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How Old Is That Lobster?

Getting older is not much fun. You look in the mirror and see the telltale wrinkles, skin blotches and other signs of passing years. Then there are those annoying birthday cards, telling the world just how many decades have gone by!

Lobsters don’t have these problems. Homarus americanus simply sheds its shell every so often, forms a sprightly new one, and continues to grow, unmarked by the depredations of time. That makes it hard to figure out the exact age of a lobster.

Unlike fish, which have tiny stones called otoliths in their ears with rings that can be counted to determine age, there isn’t a clear method to tell how old a lobster is other than an estimate based on its size. But lobsters grow at different rates due to a variety of environmental factors, so a size estimate is hardly a reliable marker of age.

Lobsters can grow larger and, it seems, very old as well.

Lobsters are known for their long lifespans. The crustaceans continue eating, reproducing and growing until the end of their lives. Like other crustaceans, such as crayfish and shrimp, lobsters have indeterminate growth. That means they don’t reach a set size limit — they will continue to grow until they die of natural causes or are killed.

One clue that a lobster is getting near the end of its life is that it stops molting. They just run out of the energy to shed their heavy shell.

A team of researchers at the University of East Anglia in Norwich, England believe they have found a new technique to accurately assess a lobster’s age. Their work was published in Evolutionary Applications this fall. Associate professor Martin Taylor and colleagues developed a DNA-based method of pinpointing the age of young lobsters to within 1.6 months.

The researchers raised the lobsters from eggs so they would know their exact age. They then took tissue samples from the legs and antennae of 155 lobsters and measured DNA methylation.

“My quick take is that if the DNA methylation method can be shown to be stable in spite of varying environmental conditions, especially temperature, then it might be a useful tool. The benefits of the technique is that it is non-lethal and relatively quick and easy,” said Rick Wahle, director of The Lobster Institute at the University of Maine.

Methylation is a process by which molecules known as methyl groups attach one by one to strands of DNA over time.

The accumulation of methyl groups on the DNA strands creates a type of clock that indicates how long the lobsters have been alive. In this study, researchers found that older lobsters had more methyl groups attached to their DNA than younger ones.

The known-age lobsters in the study were only up to 51 months old, or just over four years. Biologists believe that European lobsters — the type examined in the study — can live for 70 or more years, and American lobsters can live longer, possibly even a century.

The study showed that using DNA can provide an insight into a lobster’s age, however, extracting and analyzing DNA is a time-intensive process, using expensive equipment found only in a lab.

So it may be that lobsters can continue to keep their real ages a mystery for just a while longer.

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