Bivalve models of aging and the determination of molluscan lifespans

Abstract

a b s t r a c tBivalves 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.Ó 2009 Elsevier Inc. All rights reserved. Bivalves: a diverse set of models for aging studies and environmental recordersCommonly used animal models for cellular and molecular mechanisms underlying the process of aging, such as Drosophila melanogaster, Caenorhabditis elegans or small rodents, are bred and reared under controlled laboratory conditions. Most of these aging models are short lived (days in C. elegans, weeks in D. melanogaster, <5 y in rodents) and, hence, may not show all the age-dependent changes of long-lived species (Reznik, 1993;Kirkwood, 2002). Especially, short lived models are not representative of the negligible aging type (Finch, 1990;Terzibasi et al., 2007). Further, aging under controlled laboratory conditions may differ significantly from aging in the wild, and the applicability of the results to natural animal populations is often questionable. Good reasons to establish animal models that can be sampled from a range of environmental settings and scenarios, but at the same time provide information on their individual life history, including their chronological age (Austad, 1996).Such new models are found among bivalve molluscs. Worldwide, approximately 20,000 species (Pearse et al., 1987) of marine bivalves exist so that this class offers a rich diversity of lifestyles, adaptations to specific environmental conditions and corresponding strategies of aging, albeit based on the same filter feeder blueprint in the majority of species. Some bivalve species, like the long-lived ocean quahog, Arctica islandica or the blue mussel Mytilus edulis exhibit broad geographical distribution, with habitats spanning large latitudinal ranges and covering different climate zones. Other sp...

Cell turnover in tissues of the long-lived ocean quahog Arctica islandica and the short-lived scallop Aequipecten opercularis

“…Similarly, in the oyster Crassostrea virginica with a maximal live span (MLSP) of only 6 years, not only antioxidant enzyme activity was lower but, the density of apoptotic and mitotic cells was also diminished in gill, adductor muscle and heart of mature compared to young oysters (Ivanina et al 2008;Sunila and LaBanca 2003). It would be interesting to see whether in short-lived scallops the reported shift in energy allocation from somatic maintenance towards reproduction at the end of life (see also Heilmayer et al 2004;Abele et al 2009) leads to reductions of cell proliferation in somatic tissues, and whether or not this is accompanied by a decline of apoptotic activity. On the other hand, low metabolic activity and sustained protection from oxidative damage over age, in combination with slow but continued cell turnover, presumably slow senescent decline in A. islandica.…”

Comments on ‘The biology and functional morphology ofArctica islandica’ by Brian Morton,Marine Biology Research, 2011

“…In rodents (Buffenstein et al 2008: measuring or reviewing data on catalase, SOD and methionine sulfoxide reductase) and birds (Cohen et al 2008: measuring uric acid, carotenoids, vitamin E and total antioxidant capacities), no predictable relationships between antioxidant levels and longevity is observed. Similar inconsistencies are observed in bivalves; Abele et al (2009) report elevated catalase levels compared to the shorter-lived bivalves while Ungvari et al (2011) found no difference in total or specific antioxidant capacities between long-lived A. islandica and shorter-lived Mercenaria mercenaria. Correspondingly, observations of SOD activity in the long-lived Margaritifera margaritifera (Fernández et al 2009) were very similar to those in the shorterlived Mytilus edulis (Winston et al 1990).…”

“…Since Abele et al (2009) reviewed antioxidant capacities in bivalves, the field has considerably advanced, and if not dead, the role of oxidative stress in ageing is now severely questioned. One cannot take a component of the oxidative stress system in a species and make simplistic assumptions about its role in attenuated ageing, and there is no conclusive evidence that antioxidants play a significant role in determining lifespan in bivalves.…”

New Species Longevity Record for the Northern Quahog (=Hard Clam),Mercenaria mercenaria

“…Our work here highlights the need to have accurate demographic information on bivalve populations under study. As bivalves become increasingly utilized as models for aging research (Abele et al 2009) and biomonitoring (Byrne & O'Halloran 2001), it is essential to have an accurate grasp on what ''old'' is. The age structure at the sample site should be an important component in that process.…”

“…Bivalves are increasingly being used as new model organisms for the investigation of aging (Strahl et al 2007, Abele et al 2008, Abele et al 2009. To fully utilize bivalves in the investigation of aging and to be able to select suitable species for comparative investigations, it is necessary to obtain accurate information on the maximum life span of a species and their population growth parameters.…”