Figure 1. Kasabong stream where hairworm-infected snails were collected.
The picture was taken during the dry season.
Posted on 02/11/2013 7:23:52 PM PST by annalex
Several years ago, Dr. Ben Hanelt, from the University of New Mexico, was working as a post-doctoral fellow on a human health project in the city of Kisumu, which is located in western Kenya along the edges of Lake Victoria. The project involved the collection of snails that serve as intermediate hosts for the human parasite Schistosoma mansoni.
Hanelt had previously worked on another group of non-human parasites known as hairworms. Hairworms use insects such as crickets as hosts and can also use snails as intermediate hosts. Within the snail hosts, hairworms do not mature, but hairworm larvae simply go into a resting stage called a cyst. On a hunch, and after a long day collecting snails in the streams surrounding Lake Victoria (Figure 1), Hanelt decided to dissect a snail for hairworms from Kasabong stream.
Hanelt was surprised when the first snail, and a dozen others, contained a large number of hairworm cysts. From previous work in the United States, Hanelt immediately recognized these cysts as belonging to the genus Paragordius (Figure 2).
Figure 1. Kasabong stream where hairworm-infected snails were collected.
The picture was taken during the dry season.
Figure 2. Hairworm cyst found within snails collected in Kenya.
Note that the larva is in a resting stage called a cyst.
Hanelt had previously worked on another hairworm species calledParagordius varius, common in the United States. Hanelt and his colleague Dr. Matt Bolek, at Oklahoma State University, have been maintaining P. varius in the laboratory for many years cycling through Physa sp. snails and cricket hosts (Acheta domesticus or Gryllus spp.).
In nature, once released from their cricket hosts, male and female hairworms pair and mate. However, since gordiids rely on large and long river systems and areas with vast aquatic habitats, they must overcome the problem of release by the host distantly in space and time, which can result in worms finding themselves trapped in aquatic systems without mates. This is certainly the case in the Kenyan stream where Hanelt collected the hairworm containing snails, since it is a long stream with a moderately-fast flow of water, especially during the rainy season.
Several weeks after his discovery, Hanelt returned to his laboratory in the United States with live snails containing these hairworm cysts. In order to describe a new hairworm species, it is necessary to examine and describe adult worms. Again, on a hunch, Hanelt fed the Kenyan hairworm cysts to crickets. After 30 days, the hosts were checked for infection by placing the crickets into water. The American species, P. varius, normally matures within 28-30 days, and crickets placed into water will release up to 30 worms. However, no worms emerged from the crickets exposed to the Kenyan cysts. Crickets were checked every 5 days thereafter without success. Finally, after almost 3 months, worms began emerging from these crickets (Figure 3).
Figure 3. A female Paragordius obamai worm emerges from a cricket host.
Note that the cricket was exposed almost 3 months previously with cysts
from snail tissue collected in Kenya.
Of 12 infected crickets, 24 worms emerged. However, much to Hanelt’s dismay, all 24 of the worms shed were females! He knew that in order to successfully establish the new species in the laboratory, he needed both male and female worms; to mate and produce eggs. He separated the worms into individual containers and went home that night disappointed.
The next morning, ready to fix all worms in alcohol, Hanelt made an incredible discovery—every worm had produced eggs. After a few days it became apparent that the eggs were developing normally and a few weeks later larvae hatched and easily infected snails and turned into cysts. But, how could this be? There were no males!
For confirmation of these results, Hanelt sent samples to Bolek, who repeated the experiment and got the same result; no males but each female produced viable eggs. This was apparently the result of a process known as parthenogenesis. Parthenogenesis is a form of asexual reproduction where growth and development of embryos occur without fertilization. This type of reproduction is common in other groups of invertebrates and parasites, but has never been reported from hairworms.
Over the next months, Hanelt, Bolek, and their colleague Dr. Andreas Schmidt-Rhaesa at the University of Hamburg, Germany explored this new and unique species using molecular biology, scanning electron microscopy, and light microscopy. Hanelt, Bolek, and Schmidt-Rhaesa found that this species represented a previously undescribed hairworm and confirmed that this new species does something unique in this group—it has gotten rid of males.
In some invertebrates, males are selectively killed by “male killing” bacteria. However, the investigators found that this is not the case for this new hairworm species. Instead, Hanelt, Bolek, and Schmidt-Rhaesa suggest that becoming a female-only species is an evolutionary solution to the difficulty these worms face in finding a mate in nature. Furthermore, the results from this study and future research could advance the work of scientists who are investigating the reasons why some animals reproduce asexually. Since this new Kenyan species is closely related to the American species (P. varius) various hypotheses can now be tested about the advantages and disadvantages of sex, especially in parasites, and eventually it may allow scientists to probe the genetic determinants of reproductive strategies in parasites.
Since the initial discovery of the new hairworm species, this remote part of Kenya has gained international attention. Just 19 kilometers (11 miles) to the northwest of Kasabong stream sits the town of Kogelo, where President Barack H. Obama’s father was born and paternal step-grandmother resides. The town contains the Senator Barack Obama Primary and Secondary Schools (Figure 4). Hanelt, Bolek, and Schmidt-Rhaesa decided to name this new and unique species in honor of the 44th president of the United States—Paragordius obamai.
Figure 4. Sign to the Senator Obama Secondary School just outside of Kogelo;(Picture credit: www.kisumuhomestays.com), just a few kilometers from the collecting site of Paragordius obamai.
Science news.
Gaaaah!!
How appropriate. How pinpoint accurate.
A parasitic worm from Kenya, named in honor of President Obama.
It’s absolute poetry.
I’m sure the worms, cysts, etc. whatever feel greatly honored.
Bump!
I can’t stop giggling.
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