Figure 3.The xenohormetic, hormetic and cytostatic selective forces may drive the evolution of longevity regulation mechanisms within an ecosystem. We
propose that organisms from all domains of life within an ecosystem
synthesize chemical compounds that 1) are produced and then released into
the environment permanently or only in response to deteriorating
environmental conditions, increased population density
of competitors and/or predators, or changes in food availability and its
nutrient and/or caloric content; 2) are mildly toxic compounds that
trigger a hormetic response in an organism that senses them or,
alternatively, are not toxic for any organism within the ecosystem and do
not cause a hormetic response; 3) are cytostatic compounds that attenuate the TOR-governed signaling network or, alternatively,
do not modulate this growth-promoting network; and 4) extend
longevity of organisms that can sense these compounds (red arrows), thereby
increasing their chances of survival and creating selective force aimed at
maintaining the ability of organisms composing the ecosystem to respond to
these compounds by undergoing specific life-extending changes to their
physiology. In our hypothesis, the evolution of longevity regulation
mechanisms in each group of the organisms composing an ecosystem is driven
by the ability of this group of organisms to undergo specific
life-extending changes to their physiology in response to a compendium of
"critical" chemical compounds that are permanently or transiently released
to the ecosystem by other groups of organisms. Abbreviations: LCA, lithocholic
acid; DCA, bile acid-like dafachronic acids.
