Traumatic Insemination - Use in The Animal Kingdom

Use in The Animal Kingdom

Although traumatic insemination is most widely practiced among heteropterans (typical bugs), the phenomenon has been observed across a wide variety of other invertebrate taxa. These include:

• Oxyurida (nematodes) – Traumatic insemination has been observed in pinworm genera including Auchenacantha, Citellina, Passalurus, and "probably" Austroxyris
• Acanthocephala (parasitic, thorny-headed worms) – The presence of mating plugs on the sides of Pomphorhynchus bulbocolli suggests traumatic insemination occurs in this species. Because these parasites cannot move after anchoring themselves to a host's intestine, traumatic insemination may have evolved to compensate for their immobility.
• Rotifera (wheel animalcules) – In the Brachionus genus, the male pierces the syncytial integument (equivalent to skin) and injects sperm; in Asplanchna brightwelli the male secretes an enzyme which breaks down the female integument and injects sperm through the hole.
• Turbellaria (free living flatworms) – Hermaphroditic flatworms reproduce by "penis fencing". Individuals "fence" with penises, attempting to use their penis to pierce the skin of the other and inject sperm. The 'loser' is the flatworm which is inseminated and must bear the energy costs of reproduction. One study of Pseudoceros bifurcus found "Most inseminations were unilateral. Even when reciprocal penis insertion could be achieved by the second partner, the first to inseminate obtained a longer injection time than the second."
• Gastropod snails
• Strepsiptera (twisted-winged parasites) – In Xenos vesparum, fertilization can occur either via extragenital ducts, or by traumatic insemination into the hemocoel.
• Drosophila (flies) – Ejaculates are injected through the body wall into the genital tract, not the abdomen.
• Opisthobranchia (sea slugs) – Characterized by "repeated small injections into the dorsal surface of the partner, interrupted by synchronised circling movements", culminating in a standard genital insemination.
• Harpactea (spiders) – The male of the spider species Harpactea sadistica pierces the female's body cavity and inseminates her ovaries directly.