Sperm competition is the term used when sperm fight for an egg. For example, each ejaculation of a man’s sperm contains millions of sperm, with only one egg ready for fertilization, and the fastest, most vital, and most motile sperm decides fertilization in its favor.
What is sperm competition?
Sperm competition corresponds to the competitive behavior by which sperm compete to fertilize an egg. Sperm competition corresponds to the competitive behavior with which sperm compete to fertilize an egg. Men produce significantly more sperm than women have eggs to fertilize. In humans, the uterus usually provides only one fertilizable egg in each menstrual cycle. During ejaculation, however, a man releases several million sperm on average. The most mobile and therefore fastest sperm are the first to reach their destination. Sometimes the term sperm competition also refers to competition between sperm of different individuals. Geoffrey Parker documented this type of sperm competition in the 1970s as the cause of the extreme abundance of sperm when the number of eggs is limited. He recorded the close successive mating attempts of different males on only one female and proved that males with a higher sperm count are far superior to their competitors in this situation and have a correspondingly higher probability of fertilization.
Function and task
During an ejaculation, up to five milliliters of sperm enter the female vagina and swim from there up the fallopian tube with the help of its tail (flagellum). Only on the way do the sperm become fertile, as female enzymes remove certain proteins from the sperm. The majority of all released sperm do not survive the acidic environment of the vagina. A few hundred sperm make it into the fallopian tube and travel toward the fertilizable egg. Sperm survive in the fallopian tube for several days and can therefore wait for ovulation for a certain period of time. After ovulation, they move towards the egg and are hormone-controlled, for example by progesterone, which changes the beating pattern of the flagella and thus provides a direction. Above the egg cell lies the zona pellucida, a layer of various close-meshed glycoproteins through which the sperm must pass. Individual glycoproteins bind to the sperm heads and cause the acrosome and zona pellucida to fuse. The enzymes of the acrosome cause the zona pellucida to dissolve, allowing the sperm to reach the plasma membrane located beneath. These reactions affect the proteins of the sperm, which eventually bind to the receptors on the cell membrane of the oocyte according to the lock-and-key principle. Sperm and egg fuse upon contact and the egg membrane is depolarized to prevent further fertilization. The motility and vitality of the sperm determine which sperm wins the battle to fertilize the egg. This has evolutionary biological advantages. Fast and mobile sperm usually come from healthier and “stronger” men than slow or immobile ones. Thus, processes of natural selection are already taking place by means of sperm competition, which should result in the healthiest possible offspring. However, ejaculations of a healthy man do not only contain motile and vital sperm. In each ejaculation, the man also releases immobile sperm, which are intended to block the way to the target for any foreign sperm or can even chemically kill foreign sperm.
Diseases and ailments
A spermiogram can be used to determine the competitiveness of male sperm and thus ultimately the man’s ability to conceive. Sperm are examined in the form of a sample of ejaculate in the liquefied stage. After two to three days of sexual abstinence, a sperm sample is obtained from the patient by means of masturbation and examined in the laboratory after liquefaction. The examination is mainly equivalent to viewing under a microscope. Various parameters play a role in the assessment of the sperm’s fertility and competitiveness. Microscopic analysis focuses on motility. At least 65 percent of the sperm should be normally motile and about 25 percent clearly motile. WHO level A stands for rapidly progressive motility. Level D for lack of motility.In addition to motility, the shape of the sperm is examined under the microscope. At least 65 percent of sperm per ejaculation should have a normal shape. The concentration is also crucial for fertility. The lower limit is 20 million per milliliter. In addition, vitality, i.e. the proportion of living sperm, determines competitiveness. A healthy man releases at least 50 percent of living sperm per ejaculation. Dead sperm are stained using eosin and can be counted under the microscope in this way.
