Female-Male Conflict
Most males will invest a great deal of time and energy attempting to influence female reproductive decisions in a way that is favorable to males. Some males, however, attempt to circumvent female choice. This is the basis of conflict between the sexes.
Sexual Harassment, Coerced Copulation
Conflict between the sexes is most readily apparent when males use force or harassment to overcome sexually resistant females (Clutton-Brock and Parker, 1345). This phenomenon is found in bees, some birds, chimpanzees, and a host of other organisms. The male water strider, for example, will wrestle with a female in hopes of inseminating her. This struggle increases the risk of both the male and female participants being captured by predatory insects, since a result of the struggle is an increase in water vibrations. Eventually a female will give in if she is unable to dismount the male. There are two theories as to why a female might resign herself to copulation--it is either energetically favorable for the female to mate with the male than resist his further advances, or the female will agree to mate with the male because his persistence shows that he has good fuel resources and is in good physiological condition (Clutton-Brock and Parker, 1354).
The water strider. Unlike most aquatic organisms, the water strider never ventures underwater. Male water striders violently wrestle with females to force copulation. Photo by Dr. Robert Suter.
There are two main types of infanticide--infanticide committed by the mother and infanticide committed by the father.
Maternal infanticide generally occurs after a female has been forcibly impregnated by a male she feels is undesirable or a group of females is taken over by a new, more aggressive male. For example, after a new stallion has taken over a band of mares from another stallion, the mares that are pregnant may be forced to abort after copulation with the new harem owner. The abortion of embryos probably helps females make the best out of a bad situation after they have been lost or abandoned by a previous mate and are now faced with an aggressive new male.
The attempts of a male to kill a female's offspring in order to speed up her reproductive cycle so that he can inseminate her are generally resisted by the female. For example, female langurs and lions try to prevent the death of their young at the jaws of their new pride masters. The females are often unsuccessful. The male leaves the female no other option other than to reproduce with him. Females have developed ways to avoid paternal infanticide, such as mating with several males to make determination of paternity difficult and the likelihood of attacks on their young lower. Some horses and mice even have false estrous cycles after the takeover of their group by a new male. They will continue to copulate with the male despite their inability to be impregnated.
The female langur with baby. Infanticide is common among langurs because of intense sexual competition.