The Museum is currently undertaking research to verify whether ancient DNA has survived and can be extracted from insects that have been entombed in amber for millions of years.
Figure 1. A bee preserved in Amber.
The survival of fragments of DNA over geological time scales is both both theoretically unlikely and empirically difficult to prove. Yet there have been several recently published reports of successful DNA retrieval from amber-preserved insects ranging in age from 25 to 125 million years. Unfortunately none of these claims has yet been independently replicated, which is essential to establish their authenticity. Therefore, we are assessing the reproducibility of published experiments under strict conditions designed to minimize the risk of contamination from modern DNA. If this proves successful, our secondary aim is to investigate whether these ancient DNA sequences provide any useful information which might help our understanding of relationships amongst living taxa, and the possible evolutionary processes at the molecular level.
We have been attempting to obtain DNA sequences from the nuclear and mitochondrial small subunit ribosomal RNA genes from bees preserved in both copal resin produced by trees and the amber this eventually forms. Copal specimens (genus Trigona) are derived from the east coast of Africa and are several thousand years old. Amber specimens (genus Proplebeia) are derived from the Dominican Republic and are approximately 30 million years old. Rigorous proceedures (widely used in ancient DNA studies) are used to prevent contamination of samples by contemporary DNA. These include having a dedicated and physically isolated laboratory in which tissue is extracted from the amber-entombed insect and polymerase chain reactions (PCR) are setup to replicate any remnant DNA. We have optimized both DNA extraction and PCR conditions to be both highly efficient and sensitive to the small numbers of degraded DNA fragments expected in specimens of this age.
Given the sensitivity of our experimental procedures, contamination has proved to be extremely difficult to eradicate entirely. To date we have examined 12 tissue extracts plus controls from two amber and two copal bees showing pristine preservation. None has yielded any DNA that can be identified as being derived from the insects themselves. In most cases apparently positive PCR products were subsequently shown to be of fungal or human origin. Further identification of all PCR products obtained, is needed to confirm the absence of genuine insect DNA.
To reduce the problems of contamination still further, we have been using some insect specific PCR primers. However, it has not always been possible to find appropriate primer sites spanning useful sequence lengths. Further specimens of copal and amber bees, as well as smaller bodied phorid flies, remain to be examined and these may yet yield positive results. However, it is clear that ancient DNA from such material is neither preserved in abundance nor easy to extract, if it is present at all. Scepticism about this area of ancient DNA research must remain high as a consequence of our currnet inability to reproduce published results. As we continue to examine more specimens it will become clear whether geologically ancient DNA truly exists. Continued failure to replicate previous claims will hopefully be taken as compelling evidence for the inability of DNA to survive through geological time, while any success will provide the essential independent verification that DNA can survive over millions of years.
This project is part of the Systematics and Evolution Research Theme.
For further information contact:
Dr Jeremy Austin,
Andrew Ross, Dr Andrew Smith,
Dr Richard Thomas, Dr Richard Fortey
Departments of Palaeontology and Zoology
The Natural History Museum
Cromwell Road
London SW7 5BD UK
Tel: +44 (0) 171 938 9152 Fax: +44 (0) 171 938 8754
Email: jja@nhm.ac.uk
