sperm competition

Competition between the sperm of rival males within the body of a female. This may involve actual removal of a rival's sperm before mating, for example the penis of a male dragonfly is shaped to scoop out existing sperm; or internal competition between rival sperm cells.

In the bug Xylocoris maculipennis, sperm competition actually takes place within the male's body. Males inject sperm directly into the females body cavity by piercing her body wall, but males also mate with other males, injecting sperm into the body cavity so that it will migrate to the testes, where it remains until injected into a female.

In 1999 English biologists discovered ‘mating by proxy’, a previously unknown form of sperm competition (in flour beetles Trilobium castaneum). When a male flour beetle mates with a female that has been previously mated, he uses his spiny genitals to extract any sperm already there, but the sperm can still compete with his own by remaining viable so that when he mates next he introduces the rival sperm as well as his own. Female flour beetles can therefore be fertilized by males they have never met.