Rockfish species vary widely in lifespan. Some even exhibit negligible senescence, showing few signs of aging across the majority of their long life spans. When closely related species have divergent life spans, there is perhaps the opportunity to learn something of how metabolism determines longevity. Accordingly, researchers here report on their study of varied rockfish species, in search of the differences in the molecular biology of cells that lead to differences in life span and pace of aging.
In a new study, researchers compare the genomes of nearly two-thirds of the known species of rockfish that inhabit coastal waters around the Pacific Ocean and uncover some of the genetic differences that underlie their widely varying lifespans. Some rockfish, like the colorful calico rockfish (Sebastes dallii), live for little more than a decade, while the most long-lived of the genus Sebastes - the rougheye rockfish (Sebastes aleutianus), which can be found from Japan to the Aleutian Islands - can hang out on the seabed in cold, deep coastal waters for more than 200 years.
Their wide range of lifespans, not to mention differences in size, lifestyle, and ecological niche evolved over a mere 10 million years - one of the most rapid radiations among all fishes. To uncover the genetic determinants of lifespan in rockfish, the researchers obtained tissue samples from 88 species and sequenced their complete genomes. The researchers looked for DNA variations that were more common in fish with longer lives and found 137 longevity-associated gene variations. Not all of these have a direct effect on lifespan, however. The researchers took care to separate out the genetic variations that allowed rockfish to adapt to deeper depths and grow to larger size, since those adaptations themselves have the side-effect of increasing lifespan. Deeper, cooler waters slow metabolism, for example, which is associated with a longer lifespan in many animals.
"We can explain 60% of the variation in lifespan just by looking at the size at maturity and the depth at which a fish lives. So, you can predict lifespan with pretty high accuracy just from these factors. This allowed us to identify the genes that allow them to do those things." The remainder of the longevity-associated variation primarily involved three types of genes: an enrichment in the number of genes for repairing DNA; variations in many genes that regulate insulin, which has long been known to influence lifespan; and an enrichment for genes that modulate the immune system. More DNA repair genes could help protect against cancer, while more immune genes could help ward off infections, as well as cancer.