Sperm Swimming Performance Research Articles

Physiological functions of osmolality and calcium ions on the initiation of sperm motility and swimming performance in redside dace, Clinostomus elongatus

Reproductive potential of fish stocks is critically dependent on sperm performance in an aquatic environment. The aim of this study is to test hypotheses, which govern the initiation of sperm motility and swimming performance, through physiological functions of osmolality and Ca2+ ion, in a threatened species of freshwater fish, the redside dace, Clinostomus elongatus. Spermatozoa motility was activated in either ionic or non-ionic media spanning a range of osmolalities. The role of Ca2+ channels on induction of spermatozoa motility and velocity was experimentally investigated by diluting sperm in media that contain various Ca2+ channel blockers. Results show that initiation of spermatozoa motility is a hypo-osmolality dependent mechanism. Inhibitors for L-type Ca2+ channels partially prohibited initiation of spermatozoa motility, while velocity was significantly reduced in both L-type and T-type Ca2+ channel blockers. Examination using W-7, an inhibitor for Ca2+-dependent calmodulin, showed significant decreases in spermatozoa motility and velocity. Involvement for Ca2+ in axonemal beating was confirmed by significant increases in velocity after adding Ca2+ into the activation media, while motility remained unchanged in Ca2+ supplemented activation media. Together, these findings suggest the involvement of Ca2+ in hypo-osmolality-dependent initiation of spermatozoa motility mediated by activation of Ca2+ binding protein in the axoneme of a freshwater fish sperm. Blocking Ca2+ exchange through L- or T-type Ca2+ channel influences flagellar beating force and leads to decrease in spermatozoa velocity.

Sex cells in changing environments: can organisms adjust the physiological function of gametes to different temperatures?

AbstractOver the past decade, hundreds of studies have examined the abilities of whole organisms to modify their physiology and behaviour in response to environmental temperature changes; despite this, virtually nothing is known about the ability of sex cells to adjust to different temperature conditions. In fact, a recent meta‐analysis based on studies of 309 species and 112 physiological and ecological traits found no studies examining the influence of temperature on gamete function. Because sex cells play a critical role in the adaptation and persistence of species, this represents a severe oversight in physiological studies of thermal adaptation. Our study examines whether sex cells can respond phenotypically to variation in the thermal environment that is experienced by the whole‐organism. Specifically, we studied the thermal dependence of sperm swimming and the critical thermal limits of sperm cells in males of the poeciliid fish, Gambusia holbrooki. This species is well known for its ability to modify physiological function and maintains burst and sustained swimming performance and mating ability across a wide range of thermal conditions. In contrast, we found that sperm cells from male G. holbrooki did not adjust their physiological function as predicted by adaptive models. After acclimation of adult males to cool or warm temperatures, we found that the critical thermal limits of sperm function remained unchanged, as did the effect of temperature on sperm swimming performance. However, warm‐acclimated fish had sperm with higher swimming speeds across all temperatures. The absence of phenotypic changes in the critical thermal limits of sperm or thermal dependence of sperm swimming performance is surprising given that whole‐organism traits in G. holbrooki generally show improved performance after exposure to novel environments. As such an inability to thermally adjust gamete function may be widespread among other organisms, we urge biologists to investigate the generality of this result.

Exposure to 17α-ethinylestradiol decreases motility and ATP in sperm of male fighting fishBetta splendens

The synthetic estrogen 17α-ethinylestradiol (EE2) is an endocrine-disrupting chemical released into aquatic environments from sewage treatment facilities. We tested the effects of two environmentally relevant concentrations of waterborne EE2, 10 and 100 ng L(-1) , on reproductive endpoints in the teleost fish Betta splendens. In the first experiment, testes were removed from males and sperm were exposed to EE2 directly through the activation water. Direct exposure to EE2 had no effect on any measure of sperm swimming performance. In the second experiment, we exposed sexually mature male B. splendens to EE2 using a semi-static exposure protocol for 4 weeks. There were no significant treatment effects in the 10 ng L(-1) treatment group, but at the 100 ng L(-1) dose we found that fish had smaller gonads and reduced sperm swimming velocity. When allowed to interact freely with female conspecifics, males exposed to 100 ng L(-1) EE2 built smaller nests and showed a nonsignificant decrease in fertilization success. To investigate further the potential mechanism underlying the decrease in sperm quality, we repeated the chronic exposure experiment and analyzed the ATP content of sperm from fish in each treatment group. We found that males exposed to 100 ng L(-1) of EE2 had fewer moles of ATP per sperm than did fish in the other two treatment groups, suggesting that a decrease in intracellular ATP caused a reduction in sperm swimming velocity. The current study adds to the growing body of literature that indicates the risks to aquatic organisms of exposure to environmentally relevant concentrations of EE2.

Exposure to copper and a cytotoxic polyunsaturated aldehyde induces reproductive failure in the marine polychaete Nereis virens (Sars)

A number of metabolites from microalgae, including polyunsaturated aldehydes (PUAs), have been implicated as inducers of reproductive failure in aquatic invertebrates. Current work describes the impacts of the model PUA 2 E, 4 E-decadienal and copper sulphate applied in isolation and combination on the reproductive performance of the infaunal polychaete, Nereis virens (Sars). The reproductive and life cycle parameters investigated were; fertilisation success, larval survival, sperm motility (percent motility and curvilinear velocity) and sperm DNA damage. Exposure to decadienal and copper sulphate in isolation resulted in dose- and time-dependent reductions for each evaluated endpoint. Fertilisation success was heavily impacted at concentrations of up to 10 μM for both compounds. Copper sulphate was more toxic in larval survival assays. Sperm motility impacts, although variable, exhibited rapid onset with pronounced reductions in sperm swimming performance observed within 3 min of exposure. The extent of DNA damage was dose-dependent, and in the case of decadienal, rapid in onset. Dual compound exposures resulted in enhanced overall toxicity in all assays. Logistic regression analysis of fertilisation and larval survival assays showed significant synergistic interactions between decadienal and copper sulphate; an increase in concentration of either compound resulted in enhanced toxicity of the other. Longer exposure durations during larval survival assays demonstrated a further increase in both toxicity and synergism. The results indicate that the effects of additional environmental stressors must be considered when attempting to extrapolate laboratory-derived single compound exposures to field situations.

Females affect sperm swimming performance: a field experiment with barn swallows Hirundo rustica

Sexual conflict over fertilization may in animals with internal fertilization initiate an evolutionary arms race that causes the female reproductive tract to become hostile to sperm performance if females with more selective reproductive tracts have their eggs fertilized by sperm of superior quality. This hypothesis suggests that sperm should perform better when tested in a physiologically neutral cell culture medium (neutral medium) than in the same ‘‘neutral medium’’ to which fluid derived from the female reproductive tract has been added (female medium). We tested this prediction using in vitro tests on sperm collected from barn swallows Hirundo rustica by recording sperm performance on video in neutral medium and ‘‘female medium.’’ Sperm performance differed significantly among males but also between neutral and female medium. Sperm performed less well in female medium compared with neutral medium in terms of velocity. A principal component (PC) analysis of the 12 sperm parameters produced 4 PCs that explained 86% of the variance. The difference in the second and the third PC between neutral and female medium, reflecting sperm with a high degree of lateral head displacement and absence of straight and linear movement, many static sperm, and a small fraction of sperm with medium velocity, respectively, was positively related to an indicator of female quality: tail length. The latter result may suggest that high-quality females differentially affected the relative performance of sperm in their reproductive tract, consistent with the theory of sexual conflict. Key words: sexual conflict, sexual selection, sperm, swimming performance. [Behav Ecol]

Characterization of sperm motility in sea bass: the effect of heavy metals and physicochemical variables on sperm motility

Computer assisted sperm analysis (CASA) was used to characterize the motility of sea bass Dicentrarchus labrax spermatozoa and to study the effect of several physicochemical variables and heavy metals on sperm swimming performance. Duration of sperm motility in sea bass was very short (<50 s). During the first 20 s all the motility variables measured remained approximately constant, the velocity and linearity of the movement being maximum during this period, while both variables decreased sharply later. While slight variations in pH did not significantly modify sperm swimming performance, changes in osmolality affected all the measured motility variables. Two of the heavy metals tested, Cu2+ and Pb2+, did not affect sperm motility when the activating media contained up to 100 ppm of the metal salts. In contrast, Hg2+ modified the morphology of post‐swimming spermatozoa at 0·4–1 ppm (sperm dilution rate 1:39) and completely arrested sperm motility at concentrations as low as 0·1 ppm (sperm dilution rate 1:2500). Assuming a covalent binding to sperm cells, this revealed a finite number of c. 10 million Hg2+ binding sites per spermatozoon. Complementary results using demembranated spermatozoa suggested that the main target of HgCl2 would be located in the plasma membrane and that HgCl2 would inhibit water channels, hence preventing sperm motility.

Motility, ATP levels and metabolic enzyme activity of sperm from bluegill ( Lepomis macrochirus)

Male bluegill displays one of two life history tactics. Some males (termed “parentals”) delay reproduction until ca. 7 years of age, at which time they build nests and actively courts females. Others mature precociously (sneakers) and obtain fertilizations by cuckolding parental males. In the current study, we studied the relations among sperm motility, ATP levels, and metabolic enzyme activity in parental and sneaker bluegill. In both reproductive tactics, sperm swimming speed and ATP levels declined in parallel over the first 60 s of motility. Although sneaker sperm initially had higher ATP levels than parental sperm, by ∼30 s postactivation, no differences existed between tactics. No differences were noted between tactics in swimming speed, percent motility, or the activities of key metabolic enzymes, although sperm from parentals had a higher ratio of creatine phosphokinase (CPK) to citrate synthase (CS). In both tactics, with increasing CPK and CS activity, sperm ATP levels increased at 20 s postactivation, suggesting that capacities for phosphocreatine hydrolysis and aerobic metabolism may influence interindividual variation in rates of ATP depletion. Nonetheless, there was no relation between sperm ATP levels and either swimming speed or percent of sperm that were motile. This suggests that interindividual variation in ATP levels may not be the primary determinant of variation in sperm swimming performance in bluegill.