Sperm competition

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As sperm competition is competition from sperm designated one or more males for the chance to fertilize an egg. Sperm competition arises because the males of all animal species much more sperm than females produce its kind capable of fertilization oocytes. For example, 10 million sperm cells are still used for artificial insemination of cows by bulls with good to medium fertilization capacity. In humans, too, stands in the woman's uterus during each menstrual cycleusually only one egg is ready for fertilization, but a healthy man gives off several million sperm with each ejaculation .

In a broader sense, the competition of sperm from several individuals can also be referred to as sperm competition. This variant of the sperm competition was interpreted in 1970 by the British biologist Geoffrey Parker as one of the reasons for the extremely large excess of sperm compared to the available egg cells: If several males mate a female in quick succession, a male that has given off significantly more sperm than his own has (e) Competitor (s), greater chances that one of its sperm will fertilize an egg.

Research based on this theory has shown that sperm competition species tend to have promiscuous sexual behavior. Females typically indicate their fertility to attract males (e.g., stimulating sounds, smells, or swelling of the genitals).

Strategies to improve the competitive situation

One offensive strategy is to develop larger testicles that produce larger amounts of sperm. This is particularly beneficial for those males who only mate occasionally with females who constantly carry sperm from their own regular sexual partner in their bodies . This has been observed in monkeys: male bonobos and chimpanzees who “stray” have larger testes than male gorillas compared to their body mass , which live in stable but polygynous conditions.

In addition to the testicle size, there are other biological indications of sperm competition in certain species of great apes. There are other similarities between chimpanzees, bonobos and humans and differences to gorillas and orangutans. These concern the position of the testicles (outside or inside), the penis size (especially in relation to body mass) and the difference in body size between males and females.

A defensive strategy is to mate a female as often as possible. As a result, there is always a greater amount of her own sperm in the female's body. This means that a competitor's sperm are less likely to be fertilized.

A third option is to remove the existing sperm from competitors. Male dragonflies have special structures on their secondary copulatory apparatus that are used to actively remove foreign sperm. Similar behaviors have also been described for different types of crickets. Male sparrow pecking so much sperm from before mating cloaca of the female as possible.

Strategies to avoid competition

Sperm competition can only be avoided if the males try to control sexual access to their partner females as efficiently as possible. Animal species living in packs can, for example, be organized in such a way that a dominant male has exclusive sexual access to the female pack members and defends this vehemently (e.g. with gorillas and sometimes with lions ).

literature

  • Robin Baker: Sperm War. Why we love and suffer, connect, separate and cheat (= Bastei-Lübbe-Taschenbuch. Volume 60465) 1st edition, Bastei-Verlag Lübbe, Bergisch Gladbach 1999, ISBN 3-404-60465-2 (popular science treatise).
  • Christopher Ryan, Cacilda Jethá: Sex - the real story . 3rd edition, Klett-Cotta, 2019, ISBN 978-3-60898-050-9 (popular science treatise).
  • AH Harcourt, PH Harvey, SG Larson, RV Short: Testis weight, body weight and breeding system in primates. In: Nature . Volume 293, No. 5557, 1981, pp. 55-57, doi: 10.1038 / 293055a0 .

Web links

Individual evidence

  1. ↑ H. Schuh: Improving the use of old bulls in artificial insemination. In: Reproduction in Domestic Animals. Volume 26, No. 3, 1991, pp. 136-143, doi : 10.1111 / j.1439-0531.1991.tb01530.x .
  2. ↑ Geoffrey A. Parker: Sperm competition and its evolutionary consequences in the insects. In: Biological Reviews. Volume 45, No. 4, 1970, pp. 525-567, doi: 10.1111 / j.1469-185X.1970.tb01176.x .
  3. ↑ A. Córdoba-Aguilar, E. Uhía, A. Cordero Rivera: Sperm competition in Odonata (Insecta): the evolution of female sperm storage and rivals' sperm displacement. In: Jpurnal of Zoology. Volume 261, No. 4, 2003, pp. 381-398, doi: 10.1017 / S0952836903004357 .
  4. ↑ Tomohiro Ono, Michael T. Siva-Jothy, Aki Kato: Removal and subsequent ingestion of rivals' semen during copulation in a tree cricket. In: Physiological Entomology. Volume 14, No. 2, 1989, pp. 195-202, doi: 10.1111 / j.1365-3032.1989.tb00952.x .
  5. ↑ Dagmar von Helversen, Otto von Helversen: Pre-mating sperm removal in the bushcricket Metaplastes ornatus Ramme 1931 (Orthoptera, Tettigonoidea, Phaneropteridae). In: Behavioral Ecology and Sociobiology. Volume 28, No. 6, 1991, pp. 391-396, doi: 10.1007 / BF00164120 .