Encoded in the genes: Scientists devise a ‘lifespan clock’ for vertebrates

There’s some uncertainty about his exact age at death, but it’s now been confirmed that “Nandy,” who suffered a crushing blow to his head as a youth, lived to a ripe old age: somewhere between 35 and 45 years old. A Neanderthal (Homo neanderthalensis) like Nandy, new research shows, could only hope to last 37.8 years if they weren’t struck down by a carnivore or disease first.

A genetic tool described in the journal Scientific Reports allows scientists to predict the maximum lifespans of vertebrates, including mammals, whether extinct or still around today. “Lifespans and ageing is of interest as it is fundamental for better understanding the ecology and population dynamics of wild animals,” Benjamin Mayne, the first author of the paper, told Mongabay in an email, adding that “lifespan estimates can be used to determine the risk of animal extinction or to monitor invasive species.”

Using the “lifespan clock,” the team from Australia predicted that woolly mammoths (Mammuthus primigenius) could live up to 60 years. Although the oldest-known bowhead whale (Balaena mysticetus) died at 211 years, the study showed that the species, believed to be the longest-living mammals, can push up to 268.

Lifespans across species run a wide range: the pygmy goby fish (Eviota sigillata) live for only eight weeks, while the greenland shark (Somniosus microcephalus) can live for more than 400 years. For species that outlast humans by decades, if not centuries, pinning down lifespans can be tricky. It’s even more challenging for animals that aren’t amenable to captivity, since the longevity of many species is determined by studying sufficiently large captive populations.

Basing their estimate on genetic determinants means scientists don’t need to rely on data from many specimens of a species. The genome is the full DNA sequence of a species, which serves as a kind blueprint for the species. Thanks to rapid advances in genome sequencing in the past decade and the availability of sequences for many species, there is now enough data to develop models with predictive powers.

“I find it to be a big advance in our understanding of aging through comparative genomics,” Christopher Faulk, a specialist in the field at the University of Minnesota, who was not involved in the research, said in an email. “They studied genomes and lifespan, not by looking at overall genetic variation, but by focusing on regions of the genome that host epigenetic changes during the lifespan of a single animal.”

This involved some reverse sleuthing. Mayne and his team analyzed 252 whole genomes of species whose lifespans are already known through conventional methods. They identified 42 genes that are linked to how long an organism can live before it experiences a natural death. Genes are not disparate pieces of genetic material; they refer to a particular sequence of base pairs on the DNA molecule.

“They mined hundreds of genomes to detect a surprisingly small number of gene regions that are comparable across an incredible diversity of animal life that provide a highly accurate estimate of lifespan,” Faulk said. Because the relationship between these particular genes and maximum lifespans is modeled, lifespans of species for which only the genome data is available can be predicted.

Its most important applications, the authors argue, will be for extinct animals and for those about which scant data are available. Some species meet both the criteria, for example, the Pinta Island tortoise (Chelonoidis abingdonii), the last of which, evocatively named Lonesome George, died in 2012. Even though he was believed to be about 100 years old when he died, the lifespan clock predicated that members of this species could live up to 120 years.

Neanderthals, by contrast, are long extinct — they lived 40,000 to 400,000 years ago — and are the closest extinct relatives of present-day humans (Homo sapiens). Neanderthal DNA is difficult to obtain, even from fossilized remains, because it degrades over time. The Neanderthal nicknamed Nandy was found from a site in Iraq in 1957. The new study relied on a genome sequence assembled from DNA samples of another specimen found in Croatia in the 1970s. By plugging their genetic information into the model, the researchers arrived at the figure of 37.8 years.

Surprisingly, the lifespan clock pegged the human lifespan at 38 years, which is almost half the lifespan the average person enjoys today: somewhere between 60 and 87 years. “The lifespan clock estimate may be more reflective of human lifespan prior to advances in medicine. On the other hand, it might be that humans may be the exception to this study,” Mayne said. Though lifespans are believed to be primarily controlled by genes, to what extent is debatable. But humans have manipulated their lifespans to a degree that would be impossible for any species in the wild.

There is another class of organisms for whom the tool cannot be used: invertebrates, organisms that do not have a vertebral column, such as insects or mollusks. Of all described animal species, more than 95% are invertebrates, but research on them is sparse compared to research on invertebrates, which include mammals, birds, reptiles, fishes and amphibians.

Despite this limitation, the model is expected to be a valuable addition to the arsenal of conservation tools. Knowing its lifespan can help determine the extinction risk to a species, point to environmental factors that cut short the lives of organisms, and help ascertain the viability of threatened species populations as well as gauge the threat posed by an invasive species. It could also be used in sustainable fisheries management.

Banner Image: A mural from the American Museum of Natural History depicting woolly mammoths. Image courtesy Wikimedia Commons/Charles R. Knight

Citation:

Mayne, B., Berry, O., Davies, C., Farley, J., & Jarman, S. (2019). A genomic predictor of lifespan in vertebrates. Scientific Reports, 9 (17866). doi: 10.1038/s41598-019-54447-w

Malavika Vyawahare is a staff writer for Mongabay. Find her on Twitter: @MalavikaVy

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