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

flatworm Platyhelminthes (from the Greek language, Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") is a Phylum (biology), phylum of relatively simple bilaterian, Segmentation (biology), ...

species, such as the free-living '' Macrostomum hystrix,''Ramm, S.A., Schlatter, A., Poirier, M., & Schärer, L. (2015). Hypodermic self-insemination as a reproductive assurance strategy. ''Proc. R. Soc.'' ''B'' 282: 20150660. and some sea slugs. Species that engage in this method of reproduction are

hermaphroditic A hermaphrodite () is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are either male or female are gonochoric, which is the opposite of hermaphroditic. The individuals of many ...

, 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. 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 Subcutaneous tissue, hypodermis. The epidermal layer provides a barrier to infection from environmental pathogens and regulates the ...

and into the

parenchyma upright=1.6, Lung parenchyma showing damage due to large subpleural bullae. Parenchyma () is the bulk of functional substance in an animal organ such as the brain or lungs, or a structure such as a tumour. In zoology, it is the tissue that ...

. Sperm is injected into the

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

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

sperm Sperm (: sperm or sperms) is the male reproductive Cell (biology), 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 ...

migrate

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

to the female reproductive organs (

ovaries The ovary () is a gonad in the female reproductive system that produces ova; when released, an ovum travels through the fallopian tube/oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are endocr ...

) where

fertilization Fertilisation or fertilization (see American and British English spelling differences#-ise, -ize (-isation, -ization), spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give ...

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 in animals Out ...

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 ca ...

― 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