A mother's age can influence the physical traits and behavior of her offspring in humans and across many other animal species. Researchers refer to these changes as maternal age effects. Although the phenomenon is common throughout the animal kingdom, scientists are still working to understand the biological processes underlying it and why it has persisted over evolutionary history.
"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. "Nearly all forms of life show some level of maternal age effect, and most are negative effects caused by advanced maternal age."
Rotifers Offer Clues to Maternal Age Effects
To investigate how information about maternal age is passed to offspring, Gribble's laboratory studies rotifers, tiny aquatic animals that reproduce rapidly and are well suited for laboratory experiments.
"Understanding the mechanism in these simple invertebrates can help us understand how maternal age effects occur in people as well," she said.
Research on rotifers has led the team to an unexpected possibility. Maternal age effects may be controlled by epigenetic processes that change how genes are used rather than by mutations that alter the underlying DNA sequence.
Work in Gribble's lab by postdoctoral scientist Alyssa Liguori, who is now an assistant professor at SUNY-New Paltz, examined two different genotypes from the same rotifer species. The results showed that the effects associated with maternal age did not become progressively stronger with each generation. Instead, those effects could be reversed within a single generation.
That rapid reversal argues against the idea that maternal age effects are primarily caused by the gradual buildup of cellular damage or DNA mutations associated with aging, as many researchers had previously suspected. The findings instead point toward an epigenetic process involving histone modifications. These modifications can influence whether genes are switched on or off.
How Mothers May Pass Biological Information
Gribble's team is now testing whether histone modifications are responsible for the maternal age effects observed in the rotifers. She is also considering whether mitochondrial DNA, which is generally inherited from the mother, could play a role "in transmitting information about maternal age from moms to offspring."
Genetic differences may also determine how strongly offspring are affected by an older mother.
"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."
That finding highlights an important complication. Although advanced maternal age is often associated with harmful outcomes, genetic variation may sometimes reduce those effects or even produce benefits.
Why Maternal Age Effects Persist
A major evolutionary puzzle is why maternal age effects remain so widespread. Offspring born to older mothers often live shorter lives, reproduce less, and have lower evolutionary fitness. In theory, natural selection might be expected to gradually remove traits that produce such disadvantages. Yet maternal age effects continue to appear across an extraordinary range of species.
Gribble thinks part of the explanation may be that natural selection becomes weaker later in an organism's 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 the time female rotifers reach advanced ages, they have already produced most of their offspring. As a result, there may be less evolutionary pressure favoring traits that help older females produce especially fit offspring.
Biological Effects Across Generations
For Gribble, one of the most compelling questions is how biological information can travel beyond a single generation.
"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 explains.
Understanding how maternal effects move across generations could eventually deepen scientists' knowledge of human health and contribute to future approaches in precision medicine. The research suggests that an individual's biology may reflect more than the DNA inherited at conception. Conditions experienced by previous generations could also matter.
"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."
