Biological complexity: mammalian hibernation metabolism (Introduction)

by David Turell , Friday, January 28, 2022, 20:56 (1030 days ago) @ David Turell

Different processes for different animals:

https://www.sciencemagazinedigital.org/sciencemagazine/28_january_2022/MobilePagedArtic...

Hibernating animals do not eat or drink over a long period of time, often months, when they are inactive and spend most of their time sleeping. During this torpid state, hibernators can drastically reduce their metabolic rates, allowing them to reduce their energy demands. Despite this combination of fasting and inactivity, hibernating animals keep their lean mass relatively stable, with some even gaining muscle mass by the end of hibernation.

To elucidate how squirrels maintain their physiological functions during hibernation, Regan et al. used stable isotope labeling to track the flow of nitrogen and carbon in squirrels during the active phase and hibernation. These experiments revealed that urea, which is produced by the host during protein catabolism, is transported from the blood to the gut lumen in addition to being excreted in the urine.

All animals live in close association with a vast diversity of microorganisms—the microbiota—that contributes to various aspects of host physiology (Display footnote number. Previous research identified that hibernation alters the gut microbiota (Display footnote number, 5). In bears, the microbiota assists in extracting energy from the diet to facilitate prehibernation fattening (Display footnote number. In hibernating frogs, gut microbes encode an increased potential for nitrogen salvage. Using metagenomic sequencing, Regan et al. found that the gut lumen of squirrels contains microorganisms with urease genes, which enable the microorganisms to produce enzymes (i.e., ureases) that metabolize urea into carbon dioxide and ammonium. The ammonium is then used by the same microbiota as a source of nitrogen to produce amino acids, some of which are then absorbed by the host. As a result of this process, nitrogen loss during protein catabolism and urea formation is compensated, which counteracts muscle wasting. Although the process of urea nitrogen salvaging has been known in ruminants such as cattle, goats, and sheep, the identification and molecular delineation of urea nitrogen salvaging in hibernating mammals add another central role for intestinal microorganisms within the coordination of host physiological adaptations.

Comment: Hibernation requires symbiosis with specialized organisms. How does this adaptation work naturally? Not epigenetically since different organisms have to work together. Trial and error would kill if tried suddenly, so it has to be gradual over time and goal directed. How about design?