Environmental DNA
Environmental DNA (eDNA) refers to DNA that can be extracted from samples taken from the environment, such as water, sediment and faeces. This is possible as all living organisms, from prokaryotes to eukaryotes, will leave traces of DNA in their environment. This DNA is typically released via urine, gametes, mucus, cell sluffing, faeces etc. eDNA is characterized by nuclear, mitochondrial, or chloroplast DNA in either living cells or left behind from the decomposition of dead organisms. This allows us to detect the presence of a species regardless of its life stage, and without physically identifying the species first hand.
How it works
Environmental DNA methods use quantitative Polymerase Chain Reaction (qPCR), genetic analysis techniques to extract and detect DNA of any organism that is of interest.
This method is dependent upon the targeted organism to be shedding genetic material into their environment. However, there is rarely a lack of genetic material in the environment.
A positive result from the qPCR analysis suggests that the target taxa is either within the sampling area or surrounding area as the genetic material was identified in the sample.
How long does E-dna persist in the environment?
When DNA is released into the environment, it can be degraded by several biotic and abiotic factors (bacteria, UV radiation, temperature, fungi, endonucleases , water pH, etc.). However, much of this DNA does in fact persist in the environment as it can be absorbed by organic or inorganic particles such as sediment.
This fact alone allows us to be able to sample not only aquatic habitats but also terrestrial habitats as we are able to extract DNA from sediment cores as well as water samples.
Current Limits and Caveats of e-DNA
Currently, environmental DNA does not have the ability to distinguish between individuals of the same species, or to acquire measurements such as target taxa abundance, density, temporal proximity, or track the mobililty of species within a system.