For centuries, humans have been on the search for longevity, but nature may hold the key to unlocking this secret. Recently, this curiosity has been reignited again among the scientific community as they turn their interest in studying bivalve mollusks.
Longevity of Bivalve Mollusk
Bivalve mollusks refer to invertebrates from phylum Mollusca which possess a two-part hinged shell that covers the soft body. These include clams, scallops, cockles, pipis, mussels, and oysters.
Common coastal bivalves were once thought to be ephemeral creatures. However, longevity estimates of these organisms suggest that they can live up to 50 years or more. Meanwhile, there are some offshore species that are known to live for more than 100 years.
The oldest clam ever discovered is Ming, an ocean quahog which was born during the Ming dynasty in China in 1499. Just like other clams, Ming spent the first years of its youth wandering aimlessly in the water column before finally settling down in 260 feet (80 meters) of water off the north shoreline of Iceland.
Quest for Longer Lives
In their pursuit for the 'fountain of youth' experts from the University of Bologna turned their attention to bivalve mollusks. The astonishing range of lifespans that they exhibit makes them ideal subjects in searching the secrets of longevity.
Previous studies on aging, longevity, and senescence have mainly focused on humans and a few animal models. These studies reveal that aging is largely driven by cellular damage that gets accumulated over time.
At the genomic level, this cellular damage is brought by telomere shortening, nuclear architecture changes, and the increase in the mutations of nucleic acids. At the proteomic level, such processes result in the loss of proteases and the accumulation of errors which affect protein folding.
Unfortunately, these studies on aging have overlooked the other long-lived organisms, an oversight which the researchers sought to rectify. When they realized that nobody had ever explored this exceptional longevity within a molecular evolution framework, they knew that they had to begin studying the life duration of these animals.
Led by Mariangela Iannello and Giobbe Forni, the research team leveraged transcriptomic resources from 33 bivalve species to understand the potential mechanisms underlying their exceptionally long lifespans. Their study entitled "Signatures of Extreme Longevity: A Perspective from Bivalve Molecular Evolution" focused on four bivalves which include Lampsilis siliquoidea, Elliptio complanata, Margaritifera margaritifera, and Arctica islandica.
Among these four animals, the ocean quahog Arctica islandica holds the record for the longest-lived non-colonial animal species at 507 years. Meanwhile, the other species have maximum lifespans of 150-190 years.
The experts looked for genes that evolved differently in terms of amino acid substitutions, evolutionary rate, and signatures of positive selection. These long-lives species showed convergent patterns of evolution in their genes related to the regulation of cell death and apoptopic pathways, DNA damage response, hypoxia tolerance, and cellular responses to abiotic stimuli.
The proteins that exhibit convergent evolution in long-lived bivalves also suggest that these animals are biologically related. Aside from these shared drivers of longevity, the scientists also identified proteins in the network whose roles in longevity have not yet been confirmed. They discovered three genes involved in proteostasis which suggest that more efficient handling of misfolded or damaged proteins may be connected to the longevity of bivalves.
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