Food odor accelerated reproduction in worms that survived a day without food, while their lifespan extension persisted
Food odor accelerated reproduction in worms that survived a day without food, while their lifespan extension persisted
A team at the University of East Anglia used the microscopic roundworm C. elegans to test the hypothesis that fasting extends lifespan by reducing reproduction. The peer-reviewed version of the study was published on November 5 in Aging Cell.
One widely held hypothesis proposes that when food is scarce, organisms delay reproduction and redirect the resources this frees up toward bodily repair and maintenance. If so, faster reproduction under the same feeding conditions should reduce the lifespan extension. To test this, the researchers separated access to food from exposure to its odor.
The bacteria that the worms feed on were placed beneath a layer of gel. Their odor reached the animals, but the worms could not eat the bacteria. In the team's 2021 experiments, exposure to this odor during a two-day fast partially restored reproduction and reduced the lifespan extension. In the current experiments, fasting lasted one day. Worms that survived this regimen were randomly selected for subsequent measurements and returned to their usual food.
Worms exposed to food odor during fasting produced more offspring in the first few days afterward than those that fasted without the odor. Over their entire lives, worms that had fasted produced fewer offspring than worms that had remained fed. Both fasting groups subsequently lived longer than the fed group, and no difference in survival was detected between the two fasting groups. The authors interpret the suppression of reproduction as “reproductive restraint in an unfavorable environment.”
The authors proposed an evolutionary model to explain how this dependence of lifespan on food availability could arise. Aging biologist Peter Lidsky asked:
“I still don't understand how mutation accumulation arises here.”
The model describes changes over many generations, with prolonged periods of food abundance and scarcity. In its simplest form, reproduction does not increase the risk of death, and a lower birth rate slows population growth. When a population grows rapidly, offspring born earlier have more time to reproduce themselves and contribute disproportionately to future generations.
As population growth slows, the advantage of earlier-born offspring diminishes, and older parents make a relatively greater contribution to future generations. Death before reproduction at later ages therefore causes a greater reduction in a parent's contribution to future generations. Selection consequently favors gene variants that allow survival to these later reproductive ages more strongly.
The authors propose that heritable mutations may impair bodily repair and maintenance only at particular ages and under particular feeding conditions. When food is abundant, selection for survival is weaker than when food is scarce. Mutations that are harmful only when food is abundant can therefore accumulate over generations, shortening lifespan under those conditions. This is how the model produces an organism that lives longer when food is scarce. The model predicts that a similar response could evolve to other moderate stresses that reduce the birth rate.