Ancient DNA in
Extinct Malgasy Primates
Within the past 2,000 years, approximately 25 species of large-bodied vertebrates went to extinction on the island of Madagascar; the vast majority of these were primates. More than 15 species of primates from at least 7 genera are known from subfossil remains, some of which have been discovered only recently.
Although extinct, the fact that at least some subfossil lemurs existed as recently as 500 years ago clearly indicates that in an evolutionary sense, these primates should be considered contemporaries of the living lemurs. As with the other extinct Malagasy vertebrates, body size appears to have been a survival-determining factor, with small-bodied forms persisting and large-bodied forms disappearing. The evolutionary relationships of the subfossil lemurs to the extant lemurs is unclear, as is the mechanism by which they were driven to extinction.
The development of the Polymerase Chain Reaction (PCR) laboratory technique has made it possible to recover DNA from otherwise impossible sources and therefore may offer a potential source of information for resolving these mysteries. We are generating a mitochondrial DNA (mtDNA) data base for the extinct Malagasy primates that will be used to investigate their phylogenetic, molecular-evolutionary, and extinction history.
Many of the laboratory methods that we employ were designed specifically to overcome obstacles that are inherent to the extraction and amplification of DNA that is damaged and in low copy number, characteristics that are typical of ancient DNA. The two primary complications are:
1) contamination from exogenous DNA sources, and
2) inhibition from chemical elements that co-purify with DNA and can prevent optimal functioning of DNA polymerases.
Mitochondrial DNA is the molecule of choice for aDNA studies because it exists in high copy number within a given cell. After the DNA is successfully extracted and amplified, it is sequenced with dye-termination cycle-sequencing methods. Sequences are confirmed in independent laboratories (e.g., Dr. Tom Parsons, Armed Forces DNA Identification Lab) to control for the possibility of intra-lab contamination.
The majority of our samples have been acquired from the paleontological collections of the University of Madagascar Ð Antananarivo (courtesy of Madame Berthe Rakotosamimanana), from the collections of the Duke University Primate Center courtesy of Dr. Elwyn Simons, and from field studies conducted in Madagascar. Samples have been dated in collaboration with Dr. David Burney (Fordham University) with the 14C method at the Institute of Geological and Nuclear Sciences, Rafter Radiocarbon Laboratory. Thus far, we have acquired authentic sequences from specimens ranging in age from 1269 + 80 BP to 1815 + 80 BP (Yoder et al., 1999).
