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Do you know? Why do animal sperm gather into a 'train' to increase the chance of pregnancy?
In many organisms, sperm motility is critical for successful conception. However, these tiny cells rely on more than just their ability to move alone; recent research has found that the aggregation behavior of sperm, specifically the "train" movement in some mammals, is actually a strategy to promote conception.
Good sperm motility is a key factor in successful conception. Those sperm that cannot "swim" properly will not be able to reach the egg for fertilization.
In mammals, sperm must pass through a series of obstacles, including the cell layers surrounding the ovary and the outer matrix, to reach the egg. In some species, such as the wood rat (Apodemus sylvaticus), sperm are able to form "trains," which gives them an advantage in the slimy reproductive tract, increasing the chance of conception. These trains advance in a wave-like motion, allowing the sperm to better adapt to its environment.
Biological basis of sperm movement
The key to sperm motility and fertility lies in the structure of the sperm and how it uses chemical signals to activate movement. The tail of the sperm, the flagellum, is mainly composed of microtubules and is called an axoneme. This structure allows the sperm to create wave-like movements through a series of sliding movements.
The movement of the flagellum relies on a molecular motor called dynein, a protein that promotes sliding between microtubules, thereby driving the flagellum to swing.
In many aquatic invertebrates, sperm motility is driven by changes in environmental pH. When the pH rises to about 7.2-7.6, it activates ATPase, which causes a decrease in intracellular potassium ion concentration and triggers movement. Although sperm from different species respond differently to these signals, all show the importance of changes in pH and calcium ions in activating sperm motility.
Factors affecting sperm movement
In addition to the influence of the external environment, the quality and quantity of sperm also depend largely on internal conditions. For example, low pH can inhibit sperm motility in some mammals. In some mammals, sperm motility is also affected by other chemical factors, such as calcium ions and cAMP (cyclic adenosine monophosphate).
When sperm enters the fallopian tube, its motility is weakened due to attachment to the epithelium. When ovulation is close, hyperactivation occurs, which causes the flagellum to move at a higher curvature and long wavelength.
The initiation of hyperactivation is usually related to calcium ions, but its specific regulatory mechanism remains unclear. It should be noted that under any circumstances, sperm that cannot move or have abnormal movement cannot achieve fertilization, which makes the proportion of sperm with motile ability in semen a key indicator for measuring semen quality.
Sperm DNA damage and age factors
Sperm DNA damage is prevalent in infertile men, with approximately 31% of men with sperm motility defects showing high levels of sperm DNA fragmentation. In addition, research shows that sperm motility decreases with age, usually increasing from early adulthood to the 30s, but then gradually declining after the age of 36. For example, in men over the age of 40, the ability of sperm to move quickly will be significantly reduced.
The impact of age on semen quality highlights the complexities and challenges of male fertility.
In male sperm movement, it can usually be divided into several types: rapid progressive movement, slow progressive movement, and non-motile types. Each type has a different impact on pregnancy.
Ways to improve sperm quality
Although the quality of sperm movement will be affected by many factors, there are currently various methods to help improve its quality, including nutritional supplements, physiological health management, and professional medical intervention.
In short, the "train" movement of sperm is not only a biological miracle, but also a strategy evolved during the process of evolution to increase the chance of conception. As our understanding of these delicate processes improves, we may be able to develop more precise fertility interventions to help couples facing fertility challenges. All this makes people think about how future reproductive technology will further change our fertility concepts and treatments?
