Maternal Age Leaves a Reversible, Genotype-Dependent Biological Mark Across Generations

A mother's age at the time she gives birth can leave a biological imprint on her offspring, shaping lifespan, reproductive timing, and the number of young produced—a phenomenon observed across the animal kingdom, from invertebrates to humans, elephants, and other primates. These "maternal age effects" are widespread, yet the biological mechanisms that transmit age-related information between generations remain poorly understood.

"Maternal age effects are incredibly common, from invertebrates up through humans, elephants, other primates and other mammals," said Kristin Gribble, an associate scientist in the Bay Paul Center at the Marine Biological Laboratory (搜索)搜索该词条 (MBL). "Nearly all forms of life show some level of maternal age effect, and most are negative effects caused by advanced maternal age."

Tiny Animals Offer Clues to a Cross-Generational Signal

To investigate how information about maternal age reaches the next generation, Gribble's laboratory studied Brachionus manjavacas (搜索)搜索该疾病, a microscopic aquatic rotifer. Rotifers live for roughly one to four weeks and can reproduce without mating under certain conditions, allowing researchers to follow several generations rapidly.

Across four generations, the team compared two genetic strains—BmanRUS and BmanL5—that carry different inherited versions of genes. Offspring came from mothers that were either three days old or 10 to 11 days old, forming young- and old-mother groups. Each rotifer lived alone while researchers monitored its survival and counted its offspring daily.

"Understanding the mechanism in these simple invertebrates can help us understand how maternal age effects occur in people as well," Gribble said.

Genes Change the Direction of the Effect

The results did not reveal a single, simple rule. Maternal age had similar effects on total lifetime reproduction across generations, but those effects moved in opposite directions in the two strains. BmanRUS offspring born to older mothers produced more young over their lifetimes, while BmanL5 showed the opposite pattern—although offspring of older mothers reached a higher daily reproductive peak in both strains.

"There are likely gene variants out there that are protective of negative effects of advanced maternal age," Gribble said. "In one of our strains, we saw that offspring from older mothers had a longer lifespan, implying a genetic mechanism may be involved in that beneficial effect." The BmanRUS result raised this possibility, although the evidence was not strong enough to rule out chance.

Lifespan Effects Can Disappear Within a Generation

In BmanL5, offspring of older mothers lived just over two days less than offspring of younger mothers in the first two descendant generations. However, that gap disappeared in the third generation. This rapid reversal argues against the idea that maternal age effects simply result from a gradual buildup of age-related cellular damage or DNA mutations.

The team further tested this by switching maternal age groups in the third generation. Some descendants from older-mother lines were born to young mothers, while some from younger-mother lines were born to older mothers. In BmanL5, total lifetime reproduction followed the current mother's age, meaning earlier family history no longer predicted that outcome. BmanRUS showed a more complex pattern: no measured effect fully reset in both directions, and the grandmother's age continued to shape lifespan or reproduction in some comparisons. Rotifers with older grandmothers also reached a higher daily reproductive peak.

Epigenetics and Mitochondria as Candidate Mechanisms

One possible explanation involves epigenetics, which can change how strongly genes are expressed without altering the underlying DNA sequence. DNA wraps around proteins called histones, and chemical changes to these proteins can increase or decrease the activity of nearby genes. The paper did not measure changes to histones, so it cannot show that they caused the observed results. Still, the quick reversals and lack of steady worsening make an accumulation of permanent DNA mutations less likely to be the main explanation.

The team also considered mitochondria, the tiny structures that help cells release energy from food. Mitochondria contain their own DNA, which mothers usually pass to their offspring. Gribble suggested that mitochondrial DNA (搜索)搜索该靶点 may play a role "in transmitting information about maternal age from moms to offspring," though the experiment did not test that possibility directly.

Why Evolution Has Not Eliminated the Pattern

A larger evolutionary puzzle remains: why do maternal age effects continue to exist? Offspring of older mothers often have shorter lifespans, reproduce less, and have lower evolutionary fitness—traits that might be expected to disappear through natural selection. Gribble suspects part of the explanation is that the force of natural selection declines later in life.

"Selective pressure is much lower at advanced ages, particularly in rotifers which are really geared to do most of their living and reproducing very young," she said. By old age, female rotifers have already produced most of their offspring, leaving less evolutionary pressure for late-life reproduction to produce highly fit descendants.

This does not mean every effect is harmful. The opposite patterns in the two strains show that certain genetic backgrounds may turn advanced maternal age into an advantage for some traits.

Implications for Human Health and Precision Medicine

Gribble's broader question reaches beyond mothers and their offspring. "I want to know how it happens that information about a grandmother or great-grandmother's environment can affect the phenotype of her grandchild or great-grandchild," she said.

Learning how these maternal effects move across generations could deepen understanding of human health and eventually inform precision medicine. "It's not just about what's in your genome as an individual," Gribble said, because "your health potentially depends on the health and environment of your mom and grandmother and great grandmother."

Study Limitations

The experiment followed only two laboratory strains of a single rotifer species. Conditions in the wild may produce different patterns, and results from rotifers cannot be applied directly to humans. The team inferred possible mechanisms from the observed inheritance patterns but did not measure histone (搜索)搜索该靶点 changes, mitochondrial damage, or new DNA mutations, so these explanations remain hypotheses for future research. The results also varied across lifespan, total reproduction, reproductive timing, and reproductive decline, indicating that maternal age does not produce one simple signal with a predictable outcome.

The study, "Transgenerational and Intergenerational Maternal Age Effects Exhibit Complex, Genotype-Specific Patterns of Inheritance," by Alyssa Liguori, Sovannarith Korm, Alex Profetto, Emily Richters, and Kristin E. Gribble, is published in the journal The American Naturalist.