If you see grown scientists collecting seashells, don't worry - they're also collecting useful genetic information, writes Dick Ahlstrom
A RESEARCH TEAM at the Galway-Mayo Institute of Technology (GMIT) has opened up a novel new source for genetic information. The team successfully extracted DNA from old mussel shells that have lain in storage at the Ulster Museum for the past 37 years.
"It has huge implications," suggests senior research fellow Dr Elizabeth Gosling, who led the study. She is team leader of the Molecular Ecology Research Group at GMIT and a population geneticist.
Her approach opens up a startling range of possibilities, from providing a molecular analysis of ancient shells recovered from middens to definitive species identification and bivalve population history.
Her group studies the evolutionary and ecological forces that shape genetic structure in marine shellfish and fish species. The work took an unusual turn, however, when they were studying the potential for DNA extraction from fish otoliths, small bones associated with balance.
"We decided wouldn't it be interesting if we could get some DNA out of old shells," she says. "That is where it all came from, to see if we could get some DNA from the ligament found on almost all bivalves."
Mussels, oysters, clams and other bivalves have a ligament that joins the shell halves together, although it is an unlikely place to recover DNA. "We knew it was inorganic and you wouldn't expect it to contain cells," she explains.
Also, they didn't want to use fresh shell material as cells were readily available on these. "We wanted to look for shells that were from a museum."
She had done her PhD on mussels and knew the Ulster Museum had shells with a known and authoritative provenance that were "reasonably old", collected during the 1970s.
The Museum provided 50 samples and her team recovered new mussel shells from the same location as the Museum's shells, Kilmore Quay, Co Wexford. Details of the work were published last December in the journal Aquatic Biology by Dr Gosling and fellow authors Sandra Doherty and Dr Anna Was.
They used a DNA amplifying method called polymerase chain reaction to bring up the DNA signal from the shell ligaments.
"We found there was absolutely no difference between the DNA samples recovered recently and 37 years ago," Dr Gosling says.
They only had amplifying "primers" for a specific location on the mussel DNA, but she expects that a full analysis of DNA recovered from the ligament should be possible.
The ligament doesn't contain cells, but the DNA signal is there. The current theory is that the immature bivalve lays down DNA-containing cells where the ligament is meant to grow, and these are subsequently covered and protected by the ligament.
The work opens up significant potential for historical studies of shells recovered from middens, basically ancient rubbish tips. "One of the problems with mussels is they don't preserve well in middens," says Dr Gosling. Other species such as oysters do, however, and may yield DNA.
It is very early days, though, and a major question remains to be answered: how far back can you go and still recover DNA from the shells? If they can recover ancient shell DNA from the caves occupied by early humans it may reveal detailed information about what was on the seafood menu back in those days.