One of the challenges in biology is accurate identification of organisms. Traditionally, organisms have been identified using morphological characteristics (physical features). However, there are challenges to using morphological characteristics alone, especially when trying to identify cryptic species (species that are very similar to other species). One possible solution has arisen from the field of molecular biology, DNA Barcoding.
What has been termed DNA barcoding, is a new strategy for identifying species that has been rapidly spreading throughout all fields of biology, ecology, and conservation. The process is, theoretically, pretty simple. It relies on three basic assumptions about genetics: (1) there are certain genes that exist in the DNA of all animals; (2) the DNA code of these genes varies between organisms; (3) the DNA code of these genes is more different between two different species than between two individuals of same species (in other words, the difference is greater between a bullfrog and a toad than between two bullfrogs). If all three of these requirements are met, then we can build a unique “barcode” for every animal, much like a store has a unique barcode of vertical lines that identifies each product sold.
Scientists have found a gene that satisfies these three requirements. It is a gene found within the mitochondria of cells called cytochrome oxidase subunit or more commonly abbreviated as cox1 or COI.
So how does it work? The first step is to build a database of known organisms, organisms that have been identified by more traditional methods. Then, take a sample of DNA from the organism you want to identify. Then sequence the COI gene. You can then cross reference the sequence you obtained against a database of known organisms. If you get a match, then you know what species you have. If you don’t get a match, then much like a criminal forensics team, you have more research to do and evidence to gather.
What are the possibilities for this technology?
DNA Barcoding opens the door for several opportunities in biology, ecology, and conservation. It offers a relatively inexpensive and fast method for identifying species, especially when there are a large number of animals that need to be identified. For example, conservationists could use DNA barcoding to determine how many different species live within a threatened habitat and potentially identify the presence of critically threatened species.
DNA barcoding could be used to identify cryptic animals that are not easily recognized using morphological characteristics. For example, in the oceans, many animals have offspring that spend days to years in the plankton, during which we don’t know what is happening or where they go. Part of the reason for this mystery is the fact that larvae, the very small and young stage of many animals life cycle, have very few distinguishing features. It is easy to tell the difference between a crab larvae and a sea urchin larvae, but very difficult (often impossible) to distinguish between two different species of crab larvae. Since the genes of larvae are the same as the adults, DNA barcoding could help researchers identify to which species a particular larva belongs.
For my research, I use DNA barcoding to help me identify the species of small and cryptic parasites I find in the animals I study.
As with any other technology, there are some limitations and challenges. At this time, no similar gene for plants or microbes has been identified, and the COI gene does not work for all animals. For example, the COI gene is not useful for distinguishing species within the phylum Cnidaria (includes jellyfish, anemones, and corals). One gene, while a helpful tool for recognizing species that we already know, or finding possible new species, is not sufficient to conclusively identifying a species as “new”.
Nothing will ever replace the use of morphological characteristics for species identification (especially for on the spot identification in the field), but DNA barcoding is a useful tool, and to borrow an analogy from others, takes us one step closer to creating a ‘Star Trek tricorder’.