World’s simplest animals as different from each other as humans and mice
|September 25, 2018||Posted by News under Genomics, speciation|
The world’s simplest animal is trichoplax adhaerens. It is so simple that researchers wisely decided to forego the venerable Biological Species Concept that depends on an animal’s form (tricoplax doesn’t have much of a form) and just use genetics. But when evolutionary biologist Michael Eitel sequenced the genomes of several thousand of them, he was in for a surprise:
A quarter of the genes were in the wrong spot or written backward. Instructions for similar proteins were spelled nearly 30 percent differently on average, and in some cases as much as 80 percent. The Hong Kong variety was missing 4 percent of its distant cousin’s genes and had its own share of genes unique to itself. Overall, the Hong Kong placozoan genome was about as different from that of T. adhaerens as human DNA is from mouse DNA. “It was really striking,” Eitel said. “They look the same, and we look completely different from mice.”
So where do all those genetic changes manifest, if not in the animals’ flabby appearance?
“Even though the placozoan itself looks like a little ball of glue, it probably has cells that are doing some pretty sophisticated things,” said Holly Bik, a marine biologist at the University of California, Riverside, who studies tiny marine roundworms known as nematodes, which can also be cryptic.Charlie Wood, “World’s Simplest Animal Reveals Hidden Diversity” at Quanta
Paper. (open access)
Genetically, humans and mice have more in common than the Hong Kong placozoan and the T. adhaerens placozoan because humans and mice are both mammals. But the genetic distance between the placazoans is greater than between “most vertebrate orders.”
One can take from this the lesson that the genome is very plastic. One thinks of the strenuous efforts of Darwinian biologists to demonstrate speciation according to their concepts (Darwin’s finches come to mind). And it’s probably all for nothing (except ensuring that school textbooks continue to misrepresent the history of life).
See also: A physicist looks at biology’s problem of “speciation” in humans