Deduction of a model for sperm storage in the oviduct of the domestic fowl (Gallus domesticus)

Physiological impacts of overweight on semen parameters and fertility in male broiler breeders

A negative correlation between growth and reproductive traits has declined fertility in the second half of the flock's reproductive life. Excessive weight gain in males is one of the crucial reasons for the reduction of fertility rate in broiler breeder flocks. Field data from commercial flocks were collected at different ages to determine the excess weight of roosters. Forty-four 17-week-old breeder roosters were weighed individually and divided into two groups (Control and Overweight). With the difference in the amount of feed distribution, a 26 % difference in weight was observed between the two experimental groups after six weeks (23rd week). Sperm and blood samples were collected every four weeks from the age of 24 to 64 weeks to evaluate sperm parameters and testosterone levels. Testis weight and testicular histomorphology were evaluated on weeks 24, 44, and 64; and artificial insemination was performed at the end of the experiment. Results showed that the number of active roosters and semen volume did not differ between the two groups (P > 0.05). Sperm concentration and total sperm motility at 24, 28, 32, and 36 weeks in the overweight group were higher than control group (P < 0.05). In other weeks, there was no significant difference between the two groups for sperm concentration (P > 0.05). Semen lipids oxidation was not significantly different between the two groups at any age (P > 0.05). Testosterone levels in the overweight group up to 32 weeks and in the control group at 40 to 56 weeks of age were high (P < 0.05). The number of seminiferous tubules and Sertoli cells only at 24 weeks in the overweight group showed a higher value than the control group (P < 0.05). Artificial insemination showed no significant difference between the two groups in fertility and hatching rates (P < 0.05). Finally, being overweight during the initial stage of the experiment resulted in early testicular hyperplasia and improved sperm quality, followed by a decline with age. In contrast, the control group showed a pattern of slow increase followed by a decrease.

The relationship of the male's proctodeal gland size to sperm-egg interaction and the duration of fertility in Japanese quail

In avian species, male fertility significantly impacts reproductive success. This study investigates the relationship between proctodeal gland size in male Japanese quails and sperm function, as well as female fertility duration. Six hundred adult Japanese quails were selected and housed in individual cages. Males (n = 300) were divided into 6 groups (50/group) based on the size of their proctodeal glands. Females (n = 300) were randomly assigned to corresponding groups. After acclimatization, sperm kinematics and the frequency and weight of foam discharge were evaluated. Males were paired with females for 24 h, and eggs were collected for 20 d postcopulation. Eggs were incubated to assess fertility duration. Fresh eggs (n = 20/group/d) were used to assess sperm penetration into the perivitelline membrane on the 2nd, 9th, and 16th d postinsemination. Plasma testosterone levels and the testes' relative weight were determined. The results indicated a significant increase (p < 0.0001) in sperm concentration, total and progressive motility, and nearly all sperm kinematic parameters such as VSL, VCL, VAP, LIN, WOB, and STR values as the size of the proctodeal gland increased. Quails copulated with males having a small and average proctodeal gland area (<400 mm2) laid fertile eggs for a shorter period and had significantly fewer sperm penetration holes than those mated with males having a larger proctodeal gland area (>400 mm2). The proctodeal gland size was positively correlated with testicular weight, plasma testosterone concentrations, and sperm kinetic variables. The results indicate that the size of the proctodeal gland in males can be used to predict sperm function and the duration of fertility in Japanese quail.

Proteomic analysis reveals dynamic changes in cloacal fluid composition during the reproductive season in a sexually promiscuous passerine

Cryptic female choice (CFC) is a component of postcopulatory sexual selection that allows females to influence the fertilization success of sperm from different males. While its precise mechanisms remain unclear, they may involve the influence of the protein composition of the female reproductive fluids on sperm functionality. This study maps the protein composition of the cloacal fluid across different phases of female reproductive cycle in a sexually promiscuous passerine, the barn swallow. Similar to mammals, the protein composition in the female reproductive tract differed between receptive (when females copulate) and nonreceptive phases. With the change in the protein background, the enriched gene ontology terms also shifted. Within the receptive phase, distinctions were observed between proteomes sampled just before and during egg laying. However, three proteins exhibited increased abundance during the entire receptive phase compared to nonreceptive phases. These proteins are candidates in cryptic female choice, as all of them can influence the functionality of sperm or sperm-egg interaction. Our study demonstrates dynamic changes in the cloacal environment throughout the avian breeding cycle, emphasizing the importance of considering these fluctuations in studies of cryptic female choice.

Exploring pathogenesis and biomarkers through establishment of a rat model of male infertility with liver depression and kidney deficiency

OBJECTIVES

To establish a rat model that accurately replicates the clinical characteristics of male infertility (MI) with Liver Depression and Kidney Deficiency (LD & KD) and investigate the pathogenesis.

METHODS

After subjecting the rats to chronic restraint stress (CRS) and adenine treatment, a series of tests were conducted, including ethological assessments, evaluations of reproductive characteristics, measurements of biochemical parameters, histopathological examinations, and analyses of urinary metabolites. Additionally, bioinformatics predictions were performed for comprehensive analysis.

RESULTS

Compared to the control, the model exhibited significant manifestations of MI with LD & KD, including reduced responsiveness, diminished frequency of capturing estrous female rats, and absence of mounting behavior. Additionally, the kidney coefficient increased markedly, while the coefficients of the testis and epididymis decreased significantly. Sperm counts and viabilities decreased notably, accompanied by an increase in sperm abnormalities. Dysregulation of reproductive hormone levels in the serum was observed, accompanied by an upregulation of proinflammatory cytokines expressions in the liver and kidney, as well as exacerbated oxidative stress in the penile corpus cavernosum and testis. The seminiferous tubules in the testis exhibited a loose arrangement, loss of germ cells, and infiltration of inflammatory cells. Furthermore, utilizing urinary metabolomics and bioinformatics analysis, 5 key biomarkers and 2 crucial targets most closely linked to MI were revealed.

CONCLUSION

The study successfully established a clinically relevant animal model of MI with LD & KD. It elucidates the pathogenesis of the condition, identifies key biomarkers and targets, and provides a robust scientific foundation for the prediction, diagnosis, and treatment of MI with LD & KD.

Metabolomics profiling of seminal plasma in obesity-induced asthenozoospermia

BACKGROUND

Asthenozoospermia is one of the essential causes of male infertility, and its incidence is significantly higher in obese men. Due to its complex etiology and unknown pathomechanism, the diagnosis and treatment of obesity-induced asthenozoospermia is a prevalent problem in reproductive medicine.

OBJECTIVE

This study aims to explore major differential metabolites and metabolic pathways in seminal plasma and pathological mechanisms for obesity-induced asthenozoospermia.

MATERIALS AND METHODS

We performed non-target metabolomic studies on the seminal plasma of healthy men with normal semen parameters (HN group, n = 20), obese men with normal semen parameters (ON group, n = 20), and men with obesity-induced asthenozoospermia (OA group, n = 20) based on gas chromatography-mass spectrometry. Metabolic profilings and related pathway analyses were conducted to discriminate differential metabolites and metabolic pathways.

RESULTS

A total of 20 differential metabolites including fructose, succinic acid, aconitic acid, methylmaleic acid, glucopyranose, serine, valine, leucine, phenylalanine, glycine, glutamic acid, alanine, proline and threonine were identified in HN group and ON group; 24 differential metabolites including glucose, fructose, pyruvic acid, citric acid, succinic acid, aconitic acid, glucopyranose, glutamic acid, valine, leucine, glycine, phenylalanine, lysine, citrulline, proline and alanine were produced in OA group and ON group; and 28 differential metabolites including glucose, fructose, citric acid, succinic acid, glucopyranose, valine, glycine, serine, leucine, phenylalanine, alanine, threonine, proline, glutamic acid, citrulline, lysine and tyrosine were produced in OA group and HN group. In addition, abnormal energy metabolism including carbohydrate metabolism (TCA cycle, glycolysis/gluconeogenesis, and pyruvate metabolism) and amino acid metabolism (phenylalanine, tyrosine, and tryptophan biosynthesis, D-glutamine and D-glutamate metabolism; phenylalanine metabolism, etc.) were found in ON group and OA group.

CONCLUSION

Obesity could affect the metabolite composition in seminal plasma and abnormal energy metabolism in seminal plasma mainly including carbohydrate metabolism and amino acid metabolism were closely related to obesity-induced asthenozoospermia.

Abd Elhafeez H, S. Rutland C, M. El-Sherry T. The Relationship of Sperm Motility Pattern and Its Ability to Agglutinate with Vaginal Sperm Selection, Uptake in Sperm Storage Tubules and Competitiveness

To ensure survival, some unique features can be distinguished in birds that help them maintain reproduction. These features include the ability to store sperm for long periods within the utero-vaginal junction, a high sperm concentration per ejaculate, and polyspermy fertilization. Sperm face many challenges prior to fertilization. After copulation, most ejaculated sperm exit the female reproductive tract, and less than 1% continue in an attempt to achieve fertilization. In addition, egg size is substantially larger than sperm size because of the presence of the egg yolk. This results in a large number of sperm penetrating the egg away from the oocyte. These challenges have triggered evolutionary changes to maintain the existence of many species, such as the enormous relative size of the testis, which produces billions of sperm each day, and the ability to store viable sperm for long periods in the oviduct to ensure asynchronous fertilization. This chapter discusses several contemporary and sometimes controversial points regarding sperm behavior and their storage in the oviduct.

Fertilizing ability and survivability of rooster sperm diluted with a novel semen extender supplemented with serine for practical use on smallholder farms

Semen extenders are essential for maintaining the quality of sperm during storage and assuring the success of fertility after insemination. The objective of this study was to examine the effect of a new rooster semen extender (hereinafter, NCAB) supplemented with serine on the survivability and fertilizing ability of sperm following storage. NaCl solution, the NCAB extender, and IGGKPh extender were used as treatments. In Experiment 1, different storage temperatures (5°C and 25°C) and durations of storage (0, 12, and 24 h) were used to compare the semen quality and determine the suitable storage temperature. The fertility test was performed in in-station tests and on-farm experimental trials in Experiments 2 and 3, respectively. The results indicated that the interaction effect of duration, treatment, and storage temperature on all sperm parameters was highly significant. The NCAB extender significantly improved rooster semen quality during storage for 24 h at 5°C (P < 0.01). The sperm diluted in saline solution could not survive 24 h of storage at 25°C. The fertility and hatchability rates obtained for sperm diluted with the NCAB extender were higher than those diluted with other extenders. In addition, the fertilizing capacity of the NCAB extender-diluted sperm under field conditions was significantly higher than that of the saline solution-treated sperm. In conclusion, the NCAB extender supplemented with serine and stored at a low temperature (5°C) positively affects sperm quality and fertilization.

New insights into sperm rheotaxis, agglutination and bundle formation in Sharkasi chickens based on an in vitro study

Fertility in birds is dependent on their ability to store adequate populations of viable sperm for extended durations in sperm storage tubules (SSTs). The exact mechanisms by which sperm enter, reside, and egress from the SSTs are still controversial. Sharkasi chicken sperm showed a high tendency to agglutinate, forming motile thread-like bundles comprising many cells. Since it is difficult to observe sperm motility and behavior inside the opaque oviduct, we employed a microfluidic device with a microchannel cross-section resembling close to that of sperm glands allowing for the study of sperm agglutination and motility behavior. This study discusses how sperm bundles are formed, how they move, and what role they may have in extending sperm residency inside the SSTs. We investigated sperm velocity and rheotaxis behavior when a fluid flow was generated inside a microfluidic channel by hydrostatic pressure (flow velocity = 33 µm/s). Spermatozoa tended to swim against the flow (positive rheotaxis) and sperm bundles had significantly lower velocity compared to lonesome sperm. Sperm bundles were observed to swim in a spiral-like motion and to grow in length and thickness as more lonesome sperm are recruited. Sperm bundles were observed approaching and adhering to the sidewalls of the microfluidic channels to avoid being swept with fluid flow velocity > 33 µm/s. Scanning and transmission electron microscopy revealed that sperm bundles were supported by a copious dense substance. The findings show the distinct motility of Sharkasi chicken sperm, as well as sperm's capacity to agglutinate and form motile bundles, which provides a better understanding of long-term sperm storage in the SSTs.

Effect of tempol and straw size on rooster sperm quality and fertility after post-thawing

The aim of the present study was to investigate the effects of tempol and straw size on rooster sperm post-thaw quality and fertility. Rooster semen was cryopreserved in Lake extender containing 0 (control), 5, 10, 15 and 20 μM tempol (in two different straw size, 0.25 and 0.5). The percentage of total and progressive sperm motility, VAP and VSL increased in the 10 µM tempol group. Moreover, 10 µM tempol led to lower ROS compared to other groups. The lowest percentage of apoptotic-like changes was detected when the extender was treated with 10 µM of tempol. The minimum ROS was observed in the group treated with 0.5 straw size. Straw size did not have any significantly effect on GPx and SOD activities and TAC of frozen-thawed sperm. The highest significant percentage of fertility and hatching rate were observed in 10 µM of tempol. The results of the present study showed that supplementation of the Lake cryopreservation medium with 10 µM tempol improved cryo-survival. Also, the results of the present study suggested that Lake cryopreservation medium with 0.5-ml straw may perhaps be an appropriate method to improve the quality and fertility post-thawed rooster sperm.

Sperm Motility Regulation in Male and Female Bird Genital Tracts

Sperm drastically change their flagellar movement in response to the surrounding physical and chemical environment. Testicular sperm are immotile; however, they gain the competence to initiate motility during passage through the male reproductive tract. Once ejaculated, the sperm are activated and promptly initiate motility. Unlike mammals, ejaculated sperm in birds are stored in specialized tubular invaginations referred to as sperm storage tubules (SSTs), located between the vagina and uterus, before fertilization. The resident sperm in the SSTs are in a quiescent state and then re-activated after release from the SSTs. It is thought that avian sperm can undergo motility change from quiescent to active state twice; however, the molecular mechanism underlying sperm motility regulation is poorly understood. In this short review, we summarize the current understanding of sperm motility regulation in male and female bird reproductive tracts. We also describe signal transduction, which regulates sperm motility, mainly derived from in vitro studies.

N-Methyl-d-aspartic Acid (NMDA) Receptor Is Involved in the Inhibitory Effect of Ketamine on Human Sperm Functions

Ketamine, which used to be widely applied in human and animal medicine as a dissociative anesthetic, has become a popular recreational drug because of its hallucinogenic effect. Our previous study preliminarily proved that ketamine could inhibit human sperm function by affecting intracellular calcium concentration ([Ca²⁺]_i). However, the specific signaling pathway of [Ca²⁺]_i induced by ketamine in human sperm is still not clear yet. Here, the N-methyl-d-aspartic acid (NMDA) receptor was detected in the tail region of human sperm. Its physiological ligand, NMDA (50 μM), could reverse ketamine's inhibitory effect on human sperm function, and its antagonist, MK801 (100 μM), could restrain the effect of NMDA. The inhibitory effect caused by 4 mM ketamine or 100 μM MK801 on [Ca²⁺]_i, which is a central factor in the regulation of human sperm function, could also be recovered by 50 μM NMDA. The results suggest that the NMDA receptor is probably involved in the inhibitory effect of ketamine on human sperm functions.

Mobility of Japanese quail spermatozoa and its relationship to egg fertility

Sperm mobility (SM) appears to be primary determinant of fertility in chicken and turkey. The aims of this study were to extend the concept to the Japanese quail by developing an assay to quantify SM, explaining the basis of SM using motility properties measured by CASA, and exploring the relationship between SM and egg fertility. The study was carried out in three stages: i) males (n = 20) and females (n = 20) were mated individually; ii) ejaculates were collected from 20 males, and SM was measured; iii) males (n = 20) and females (n = 20) were mated individually. In Stages I and III, data were collected for egg fertility, Sperm_OPVL and Holes_IPVL . In Stage II, SM assay was developed and assay conditions were defined: effect of sperm numbers on absorbance in Accudenz solution; effect of Accudenz concentration on sperm motility and mobility; effect of quail proctodeal gland foam extract and incubation temperature on SM at 37 and 41°C. The recorded absorbance of sperm movement was dependent on sperm numbers in the sperm suspension overlaying the Accudenz (p < .001). At 41°C, SM, progressively motile sperm, VCL, VSL and VAP were negatively affected by Accudenz concentration (p < .05). The effect of foam on SM and motility depended on an interaction between the concentration of foam extract and incubating temperature. Males were categorized into low, average and high SM phenotypes. These categories differed significantly (p < .001), but sperm motility and SM were not related to egg fertility. In conclusion, SM assay can be used to identify mobility phenotypes, but the poor relationship between SM and egg fertility indicates a need for further studies on interaction between the concentration of foam extract, incubating temperature, and in vivo sperm movement and egg fertilization success.

Effect of Anserine and Carnosine on Sperm Motility in the Japanese Quail

Sperm motility is considered as one of the most important traits for successful fertilization, but the motility of an ejaculated sperm decreases with time when stored as liquid. It is reported that seminal plasma serves as a nutrient rich medium for sperm and plays an important role in sperm motility and its fertilization ability. Several studies have reported that imidazole dipeptides such as anserine and carnosine affect sperm motility and its fertilization ability in mammals. In this study, we report the presence of anserine and carnosine in the male reproductive tract of the Japanese quail. Abundant levels of anserine (44.46 µM) and carnosine (41.75 µM) were detected in the testicular fluid and seminal plasma respectively using the amino acid analyzer; however, seminal plasma solely contained carnosine. When the ejaculates were incubated with anserine or carnosine, we found that both the dipeptides improve sperm motility parameters such as straight line velocity, curvilinear velocity, average path velocity and amplitude of lateral head displacement after in vitro sperm storage at 15°C. These results indicate that imidazole dipeptides are present in the male reproductive tract and may improve sperm quality during in vitro sperm storage in the liquid states.

Type III antifreeze protein (AFP) improves the post-thaw quality and in vivo fertility of rooster spermatozoa

Antifreeze proteins (AFP) have the potential for improving sperm cryopreservation. We have applied Type III antifreeze protein (AFP3) on the cryopreservation of spermatozoa from broiler breeder roosters, aiming to enhance post-thawing quality and fertility. Semen was extended at 37°C in Lake's extender containing AFP3 at 0.01, 0.1, 1, 5, and 10 µg/mL (no AFP3 as control). Post-thawing sperm assessment included sperm motility (CASA), morphology, membrane functionality by hypoosmotic swelling test (HOST), lipoperoxidation as malondialdehyde (MDA) production, and sperm viability, early apoptosis (phosphatidylserine exposure as annexin V-positive staining in viable spermatozoa), and mitochondrial activity by flow cytometry. Fertility was assessed after artificial insemination (30 hens/treatment). Total and progressive motility, membrane functionality, and mitochondrial activity increased in 0.1 and 1 µg/mL AFP, compared to control and other concentrations, whereas apoptosis was significantly lower. VAP, VSL, and viability were significantly higher for 1 µg/mL AFP3 than with the other treatments except for 0.1 µg/mL (which was not always significantly different from the control or other concentrations), and with abnormal forms being significantly lower. The proportion of fertilized and hatched eggs was also higher for 1 µg/mL AFP3, with 0.1 µg/mL also showing significantly higher results than the control, and no differences with other concentrations). In conclusion, 1 µg/mL AFP3 could improve the post-thawing results of rooster spermatozoa frozen in Lake's extender. According to our results, concentrations between 1 and 0.1 µg/mL could be similarly efficient.

Transcriptomic and metabolomic insights into the variety of sperm storage in oviduct of egg layers

In birds, the sperm storage tubules (SST) are dispersed in uterovaginal junction (UVJ) and highly correlated with differential capacity of sperm storage (SS) in and among species with unspecified mechanisms. Here, the SS duration of 252 egg layer breeders was evaluated in 5 rounds with 3 phenotypic traits to screen high- and low-SS individuals, respectively, followed with transcriptome of UVJ tissues and metabolome of serum (high-SS vs. low-SS) to decipher the candidate genes and biochemical markers correlated with differential SS capacity. Histological characterization suggested slightly higher density of SST in UVJ (high-SS vs. low-SS). Transcriptome analyses identified 596 differentially expressed genes (336 upregulated vs. 260 downregulated), which were mainly enriched in gene ontology terms of homeostasis, steroid and lipid metabolism and hormone activity, and 12 significant pathways (P < 0.05) represented by calcium, steroid, and lipid metabolism. Immunohistochemical staining of GNAQ, ST6GAL1, ADFP, and PCNA showed similar distribution in UVJ tissues between 2 groups. Several candidates (HSD11B2, DIO2, AQP3, GNAQ, NANS, ST6GAL1) combined with 4 (11β-prostaglandin F2α, prostaglandin B1, 7α-hydroxytestosterone, and N-acetylneuraminic acid) of 40 differential metabolites enriched in serum metabolome were considered as regulators and biomarkers of SS duration in egg layer breeders. The integrated transcriptome and metabolome analyses of chicken breeder hens will provide novel insights for exploration and improvement of differential SS capacity in birds.

Effect of sperm surface oligosaccharides in sperm passage into sperm storage tubules in Japanese quail (Coturnix japonica)

In birds, the ejaculated spermatozoa do not directly pass to the site of fertilization but rather are stored initially in specialized structures, referred to as sperm storage tubules (SSTs), located in the utero-vaginal junction (UVJ) of the oviduct. The fertilizing capacity of spermatozoa in the SSTs is maintained for an extended period (i.e., several days to months). Although many studies have been conducted to ascertain the mechanisms involved in sperm storage, the understanding of the phenomenon is limited. In this study, there was investigation of the effects of sperm surface oligosaccharides in sperm passage into SSTs in Japanese quail. Results from lectin staining of ejaculated spermatozoa indicated galactose/N-Acetylgalactosamine (Gal/GalNAc), N-Acetylglucosamine (GlcNAc) or mannose/glucose (Man/Glc) moieties were present on the sperm surface, indicating the presence of glycoproteins/glycolipids containing these oligosaccharides. When ejaculated spermatozoa were co-incubated with UVJ explants, the lectins derived from Agaricus bisporus and Canavalia ensiformis had marked inhibitory effects on sperm passage into SSTs. Preincubation of UVJ explants with these lectins, however, had no effect indicating there were no effects of UVJ oligosaccharides in this process. Furthermore, none of these lectin had effects on values of sperm motility variables. These results indicate that O-glycans with terminal β-Gal or GalNAc and N-glycans with terminal α-D-Man or α-D-Glc may have functions in the process of sperm passage into SSTs.

How sperm competition shapes the evolution of testes and sperm: a meta-analysis

Females of many species mate with multiple males, thereby inciting competition among ejaculates from rival males for fertilization. In response to increasing sperm competition, males are predicted to enhance their investment in sperm production. This prediction is so widespread that testes size (correcting for body size) is commonly used as a proxy of sperm competition, even in the absence of any other information about a species' reproductive behaviour. By contrast, a debate about whether sperm competition selects for smaller or larger sperm has persisted for nearly three decades, with empirical studies demonstrating every possible response. Here, we synthesize nearly 40 years of sperm competition research in a meta-analytical framework to determine how the evolution of sperm number (i.e. testes size) and sperm size (i.e. sperm head, midpiece, flagellum and total length) is influenced by varying levels of sperm competition across species. Our findings support the long-held assumption that higher levels of sperm competition are associated with relatively larger testes. We also find clear evidence that sperm competition is associated with increases in all components of sperm length. We discuss these results in the context of different theoretical predictions and general patterns in the breeding biology and selective environment of sperm. This article is part of the theme issue 'Fifty years of sperm competition'.

Functional Aspects of Seminal Plasma in Bird Reproduction

This review provides an updated overview of the seminal plasma composition, and the role of metabolic and protein components on the sperm function of avian species. In addition, the implication of seminal plasma on assisted reproductive techniques of birds was discussed. The semen of birds usually has exceptionally high sperm concentration with relatively little seminal plasma, but this contributes to very fast changes in sperm metabolism and function. The biochemical characteristics and physiological roles of the various seminal plasma components in birds (carbohydrates, lipids, amino acids, hormones, and proteins) are poorly understood. Seminal plasma content of proteins has an action on most cellular functions: metabolism, immunity, oxido-reduction regulation, proteolysis, apoptosis, ion homeostasis, and antimicrobial defenses. The variable amount of many proteins is related to a different fertility capacity of poultry sperm. The role of seminal plasma on semen conservation (chilling and freezing) remains largely a matter of speculation, as both inhibitory and stimulating effects have been found. Whereas the presence of seminal plasma did not seem to affect the sperm survival after freezing-thawing, DNA fragmentation is lower in the absence of seminal plasma. The molecular basis of the influence of seminal plasma on sperm cryo-resistance was also discussed in the present review.

Avian uterine fluid proteome: Exosomes and biological processes potentially involved in sperm survival

Uterine fluid is an aqueous milieu to which sperm are exposed during their storage and ascent. In this study, a bottom-up proteomic strategy and bioinformatic analysis of hen uterine fluid was performed to improve the understanding of this fluid and its potential role in sperm survival mechanisms. The proteomic data were submitted to ProteomeXchange. Among the 913 proteins identified, 160 are known to be secreted and 640 are referenced in exosomes databases. We isolated exosomes from the avian uterine fluid, analyzed them using electron microscopy, and targeted several exosomes markers (ANXA1/2/4/5, VCP, HSP90A, HSPA8, PARK7, and MDH1) using immunoblotting. Electron microscopy and immunohistochemistry were also used to analyze uterovaginal junctions for the exosomal proteins ANXA4, VCP, and PARK7. Exosomes were observed both at the surface epithelium and inside sperm storage tubules. Our data were compared with two previously published studies on proteomic of hen uterine fluid, and with one study describing the proteomic content of rooster seminal plasma and sperm. In conclusion, we demonstrated for the first time that avian uterine fluid contains exosomes. These may play a key role in preserving sperm functions within the female genital tract. Their presence in the sperm storage tubules may represent an important mechanism regarding interaction between the female genital tract and sperm.

Sperm quality and quantity evolve through different selective processes in the Phasianidae

Sperm competition is often considered the primary selective force underlying the rapid and diversifying evolution of ejaculate traits. Yet, several recent studies have drawn attention to other forms of selection with the potential of exceeding the effects of sperm competition. Since ejaculates are complex, multivariate traits, it seems plausible that different ejaculate components vary in their responses to different selective pressures. Such information, however, is generally lacking as individual ejaculate traits tend to be studied in isolation. Here, we studied the macroevolutionary patterns of ejaculate volume, sperm number, sperm length and the proportion of viable normal sperm in response to varying levels of sperm competition, body size and the duration of female sperm storage in pheasants and allies (Phasianidae). Ejaculate volume, sperm number and sperm viability were all relatively higher in polygamous than in monogamous mating systems. However, whereas ejaculate volume additionally covaried with body size, sperm number instead increased with the female sperm-storage duration, in conjunction with a decrease in sperm length. Overall, our results revealed important details on how different forms of selection can jointly shape ejaculates as complex, composite traits.

The effect of zinc oxide on rooster semen cryopreservation

1. Deleterious effects from the freeze-thawing process on post-thawed sperm quality attributes are main limiting factors in cryopreservation. The current study was conducted to determine the effect of semen extender containing zinc oxide (ZnO) on post-thaw rooster sperm quality indices.2. Semen samples from six, 60-week-old broiler breeder roosters were collected weekly during five successive weeks. The samples were mixed and divided into three equal parts and diluted with semen extender containing different levels of ZnO; 0 (ZnO-0), 1 (ZnO-1) or 2 (ZnO-2) µg/ml. After thawing, motility and velocity parameters, plasma membrane functionality, apoptotic like changes, mitochondrial membrane potential (MMP), and DNA fragmentation index (DFI) were evaluated.3. Results showed that the addition of ZnO in the extender quadratically affected (P < 0.01) total motility (TM), progressive motility (PM), and average path velocity (VAP) with the highest values were noted in the ZnO-1 group. Levels of ZnO quadratically affected percentages of live (P < 0.01), apoptotic (P < 0.03) and dead (P < 0.10) spermatozoa, where the highest percentage of live, and the lowest percentage of apoptotic or dead spermatozoa was for the ZnO-1 group. Although adding ZnO quadratically affected plasma membrane functionality and MMP (P < 0.01), it did not affect (P > 0.05) DFI.4. In conclusion, there were some beneficial effects of ZnO supplementation in semen extender on post-thawed rooster sperm quality which may result in a better freezability.

Sperm Gatekeeping: 3D Imaging Reveals a Constricted Entrance to Zebra Finch Sperm Storage Tubules

Females across many internally fertilizing taxa store sperm, often in specialized storage organs in their reproductive tracts. In birds, several hundred sperm storage tubules exist in the utero-vaginal junction of the oviduct, and there is growing evidence that sperm storage in these tubules is selective. The mechanisms underlying female sperm storage in birds remain unknown because of our limited ability to make three-dimensional, live observations inside the large, muscular avian oviduct. Here, we describe a new application of fluorescence selective plane illumination microscopy to optically section oviduct tissue from zebra finch Taeniopygia guttata females label free by harnessing tissue autofluorescence. Our data provide the first description of the three-dimensional structure of sperm storage organs in any vertebrate to the best of our knowledge and reveal the presence of gate-like constricted openings that may play a role in sperm selection.

NMDA-type glutamate receptors mediate the acrosome reaction and motility initiation in newt sperm

The N-methyl d-aspartate type glutamate receptor (NMDAR) is a ligand-gated cation channel that causes Ca²⁺ influx in nerve cells. An NMDAR agonist is effective to the sperm motility in fowls, although the actual role of NMDAR in sperm function is unknown. In the present study, RNA-seq of the spermatogenic testes suggested the presence of NMDAR in the sperm of the newt Cynops pyrrhogaster. Glutamate of at least 0.7 ± 0.5 mM was detected in the egg-jelly substances along with acrosome reaction-inducing substance (ARIS) and sperm motility-initiating substance (SMIS). In the egg-jelly extract (JE) that included the ARIS and SMIS, the acrosome reaction was inhibited by a NMDAR antagonists, memantine and MK801. MK801 also inhibited the spontaneous acrosome reaction in Steinberg's salt solution (ST). Furthermore, memantine and MK801 suppressed the progressive motility of the sperm in JE and spontaneous waving of the undulating membrane, which is the tail structure giving thrust for forward motility, in ST. The spontaneous waving of the undulating membrane was promoted when Mg²⁺ , which blocks Ca²⁺ influx through gated NMDARs, was removed from the ST. In addition, the ARIS-induced acrosome reaction was inhibited by a selective antagonist of the transient receptor potential vanilloid 4, whose activation might result in the membrane depolarization to release Mg²⁺ from the NMDAR. These results suggest that NMDAR acts together with other cation channels in the induction of the acrosome reaction and motility of the sperm during the fertilization process of C. pyrrhogaster.

Seminal plasma amino acid profile in different breeds of chicken: Role of seminal plasma on sperm cryoresistance

Seminal plasma is a key biological fluid that modulates sperm function in the reproduction process. However, its role in sperm biotechnologies is scarce in poultry. The aims of the present study were to study the amino acids profile and total proteins of seminal plasma in 12 Spanish chicken breeds and to investigate the role of seminal plasma on cryoresistance of rooster sperm. To investigate the role of seminal plasma on cryoresistance, diluted pooled semen samples were cryopreserved in the presence and absence of seminal plasma. Glutamic acid was the most abundant free amino acid in seminal plasma, followed by alanine, serine, valine, and glycine. There was an influence of breed (P<0.05) on the percentage of viable sperm after freezing-thawing of samples with seminal plasma. Cluster analysis revealed that White Prat, Black Castellana, Blue Andaluza, Quail Castellana, and Red-Barred Vasca returned the best freezing-thawing response (good freezers). There was a positive correlation between seminal plasma concentrations of valine, isoleucine lysine, leucine and post thaw viability. The evaluation of fertilization capacity of frozen-thawed semen from the breeds White Prat ('good freezer') and Black-Red Andaluza ('bad freezer') showed that good freezer had higher fertility (20/68, 29.4%) compared to bad freezer breed (14/76, 18.4%), even if the difference was not significant (P = 0.08). The TUNEL assay revealed that freezing/thawing procedures in presence of seminal plasma provoked higher DNA fragmentation in most of the breeds, with a positive correlation between seminal alanine, valine, isoleucine, methionine, leucine, tyrosine, phenylalanine concentrations and DNA integrity. DNA fragmentation was lower in absence of seminal plasma and the breed effect on sperm viability was highly reduced. It is concluded that specific seminal plasma amino acids were associated with post-thaw percentage of viable sperm and DNA integrity. The removal of seminal plasma decreases the variability of the results and DNA fragmentation damages.

Expression of gonadotropin and sex steroid hormone receptor mRNA in the utero-vaginal junction containing sperm storage tubules of oviduct during sexual maturation in Japanese quail

Sex steroid hormones play an important role in reproductive tissue development of avian species. However, their role in Japanese quail is yet to be established. To understand the physiological role of hormones involved in the development of sperm storage tubules (SSTs) in quail, we investigated expression profiles of gonadotropin (LH-R and FSH-R) and sex steroid hormone (PR-R, ER-α and ER-β) receptors in the uterovaginal junction (UVJ) containing SSTs before and during sexual maturation i.e. four to eight weeks. Every week four birds were sacrificed to collect blood and UVJ for sex steroid hormone (progesterone and estrogen) estimation and gene expression profiling of sex steroid hormone (PR-R, ER-α and ER-β) and gonadotropin receptors (LH-R and FSH-R) using qRT-PCR. Receptor expression results showed that the expression of sex steroid receptor (PR-R, ER-α and ER-β) genes were upregulated significantly (P < .05) in SSTs with the advancement of age. The expression of gonadotropin receptors (LH-R and FSH-R) was only high at week 5 and 6 respectively. Serum hormone analysis indicated a significant (P < .05) rise in estradiol till 7th week and progesterone from 7th week onwards. These results suggest that the gonadotropin and sex steroid hormone receptors may have the role in the development and maintenance of UVJ that contains predominantly SSTs during sexual maturation.

Sperm morphology, sperm motility and paternity success in the bluethroat (Luscinia svecica)

Postcopulatory sexual selection may select for male primary sexual characteristics like sperm morphology and sperm motility, through sperm competition or cryptic female choice. However, how such characteristics influence male fertilization success remains poorly understood. In this study, we investigate possible correlations between sperm characteristics and paternity success in the socially monogamous bluethroat (Luscinia svecica svecica), predicting that sperm length and sperm swimming speed is positively correlated with paternity success. In total, 25% (15/61) of broods contained extra-pair offspring and 10% (33/315) of the offspring were sired by extra-pair males. Paternity success did not correlate significantly with sperm morphology or any aspects of sperm motility. Furthermore, sperm morphology and sperm motility did not correlate significantly with male morphological characters that previously have been shown to be associated with paternity success. Thus, the sperm characteristics investigated here do not appear to be strong predictors of paternity success in bluethroats.

Differential sperm storage by female zebra finches Taeniopygia guttata

When females mate promiscuously, female sperm storage provides scope to bias the fertilization success towards particular males via the non-random acceptance and utilization of sperm. The difficulties observing post-copulatory processes within the female reproductive tract mean that the mechanisms underlying cryptic female choice remain poorly understood. Here, we use zebra finches Taeniopygia guttata, selected for divergent sperm lengths, combined with a novel technique for isolating and extracting sperm from avian sperm storage tubules (SSTs), to test the hypothesis that sperm from separate ejaculates are stored differentially by female birds. We show that sperm from different inseminations enter different SSTs in the female reproductive tract, resulting in almost complete segregation of the sperm of competing males. We propose that non-random acceptance of sperm into SSTs, reflected in this case by sperm phenotype, provides a mechanism by which long sperm enjoy enhanced fertilization success in zebra finches.

Sperm morphology, adenosine triphosphate (ATP) concentration and swimming velocity: unexpected relationships in a passerine bird

The relationship between sperm energetics and sperm function is poorly known, but is central to our understanding of the evolution of sperm traits. The aim of this study was to examine how sperm morphology and ATP content affect sperm swimming velocity in the zebra finch Taeniopygia guttata. We exploited the high inter-male variation in this species and created extra experimental power by increasing the number of individuals with very long or short sperm through artificial selection. We found a pronounced quadratic relationship between total sperm length and swimming velocity, with velocity increasing with length up to a point, but declining in the very longest sperm. We also found an unexpected negative association between midpiece length and ATP content: sperm with a short midpiece generally contained the highest concentration of ATP. Low intracellular ATP is therefore unlikely to explain reduced swimming velocity among the very longest sperm (which tend to have a shorter midpiece).

Letrozole, an aromatase inhibitor, reduces post-peak age-related regression of rooster reproductive performance

This study was designed to evaluate orally administrated Letrozole (Lz) on reproductive performance, plasma testosterone and estradiol concentrations and relative abundance of mRNA of GnRH, FSH and LH in roosters. Ross 308 roosters (n=32) that were 40-weeks of age were individually housed and received a basal standard diet supplemented different amounts of capsulated Lz [0 (Lz-0), 0.5 (Lz-0.5), 1 (Lz-1) or 1.5 (Lz-1.5), mg Lz/bird/day] for 12 weeks. Sperm quality variables and plasma testosterone and estradiol concentrations were assessed from the first to the tenth week of the treatment period. Semen samples from the 11th to 12th week were used for artificial insemination and eggs were collected and allotted to assess fertility and hatchability rates. Relative abundance of hypothalamic and pituitary GnRH, LH and FSH mRNA was evaluated at the end of 12th week. The results indicated that total and forward sperm motility as well as egg hatchability rate were greater in the Lz-0.5 group. Greater sperm concentrations, ejaculate volume, sperm plasma membrane integrity, testis index and fertility rates were recorded for both Lz-0.5 and Lz-1 groups compared with the Lz-0 group (P<0.05). Body weight, percentage of sperm abnormalities, and sperm plasma membrane functionality were not affected by treatment. Testosterone and estradiol concentrations were negatively related with greater testosterone concentrations in the Lz-1.5 group which had lesser estradiol concentrations. Relative mRNA transcript abundance for GnRH, LH and FSH was Lz dose responsive being greater in the treated groups; however, this trend plateaued for GnRH and for the relative abundance of both LH and FSH mRNA was less in the Lz-1.5 group than the other treatment groups. It is concluded that Lz may be an effective treatment to improve age related post-peak reproductive performance of roosters.

Deduction of a calcium ion circuit affecting rooster sperm in vitro

Four premises for rooster sperm preservation were outlined previously. Understanding mitochondrial Ca cycling in terms of whole-cell Ca flux was one premise. The present work tested the hypothesis that sperm mitochondria can be damaged by intracellular as well as extracellular Ca. Sperm were washed by centrifugation through 12% (wt/vol) Sperm were washed by centrifugation through 12%(at/vol) Accudenz to procure sperm at a physiological concentration within a chemically-defined suspension. Five solutions were tested. Each solution contained 30 m glucose, and had an osmolality of 320 mmol/kg and a pH of 7.4. Washed sperm were diluted to 2.0 × 10 sperm/mL. Each replicate sperm suspension was cooled to 10°C. Sperm mobility was measured after 1, 2, 4, 8, 12, and 24 h. Data were plotted as a function of time in each experiment. Function type was confirmed by lack of fit analysis. A parabola with a maximum at 3.7 h was observed when sperm were suspended in 205 m taurine buffered with 50 m-tris[hydroxyl-methyl]methyl-2-amino-ethanesulfonic acid (TES). This effect was attributed to a Ca flux from the nuclear envelope into mitochondria. An exponential decay was observed when TES-buffered taurine contained 2 m Ca. This effect was attributed to mitochondrial Ca overload induced by uptake of extracellular Ca. Exponential decay also was observed when TES-buffered taurine contained a Ca chelator. This effect was attributed to a Ca flux from the nuclear envelope through mitochondria and then into an extracellular Ca sink. This possibility was supported by the response of sperm to thapsigargin. Specifically, inhibition of sarcoendoplasmic reticulum Ca-ATPase compromised sperm mobility relative to a buffer control. Finally, a 60 m phosphate buffer containing 2 m citrate yielded a linear relationship in contrast to the TES-buffered solutions tested. Sperm mobility after 24 h of storage in the phosphate buffer was 92% of that observed for prewashed sperm. The linear response was attributed to weak chelators providing resistance within a Ca circuit and thereby preventing mitochondrial Ca overload. Fertility, however, was compromised when hens were inseminated with mobile sperm recovered after either 8 or 24 h of storage at 10°C. In conclusion, sperm cell Ca homeostasis was proven to be critical for maintaining sperm mobility in vitro, but mitochondrial Ca uptake is not the sole phenomenon that compromises sperm function during in vitro storage.

Directional postcopulatory sexual selection is associated with female sperm storage in Trinidadian guppies

Female sperm storage (FSS) is taxonomically widespread and often associated with intense sperm competition, yet its consequences on postcopulatory sexual selection (PCSS) are poorly known. Theory predicts that FSS will reduce the strength of PCSS, because sperm characteristics favored before and after FSS may be traded-off, and opportunities for nondirectional PCSS should increase. We explored these questions in the guppy (Poecilia reticulata), by allowing females to mate multiply and by comparing the paternity pattern in two successive broods. Contrary to predictions, the variance in male fertilization success increased after FSS, driven by a change in male paternity share across broods. This change was positively associated with sperm velocity (measured before FSS) but not with the duration of FSS, indirectly suggesting that faster sperm were better in entering female storage organs, rather than in persisting within them. Other male traits, such as male size and orange color, heterozygosity, and relatedness to the female, did not influence paternity after FSS. These results indicate that processes associated with FSS tend to reinforce the strength of PCSS in guppies, rather than weaken it. Further work is necessary to test whether this pattern changes in case of more prolonged FSS.

Lactic acid is a sperm motility inactivation factor in the sperm storage tubules

Although successful fertilization depends on timely encounters between sperm and egg, the decoupling of mating and fertilization often confers reproductive advantages to internally fertilizing animals. In several vertebrate groups, postcopulatory sperm viability is prolonged by storage in specialized organs within the female reproductive tract. In birds, ejaculated sperm can be stored in a quiescent state within oviductal sperm storage tubules (SSTs), thereby retaining fertilizability for up to 15 weeks at body temperature (41 °C); however, the mechanism by which motile sperm become quiescent within SSTs is unknown. Here, we show that low oxygen and high lactic acid concentrations are established in quail SSTs. Flagellar quiescence was induced by lactic acid in the concentration range found in SSTs through flagellar dynein ATPase inactivation following cytoplasmic acidification (<pH 6.0). The long-term preservation of sperm morphology under hypoxic and high temperature conditions indicates that a combination of these factors enables sperm cells to survive during the ovulation cycles. Our findings suggested a novel physiological role for lactic acid in promoting sperm quiescence in SSTs and opened up a new opportunity for technological improvement in prolonging sperm longevity at ambient or body temperature.

Sperm Storage in the Female Reproductive Tract

The capacity for sperm storage within the female reproductive tract occurs widely across all groups of vertebrate species and is exceptionally well developed in some reptiles (maximum duration seven years) and fishes (maximum duration >1 year). Although there are many reports on both the occurrence of female sperm storage in diverse species and its adaptive benefits, few studies have been directed toward explaining the mechanisms involved. In this article we review recent findings in birds and mammals in an effort to develop hypotheses that could be translated into research applications in animal breeding technologies. There are pockets of evidence to suggest that the local epithelial cells, sometimes arranged as sperm storage tubules, can respond to spermatozoa by producing heat shock proteins as well as providing an environment rich in antioxidants. Moreover, the local immune system seems to tolerate the arrival of spermatozoa, while retaining the ability to combat the arrival of infectious microorganisms.

Long sperm fertilize more eggs in a bird

Sperm competition, in which the ejaculates of multiple males compete to fertilize a female's ova, results in strong selection on sperm traits. Although sperm size and swimming velocity are known to independently affect fertilization success in certain species, exploring the relationship between sperm length, swimming velocity and fertilization success still remains a challenge. Here, we use the zebra finch (Taeniopygia guttata), where sperm size influences sperm swimming velocity, to determine the effect of sperm total length on fertilization success. Sperm competition experiments, in which pairs of males whose sperm differed only in length and swimming speed, revealed that males producing long sperm were more successful in terms of (i) the number of sperm reaching the ova and (ii) fertilizing those ova. Our results reveal that although sperm length is the main factor determining the outcome of sperm competition, complex interactions between male and female reproductive traits may also be important. The mechanisms underlying these interactions are poorly understood, but we suggest that differences in sperm storage and utilization by females may contribute to the outcome of sperm competition.

Performance of Rodent Spermatozoa Over Time Is Enhanced by Increased ATP Concentrations: The Role of Sperm Competition

Sperm viability, acrosome integrity, motility, and swimming velocity are determinants of male fertility and exhibit an extreme degree of variation among closely related species. Many of these sperm parameters are associated with sperm ATP content, which has led to predictions of trade-offs between ATP content and sperm motility and velocity. Selective pressures imposed by sperm competition have been proposed as evolutionary causes of this pattern of diversity in sperm traits. Here, we examine variation in sperm viability, acrosome integrity, motility, swimming velocity, and ATP content over time, among 18 species of closely related muroid rodents, to address the following questions: (a) Do sperm from closely related species vary in ATP content after a period of incubation? (b) Are these differences in ATP levels related to differences in other sperm traits? (c) Are differences in ATP content and sperm performance over time explained by the levels of sperm competition in these species? Our results revealed a high degree of interspecific variability in changes in sperm ATP content, acrosome integrity, sperm motility and swimming velocity over time. Additionally, species with high sperm competition levels were able to maintain higher levels of sperm motility and faster sperm swimming velocity when they were incubated under conditions that support sperm survival. Furthermore, we show that the maintenance of such levels of sperm performance is correlated with the ability of sperm to sustain high concentrations of intracellular ATP over time. Thus, sperm competition may have an important role maximizing sperm metabolism and performance and, ultimately, the fertilizing capacity of spermatozoa.

Evaluation of a semen extender from a bioenergetic perspective

Four premises for sperm preservation were previously outlined. The present work tested 2 of these. The first premise was that sperm mobility phenotype affects procedural efficacy. Random bred roosters were phenotyped with the sperm mobility assay. A normal frequency distribution was observed with 35% (SD = 16.4) mobile sperm. Test subjects had values >51% (high) or between 19 and 35% (below average). Phenotypes were confirmed by repeated measure analysis. Ejaculates were pooled by phenotype. Sperm were washed by centrifugation through 12% (wt/vol) Accudenz. Washed sperm were suspended in Beltsville Poultry Semen Extender (BPSE) at 2 × 10 sperm/mL. Such sperm were stored at 10°C for 24 h. In the case of highly mobile sperm, an exponential decay was observed with a -intercept of 72% and an asymptote of 53%. In contrast, postwash values for below-average males decreased linearly from a -intercept of 31 to 17% after 24 h. A logistic decay was observed when sperm from high phenotype subpopulation males were extended with BPSE rather than washed before storage. Whereas -intercepts were equivalent between experiments, end points were not, that is, 53 vs. 17% mobile sperm. This difference was attributed to the extent of cytotoxic edema. The second premise tested was that the sperm mobility assay can predict the status of sperm cell mitochondria in response to sperm manipulation. Highly mobile sperm were washed and then suspended in either saline or glucose-free extender. Solution pH and osmolality were equivalent. Extender osmolality was controlled by replacing glucose with mannitol. Sperm were stressed by incubation at 2 × 10/mL at 20°C for 8 h. In each case, loss of sperm mobility approximated a logistic function. Whereas -intercepts were equivalent, the time at which loss of function was half maximal was prolonged with the extender ( < 0.01). This difference was attributed to a diminution of the process whereby energy-deprived sperm were rendered immobile by cellular edema. An a posteriori analysis was limited to pretreatment data from males categorized a priori with the high phenotype. Phenotype was independent of time ( = 0.81) during the 14-wk interval in which experiments were performed. In summary, extender efficacy was affected by sperm mobility phenotype as well as the means by which the extender was used. To date, such effects have not been addressed in attempts to preserve chicken sperm in vitro.

Apical blebs on sperm storage tubule epithelial cell microvilli: their release and interaction with resident sperm in the turkey hen oviduct

Located at the anterior end of the turkey hen's vagina are numerous discrete tubular invaginations of the surface epithelium, collectively referred to as the sperm storage tubules (SSTs). After mating or artificial insemination, sperm ascend the vagina, enter the SSTs, and over the ensuing days and weeks, gradually exit the SSTs and are transported to the anterior end of the oviduct to fertilize a daily succession of ova. Little is known regarding the cellular and molecular mechanisms responsible for sperm subsistence in the lumen of the SST. In this study, the origin of microvillus blebs (MvBs) on the apical tips of SST epithelial cells was examined, and their possible role in sperm survival was discussed. Regardless, if sperm are present or not, transmission electron microscopy revealed two types of microvilli differentiated by the presence or absence of pleomorphic unilaminar MvBs localized to their apical tips. Although some MvBs appeared to be discharging their contents into the SST lumen, others appeared to have pinched off the microvillus stem. When SSTs contained clusters of densely packed sperm, the sperm heads of those sperm adjacent to the SST epithelial cell surface were surrounded by the microvilli. Associated with the plasmalemma of sperm throughout the SST lumina were membrane fragments and small vesicles (30-130 nm in diameter), some of which appeared to have fused with sperm. It is concluded that the MvBs are a form of shedding vesicle released from the SST epithelial cell microvilli by apocrine secretion. On the basis of observations described herein and those of other authors, it is suggested that the MvBs contribute to sustained sperm storage in the SSTs by (1) supplying metabolic substrates used by resident sperm, (2) serving as fusogenic vehicles providing exogenous macromolecules that reversibly suppress sperm functions associated with fertilization (decapacitation?) and stabilize the sperm plasmalemma, and (3) acting as transport vesicles actively transporting fluid from the SST epithelial cells to the SST lumen.