A hermaphrodite is an organism that possesses either a complete or partial set of both male and female reproductive organs. This article will explore hermaphroditism in worms: what it means to be hermaphroditic and why it is beneficial.
While hermaphroditism is an anomaly in humans, it is common for worms, and invertebrates in general, to be hermaphroditic. Some common examples include: flatworms, slugs and earthworms. Hermaphroditic invertebrates will almost always possess a full set of male and female genitalia, meaning they can mate with any organism from their species that they come across. This erases the need for mating rituals and competition that hinders so many other animals as there is someone for everyone! However, there are still varying degrees of hermaphroditism between the different species of worm-like creatures, and even different types of hermaphroditism.
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Firstly, what we have been discussing so far, where an organism possesses both male and female genitalia, is the most common form of hermaphroditism, and it is referred to as simultaneous hermaphroditism. What this means is that the organism is born with male and female reproductive organs, and can use both simultaneously. For example, when earthworms engage in intercourse, although one could take on the male role and one the female role, the most favorable outcome is that they both impregnate each other. Slugs are able to do the same, though their mating ritual can be a tad more aggressive and competitive, depending on the species.
Secondly, there is another form of hermaphroditism referred to as sequential hermaphroditism. A sequential hermaphrodite is an organism that is born as one sex, but can ultimately change into the other at some point in their life (for purposes of reproduction, of course); an example of this is the flatworm Hymanella retenuova. Males that turn into females are called protandrous hermaphrodites, whilst females that turn into males are protogynous hermaphrodites. Interestingly enough, sequential hermaphrodites change into the other sex as a result of extraneous variables that trigger the change, and not necessarily because they decide to change. Yet, in the cases that the change is internally triggered, the decision is based on the extent to which they can fulfill their reproductive potential. For example, some males will turn into females because they are of a larger size, and will thus be able to carry more eggs. As a side note, we do want to point out that it is unclear if decision made by the worms really is a conscious choice, or an instinctual reaction to interior and exterior triggers.
The thing is, simultaneous hermaphroditism is far more advantageous for the survival of a species than sequential hermaphroditism, and it is fortunately more common. As we said before, during intercourse, both partners are able to impregnate each other due to their simultaneous hermaphroditism, and thus they are potentially producing twice the amount of offspring than they would if only one of the partners was impregnated. In the case of slugs, they can even self-impregnate, not even needing to find a partner to produce offspring. This speaks to the potential longevity of these species. Earthworms have been around for over 600 million years, and slugs — which have been around nearly as long — have already evolved once from snails, and it is clear that their hermaphroditism has played a key part in their survival. Fertility is, after all, the most important component in keeping a species from declining.
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All in all, this article has explained the meaning of hermaphroditism and how it relates to worms and worm-like creatures and has moreover demonstrated its importance. The reproductive systems and abilities of the animal kingdom are varied and fascinating, and so we hope that with this small glimpse into worm reproduction, our readers can take away something interesting, if not enlightening.