefori has a relatively larger cloacal tube and a tubular rather than acinar spermatheca. As a common trait, the spermatheca has a common tube that diverges into two tubules, before branching into spermathecal tubules, horizontally arranged on frontal planes. The secretions of the spermathecal glands differed between reproductive and nonreproductive adult females. This secretory product consists of prevailing neutral carbohydrates that were related to the increase in ovarian follicular size during the breeding season. Sperm was found only in the spermatheca of reproductive periovulatory females, suggesting that the reproductive cycle involves a no long-term storage of sperm. Although males can produce sperm throughout the year, spermatophores, namely specialized structures involved in sperm transport, were found in their cloaca only during the breeding season. In these males, some of the cloaca-associated glands were seen to undergo change their secretory activity and their secretory products were related to spermatophore formation.

Maturation of mosquito spermatozoa during their transit throughout the male and female reproductive systems

The testes, seminal vesicles and spermathecae of 22 species of mosquitoes belonging to the genera Aedes, Anopheles, Culex, Mansonia and Toxorhynchites are investigated under the electron microscope. Modifications of the acrosome and sperm wall occur during the transit of the spermatozoon from the lower region of the testes to the spermathecae throughout the seminal vesicles. The origin and fate of the cell coat and the possible roles of somatic cell layers both in the testes and the seminal vesicles are discussed.

Ultrastructure of anterior uterus of the oviduct and the stored sperm in female soft-shelled turtle, Trionyx sinensis

Ultrastructure of sperm storage in female soft-shelled turtle, Trionyx sinensis was examined under light and electron microscopes. Sperm storage tubules are restricted to the anterior of the uterus. These tubules developed either by folding or fusion of the oviductal mucosal folds and are lined by both ciliated and secretory cells. Ciliated cells are characterized by a few microvilli and prominent cilia in the apical membranes. A prominent feature of the secretory cell is the presence of secretory granules in the supranuclear region. The size, shape, and electron density of these granules vary markedly. The secretory product is released mainly by exocytosis into the oviductal lumen, where it appears as flocculent material. The unique structure in the base of the epithelium, the basal border of the cell -- the basal lamina -- and a blood vessel layer, is presumed to be a important barrier, by which the nourishment exchange and the microenvironment maintenance are ensured. The gland cell is presented with numerous, round, membrane-bound secretory granules of moderate to high electron densities. We divide these granules into three types according to their appearance: (1) membrane bounded granules with high-homogeneous electron density, (2) membrane bounded granules with moderate-homogeneous electron density, (3) membrane bounded, electron dense granules with concentric structures. These granules are presented as different stages of the secretions in the gland cell. The junction complexes are markedly distributed between cells, which are important in keeping stability and the microenvironment maintenance of the sperm storage tubules. Sperm stored in the tubules are heterogeneous in cytology. In addition to the mature sperm in the lumen, sperm with large chromatic granules are found, which are presumed to be immature sperm and are being in the process of nuclear condensation. Several spermatozoa in the tubules are exhibited with definitive indications of degeneration of the nuclei. The nuclear volume increases. The electron density of the central cores in mitochondria declines, combined with the deterioration of concentric membrane structure. Those changes are possibly due to the long time storage of the sperm in sperm storage tubules, and the leakage of reactive oxygen species is suggested to be a major cause. We conclude that the ultrastructure character of sperm storage in the oviduct of Trionyx sinensis is unique, in addition to having a basal function in secretion and the cilia swing, the tubules also provide an available microenvironment for the sperm to long time stored. The degenerative sperm in the tubules might be related to paternity-specific reproductive adaptations, and the sperm competition might occur during long time storage.

Ultrastructure of the annual cycle of female sperm storage in spermathecae of the torrent salamander, Rhyacotriton variegatus (Amphibia: Rhyacotritonidae)

This study is the first report on the ultrastructure of the sperm storage glands (spermathecae) in the salamander Rhyacotriton variegatus. The population studied is associated with cold-water, rocky streams of the redwood (Sequoia) zone in northern California. Males possess sperm in their vasa deferentia and undergo spermiation throughout the year, but mating is seasonal. Most females with large, vitellogenic follicles (2.0-3.9 mm mean dia.) collected from February-June contain sperm in their spermathecae, although some females with large follicles lack sperm. Other mature-size females collected during this period have small ovarian follicles (0.9-1.2 mm mean dia.) and lack stored sperm. All females collected from September-November have small follicles (0.6-1.6 mm mean dia.) and lack sperm, except in one instance in which a female collected in November had a small amount of degraded sperm, apparently retained from the previous breeding season. The spermathecae consist of simple tubulo-alveolar glands in which the neck tubules produce a mucoid secretory product, and the distal bulbs, where sperm are stored, contain secretory vacuoles of uniform density that stain positively for glycosaminoglycans. In specimens containing sperm, some bulbs have abundant sperm and others lack sperm, but the ultrastructure is similar in both conditions. The acini contain columnar epithelial cells with wide intercellular canaliculi, and a merocrine process releases the secretion. Spermiophagy occurs. In specimens from spring and summer with small ovarian follicles, the neck tubules are similar to those of breeding females, but the distal bulbs are reduced to cords of cells lacking a discernible lumen. Secretory activity in the distal bulbs is initiated in the fall. Spermathecae of R. variegatus are most similar to those of a stream-dwelling plethodontid, Eurycea cirrigera.

Female sperm storage in amphibians

The three orders of extant amphibians are Gymnophiona, Anura, and Urodela. Although all gymnophionans apparently have internal fertilization and many are viviparous, female sperm storage is unknown. Internal fertilization has convergently evolved in a few anurans, but females of just one species, Ascaphus truei, are known to possess oviductal sperm storage tubules (SSTs). The SSTs of A. truei are similar anatomically to such glands in squamate reptiles. This similarity is convergence due to similar functional adaptations and/or internal design constraints. In salamanders and newts (Urodela), absence of sperm storage in females is the ancestral condition (three families). In the derived condition, sperm storage occurs in cloacal glands called spermathecae, and their possession is a synapomorphy for females in the suborder Salamandroidea (seven families). Salamandroids are the only vertebrates with cloacal sperm storage glands. In this paper, a phenetic analysis of variation in spermathecal characters reveals patterns of convergence in certain spermathecal characters in unrelated taxa that breed in similar habitats. In the family Salamandridae, a role in sperm nutrition for the spermathecal epithelium is questioned, and the widespread occurrence of spermiophagy is related to other reproductive strategies. I propose how the packaging of sperm in structurally different types of spermathecae may influence male paternity.

Sperm storage in females of the smooth newt (Triturus v. vulgaris L.): I. Ultrastructure of the spermathecae during the breeding season

Sperm storage in cloacal spermathecae was studied in females of Triturus v. vulgaris collected early in the breeding season in southern England. Females collected in terrestrial situations, presumably unmated, were mated in the laboratory, and the ultrastructure of the transferred sperm and the spermathecae was observed at various intervals after mating. Sperm from a spermatophore cap lodged in a female's cloacal orifice can migrate into spermathecae within 1 hr after mating. Spherical structures on the axial fibers of some sperm in the cap could indicate immaturity. Disorderly clusters of sperm from the cap are still present in the cloacal chamber 12 hr after mating but are absent 24 hr after mating. During storage, sperm often are in tangled masses in the spermathecal tubules. The sperm are coated with spermathecal secretions, and some sperm nuclei were observed embedded in the spermathecal epithelium. Little evidence for spermiophagy early in the breeding season was found. During oviposition, mazes of sperm occur external to the spermathecal orifices, and sperm may be released in this condition onto eggs as they pass through the cloaca. The tangled clusters in which sperm are found from pick-up to oviposition are hypothesized as an adaptation to reduce the effectiveness of sperm competition from the ejaculates of rival males. Additional studies, using the same protocol and covering the entire cycle of sperm storage, are necessary to enable interspecific comparisons leading to phylogenetic hypotheses.

Sperm storage in the spermatheca of the red-back salamander, Plethodon cinereus (Amphibia: Plethodontidae)

In northern Indiana, the mating season of Plethodon cinereus occurs after hibernation from March until June, when oviposition begins. During the mating season, a female stores sperm in its spermatheca, a compound tubular gland in the roof of the cloaca. The apical cytoplasm of the spermathecal epithelium is filled with large secretory vacuoles whose product is released while sperm are stored. Females induced to oviposit in June and July by injections of human chorionic gonadotropin (hCG) still retain much sperm 1 month after oviposition, but secretory vacuoles are absent in all specimens sacrificed in July and August. Instead, some sperm are embedded in the spermathecal epithelium with resultant spermiophagy involving lysosomes. A female sacrificed in September 2 months after oviposition possesses scant sperm, but spermiophagy alone does not seem extensive enough to account for the decrease in sperm numbers. Females sacrificed in October prior to hibernation lack sperm in their spermathecae; some secretory vacuoles are present, but they are not as numerous or as enlarged as in specimens collected in March and May. Inter- and intrafamilial differences in the cytology of sperm storage may not be phyletically informative at the family level but related to species-specific reproductive adaptations.

Spermathecal cytology of Ambystoma opacum (Amphibia: Ambystomatidae) and the phylogeny of sperm storage organs in female salamanders

Sperm storage glands, spermathecae, were examined from mated female Ambystoma opacum during the breeding season. No differences occur in the spermathecal ultrastructure of individuals sacrificed prior to oviposition and those sacrificed within 3 days of removal from tended clutches of recently oviposited eggs. The simple tubuloalveolar glands produce two types of secretory vacuoles. Apical secretory vacuoles contain glycosaminoglycans for export into the lumen to bathe stored sperm, perhaps providing the chemical/osmotic environment necessary for sperm quiescence. The other type of secretory vacuole contains an unsaturated lipid that is produced for export into the connective tissue surrounding the spermathecae. The role of this secretion may involve the contraction of myoepithelial cells, resulting in sperm expulsion. Some sperm undergo degradation in the spermathecal epithelium, and an interepithelial leukocyte was observed in one specimen. Apical secretory vacuoles and sperm are absent from the spermathecae of a specimen sacrificed 62 days after removal from a tended egg clutch. This is the first report on the spermathecal cytology of a salamander from the Ambystomatidase, and comparisons with salamanders from other families provide a morphological basis for considering spermathecae polyphyletic within the Caudata.