An Alternative to Evolution: borrowed immunity (Introduction)

by David Turell , Thursday, July 18, 2024, 16:12 (126 days ago) @ David Turell

From horizontal gene transfer:

https://www.science.org/content/article/these-microscopic-animals-fight-infection-using...

"At half a millimeter long—about the width of a human hair—bdelloid rotifers might be easy to miss. But these tiny freshwater critters are some of the toughest animals on the planet. Comprised entirely of females, they’re particularly notorious for “stealing” genes from other organisms. That ability has allowed them to go 40 million years without sex, once leading biologist John Maynard Smith to call them an “evolutionary scandal.”

"New research may explain how this weird little animal got to where it is today. According to a study published today in Nature Communications, some bdelloids can protect themselves against infection using chemical “recipes” pilfered from bacteria. The discovery is an “exciting example of foreign genes functioning in animal genomes,” says Isobel Eyres, an evolutionary biologist at the University of Sheffield who wasn’t involved in the work. It could also help explain how this group of “ancient asexuals” has survived for so long, she adds.

"First described more than 300 years ago, bdelloid (pronounced “dell-oid,” with a silent “b”) rotifers—some of the first organisms to be witnessed through a microscope—look a bit like tiny, transparent leeches. They can be found in nearly every pond, stream, and puddle in the world. Scientists have now identified more than 450 different species, all female.

“'They’re the only major class of animals where no males whatsoever have been described or reported,” says Chris Wilson, an evolutionary biologist at the University of Oxford and co-author of the new study. Each daughter rotifer is a perfect copy of her mother.

"This lack of sex has long baffled evolutionary biologists, Eyres says, because it ought to make bdelloids extremely vulnerable to extinction. Sexual reproduction gives species an advantage by allowing them to shuffle their genes around and rapidly evolve defenses against other organisms. A field of genetically identical crops, by contrast, can be easily wiped out by a single pathogen. “This is not the case for bdelloids,” she notes, which have managed to survive a host of extreme conditions, including extreme drought, blasts of radiation, and 24,000 million years frozen in Siberian permafrost.

"Part of the reason bdelloids are so tough, Wilson says, is because they have “one of the strangest genomes of any animal.” Scientists have known for decades that the DNA of the bdelloid rotifer contains an unusual amount of material “borrowed” from other species through a process known as horizontal gene transfer. In fact, a whopping 10% of the bdelloids’ active genes appear to have originated from other organisms, such as bacteria, fungi, and plants.

“'One in 10 of the genes are not even animal genes,” Wilson says. “They have no business being there.”

***

"When the scientists looked closer, they discovered hundreds of genes that the bdelloids seem to have acquired from bacteria. These genes code for enormous enzymes known as synthetases, which serve as “recipes” for complex chemicals—including those with antimicrobial abilities. Although bacteria frequently use these recipes to ward off competitors, Wilson explains, this is the first time they have been found in animals.

"But even though these genes were originally stolen from bacteria, they appear to have evolved in bdelloids to produce compounds that are toxic to some pathogens while not being toxic to bdelloids’ own cells."

Comment: Celibate and still here is just one surprise. Stealing genes so massively is the other. Sexual reproduction requires a large energy expenditure. This proves it is OK to be asexual.