Providing the strongest evidence to date that some animals have the potential for immortality, new research released today confirms the tiny hydra does not age and, if kept in ideal conditions, may just live forever.
In a co-authored paper published in the Proceedings of the National Academy of Sciences (PNAS) journal, Pomona College Biology Professor Daniel Martínez caps a decade of research into these centimeter-long freshwater polyps with a knack for longevity.
The paper titled “Constant mortality and fertility over age in Hydra” shows hydra could live in ideal conditions without showing any sign of senescence – the increase in mortality and decline in fertility with age after maturity, which was thought to be inevitable for all multicellular species.
Working with James W. Vaupel of the Max Planck Institute for Demographic Research (MPIDR) in Rostock, Germany, Martínez duplicated earlier findings regarding hydra immortality, but on a much larger scale. That scale, Martinez says, is key to the study’s significance, along with the fact that the hydra showed constant fertility over time, defying expectations for most organisms.
The latest study took 2,256 hydra from two closely related species and conducted experiments in two laboratories (at Pomona College and the MPIDR) over an eight-year period, doubling the amount of time from Martinez’s previous experiments showing hydra living for four years.
“I do believe that an individual hydra can live forever under the right circumstances,” says Martínez. “The chances of that happening are low because hydra are exposed to the normal dangers of the wild -- predation, contamination, diseases. I started my original experiment wanting to prove that hydra could not have escaped aging. My own data has proven me wrong -- twice.”
As one of the world's leading scholars on hydra phylogeny and the evolution of aging, Martínez in 2010 received a $1.2 million grant from the National Institutes of Health for research on the mechanisms underlying lack of senescence in members of the genus Hydra. In 2013, he received a grant from The Immortality Project at UC Riverside to study the implications of hydra's lifespan on medicine and increasing human longevity.
Martínez’s interest in the tantalizing prospect of animal immortality goes back to the ’90s when he was in grad school at Stony Brook University and heard about the possibility that hydra may be immortal. But no one was conducting research to see if it was true.
“When I started experiments in graduate school, the dogma at the time was that animals should not be able to escape aging, all animals should age,” explains Martínez. “When I started my studies , I wanted to prove that hydra could not escape aging but after four years of basically detecting no mortality, I was convinced that hydra would not age and I published my paper in 1998.”
That paper drew international attention. “My initial findings made people rethink the idea that all animals should age. It forced people to think outside of the box,” says Martínez. “Before the study, models predicted that aging was unavoidable for animals. My results questioned the validity of those models.”
Martínez’s study caught the attention of Vaupel, founding director of the Max Planck Institute for Demographic Research in Germany. Vaupel came to Martínez in 2004 proposing collaboration between the institute and Pomona College, with funding to continue his research into the longevity of hydra.
The idea was to do the experiments in parallel in both labs and at a much larger scale, providing better statistical power. In the 1998 paper, Martínez says, there was quite a bit of “noise” regarding the fertility (budding rates) of the hydra over time. The rates went up and down making it difficult to determine if there was a decline in fertility, perhaps correlated with aging.
More than a decade later, and Vaupel and Martínez are both senior authors on the latest study confirming Martínez’s earlier results showing hydra are seemingly immortal. And there is no such “noise” in the new, larger study, in which hydra showed no mortality and constant fertility over time.
But why is this tiny organism able to carry on living while humans have to continue their search for the mythical fountain of youth?
“Hydras are made of stem cells,” Martínez says. “Most of the hydra’s body is made of stem cells with very few fully differentiated cells. Stem cells have the ability to continually divide, and so a hydra's body is being constantly renewed. The differentiated cells of the tentacles and the foot are constantly being pushed off the body and replaced with new cells migrating from the body column.”
The project was labor-intensive and, at times, tedious. Each hydra was kept in its own dish and had to be individually fed three times a week with freshly hatched brine shrimp. The man-made freshwater in which the hydra lived needed to be changed three times a week. “Many, many hours of work went into this experiment,” says Martínez. “I’m hoping this work helps sparks another scientist to take a deeper look at immortality, perhaps in some other organism that helps bring more light to the mysteries of aging.”
Martínez is one of the world's leading scholars on hydra phylogeny and the evolution of aging. In 2010, he received a $1.2 million grant from the National Institutes of Health for research on "Mechanisms underlying lack of senescence in members of the genus Hydra." Senescence is the biological process of aging. In 2013, he received a grant from The Immortality Project at the University of California Riverside to study the implications of hydra's lifespan on medicine and increasing human longevity. His research has been featured on the NPR Krulwich Wonders blog and Science Magazine.