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Penis fencing is a

mating In biology, mating is the pairing of either opposite-sex or hermaphroditic organisms for the purposes of sexual reproduction. ''Fertilization'' is the fusion of two gametes. ''Copulation'' is the union of the sex organs of two sexually reproduc ...

behavior Behavior (American English) or behaviour (British English) is the range of actions and mannerisms made by individuals, organisms, systems or artificial entities in some environment. These systems can include other systems or organisms as wel ...

engaged in by many species of

flatworm The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") are a phylum of relatively simple bilaterian, unsegment ...

, such as '' Pseudobiceros hancockanus''. Species which engage in the practice are

hermaphroditic In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many taxonomic groups of animals (mostly invertebrates) do not have separ ...

; each individual has both egg-producing

ovaries The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...

and sperm-producing

testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoster ...

. The flatworms "

fence A fence is a structure that encloses an area, typically outdoors, and is usually constructed from posts that are connected by boards, wire, rails or netting. A fence differs from a wall in not having a solid foundation along its whole length. ...

" using extendable two-headed

dagger A dagger is a fighting knife with a very sharp point and usually two sharp edges, typically designed or capable of being used as a thrusting or stabbing weapon.State v. Martin, 633 S.W.2d 80 (Mo. 1982): This is the dictionary or popular-use de ...

-like stylets. These stylets are pointed (and in some species hooked) in order to pierce their mate's epidermis and inject sperm into the

haemocoel The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...

in an act known as intradermal hypodermic insemination, or

traumatic insemination Traumatic insemination, also known as hypodermic insemination, is the mating practice in some species of invertebrates in which the male pierces the female's abdomen with his aedeagus and injects his sperm through the wound into her abdominal c ...

. Pairs can either compete, with only one individual transferring sperm to the other, or the pair can transfer sperm bilaterally. Both forms of sperm transfer can occur in the same species, depending on various factors.

Unilateral sperm transfer

One organism will inseminate the other, with the inseminating individual acting as the "father". The sperm is absorbed through pores or sometimes wounds in the skin from the partner's stylet, causing fertilization in the other, who becomes the "mother".Hermaphrodites duel for manhood
''Science News Online''. Accessed 14 March 2009. The battle may last for up to an hour in some species. Parturition, while necessary for successful offspring production, requires a considerable

parental investment Parental investment, in evolutionary biology and evolutionary psychology, is any parental expenditure (e.g. time, energy, resources) that benefits offspring.Clutton-Brock, T.H. 1991. ''The Evolution of Parental Care''. Princeton, NJ: Princeton ...

in time and energy, and according to

Bateman's principle Bateman's principle, in evolutionary biology, is that in most species, variability in reproductive success (or reproductive variance) is greater in males than in females. It was first proposed by Angus John Bateman (1919–1996), an English geneti ...

, almost always burdens the "mother". Thus, from an

optimality model In biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process h ...

it is usually preferable for an organism to inseminate than to be inseminated. However, in many species that engage in this form of copulatory competition, each "father" will continue to fence with other partners until it is inseminated. In '' Alderia modesta'', individuals will store sperm from several "fencing matches" before laying their eggs, and smaller individuals will more often inseminate a larger partner, with larger individuals spending more energy on laying eggs when paired with a smaller partner on the occasion that they transfer sperm unilaterally. In the absence of potential mates, some species such as '' Neobenedenia melleni'' are capable of reproducing through

self-insemination Self-insemination (also known as "selfing") is a mating behavior engaged in by individuals of multiple flatworm species, such as the free-living ''Macrostomum hystrix''.Ramm, S.A., Schlatter, A., Poirier, M., & Schärer, L. (2015). Hypodermic self- ...

Bilateral sperm transfer

Commonly, many hermaphroditic species mutually inseminate, or trade sperm, rather than compete, ''

Chelidonura sandrana ''Chelidonura sandrana'' is a species of sea slug, or "headshield slug", a marine opisthobranch gastropod mollusk in the family Aglajidae.Bouchet, P. (2012). Chelidonura sandrana Rudman, 1973. Accessed through: World Register of Marine Species ...

'' as an example. The tiger flatworm, ''Maritigrella crozieri'', also transfers sperm bilaterally. In many species that engage in bilateral insemination, sperm trading is conditional. If one partner "cheats", and does not transfer sperm, the other partner will either prematurely abandon the partner, or will engage in typical mating behavior without transferring sperm. Other species will alternate which partner transfers sperm, engaging in multiple bouts of fencing with the same partner over time. In '' A. modesta,'' bilateral sperm transfer is the most common, especially in similarly sized mate pairs.

Other uses

The term is also applied, usually informally, to homosexual activity between two males among

bonobo The bonobo (; ''Pan paniscus''), also historically called the pygmy chimpanzee and less often the dwarf chimpanzee or gracile chimpanzee, is an endangered great ape and one of the two species making up the genus '' Pan,'' the other being the comm ...

s; same-sex genital-genital rubbing is used in bonobo society to cement bonds, reduce conflict, and express communal excitement over food. Several

whale Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...

species also engage in penis fencing.Bruce Bagemihl, ''Biological Exuberance: Animal Homosexuality and Natural Diversity,'' St. Martin's Press, 1999;

References

{{reflist, 2

External links

Bizarre Animal Mating Rituals
Mating Platyhelminth biology Sexual acts Penis

Unilateral sperm transfer

Bilateral sperm transfer

Other uses

See also

References

External links