"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

April 19, 2012

Paragordius obamai

Sex is one of the great mysteries of evolutionary biology - why do organisms have it? It has numerous costs associated with it, including the two big ones, which are that only half the population will produce offspring in the next generation (technically really a problem more of anisogamy than sex, per se) and that successful gene combinations can be broken up via recombination. There are other costs as well. For instance, finding and wooing mates can be costly to an organism.

Nematomorphs, sometimes called hairworms, are parasites that live inside arthropods as larvae, but then exist as free-living aquatic adults. They often induce suicide in their insect hosts, by causing them to jump into water, where the worms then escape (see this previous post for another example). The adults typically seek out the opposite sex and can form "Gordian knots" of mating worms. Today's species, however, is found in larger and faster-moving waters - and in these big, complicated habitats, finding a suitable mate can be really tricky. So, today's parasite, has solved this problem through the evolution of parthenogenesis. Meet Paragordius obamai, (named after President Obama, in honor of it being discovered in Kenya, where his father was raised), a species of nematomorph that has completely given up on males. When brought into the lab, P. obamai only released female worms and nowhere inside these stringy parasites could male reproductive organs be found. Because bacterial symbionts can sometimes produce severe sex-ratio biases or even male-killing in insects and other invertebrates, the authors used pyrosequencing to look for evidence of these micro-manipulators, yet found no sequences similar to the taxa that have been observed to cause these biases in other hosts.

The authors now plan to use this new species, in comparison with a sexual congener, to test hypotheses on the evolution of and genetic mechanisms responsible for this novel parthenogenetic situation.

Source: Hanelt B, Bolek MG, Schmidt-Rhaesa A (2012) Going Solo: Discovery of the First Parthenogenetic Gordiid (Nematomorpha: Gordiida). PLoS ONE 7(4): e34472. doi:10.1371/journal.pone.0034472

Image from the paper.

Contributed by Susan Perkins.


  1. Does Obama know he has such a cool parasite named after him?

  2. This finding is among the most fantastic discoveries I have read about lately. The sole possibility that these micromanipulators can be more widespread in nature is intriguing and opens up new avenues in the research on the evolution of sex.

  3. I ticked funny here because naming parasites after a politicians should be compulsory!

  4. I found it interesting that the parasite induces their insect host to commit suicide. Most of the time we see parasites trying not to kill their hosts and use them to sustain themselves. I also found it cool that it was named after Obama.

  5. I find this parasite very interesting as the adults are actually free-living aquatic adults. In addition, the larvae actually cause arthropod hosts to commit suicide by jumping into water – where the worms escape. Parasites usually look for the other sex to reproduce but they have evolved parthenogenesis as the environmental conditions have gotten difficult. In fact, this specific species has actually given up on males completely and only female worms are released.