Some parasites have taken the simple life to whole new extremes.
Scientists have recently discovered a strange, mind-controlling worm that is missing some of the most basic genes in the animal kingdom.
Ironically, the extremely long and thin ‘hair worm’ (also known as a ‘horse worm’) does not have the ‘hairs’ at the cellular level that allow most animal cells to move, sense or filter liquids.
These microscopic filaments are called cilia and they extend from the surface of almost every cell in the human body.
But somehow, someway, two distant species of hairworms – one based on fresh water (Acutogordius australensis) and one based on saline (Nectonema Munidae) – have learned to live without these vital appendages.
According to a team of researchers from Harvard University, the University of Copenhagen, and the Field Museum of Chicago, the two species are missing about 30 percent of the genes thought to be responsible for the development of cilia across almost all animal groups.
The authors concluded that a distant common ancestor of hairworms must have lost these genes long ago. But why they did so is a mystery.
“Cilia are organelles, small structures at the cellular level, which are present basically throughout all animals and even more widely, in protozoa and in some plants and fungi,” explains Field Museum evolutionary biologist Mr. Cunha.
“So they are present across a wide variety of life on Earth.”
But the hairworm is special.
In the animal kingdom, it is parasites are not uncommon be missing many of the genes. Like the hairworm, many of these creatures lack excretory, respiratory or circulatory systems. Instead, they rely on the bodies of other animals to do most of the hard work.
In evolutionary biology, if an animal doesn’t use a structure or function, they tend to lose it gradually while reclaiming the cost it requires.
However, the existence of null genes for cellular cilia is remarkable. Hairworm sperm do not even have a tail-like filamentous projection.
“There are plenty of other parasitic organisms that lack these specific genes, so we can’t say that the genes are missing because of their parasitic lifestyle,” say Cunha.
Researchers had previously noticed that hairworms lacked cilia in some cells. But until now, it was not clear if this pattern existed across all cells of the parasite in all stages of its life.
“Now with the genomes, we saw that they actually lack the genes that produce cilia in other animals – they don’t have the machinery to make cilia in the first place,” explains Cunha.
“The loss probably happened early in the group’s evolution, and they’re continuing that way.”
The authors hope their study will help scientists further explore the “genomic mechanisms underlying parasitism” to show how these webbed creatures pull off their entire body surfaces.
After invading a cricket’s brain, maturing hairworms eat the insect from the inside out, sparing enough of its body to keep it alive.
Once they’ve had their fill, the hairworm triggers the cricket’s nervous system, moving the host in spurts towards a body of water.
When its grumpy pupa is drowned, the worm jumps ship, crawling out of the cricket’s body in long, thin skins so it can reproduce.
Something in this macabre reproductive process may require specialized sensory organs that have no use for cilia. Future investigations into this strange puppet master will no doubt continue to reveal why he is so unique.
The study was published in Current Biology.