Credit: Michael Shribak
For most animals, growing older changes more than their own bodies. A mother’s age can also shape the health, lifespan and reproductive success of her offspring — sometimes for more than one generation.
Scientists have documented these “maternal age effects” across the animal kingdom, from insects and worms to birds, elephants and humans. But they have struggled to explain what carries the effect forward. Does an older mother accumulate DNA damage that she passes to her young? Does she provision her offspring differently? Or does age leave some other, more reversible biological mark?
A new experiment with tiny aquatic animals called rotifers points toward the last possibility. Researchers followed two genetic strains of Brachionus manjavacas rotifers across multiple generations and found that the effects of maternal age did not simply grow worse from generation to generation. Some disappeared after just one generation, while others depended strongly on the animals’ genetic background.
That rapid reversibility makes accumulating DNA mutations an unlikely primary explanation and instead points toward more flexible mechanisms that regulate how genes work, including epigenetic changes.
“Maternal age effects are incredibly common, from invertebrates up through humans, elephants, other primates and other mammals,” Kristin Gribble, an aging researcher at the Marine Biological Laboratory and senior author of the study. “Nearly all forms of life show some level of maternal age effect, and most are negative effects caused by advanced maternal age.”
A 2020 review of maternal-age effects across 97 animal species helps put that claim in perspective. In the review, researchers found an effect on survival before adulthood in 252 of 272 populations studied, or 93% of cases. The effects tended to become harmful with increasing maternal age in invertebrates and mammals, including humans, although birds often showed the opposite pattern.
For a rotifer, 11 days is old
Female Brachionus manjavacas rotifer and offspring. Credit: Michael Shribak
Rotifers make the phenomenon unusually easy to dissect. B. manjavacas typically lives only one to four weeks. Females can reproduce asexually, produce several offspring a day and provide no parental care after hatching, allowing researchers to separate the effects of a mother’s age from what she might later do for her young.
Liguori and her colleagues created lineages in which offspring repeatedly came from either young mothers or old mothers. A “young” mother was three days old. Depending on the strain and generation, an “old” mother was 10 or 11 days old — an advanced age for an animal whose reproductive output peaks early.
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Researchers checked every rotifer daily until it died, recording its survival and reproduction. In the final experimental generation, they performed the critical switch: descendants of old mothers were produced by a young mother, while descendants of young mothers were produced by an old one. That allowed the team to ask whether the biological legacy of previous generations could be erased quickly.
In the BmanL5 strain, offspring of older mothers initially lived around two days less, on average, than offspring of young mothers. By the third generation, that lifespan difference had vanished. Also, in the same strain, young mothers produced offspring with greater lifetime reproductive output.
But in the BmanRUS strain, older mothers produced offspring with greater lifetime reproductive output. Those opposite effects remained roughly stable instead of becoming stronger generation after generation.
So, advanced maternal age was not simply transmitting a universal form of biological deterioration.
A 79-year-old aging experiment gets another look
Female Brachionus manjavacas rotifer and offspring. Credit: Emily Corey
Rotifers have been at the center of this question for almost eight decades.
In 1947, anatomist Albert Lansing reported that successive generations descended from old rotifer parents lived progressively shorter lives and reproduced less. His famous experiment on a “transmissible, cumulative, and reversible factor in aging” helped establish what researchers still call the “Lansing effect.”
The new results do not reproduce that simple cumulative decline neatly. Neither strain showed maternal-age effects steadily piling up through three generations.
Other experiments have already hinted that inheritance can behave much less predictably. A 2021 study of the nematode Caenorhabditis elegans found something almost opposite to Lansing’s result: offspring of older parents became increasingly reproductively successful over six generations. Yet one generation of young parents reversed that accumulated advantage.
The rotifer experiment goes further by showing how strongly genetics can alter the pattern. In BmanL5, the maternal-age effect on lifetime reproduction could be fully reset within one generation. In BmanRUS, it could not; effects of grandmaternal age remained entangled with the mother’s age.
This strain dependence was similarly observed by the same team’s 2024 study of four rotifer strains, which found that advanced maternal age could have positive, negative or negligible effects depending on genotype.
In other words, it’s all much more complicated than anyone thought.
If it is not a mutation, what is being inherited?
Accumulating DNA mutations make an awkward explanation for something that can disappear in a generation.
If mutations in the maternal germline were the main driver, the researchers argue, they would expect harmful effects to build over generations and resist such rapid reversal. The results also fit poorly with a simple explanation based on older mothers giving their offspring more or fewer resources.
That leaves several intriguing candidates.
One is epigenetics. This refers to the chemical modifications that alter which genes are active without rewriting the DNA sequence. DNA methylation appears unlikely in these rotifers because researchers have not detected the usual form of it, 5-methylcytosine, or the enzymes that install it. But Brachionus possesses machinery that chemically modifies histone proteins around which DNA is packaged. And the activity of those histone-modifying genes changes with age. Small regulatory RNAs could provide another route.
Mitochondria offer another possibility. These energy-producing structures are usually inherited from the mother, and damaged mitochondria can sometimes be repaired, removed or reset — behavior that could produce inheritance without permanent nuclear DNA changes. The authors therefore conclude that epigenetic and mitochondrial mechanisms currently fit their results better than accumulating nuclear mutations, while stressing that experiments must now test those possibilities directly.
Next steps
Gribble’s laboratory is now planning exactly that, investigating histone modifications and mitochondrial inheritance.
“Understanding the mechanism in these simple invertebrates can help us understand how maternal age effects occur in people as well,” she said.
Rotifers are, of course, not tiny humans. The study does not show that human maternal-age effects work through the same pathway. What it does show is that a mother’s age can leave descendants with biological information that behaves less like a permanent scar in the genome and more like a message — one that, under the right circumstances, can be changed.
The findings were reported in the journal The American Naturalist.
