Muddy Waters When it Comes to Quahog Biochemistry and Longevity

Yes, we're back to clams again: four hundred year old clams in this case. The ocean quahog, Arctica islandica, is a very long-lived bivalve that, like other unusually long-lived species, is attracting the attention of researchers. How is it that these animals manage to live so much longer than their near relatives? You'll find some background reading in the archives:

Researchers to date have focused on resistance to oxidative damage in quahogs, but the more research is done, the more ambiguous that picture becomes. It doesn't seem to be the case that we can simply point to very high levels of antioxidants or an aggressive antioxidant response that preserves cells from the accumulating damage caused by oxidative byproducts of metabolism. In many ways this parallels research into the biochemistry of the naked mole-rat: the initial focus on examining natural antioxidants gave way to the present view that their comparatively long life span depends on differences in the construction of their vulnerable cell membranes. They are better built in the places where it matters - their cells are buzzing with reactive oxidant compounds, but their resistant cell membranes shrug it off.

That may be the case for the quahog as well, but researchers aren't there yet. This recent paper manages to continue the present trend of muddying the waters:



Following TBHP exposure, we observed not only an association between longevity and resistance to oxidative stress-induced mortality but also marked resistance to oxidative stress-induced cell death in the longer-living bivalves. Contrary to some expectations from the oxidative stress hypothesis, we observed that A islandica exhibited neither greater antioxidant capacities nor specific activities than in M mercenaria nor a more pronounced homeostatic antioxidant response following TBHP exposure. The study also failed to provide support for the exceptional longevity of A islandica being associated with enhanced protein recycling.

Which is really saying little that is new and definitive - just better ruling out some of the options. The quahog could be producing fewer oxidants, or it could be efficiently mopping up oxidants at their source in the mitochondria due to a natural source of localized antioxidant compounds. In either case, that says nothing about how it or its cells might react to an externally provided and artificial source of oxidative stress like TBHP. Given the present pace of work, however, I'd expect that researchers will have developed a well-supported consensus explanation for the extreme longevity of this species and the naked-mole rat by the time 2020 rolls around.


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