Traumatic insemination

However experiments found no conclusive evidence for that hypothesis; as of 2003, the preferred explanation for that organ is hygienic protection against bacteria.

Although it evolved independently in many invertebrate species, traumatic insemination is most highly adapted and thoroughly studied in bed bugs, particularly Cimex lectularius.

Insects, however, have an open circulatory system in which blood and lymph circulate unenclosed, and mix to form a substance called hemolymph.

[9] Traumatic insemination allows subsequent males to bypass the female's plugged genital tract, and inject sperm directly into her circulatory system.

Others have argued that the practice of traumatic insemination may have been an adaptation for males to circumvent female resistance to mating[1] to eliminate courtship time, allowing one male to inseminate many mates when contact between them is brief;[10] or that it evolved as a new development in the sperm competition as a means to deposit sperm as close to the ovaries as possible.

Some male insects evolved long penises with which they enter the vagina but bypass the female's storage pouch and deposit their sperm further upstream close to the ovaries.

A few males, notably among bed bugs, evolved traumatic insemination instead, and eventually this strange procedure became the norm among these insects.

[11]It has recently been discovered that members of the plant bug genus Coridromius (Miridae) also practice traumatic insemination.

Females also exhibit paragenital modifications at the site of intromission, which include grooves and invaginated copulatory tubes to guide the male paramere.

The evolution of traumatic insemination in Coridromius represents a third independent emergence of this form of mating within the true bugs.

This suggests infections from these species may contribute to the increased mortality rate in bed bugs due to traumatic insemination.

Female bed bugs have evolved a pair of specialized reproductive organs ("paragenitalia") at the site of penetration.

Known as the ectospermalege and mesospermalege (referred to collectively as spermalege), these organs serve as sperm-receptacles from which sperm can migrate to the ovaries.

The ectospermalege is visible externally in most bed bug species, giving the male a target through which to impale the female with the paramere.

In species without an externally visible ectospermalege, traumatic insemination takes place over a wide range of the body surface.

The ectospermalege appears to act as a mating guide, directing the male's copulatory interest, and therefore damage, to a restricted area of the female's abdomen.

In some species, the ectospermalege directly connects to the ovaries – thus, sperm and ejaculate never enters the hemolymph and thus never trigger an immune reaction.

[1]Klaus Reinhardt of the University of Sheffield and colleagues observed two morphologically different kinds of spermalege in Afrocimex constrictus, a species in which both male and females are traumatically inseminated.

Cited reasons for this being beneficial to the paired males include successful reproduction, and chasing away intruders from their territory.

[35] Bachelor herds of bottlenose dolphins will sometimes gang up on a female and coerce her to have sex with them, by swimming near her, chasing her if she attempts to escape, and making vocalized or physical threats.

[36][37] In the insect world, male water striders unable to penetrate her genital shield, will draw predators to a female until she copulates.