Remain clam: Bivalves as models for aging research

Since the observation that the Arctic quahog can live for centuries, clams have been receiving increased attention from biogerontologists. So far, bivalves have been used to experimentally test hypotheses about the role of oxidation and chaperones in determining longevity.

The value of these molluscs in the study of aging is the subject of a review by Abele et al.:

Bivalve models of aging and the determination of molluscan lifespans
Bivalves are newly discovered models of natural aging. This invertebrate group includes species with the longest metazoan lifespan approaching 400 y, as well as species of swimming and sessile lifestyles that live just for 1 y. Bivalves from natural populations can be aged by shell growth bands formed at regular intervals of time. This enables the study of abiotic and biotic environment factors (temperature, salinity, predator and physical disturbance) on senescence and fitness in natural populations, and distinguishes the impact of extrinsic effectors from intrinsic (genetic) determinants of animal aging. Extreme longevity of some bivalve models may help to analyze general metabolic strategies thought to be life prolonging, like the transient depression of metabolism, which forms part of natural behaviour in these species. Thus, seasonal food shortage experienced by benthic filter feeding bivalves in polar and temperate seas may mimic caloric restriction in vertebrates. Incidence of malignant neoplasms in bivalves needs to be investigated, to determine the implication of late acting mutations for bivalve longevity. Finally, bivalves are applicable models for testing the implication of heterozygosity of multiple genes for physiological tolerance, adaptability (heterozygote superiority), and life expectancy.

One of the great advantages of bivalves is their variety: even though they’re anatomically quite similar, they occupy a wide range of niches and consequently exhibit a large variation in aspects of their natural histories, including longevity. This makes clams and oysters excellent candidates for comparative biogerontology: studying organisms with basically identical body plans but wildly different lifespans allows us to focus more tightly on the features (molecular, cellular, systemic) that might explain the change in longevity. This theme is currently being developed — outside the mollusk community — into a large-scale project that will study dozens of species in four or five vertebrate clades.

Chances are that aging labs won’t start buying big refrigerated seawater tanks anytime soon: the authors focus on work that can be accomplished on wild-caught bivalves, especially in the context of the very long-lived species. Even by modern standards, 400 years is a very long postdoc.


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