Range Of Sperm Concentrations Research Articles

Population density effects on gamete traits and fertilisation dynamics under varying sperm environments in mussels.

Gamete traits can vary widely among species, populations and individuals, influencing fertilisation dynamics and overall reproductive fitness. Sexual selection can play an important role in determining the evolution of gamete traits with local environmental conditions determining the strength and direction of sexual selection. Here, we test for signatures of post-mating selection on gamete traits in relation to population density, and possible interactive effects of population density and sperm concentration on sperm motility and fertilisation rates among natural populations of mussels. Our study shows that males from high-density populations produce smaller sperm compared with males from low-density populations, but we detected no effect of population density on egg size. Our results also reveal that females from low-density populations tended to exhibit lower fertilisation rates across a range of sperm concentrations, although this became less important as sperm concentration increased. Variances in fertilisation success were higher for females than males and the effect of gamete compatibility between males and females increases as sperm concentrations increase. These results suggest that local population density can influence gamete traits and fertilisation dynamics but also highlight the importance of phenotypic plasticity in governing sperm-egg interactions in a highly dynamic selective environment.

Eggs with larger accessory structures are more likely to be fertilized in both low and high sperm concentrations in Styela plicata (Ascidiaceae)

The evolution of egg size has been intensively studied due to its influence on both fecundity and offspring performance. In marine broadcast spawners, egg size influences the probability of sperm–egg collision, and therefore, egg size can also influence fertilization success, depending on the local concentration of sperm. Many broadcast-spawning species have egg accessory structures that are thought to be a cheap means of altering egg size, but their influence on fertilization remains controversial. To determine the relative influences of ovicell size and follicle cell size on fertilization success in the ascidian Styela plicata, the size distribution of eggs that were not successfully fertilized in both high and low sperm concentrations was compared to that of unfertilized controls. At high sperm concentrations, a greater proportion of eggs with smaller ovicells were fertilized, resulting in smaller larvae hatching from this treatment. Eggs with a large follicle cell area relative to ovicell area were preferentially fertilized in both high and low sperm concentration treatments. Hence, follicle cells do not eliminate selection on ovicell size at fertilization in S. plicata. Furthermore, follicle cells appear to increase fertilization success across a range of sperm concentrations by performing different functions in each environment—increasing the target size of eggs in low-sperm concentrations and presumably reducing polyspermy in high sperm concentrations.

Effects of ocean warming and acidification on fertilization in the Antarctic echinoid Sterechinus neumayeri across a range of sperm concentrations

The gametes of marine invertebrates are being spawned into an ocean that is simultaneously warming and decreasing in pH. Predicting the potential for interactive effects of these stressors on fertilization is difficult, especially for stenothermal polar invertebrates adapted to fertilization in cold, viscous water and, when decreased sperm availability may be an additional stressor. The impact of increased temperature (2–4 °C above ambient) and decreased pH (0.2–0.4 pH units below ambient) on fertilization in the Antarctic echinoid Sterechinus neumayeri across a range of sperm concentrations was investigated in cross-factorial experiments in context with near future ocean change projections. The high temperature treatment (+4 °C) was also used to assess thermal tolerance. Gametes from multiple males and females in replicate experiments were used to reflect the multiple spawner scenario in nature. For fertilization at low sperm density we tested three hypotheses, 1) increased temperature enhances fertilization success, 2) low pH reduces fertilization and, 3) due to the cold stenothermal physiology of S. neumayeri, temperature would be the more significant stressor. Temperature and sperm levels had a significant effect on fertilization, but decreased pH did not affect fertilization. Warming enhanced fertilization at the lowest sperm concentration tested likely through stimulation of sperm motility and reduced water viscosity. Our results indicate that fertilization in S. neumayeri, even at low sperm levels potentially found in nature, is resilient to near-future ocean warming and acidification.

The response of two ecologically important Antarctic invertebrates (Sterechinus neumayeri and Parborlasia corrugatus) to reduced seawater pH: effects on fertilisation and embryonic development

Ocean acidification, or the lowering of seawater pH, is caused by sequestration of atmospheric CO2 into the oceans. This study investigated the effects of present-day pH 8.0, predicted ocean surface pH for the years 2100 and 2300 (pH 7.7 and pH 7.3, respectively) and an extreme pH (pH 7.0) on fertilisation and embryogenesis in the Antarctic nemertean worm Parborlasia corrugatus and sea urchin Sterechinus neumayeri. Fertilisation success was not affected by pH in P. corrugatus across a range of sperm concentrations. Fertilisation success in S. neumayeri declined significantly in pH 7.0 and 7.3 seawater, but only at a low sperm concentration. Seawater pH had no effect on the rate of egg cleavage in S. neumayeri, or the proportion of abnormal embryos 1-day post-fertilisation. P. corrugatus embryogenesis was also relatively robust to pH changes, with a significant effect detected only when the seawater pH was decreased to 7.0. While fertilisation and early cell division were relatively robust, later development through to the gastrula was sensitive to pH. In S. neumayeri, an effect of pH on development was evident by the gastrula stage, while there were significantly more abnormal P. corrugatus embryos in pH 7.0 up to the blastula stage, and in pH 7.0 and pH 7.3 at the coeloblastula stage. Our results are similar to the observations on other marine invertebrate species where fertilisation and early embryonic development are generally robust to lowered seawater pH, while the older coeloblastula and gastrula stages are more responsive. We also found no evidence to suggest that Antarctic species are more adversely affected by lower seawater pH compared with the findings for non-Antarctic counterparts. We conclude that in the two species we examined, near-future decreases in pH (decreases of ≈0.3–0.5 pH units) may not have a significant effect on fertilisation and early embryogenesis, while predicted longer term decreases (decreases of ≈0.7–0.77 pH units) could reduce fertilisation success in S. neumayeri if sperm concentrations are low and may increase abnormalities in P. corrugatus during later embryogenesis.

Sperm proteomic profiles reflect the occurrence of DNA fragmentation

OBJECTIVE: Sperm DNA integrity is crucial for reproductive success. Developments in proteomic technologies are contributing to our understanding of sperm function in connection with male factor infertility. The aim of this study was to investigate a relationship between sperm DNA fragmentation and proteomic profiles that may be reflective of sperm dysfunction. DESIGN: Experimental study. MATERIALS AND METHODS: Couples with a history of poor embryo development during prior IVF cycles underwent sperm DNA fragmentation testing using TUNEL assay (n=29). From the same ejaculate, sperm was donated with IRB consent for proteomic profiling. Individual sperm proteomic profiles were generated using surface enhanced laser desorption ionization time-of-flight mass spectrometry (Bio-Rad). Statistical analysis compared 2 groups: Group A = ≥15% DNA fragmentation (n=7) and Group B = <15% DNA fragmentation (n=22) with similar paternal age (A=44.4 v. B=43.1 years). RESULTS: Sperm DNA fragmentation (A=27.7% v. B=4.91%, P<0.0001) and motility (A=38.4% v. B=48.45%, P<0.05) were calculated to be significantly different between the groups. In contrast, the range of sperm concentration in each group was broad with no significant differences (mean A=49.6 v. B=83.65 million/ml). Unsupervised hierarchical clustering of all sperm proteomic profiles created two main branches. One main branch contained all 7 Group A samples along with 5 Group B samples. These 5 Group B samples shared a significantly similar lower sperm concentration (mean 47.2) with Group A samples. Statistical analysis revealed 5 protein biomarkers within the mass range of 10-20kDa with significant decrease in expression in all Group A samples compared to Group B (P<0.05). CONCLUSION: Sperm proteomic profiles were reflective of sperm DNA fragmentation and revealed differentially expressed protein biomarkers. Ongoing protein identification and molecular studies could provide insight regarding the function of these potential biomarkers as well as correlation with male fertility factors.

Copper reduces fertilisation success and exacerbates Allee effects in the field

The reproductive success of marine broadcast spawners depends on the concentration of sperm that surrounds eggs. Because sperm quickly dilute in the ocean, spawners must be sufficiently close to one another to ensure high rates of fertilisation. Thus, broadcast spawners can experience Allee effects-decreasing density can result in lower reproductive success because the costs of low fertilisation outweight any benefits of reduced intraspecific competition. Recently, there has been a dramatic increase in the number of studies examining the effects of toxicants on fertilisation success. These studies suggest that fertilisation is a highly sensitive stage and exposure to pollutants could severely reduce reproductive success in the field. However, we remain limited in our ability to predict the effects of toxicants under field conditions because most ecotoxicological studies utilise only a single sperm concentration. Moreover, all ecotoxicological studies of fertilisation to date have been limited to laboratory investigations, and it remains unclear whether the effects of a toxicant are overwhelmed in the dynamic and turbulent environment of the real world. We examined the effects of a common pollutant, copper, on the fertilisation success of the intertidal polychaete Galeolaria caespitosa in the laboratory and the field. In the laboratory, we examined the effects of copper over a range of sperm concentrations and in the field, we developed a new apparatus for examining fertilisation success in intertidal organisms. In the laboratory, copper had much stronger effects on fertilisation at low sperm concentrations than at high concentrations. We suggest that the use of single sperm concentrations in ecotoxicological. assays of fertilisation is inappropriate because the magnitude of the effect of the toxicant can be estimated incorrectly. Copper also reduced fertilisation success in the field, with eggs having to be much closer to a sperm source in order to achieve any fertilisation success in the presence of copper. For populations of marine invertebrates in which reproduction is limited by sperm availability, the presence of a toxicant has the potential to dramatically reduce fertilisation success and greatly exacerbate Allee effects.

A delta 4-3-keto pathway for testosterone synthesis in the human spermatozoa.

The ability of human spermatozoa to metabolize pregnenolone to progesterone and progesterone to testosterone was assessed. Sonicated specimens of freshly ejaculated sperm from two groups of husbands (n = 6, age 32-38 years; n = 6, age 30-51 years) of infertile couples in the range of sperm concentration between 237.5 and 568.5, 100.1 and 248.8 millions per ejaculate, were separately incubated with [7n-3H]pregnenolone and [1,2,6,7,16,17-3H]progesterone. Using the classical reverse-isotope dilution technique the desired products [3H]progesterone and [3H]testosterone formed from the respective substrates were isolated and characterized, yielding 1.4 to 12.2% and 3.1 x 10(-2) to 2.0 x 10(-1)%. Such metabolites were not evident in the controls. The results indicate that the human spermatozoa contain the enzymes necessary for the transformation of pregnenolone to testosterone via the delta 4-3-keto route.

Characterization of a delta 5-3 beta-hydroxy pathway of testosterone synthesis in the human spermatozoa.

Sonicated specimens of freshly ejaculated sperm from two groups of husbands (n = 6, age 32-38 years; n = 7, age 27-38 years) of infertile couples in the range of sperm concentration between 237.5 and 568.5; 131.1 and 256.7 millions per ejaculate were separately incubated with [7n-3H]pregnenolone and [1,2,6,7(-3)H]dehydroepiandrosterone. Using the reverse-isotope dilution technique [3H]dehydroepiandrosterone and [3H]testosterone formed from the respective substrates were isolated and characterized, yielding 1.2 x 10(-2) to 4.6 x 10(-20/0) and 7.1 x 10(-2) to 2.5 x 10(-10/0)/ Such metabolites were not evident in the controls. These results provide evidence for metabolic transformation of pregnenolone to testosterone via the delta 5-3 beta-hydroxy route.

Concentrations of intracellular sex steroids in human spermatozoa.

In an attempt to determine whether human spermatozoa contain steroid hormones, the immunoreactive levels of progesterone, testosterone, and estradiol-17 beta were measured in the extracts of sonicated specimens of sperm obtained as ejaculates from husbands of infertile couples (n = 67, age 26-44 years). In the range of sperm concentration between 3.0 and 869.6 million per ejaculate (143.2 +/- 13.6 mean +/- SEM), the concentrations were as follows: progesterone 127.3-6685.4 fmol/ml (1434.5 +/- 178.6), testosterone 98.3-2219.1 fmol/ml (611.6 +/- 49.0), and estradiol-17 beta 33.0-678.1 fmol/ml (206.9 +/- 19.7). Using Pearson's correlation coefficient, the steroid hormone levels correlated significantly with the total sperm number (p < .02). The spermatozoa contained small but measurable amounts of the sex steroids.