Published online 11 August 2008 | Nature | doi:10.1038/news.2008.1027

News

Pulling DNA from sharks' teeth

Method tracks genetic changes in endangered animals.

A technique that can analyse DNA from sharks' teeth is helping conservation biologists to study endangered species of the poorly understood fish.

sharkThe teeth of the grey nurse shark betray its poor genes.punchstock

Until now scientists have not been able to extract DNA from old shark samples, as the fish do not have the bony skeletons that are essential for conventional methods. Although biopsies of flesh from live sharks are possible, the fish are generally quite uncooperative research subjects.

The new technique, developed by scientists at Macquarie University in Sydney, Australia, is allowing them to assess genetic variation in both modern and historical populations of shark, which is crucial for conservation assessments.

“Sadly, trophy jaws and teeth from sharks are relatively commonplace, whereas living sharks are becoming increasingly rare,” says Heidi Ahonen, one of the researchers. “This method allows information locked away within the teeth and jaws to be exploited to assist with conservation management.”

Using a hand drill, Ahonen and her colleague Adam Stow extract about a quarter of a teaspoon (1.5 millilitres) of material from a shark's tooth or jaw. They mixed the material with just the right cocktail of detergents and enzymes to break open cells and release the DNA.

“Sharks have continual turnover of dentition throughout their lifespan, and consequently teeth may be collected from the seafloor in areas where sharks aggregate without the need to use invasive sampling methods such as biopsy,” says Ahonen. So the method can be applied to museum specimens and trophy samples as well as for endangered or elusive living sharks. The research is reported in the Journal of Fish Biology1.

Grey crash

The team are collecting samples from several species to determine whether declines in shark populations are being exacerbated by low genetic variation.

The technique has already yielded useful results for the highly endangered east Australian population of grey nurse sharks (Carcharias taurus), which were heavily fished in the 1960s and 1970s. Previous research has shown that this population has very low genetic variation compared with populations elsewhere in the world, indicating that the population descended from a small number of sharks2.

Using their new method the researchers amplified DNA from nine specimens aged 20 to 40 years old, and found similarly low levels of genetic variation. “These data support our hunch that low genetic variation in grey nurse shark is probably due to longer term processes than the recent human-induced population crash,” says Ahonen.

Noble intent

Les Noble, of the University of Aberdeen, UK, is about to publish a similar method for extracting DNA from sharks' teeth. “It’s not going to replace biopsy, but it is going to be useful for looking at past specimens,” he says.

“We also have plans to use approaches like this to identify rogue individuals,” he says. Noble says that scientists could analyse fragments of tooth found in a survivor’s wound after a shark attack. It should be possible to compare that sample with any sharks killed in the subsequent hunt — confirming that the rogue fish had been bagged.

Noble’s team is using his method to study the genetics of great white sharks. “We know very little about how these animals are using the oceans,” he says. “And without knowing a bit more about the genetics of these animals we can’t legislate properly for conservation.” 

  • References

    1. Ahonen, H. & Stow, A. J. Fish Biol. 73, 450-455 (2008). DOI: 10.1111/j.1095-8649.2008.01896.x | Article |
    2. Stow, A. et al. Biol. Lett. 2, 308-311 (2006). | Article | PubMed |
Commenting is now closed.