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Humanity has been chasing longer life since time before history, probably since about five minutes after we first realized we would die one day. We’ve invented stories of stones, elixirs, and fountains, all of which promise eternal youth if only we could find them.
A new study by Gregory L. Owens from the Department of Integrative Biology at the University of California, Berkeley, and colleagues, draws a map to a new location of the fountain of youth hidden in the genome of rockfish. Their findings were published in the journal Science.
There are dozens of species of rockfish, all of which have wildly different lifespans that depend largely on their size and where they live. The shortest-lived swim the waters of the North Pacific for little more than a decade. At the other end of the spectrum, some species can live more than two centuries. Scientists sequenced the genome of 88 species in order to identify the genes and gene families responsible for their incredible longevity.
“We sequenced the whole genome of 88 species and then we did high-level chromosome analysis for five of those species,” Owens told SYFY WIRE.
For most of the species the genome was sequenced, but those sequences weren’t placed in order. It’s akin to having all of the puzzle pieces but not putting the puzzle together. For the five species which were the focus of the study, the team completed as much of the puzzle as was possible.
“That’s a logistical constraint. It takes a lot of money to get to that level, so we picked five of them which spanned across the range of rockfish from short-lived to long-lived and focused on them,” Owens said.
There’s a strong correlation between size, living depth, and lifespan. Those rockfish who live the longest tend to be larger and live hundreds of meters below the ocean’s surface. The relationship with size makes intuitive sense, animals which are larger will have fewer predators and are less likely to be eaten, allowing them to live longer by simple virtue of avoiding snack time. This trend largely holds true outside of fish populations as well. In general, larger animals, whether fish, mammal, or otherwise, live longer than their smaller neighbors. The reason fish at lower depths live longer could have something to do with temperature.
“It tends to be colder deeper down,” Owens said. “The prevailing wisdom is colder means slower metabolism, which means longer life. How fast organisms live energetically is often correlated with lifespan. So, perhaps some of the species live longer because they’re modifying their metabolism.”
Those surface-level observations were validated by the genetic analysis. Those fish which are documented to have longer lifespans had key differences in their DNA, related to mutation and metabolic rates.
“We found there was an enrichment in DNA repair genes. This makes sense because cancer is often driven by mutations. This natural selection helps the long-lived species have fewer mutations and prevent cancer in old age. We also see genes involved in insulin-signaling,” Owens said.
Being born with the potential for longevity doesn’t necessarily ensure a long life, however. Those deep-dwelling rockfish also have lower populations than their smaller, shallow-swimming relatives. They might lay millions of eggs over their centuries-long lifetimes, but very few of those offspring will survive childhood. Being a baby rockfish puts you at risk of predation, but there might also be self-regulating ecological limits on the overall population.
“The bigger fish tend to have lower population size, probably because they take up more niche space in the environment. If fish are bigger, they eat more, they take up more ecological space. They have millions of babies but have very high mortality of the young,” Owens said.
The research also indicated the longevity of rockfish might continue to expand, due to their unusual reproductive strategy. Many animals have a reproductive stage, then begin to decline and become less reproductively active. Mutations in the genome during this stage don’t hold much evolutionary weight because they aren’t passed on. For rockfish, that isn’t the case.
“They just become bigger and have more and more eggs. They become more fecund,” Owens said. “That’s an evolutionary scenario where there could be selection for even longer life. We think this could be the deeper evolutionary reason for why they are living this long.”
The presence of these genes isn’t just good news for rockfish. Although our evolutionary relationship with rockfish is distant, identifying these genes can inform scientists looking at aging in model systems and in humans. Some of the beneficial mutations present in the longest-lived rockfish regulate processes which cause cancers and aging in humans.
If you want to live forever, or at least for a couple centuries, it pays to be a big, cold fish. Failing that, it helps to understand them better.