According to a research published in the journal Proceedings of the Royal Society B aquatic flatworms are capable of self-fertilization. The species known as Macrostomum hystix is a hermaphrodite and it consequently has both female and male reproductive organs and thus is able to produce not only sperm but eggs too.
In usual circumstances aquatic flatworms mate with another partner, but if they do not have whom to mate with, the creatures use a hypodermic-like penis in order to inject their own head with sperm. Afterwards the sperm travels down the body until it reaches and fertilizes the eggs. This usually occurs in particularly harsh conditions when the worm cannot find a partner. The type of fertilization used by the Macrostomum hystrix is called hypodermic insemination.
The organs of flatworms are not covered by specialized layers which set them apart in distinct compartments. The respiratory, digestive, excretory and reproductive system of the flatworm fits in the same compartment which is simply delimited by the outer layer of the worm. That is why when the creature injects the sperm it can migrate towards the eggs. After the injection the outer layer can heal since the damage is not lethal or permanent. The elongated form of the flatworm’s body also makes the process of self-fertilization easy because all the worm has to do is curve itself and simply stick the needle-like penis in its own head.
Steven Ramm from Bielefeld University in Germany explained:
“To us it sounds very gruesome, but to them it may be their best option. The alternative is not reproducing at all, so it’s making the best of a bad situation.”
Researchers have even coined a term for the ability to self-fertilize: “selfing”. So far scientists did not believe that selfing could be performed in the case of hermaphroditic species due to the fact that the reproductive organs are isolated and therefore separated from each other, but in the case of the Macrostomum hystix this does not seem to be a problem.
Even though reproduction by selfing is not the best option due to the fact that the offsprings resulted present no genetic variation it is still good because it makes reproduction possible when there are no mates available. Genetic variation is important because populations which are genetically diverse are more prepared to resist in threatening environments.
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