DNA and the Modern Museum
Traditional natural history collections have been essential to the study of taxonomy, systematics, evolution and biogeography. In taxonomy, species are generally described and classified on the basis of their morphological characters - shape, colour and other external features, as well as internal features of anatomy and skeletal structure. Systematics is an extension of taxonomy whereby species are classified in relation to their evolutionary links to other species. While museum curators worked on their collections and adopted new tools, such as electron microscopy and computerised data basing, as extensions of traditional morphological research, advances in molecular genetics were changing forever the study of taxonomy and systematics.
DeoxyriboNucleic Acid (DNA) is the biological molecule that carries genetic information. It is composed of two chain-like strands of genetic information. Each strand is a long sequence of four bases, adenine (A), cytosine (C), guanine (G) and thymine (T). With few exceptions this code is universal - the same four bases encode the information contained within the DNA of all organisms. This universality of the code allows direct comparison of the DNA of different organisms. Since DNA molecules accumulate changes through mutations, measuring the number of differences between the DNA sequences of two species will tell us how closely related they are. The more similar the DNA sequences, the more closely related are the two species.
In 1983 an American researcher, Kary Mullis, developed the polymerase chain reaction or PCR. Ten years later he was awarded the Nobel Prize (Chemistry) for this. PCR made DNA sequencing a relatively fast and affordable procedure. The two worlds of museums and molecular genetics were about to become partners for life.
Only small amounts of material are required for DNA analysis. Suitable DNA for sequencing using PCR can be obtained from a variety of museum sources, including dried specimens, ethanol-preserved material, feather bases, hair, skin, scrapings from feet pads and bone. Nevertheless, obtaining DNA from such sources is unreliable and often difficult, and the types of DNA analyses that can be undertaken with such materials are limited. DNA is most efficiently extracted from tissue material such as heart, liver, blood and skeletal muscle stored at temperatures below -70° C, so museums around the world are establishing and building up large cryogenic frozen tissue banks.
DNA sequence data can be used at a range of levels from answers to questions about the taxonomic status of populations through to the systematic relationships between species, genera, families and even phyla. DNA characters provide an independent data set for the recognition of taxonomic diversity that may not be apparent from traditional morphological assessments. As such, DNA information is an important tool in recognising diversity and its relationship to conservation needs. Understanding the nature and partitioning of genetic diversity in a species is critical to formulating effective conservation strategies.
DNA research also adds information to existing collections. It is possible to use DNA methods to sex unique or rare unsexed specimens, juveniles, or those with doubtful sex labels. DNA sequencing can also be used to determine the taxonomic status of species that have been described from a single museum specimen - are they colour variants or hybrids or has the method of preservation altered their colouration to such an extent that they appear unique?
In 1987, I was appointed Curator of Birds. A geneticist by training, my research focus was the evolutionary genetics of birds. At first, continuing my DNA-based research required a great deal of enterprise and lateral thinking. Initially I had the work undertaken in my old laboratory at the Australian National University, Canberra. Then I secured laboratory space closer to home at La Trobe University, Melbourne. When space became an issue there, my research assistants used laboratory facilities at the Royal Children's Hospital and the Victorian Institute of Animal Science.