Tuesday, July 21, 2020

Sex and Death among Holobionts and Organisms

My mother in law, Liliana, turns 100 today. Happy Birthday, Liliana!

Both holobionts and organisms have to fight entropic decay. Holobionts do that by continuously changing their hologenome in a horizontal exchange of information. Organisms do the same by the vertical mixing of their genome in the process called sexual reproduction. Both methods are driven by natural selection.
The second strategy, sexual reproduction, brings the need of eliminating the old genomes by the process of aging. True holobionts never die (think of a forest), but organisms do. Too bad for organisms, but it is a choice (and a lot of fun, too!). 
Liliana turned out to be a successful and resilient organism. So far, she has three daughters, a son, three grandsons, one grand-daughter and, recently, two great-grand daughters. Not bad!


  1. How to separate the organism from the holobiont? For instance, reproduction of a human also involves asexual reproduction: inheritance of the mother's mitochondria and her microbiome.

    1. Yes, the mitochondria have their own genetic line, indeed. But the organisms within a holobiont are easily separated, I think: they are the groups which have the same DNA. In this sense, mitochondria are guests in our bodies, just like the gut flora. But they use a different kind of transmission, not vertical but horizontal, they take a ride with the female cells during reproduction. Lots of interesting stories.....

    2. Yes, other interesting stories: the symbiosis of plants and chloroplasts, and corals and zooxanthellae.
      The ancient symbiogenesis of eukaryotes may be related to the early Palaeoproterozoic Great Oxidation Event:

  2. buon compleanno, tanti auguri Liliana



Ugo Bardi is a member of the Club of Rome, faculty member of the University of Florence, and the author of "Extracted" (Chelsea Green 2014), "The Seneca Effect" (Springer 2017), and Before the Collapse (Springer 2019)