On Nov. 24, 1859, British naturalist Charles Darwin published his most famous book, “The Origin of Species by Means of Natural Selection.” Darwin showed that species could change over time, and that nature was doing the selecting for the changes. In 1859, the idea was controversial because many believed species to be immutable and unable to change.
Fossils of long-extinct species were a hot topic then, and the term “dinosaur” was pretty new, coined by Richard Owen just over a decade before Darwin’s publication.
Darwin would live to see his ideas verified by fossils, comparative anatomy and biogeography by the time he died in 1882, but he would pass without a concept of the details of how species change. The structure and function of DNA would not be unveiled until the 1950s, and comparing genomes would not happen in full for another 30 years. He surely would have loved to see the time when the exact change in a species and mechanism of the alteration could be seen. Nature was selecting for genes.
It has been 160 years now, and the details of the power of natural selection are still being published at breakneck speeds. Scientists just published, “The genome of a subterrestrial nematode reveals adaptations to heat” in the journal Nature Communications. The article is another example of discovering the details of natural selection.
The worm in question is Halicephalobus mephisto, also known as the devil worm. The species was only recently found in South American gold mines, living at depths between 1.3 and 3.6 kilometers below the ground. As you might imagine, the conditions it was thriving are not hospitable to most life, so how was this tiny nematode pulling off living in such an inhospitable world? What was nature selecting for so that it could live 2 miles below our feet?
Once the genome of this worm was explored, a few key features emerged. Their genome was loaded with Hsp70 genes that code for heat-shock proteins. These proteins act to keep cells functioning at temperatures that would shut down cellular life and helps refold proteins that are damaged by heat. They are common in most species, but this little worm had extra copies or duplications of the genes. The researchers also noted that the worm had additional AIG1 genes that also code for proteins that aid in the survival of cells under stress.
The researchers compared the genome of the devil worm to its famous close relative, C. elegans, which is found commonly in the soil above the ground. The devil worm had 126 Hsp70 domains compared to only 15 in the above-ground cousin, and 84 AIG1 domains compared to none in the above-ground C. elegans. The team shows that the AIG1 genes were most likely picked up by horizontal gene transfer from a fungus and then duplicated many times.
This is another mechanism Darwin would have marveled at in which different species swap gene segments. In short, the article details out the changes that nature has selected as the devil worm evolved in new environments.