Hairworms are parasitic worms that manipulate the behavior of their hosts; what some refer to as "mind control." They are found all over the world, look like strands of spaghetti, and are only a few inches long. Even more bizarre, they have no excretory, respiratory, or circulatory systems, spending most of their life inside the bodies of other animals.
In keeping with the strange traits of these animals, a new study in Current Biology reveals they're also missing about 30% of the genes researchers expected them to have. The missing genes are responsible for the development of cilia, hair-like structures that are present in some cells of every other animal. Cilia are organelles that are present in animals, protists, and some plants and fungi. They are even present in humans in the tails of sperm cells and in the retinas of our eyes.
The study, led by former graduate student, Tauana Cunha (PhD '19), collected DNA samples from two hairworm species (one freshwater and one saltwater) and sequenced them. Upon comparing the genetic codes to other animals, the researchers discovered the hairworms were missing 30% of the set of genes normally present across groups of animals. The majority of the missing genes were also the same between the two hairworm species.
Tauana and co-authors', including alumni Bruno de Medeiros (PhD '19), PhD candidate Arianna Lord, and Professor Gonzalo Giribet, genomic work confirms that hairworms lack the genes to produce cilia. Further, the connection between both freshwater and marine hairworm species loss of cilia genes suggests this evolutionary change occurred deep in the past to a common ancestor.
While it's unclear if the lack of cilia could have an effect on hairworms' parasitic behavior -- parasitic organisms in general are often missing genes -- the researchers hypothesize that parasites may come to rely on their hosts, therefore losing the need for these genes. The study could aid in finding common threads for parasitic behavior across organisms.