Self-insemination (also known as "selfing") is a mating behavior engaged in by individuals of multiple

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 ...

species, such as the free-living ''

Macrostomum hystrix ''Macrostomum hystrix'' is a free-living flatworm in the family Macrostomidae. It is small, transparent, and a simultaneous hermaphrodite. Biology ''Macrostomum hystrix'' is capable of hypodermic insemination. In this process, sperm is inject ...

''.Ramm, S.A., Schlatter, A., Poirier, M., & Schärer, L. (2015). Hypodermic self-insemination as a reproductive assurance strategy. ''Proc. R. Soc.'' ''B'' 282: 20150660. Species that engage in this method of reproduction 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 ...

, meaning they possess both male and female reproductive organs. Selfing is referred to as a conditional reproductive strategy in this species, which means that there is a preference to reproduce with a mate.Ramm, S. A., Vizoso, D. B., & Schärer, L. (2012). Occurrence, costs and heritability of delayed selfing in a free-living flatworm. ''Evolutionary Biology'', ''25'', 2559-2568. Sea slugs have also been found to reproduce through self-insemination. Macrostomum hystrix

Mechanics

Self-insemination has been demonstrated in isolated individuals of the flatworm species ''M. hystrix''. This is achieved by using their male copulatory organ, a needle-like stylet, to pierce through the

epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rele ...

and into the

parenchyma Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms. Etymology The term ''parenchyma'' is New Latin from the word π ...

. Sperm is injected into the

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

region of their body due to physical limitations, which is inclusive of their own head. From the site of injection,

sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...

migrate

posteriorly Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

to the female reproductive organs (

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 ...

) where

fertilization Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...

occurs. Flatworms that were studied in isolation contained significantly more sperm in their anterior region than those who were placed in triplet groups.

As a conditional reproductive strategy

''M. hystrix'' has been shown to prefer

outcrossing Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing genetic diversity. Outcrossing can be a useful ...

under normal conditions. Another study showed the onset of reproduction is significantly delayed in isolated individuals in comparison to those who were placed in triplet groups. There is also a reduction in the number of hatchlings produced through self-insemination and a decrease in the survival of these offspring, which suggests that this method of reproduction is costly to the parent. While survival of the species is more likely via their ability to produce offspring in the absence of potential mates, these offspring will further lack genetic variety.Kearn, G., & Whittington, I. (2014). Sperm transfer in monogenean (platyhelminth) parasites. ''Acta Parasitologica'', ''60''(4), 567-600. Therefore, members of this species avail of delayed self-insemination as a conditional reproductive strategy to endure through periods where mates are scarce.

In sea slugs

It may be beneficial for hermaphroditic species to seldom reproduce via self-insemination since they can avoid the laborious costs of reproduction to the female function as experienced through

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 ...

― such as in the case of the sea slug '' Alderia willowi''.Smolensky, N., Romero, M. R., & Krug, P.J. (2009). Evidence for Costs of Mating and Self-Fertilization in a Simultaneous Hermaphrodite With Hypodermic Insemination the Opisthobranch ''Alderia willowi''. ''Biol. Bull. 216'',188-199.

References

{{Reflist Wikipedia Student Program Mating systems Platyhelminth biology Mollusc anatomy