A Nematode in Love

How can nematode reproduction help you write an interesting alien species? Several science fiction tales have explored the possibilities of alternative forms of reproduction from what humanity uses. Ursula Le Guin explored this in much of her work, most notably The Left Hand of Darkness. I recently came upon some research that gives another possibility to explore.

a nematode in love

In 1949, the young biologist Victor Nigon described the reproduction of various species of nematodes, small roundworms that live in the soil, in his doctoral thesis. These include Mesorhabditis belari, whose rare male specimens are required for reproduction, even though the genetic material found in sperm is rarely used by eggs. The resulting embryo produces a female, who is a clone of its mother.

In 2019, researchers from the CNRS, l’ENS de Lyon, l’Université Claude Bernard Lyon 1, and the Muséum national d’Histoire naturelle published in the journal Science, further research on this nematode, confirming Victor Nigon’s initial observations, but also noting that in 9% of cases the embryo produced a male when the sperm’s genetic material was used after fertilization.

This is how the nematode’s reproduction works: The primary purpose of males in this species of nematode is to help females produce clones of themselves. Males can transmit their genes only to their sons. This makes M. belari a unique case in which males make no genetic contribution, and can instead be seen as a simple extension of females by helping them initiate the development of their eggs.

This raises the question, “If males do not transmit the genes of their mothers, then at least they must help their mothers produce as many descendants as possible, right?” This is possible only if the sons produced by a female help her daughters produce a large number of embryos. In other words, if the males preferentially fertilize their sisters.

The question then becomes, if this is true, why would this lead to 9% males, instead of 2% or 20% for instance? By using “game theory,” the researchers showed that producing 9% males is a stable evolutionary strategy, as this quantity is enough to ensure that a maximum number of female descendants are produced, without wasting too many resources in the production of males whose genes have no future.

In most asexually reproducing species, there are no males. The females simply produce clones of themselves. In sexual reproduction, the genetics from both female and male mix to product the offspring. However, with the M. belari nematode, there is an alternative reproductive strategy in which males can be useful to female reproduction, but with no genetic mixing. The research team now plans to explore how this type of reproduction emerged and will test the long-term stability of the M. belari species through the study of its genome.

Writing Prompts Based on Nematode Reproduction

I’ve experienced quite a few science fiction stories that explore reproductive alternatives for aliens. However, I don’t think I’ve come across one quite like M. belari. Here are some ideas to explore using this nematode as a reference in your next story.

What if …

  • What would a society look like if females were dominant and males were only needed for reproduction? Would this elevate or demote the standing of a male in this society? In other words, would they be looked upon as servants or slaves? Or would they be valued because the species would not continue without then, and yet they are so rare?
  • How would a built-in genetic reason for incest affect a civilization? Would it lead to a monarchy or caste system where some lineages were more valued than others? How would it affect this society’s relationship with a society like our own that find incest appalling?
  • What would a species like this do to avoid genetic bottlenecks? Would they be more susceptible to extinction because of a lack of genetic diversity? What would they do to lessen the risk?

Check out more writing prompts inspired by actual science stories in my “Writing Prompts” category.

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