Why are the offspring of older mothers less fit to live long and prosper?

According to a study that was conducted, offsprings of older mothers don’t fare as well as younger mothers, both humans and other species. This has been a longstanding question upon evolutionary traits amongst scientists.

Through a new study on rotifers, scientists tested the evolutionary fitness of an older mother in several real and simulated environments, including the relative luxury of laboratory culture, under threat of predation in the wild, or with reduced food supply. They confirmed that this effect of older maternal age, called maternal effect senescence, does reduce evolutionary fitness of the offspring in all environments, primarily through reduced fertility during their peak reproductive period. They also suggest an evolutionary mechanism for why this may occur. The study was led by Kristin Gribble of the Marine Biological Laboratory and Christina Hernández of Woods Hole Oceanographic Institution.

“This study is unique in that it combines laboratory data from our prior work with mathematical modeling to address a longstanding question in the evolution of aging. Natural selection should weed out these less-fit offspring of older mothers. So why do we see this phenomenon across so many species?”

Kristin Gribble of the Marine Biological Laboratory

Hernandez and the other collaborators decided to address this problem by creating mathematical models for calculation of data. And their results show that as the strength of natural selection becomes a pressured phenomenon on the survival and fertility of an older mother, the “selection gradient” (the term used to define this phenomenon) declines with age.

“Because the selection pressure decreases as the mothers age, it may not be strong enough to remove these less-fit [offspring] from the population”

Christina Hernández of Woods Hole Oceanographic Institution.

“Because of this, maternal effect senescence will persist and continue to evolve in the population, even though it results in decreased fitness,” Gribble adds. They don’t yet fully understand the genetic mechanisms that cause offspring quality to decrease with maternal age.

Kristin Gribble

This model can be applied on various other species with the same evolutionary phenomenon as well to evaluate maternal senescence.

“As long as you have experimental data, as we did, on lifespan and fecundity of offspring from mothers of different ages, you can address this question in many organisms”

Kristin Gribble

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