Ageless Animals, the Pearl Mussel Edition

The freshwater pearl mussel (Margaritifera margaritifera) is a very long-lived beast, though as for many of these species its life span is poorly studied. There are too many bivalves and not enough researchers - remember that we live in a world in which we can't even determine lobster ages with any degree of certainty. Like many bivalves, lobster biochemistry doesn't seem to change with age in any usefully measurable way.

You might recall research into the longevity of another bivalve, the arctic quahog clam, that suggests its longevity is a matter of excellent natural antioxidants:

The ocean quahog Arctica islandica is the longest-lived of all bivalve and molluscan species on earth. Animals close to 400 years are common and reported maximum live span around Iceland is close to 400 years. High and stable antioxidant capacities are a possible strategy to slow senescence and extend lifespan

Compare that with this recent open access paper on the pearl mussel wherein the researchers found a different story when looking at superoxide dismutase (SOD) and catalase (CAT):

Free radicals are extremely reactive and produce damage and modify cell functions. Furthermore, superoxide dismutase and catalase are believed to play a key role in the enzymatic defence of the cells. Indeed, some authors have argued that reduced free-radical damage could explain increased longevity. Margaritifera margaritifera is one of the longest-lived animals in the world (up to 100-200 years). Furthermore, this organism may serve as a useful model for gerontologists interested in exploring the mechanisms that promote long life and the slowing of senescence. The present study estimated for the first time individual enzymatic activity for superoxide dismutase [and] catalase in tissue preparations of gills, digestive glands and mantles of two natural populations of M. margaritifera.

...

the SOD levels in the digestive gland of the short-lived marine bivalve Mytilus edulis are of a similar order to those shown by the long-lived M. margaritifera, and the CAT levels were lower in M. margaritifera. Although the activity of these enzymes in M. margaritifera slightly increases with age, we cannot find a correlation between CAT and SOD activity in respect to age.

So the mussels don't have high levels of antioxidant enzymes, but they are stable with age. Different populations have quite radically different levels of SOD and CAT, uncorrelated to longevity, and which the authors attribute to local environmental conditions and growth rates:

Bauer (1992) analysed the variation in longevity across Europe in M. margaritifera, and he found that as temperature decreases (toward the North), the metabolic rate declines and the rate of growth decreases and this leads to a long life. According to Bauer (1992) latitude (and therefore metabolic rate) alone explained around 50% of the variation in maximum life-span (the remaining variation attributed in part to differences in hydrochemistry). Spanish populations (including those of the rivers Eo and Masma) of freshwater pearl mussel show the highest growth rates from Europe and their variation in maximum life-span is comparable to that reported for others living farther North; growth rates also showed remarkable differences (San Miguel et al., 2004) even within the same river (for example, the Eo River). Indeed, the huge variation in SOD and CAT levels found in the present study can be principally interpreted as an adaptation to the unpredictable and changing nature of freshwater natural habitats.

Once again, one is left pondering the role of naturally produced antioxidant compounds. Clearly demonstrated to be related to longevity in some studies, and much more ambiguous in others. Here, ambiguous. All this tells us is that consistent levels of natural antioxidants with age are a good marker for species that are extremely long-lived, which says nothing about whether this is a contributory cause or an effect of other mechanisms that ensure longevity. Further, here we have another example of a long-lived species with similar or less active antioxidant enzymes than a much shorter-lived cousin.

No-one ever said the biology of aging was simple.

ResearchBlogging.orgCARLOS FERNÁNDEZ, EDUARDO SAN MIGUEL, & ALMUDENA FERNÁNDEZ-BRIERA (2009). Superoxide dismutase and catalase: tissue activities and relation with age in the long-lived species Margaritifera margaritifera Biological Research, 42 (1), 56-57 DOI: 19621133

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