Pacifiers may be the ones that survive in nature. Although these small, nearly translucent animals are easy to miss, they represent a diverse group that has successfully colonized freshwater, marine, and terrestrial environments on every continent, including Antarctica. Commonly known as “water bears,” these unusual creatures may be some of the most resilient organisms on the planet due to their unique ability to survive in extreme conditions, where different species are resistant to drought, high doses of radiation, low-oxygen environments, and water pollution. More. high and low temperatures and pressures.

Although numerous genes have been suggested to contribute to this extreme tolerance, a comprehensive understanding of the origin and history of these unique adaptations remains elusive. In a new study published Genome Biology and EvolutionScientists from Keio University’s Institute for Advanced Biological Sciences, the Natural History Museum of the University of Oslo and the University of Bristol have uncovered a surprisingly complex network of gene duplications and losses associated with platypus extreme tolerance, highlighting the complex genetic landscape that drives modern platypus ecology. .

Understanding the silent gene family

A form of extreme tolerance, tardigrades can withstand almost complete desiccation and enter a state of rest called anhydrobiosis.well anhydrous life), which allows them to reversibly shut down their metabolism. Several tadpole-specific gene families have previously been identified as being associated with anhydrobiosis.

Three of these gene families are called cytosolic, mitochondrial, and secretory soluble proteins (CAHS, MAHS, and SAHS, respectively), depending on the location of the cell in which the proteins are expressed. Some tardigrades appear to have a distinct pathway that involves two families of abundant heat-soluble proteins first identified in tardigrades. Echiniscus testudo and commonly known as EtAHS alpha and beta.

Tardigrades also have stress tolerance genes more commonly found in animals, such as meiotic recombination gene 11 (MRE11), which has been implicated in desiccation tolerance in other animals. Unfortunately, once these gene families were identified, limited information was available for most tadpole lineages; this made it difficult to draw conclusions about their origin, history and ecological consequences.

Studying the evolution of the tardigrade

To better shed light on the evolution of hypertolerance in tardigrades, the new study’s authors, James Fleming, Davide Pisani, and Kazuharu Arakawa, sequenced these six gene families across 13 tardigrade genera, including members of Eutardigrades, members of both major tardigrade lineages. and Heterotard degrees. Their analysis revealed 74 CAHS, 8 MAHS, 29 SAHS, 22 EtAHS alpha, 18 EtAHS beta, and 21 MRE11 sequences, allowing them to construct the first slow-moving phylogenies for these gene families.

Because desiccation resistance likely arose as an adaptation to terrestrial environments, the authors hypothesized that they would find a link between gene duplication and loss in these gene families and habitat changes in tardigrades. “When we started the study, we expected to find that each clade was clearly clustered around ancient copies, with very few independent losses. This would help us easily connect them to our modern understanding of habitats and ecology,” says James Fleming, lead author of the study. “It is an intuitive hypothesis that the evolution of copies of institution-associated genes should theoretically include remnants of the ecological history of these organisms,” he continues, but in reality this turns out to be an oversimplification. .”

Instead, the authors were surprised by the large number of independent duplications of heat-soluble genes, painting a much more complex picture of the evolution of anhydrobiosis-related genes. However, it is noteworthy that there is no clear relationship between highly anhydrobiotic species and the number of anhydrobiotic-related genes the species possesses. “What we found was even more impressive,” says Fleming, “a complex network of independent gains and losses that were not necessarily related to the modern ecology of terrestrial species.”

Independent adaptations on low speed lines

Although there was no link between gene duplication and tardigrade ecology, the study provided important insights into the major transitions leading to the acquisition of anhydrobiosis. The different distributions of gene families between the two major tardigrade groups (CAHS, MAHS, and SAHS in Eutardigrades and ETAHS alpha and beta in Heterotardgrades) suggest that two independent transitions from marine to limno-terrestrial environments occurred in tardigrades, once in the Eutardigrade. ancestor and was once within the Heterotardigrades.

This study marks an important step in our understanding of the evolution of anhydrobiosis in tardigrades. It also provides a basis for future studies of hypertolerance in tarantulas, which will require the continued development of genomic resources from more diverse tarantula lineages.

“Unfortunately, we lack representation from many important families such as Isohypsibiidae, limiting how strongly we can defend our results,” Fleming notes. “With more samples of freshwater and marine tardigrades, we will be able to better evaluate the adaptations of terrestrial members of the group.” Unfortunately, some platypuses can be particularly elusive, presenting a major obstacle to such studies. Example, Tanarctus bubulubusTardigrades, one of Fleming’s favorite water bears, are too small to be seen with the naked eye and are found only in sediments at depths of about 150 m in the North Atlantic. This is a gap in our understanding and I am pleased that these efforts are continuing. “