Female turtles suffer a steep dip in fertility before the end of their lives, a finding that flies in the face of what has long been believed about turtles and aging.
“Turtles are these icons of longevity,” says Fredric Janzen, professor of ecology, evolution, and organismal biology at Iowa State University. “People assumed there was never a cost to reproduction right up to the end of life.”
“This was a rare opportunity to look at the data and go, ‘wow, that’s weird.'”
Published in the Proceedings of the National Academy of Sciences, the findings follow nearly 30 years of data collected on painted turtles in the Mississippi River near Clinton, Iowa. Every year in May and June, students measure the turtles, take blood samples, and count the number of eggs laid by females. They also keep track of how many of those eggs hatch successfully.
Painted turtles enjoy a long period of relatively graceful aging, as the researchers expected. But that long plateau consistently ends with a steep drop in fertility near the end of the females’ lifespans. The older females tended to lay larger eggs, which would normally improve the odds of successful offspring, but the data show just the opposite.
“This was a rare opportunity to look at the data and go, ‘wow, that’s weird.’ It’s one of those head-scratching moments,” Janzen says.
Anne Bronikowski, professor of ecology, evolution and organismal biology, has studied senescence—the way in which organisms deteriorate as they age—in multiple species, including humans. She thought the turtle data presented an attractive opportunity to run demographic analyses on adult survival rate senescence. But the results of that analysis came as a surprise.
“Similar to the finding that reproduction declines, we also found that survival rates decline as the turtles age but at rates slower than mammals—including humans and non-human primates,” Bronikowski she says. “Our next steps are to delve into the cellular mechanisms that afford turtles these lower mortality rates.”
Female painted turtles reach maturity between 5 and 8 years old and can live to reach about 25 years old. Turtle lifespan shares some similarities with humans, who also take years to mature and tend to have long lives. That means studying turtle senescence may have implications for human health and aging.
Researchers from Penn State and Auburn University are coauthors of the study.
Source: Iowa State University