Is Natural Selection Against Offsprings of Older Mothers?

A study published in the Proceedings of National Academy of Sciences has explained what they have termed as, the maternal effect senescence. This effect falls under a bigger concept of reproductive senescence, which is widely seen in almost all species of animals. Underneath this effect is also the fertility senescence, which is decribed as the aging of reproductive physiology, while maternal effect senescence examines the inverse relation between maternal age and offspring quality. The accepted definition of the term, maternal effect senescence is, ‘​the reduced success or quality of offspring with advancing age of the mother’.Pregnancy

Researchers Explore The Mechanism Of Maternal Effect Senescence

The exact mechanism of Maternal Effect Senescence is not known and neither does enough literature exist to clarify the mechanism behind it. However, in the above-mentioned study performed by Kristin Gribble of the Marine Biological Laboratory and Christina Hernández of Woods Hole Oceanographic Institution, the researchers have aimed to improve our understanding of this effect which affects all species, animals, humans and plants alike.

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Researchers, after studying rotifers, concluded that all species underwent this effect as part of their evolution. Specifically, the study demonstrated that natural selection affected these offsprings by reducing the fertility of mothers during peak years. This, according to the researchers, leads to less fitness of offspring, and overall lesser viability. They also found that most offspring of older mothers had a lower survival rate when compared to the offsprings of younger mothers. However, the question remains, how exactly does it affect the offsprings.

According to Gribble, ​”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,”. This shows the credibility of the work done, even if it fails to answer all the questions that the study raises.

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Building on the work of Gribble, Hernandez and et.al. conducted another study in which they developed a selection gradient, which was a difference of measurement between the offspring viability and the maternal age. It also
showed an inverse relationship, building a concrete support model for maternal effect senescence. Although a clear etiology behind it could not be found.

Maternal Senescence Affects Fertility Across All Species

Researchers concluded that the maternal-effect senescence, which is a component of widely accepted reproductive senescence along with fertility senescence, affects all species by decreasing the viability of offspring born to older mothers. They also tried to answer the question of why evolution would allow a process that could potentially wipe out an entire species. However, the study discovered that the effect wasn’t strong enough to wipe out a species but was nevertheless strong enough to reduce overall fitness in these offsprings. The study proves the efficiency of maternal-effect senescence and its impact in the evolutionary process.

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References

A demographic and evolutionary analysis of maternal effect senescence

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