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Why are the offspring of older mothers less likely to live and thrive?



Why are the offspring of older mothers less likely to live and thrive?

Mother Rotifer (Brachionus manjavacas) with four eggs (right) and a newly hatched daughter (left). Image of living rotifers, recorded with polychromatic polarization and phase contrast. Photo credit: Michael Shribak, Evgeny Ivashkin, Kristin Gribble

The descendants of older mothers do not perform as well in humans and many other species as younger mothers. They are not so healthy or they do not live that long or they have fewer offspring themselves. A long-standing mystery is why evolution would maintain this maternal effect in so many species, as these late-born offspring are less viable and reproductive.

In a new study on rotifers (microscopic invertebrates), scientists tested the evolutionary fitness of offspring of older mothers in multiple real and simulated environments, including the relative luxury of laboratory culture, under the threat of wild animals or with reduced food supply. They confirmed that this effect of older maternal age, known as maternal senescence, lowers the evolutionary fitness of offspring in all environments, primarily through decreased fertility during their peak reproductive period. They also suggest an evolutionary mechanism as to why this can occur. The study, led by Kristin Gribble from the Marine Biological Laboratory and Christina Hernández from the Woods Hole Oceanographic Institution, will be published this week in National Academy of Sciences procedure.

“This study is unique in that it combines laboratory data from previous work with mathematical models to answer a longstanding question in the development of aging,”

; says Gribble. “Natural selection should eradicate these less healthy offspring of older mothers. So why do we see this phenomenon in so many species?”

To remedy this, Hernández and co-workers created mathematical models to calculate for the first time the strength of the natural selection pressure on the survival and fertility of offspring populations as a function of the age of their mothers. They found that this pressure, known as the selection gradient, decreases with the age of the mother.

“As the selection pressure decreases with increasing age of the mother, it may not be strong enough to remove her less fit [offspring] from the population, “says Hernandez.

“For this reason, the senescence of the maternal effect in the population will continue and develop, even though this leads to reduced fitness,” added Gribble. They do not yet fully understand the genetic mechanisms that cause the quality of the offspring to decrease with the age of the mother.

The models developed by the team can be used in a variety of ways to assess the fitness effects of senescence from mother effects. “As long as we have experimental data on the lifespan and fertility of offspring from mothers of different ages, you can answer this question in many organisms,” says Gribble.


Study results show that the offspring of older mothers react more strongly to aging measures


More information:
Christina M. Hernández et al., A Demographic and Evolutionary Analysis of the Senescence of Maternal Effects, National Academy of Sciences procedure (2020). DOI: 10.1073 / pnas.1919988117

Provided by
Marine biological laboratory




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Why are the offspring of older mothers less likely to live and thrive? (2020 July 2nd)
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