Regulation of sperm motility in Eastern oyster (Crassostrea virginica) spawning naturally in seawater with low salinity

Serotonin-Induced Sperm Hyper-Motility In Pacific Oyster (Crassostrea Gigas) Associates With K+ Efflux and Membrane Hyperpolarization

Serotonin (5-HT) induces sperm hyper-motility in bivalves. This process has been suggested to be associated with K+ efflux due to higher concentrations of K+ ions in testicular fluid compared to that of seawater. This hypothesis was supported by inhibition of 5-HT-induced sperm hyper-motility in artificial seawater (ASW) containing high extracellular K+ ions or in the presence of a voltage-dependent K+ channel blocker (4-AP). Here, we studied changes of sperm membrane potential to elucidate 5-HT-induced sperm hyper-motility signaling in Pacific oyster (Crassostrea gigas). Sperm motility was partially initiated (48.34 ± 7.80%) in ASW, and decreased at 5 min post-activation (p < 0.05). In the presence of 10-5 M 5-HT, sperm motility was recorded 81.63 ± 3.55%, which remained unchanged within 60 min post-activation. After sperm activation in ASW with or without 5-HT, fluorescence intensity of membrane potential-sensitive fluorescent (DiSC3(5)) was decreased to lower than that of the resting stage, indicating membrane hyperpolarization. Induction of membrane hyperpolarization, using valinomycin or in K+-free ASW (KF-ASW) could not trigger sperm hyper-motility, suggesting that hyperpolarization itself did not induce sperm hyper-motility. Next, we showed that membrane hyperpolarization was due to K+ efflux. The fluorescence intensity of DiSC3(5) was increased in ASW or KF-ASW containing 4-AP, suggesting membrane depolarization due to inhibition of K+ efflux. The valinomycin-induced membrane hyperpolarization was changed to depolarization by subsequent additions of KCl, suggesting that changes in the electrochemical gradient of K+ ions resulted in the retention of intracellular K+ ions. Observed membrane depolarization in the presence of 4-AP or high K+ ions was associated with inhibition of 5-HT-induced sperm hyper-motility. Taken together, this study shows that 5-HT-induced sperm hyper-motility was associated with membrane hyperpolarization due to K+ efflux.

Suspended sediment and reduced salinity decrease development success of early stages of Acropora tumida and Platygyra carnosa in a turbid coral habitat, Hong Kong

Suspended sediment and salinity stresses may escalate under climate change in inshore turbid habitats. We test whether fertilization and embryonic development of Acropora tumida and Platygyra carnosa are less prone to both stressors in turbid coral habitats compared to thresholds reported in literature for species found in clear water reefs. Under optimal sperm concentration (106 sperm mL-1), fertilization of A. tumida declined by 50 % when exposed to combined sediment (92 mg L-1) and salinity stresses. However, these stressors had no significant impact on P. carnosa. We found ∼20- and ∼ 7-fold increases in abnormal embryos for A. tumida and P. carnosa, respectively, under combined stressors. Furthermore, silicon-rich terrestrial-originated sediment caused 50 % larval mortality for A. tumida at a lower concentration of 53 mg L-1. We showed that climate change-related salinity and sediment stresses may hinder coral reproduction and challenge coral recovery, questioning the coral survival in nearshore turbid habitats.

Effects of Ammonia Concentration on Sperm Vitality, Motility Rates, and Morphology in Three Marine Bivalve Species: A Comparative Study of the Noble Scallop Mimachlamys nobilis, Chinese Pearl Oyster Pinctada fucata martensii, and Small Rock Oyster Saccostrea mordax

Ammonium (NH4+) plays a crucial role in the reproductive processes of key biotic groups in aquatic ecosystems-bivalves. This study aims to elucidate the effects of three different ammonium ion concentrations on sperm vitality, swimming kinematics, and morphology of Mimachlamys nobilis, Pinctada fucata martensii, and Saccostrea mordax. The results indicate that the sperm vitality and motility rates of M.nobilis and S. mordax are inversely proportional to the ammonium concentration, especially in the treatment group with an ammonium concentration of 3 mmol/L, where the decrease in sperm vitality and motility is most significant. In contrast, the sperm of P. fucata martensii reacted differently to increasing ammonium concentrations. After the addition of 2 mmol/L of ammonium, the sperm vitality and motility of P. fucata martensii reached a peak, showing a significant stimulatory effect. Additionally, as the ammonium concentration increased, the curling of the sperm flagella in M.nobilis and S. mordax increased. However, sperm flagella curling in P. fucata martensii showed no change compared to the control group. This study provides insights into the effects of ammonium concentrations on the sperm vitality and motility of three marine bivalve species and highlights the importance of sperm flagella curling as a factor affecting sperm.

Unravelling the ecotoxicological impacts of gadolinium (Gd) on Mytilus galloprovincialis embryos and sperm in seawater: A preliminary study

As the demand for rare earth elements (REEs) continues to surge in diverse industrial and medical domains, the ecological consequences of their ubiquitous presence have garnered heightened attention. Among the REEs, gadolinium (Gd), commonly used in medical imaging contrast agents, has emerged as a pivotal concern due to its inadvertent introduction into marine ecosystems via wastewater release. This study delves into the complex ecotoxicological implications of Gd contamination, focusing on its impact on the embryonic development and sperm functionality of Mytilus galloprovincialis. The findings from this study underscore the potential hazards posed by this rare element, offering a critical perspective on the ecological risks associated with Gd. Notably, this exploratory work reveals that Gd exerts a significant embryotoxic effect at elevated concentrations, with an observed half maximal effective concentration (EC50) value of 0.026 mg/L. Additionally, Gd exposure leads to a considerable reduction in sperm motility and alters sperm morfo-kinetic parameters, especially at a concentration of 5.6 mg/L. The results highlight a dose-dependent relationship between Gd exposure and the prevalence of specific malformation types in Mytilus embryos, further providing crucial insights into the potential risks imposed by this rare earth element.

Angiotensin-(1-7) plays an important role in regulating spermatogenesis in Trachemys scripta elegans under salinity stress

Elevation in water salinity can threaten the spermatogenesis and fertility of freshwater animals. The role of the renin-angiotensin system (RAS) in regulating spermatogenesis has attracted considerable attention. Our previous study found that red-eared sliders (Trachemys scripta elegans), could survive in 10 PSU water for over 1 year. To understand the chronic impact of salinity on testicular spermatogenesis and underlying mechanisms, male T. s. elegans were subjected to treatment with water of 5 PSU and 10 PSU for a year, and spermatogenesis and regulation of the RAS signal pathway was assessed. Results showed induced inflammation in the testes of T. s. elegans in the 10 PSU group, as evidenced by a decrease in the number of testicular germ cells from 1586 to 943. Compared with the control group, the levels of proinflammatory genes, including TNF-α, IL-12A and IL-6 were elevated 3.1, 0.3, and 1.4 times, respectively, in animals exposed to 10 PSU water. Testicular antiapoptotic processes of T. s. elegans might involve the vasoactive peptide angiotensin-(1-7) in the RAS, as its level was significantly increased from 220.2 ng ml-1 in controls to 419.2 ng ml-1 in the 10 PSU group. As expected, specific inhibitor (A-779) for the Ang-(1-7) acceptor effectively prevented the salinity-induced upregulation of genes encoding anti-inflammatory and antiapoptotic factors (TGF-β1, Bcl-6) in the testis of the 10 PSU animals, whereas it promoted the upregulation of proinflammatory and proapoptotic factors (TNF-α, IL-12A, IL-6, Bax and caspase-3). Our data indicated that Ang-(1-7) attenuates the effect of salinity on inflammation and apoptosis of the testis in T. s. elegans. A new perspective to prevent salinity-induced testis dysfunction is provided.

Polystyrene Nanoplastics in Aquatic Microenvironments Affect Sperm Metabolism and Fertilization of Mytilus galloprovincialis (Lamark, 1819)

The continuous and unregulated discharge of wastes and pollutants into the aquatic environment has required constant monitoring of the risks incurred by aquatic ecosystems. Alarmism arises from plastic pollution as larger artifacts release nanoscale fragments that can contact free-living stages such as gametes, embryos, and larvae. Specifically, the interaction between spermatozoa, released in water in externally fertilizing species, and the surrounding microenvironment is essential for successful fertilization. Activation and kinematics of movement, proper maintenance of ionic balance, and chemotactism are processes highly sensitive to even minimal perturbations caused by pollutants such as polystyrene nanoplastics. Spermatozoa of Mytilus galloprovincialis (M. galloprovincialis), an excellent ecotoxicological model, undergo structural (plasma membrane ruptures, DNA damage) and metabolic (reduced motility, fertilizing capacity) damage upon exposure to 50 nm amino-modified polystyrene nanoplastics (nPS-NH2). Nanoplastics of larger diameter (100 nm) did not affect sperm parameters. The findings highlighted the negative impact that plastic pollution, related to nanoparticle diameter and concentration, could have on sperm quality and reproductive potential of organisms, altering the equilibrium of aquatic ecosystems.

Deleterious effect of gestagens from wastewater effluent on fish reproduction in aquatic environment: A review

Gestagens are common pollutants accumulated in the aquatic ecosystem. Gestagens are comprised of natural gestagens (i.e. progesterone) and synthetic gestagens (i.e. progestins). The major contributors of gestagens in the environment are paper plant mill effluent, wastewater treatment plants, discharge from pharmaceutical manufacturing, and livestock farming. Gestagens present in the aquatic environment interact with progesterone receptors and other steroid hormone receptors, negatively influencing fish reproduction, development, and behavior. In fish, the gonadotropin induces 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) production, an important steroid hormone involved in gametogenesis. DHP interacts with the membrane progestin receptor (mPR), which regulates sperm motility and oocyte maturation. Gestagens also interfere with the hypothalamic-pituitary-gonadal (HPG) axis, which results in altered hormone levels in fish. Moreover, recent studies showed that even at low concentrations exposure to gestagens can have detrimental effects on fish reproduction, including reduced egg production, masculinization, feminization in males, and altered sex ratio, raising concerns about their impact on the fish population. This review highlights the hormonal regulation of sperm motility, oocyte maturation, the concentration of environmental gestagens in the aquatic environment, and their detrimental effects on fish reproduction. However, the long-term and combined impacts of multiple gestagens, including their interactions with other pollutants on fish populations and ecosystems are not well understood. The lack of standardized regulations and monitoring protocols for gestagens pollution in wastewater effluent hampers effective control and management. Nonetheless, advancements in analytical techniques and biomonitoring methods provide potential solutions by enabling better detection and quantification of gestagens in aquatic ecosystems.

Silver nanoparticles and silver ions indistinguishably decrease sperm motility in Pacific oysters (Magallana gigas) after short-term direct exposure

The present study aimed to evaluate the reprotoxicity of environmental (0.25μg.L^-1) and supra-environmental (25μg.L^-1 and 250μg.L^-1) levels of silver nanoparticles (Ag NP) on the Pacific oyster (Magallana gigas), by determining sperm quality. For that, we evaluated sperm motility, mitochondrial function and oxidative stress. To determine whether the Ag toxicity was related to the NP or its dissociation into Ag ions (Ag⁺), we tested the same concentrations of Ag⁺. We observed no dose-dependent responses for Ag NP and Ag⁺, and both impaired sperm motility indistinctly without affecting mitochondrial function or inducing membrane damage. We hypothesize that the toxicity of Ag NP is mainly due to adhesion to the sperm membrane. Blockade of membrane ion channels may also be a mechanism by which Ag NP and Ag⁺ induce toxicity. The presence of Ag in the marine ecosystem is of environmental concern as it may affect reproduction in oysters.

The influence of salinity on the toxicity of chemical UV-filters to sperms of the free-spawning mussel Mytilus galloprovincialis (Lamark, 1819)

Marine-coastal systems have been increasingly exposed to multiple stressors, including anthropogenic pollution and variations of Climate Change (CC) related factors, whose coexistence could create associated environmental and ecotoxicological risks. Among emergent stressors, 4-methylbenzylidenecamphor (4-MBC) and benzophenone-3 (BP-3) UV-filters are compounds widely used in increasing consumer products, resulting in their ubiquity in aquatic environments and possible pressing challenges on gamete susceptibility. Since most marine invertebrates reproduce by external fertilization, after spawning, gametes may be exposed to several pressures, affecting reproductive success and outcome. The present study focuses on the spermiotoxicity of the environmentally relevant UV-filters 4-MBC and BP-3 combined with salinity shifts, as potential modulators of their harmful effects. For this, Mytilus galloprovincialis male gametes were exposed in vitro to environmentally relevant and slightly higher concentrations (1, 10 and 100 µg/L) of 4-MBC or BP-3 under three different salinities (S 20, 30 and 40). Sperm quality endpoints associated with oxidative status, viability, motility, kinetics, and genotoxicity were evaluated. Similarities and differences in sperm responses among all conditions were highlighted by principal coordinates analysis (PCO). Results showed that salinity acting alone posed greater sperms impairments at the lowest (20) and highest (40) tested levels. When salinity acts as a co-varying stressor, salinity-dominant interactive effects resulted evident, especially for 4-MBC at S 40 and BP-3 at S 20. These findings were pointed out as the worst exposure conditions for M. galloprovincialis sperms, since caused major toxicological effects in terms of: (I) oxidative stress, sperm structural impairments, motility and kinetic alterations in 4-MBC-exposed sperms; (II) DNA damage, compromised mitochondrial activity and hyperactivation in BP-3-exposed ones. Overall, it stands out that salinity influences UV-filter toxicological pathways and, thereby, the potential environmental risk of these contaminants on M. galloprovincialis male gametes, especially in an expected salinity stress scenario.

Hdh-Tektin-4 Regulates Motility of Fresh and Cryopreserved Sperm in Pacific Abalone, Haliotis discus hannai

As structural components of sperm, tektins are thought to play a fundamental role in sperm flagellar motility. In this study, Tektin-4 (Hdh-TEKT4) gene was successfully cloned and characterized from the testis tissue in Pacific abalone, Haliotis discus hannai. The full-length cDNA of Hdh-TEKT4 was 1,983 bp, with a coding region of 1,350 bp encoding 51.83 kDa putative protein of 449 deduced amino acids. Hdh-TEKT4 contains a tektin domain including a nonapeptide signature motif (RPGVDLCRD). Fluorescence in situ hybridization revealed that Hdh-TEKT4 localized in the spermatids of Pacific abalone testis. qRT-PCR analysis showed that Hdh-TEKT4 was predominantly expressed in testis tissues. Hdh-TEKT4 mRNA expression was upregulated during the fully mature testicular developmental stage in both seasonal development and EAT exposed abalone. Furthermore, mRNA expression of Hdh-TEKT4 was significantly higher in sperm with higher motility than in sperm with lower motility during peak breeding season, induced spawning activity stages, and after cryopreservation in different cryoprotectants. Taken together, these results indicate that the expression of Hdh-TEKT4 in Pacific abalone sperm might have a positive correlation with sperm motility.