A Lake Whisperer guide to how environmental DNA testing works, adapted from Wilderlab's FAQs.
Can I detect every species that's present?
No. Metabarcoding is a powerful way to survey species across the tree of life, from microbes to mammals, but it can't provide a complete biodiversity audit. A few reasons why:
- Reference gaps: Many species haven't had their DNA sequenced and added to a reference database yet.
- Shared barcodes: Some species share DNA barcodes with close relatives, so we can only identify them to genus level or higher.
- Assay panels: Each sample runs several "assays," each targeting a specific group of organisms. Detecting every species would require thousands of assays, which isn't cost-effective. Instead, we use an effective panel covering key groups like fish, mammals, plants, insects, and microbes. If you're after one or a few specific species, check with us that they're in scope before ordering.
- DNA shedding rates: Some species shed far more DNA than others. Fish are reliably detected because they leave lots of DNA as they swim. Birds leave very little (except ducks and pūkeko, who defecate profusely), so standard aquatic kits aren't recommended as a primary survey method for terrestrial species like bats, birds, stoats, or lizards.
For biodiversity assessments, we always recommend pairing eDNA with other visual survey methods.
How long does eDNA stay in the environment?
Once shed from an organism, eDNA typically lasts from a few hours to a few days. Biological and environmental factors break it down, and the rate depends on conditions such as whether the water is fresh, marine, stagnant, or flowing.
When is the best time to sample?
Sample during low-rainfall periods, or where there's been less than 10 mm of rain in the last 24 hours. Rain dilutes DNA in the water and stirs up sediment, which can clog the filters.
Can DNA sequence counts tell me how abundant a species is?
Generally, no. Treat eDNA results as a presence/absence tool. Several factors affect how much DNA is detected, including proximity (closer organisms leave stronger signals), mortality (dead organisms release a lot of DNA), and spawning (gametes in the water can flood the signal).
How long until I get my results?
From when samples arrive at the lab (assuming they've been submitted online), results take on average 10–15 working days for comprehensive analysis, or 15–20 working days for basic analysis. Seasonal surges can occasionally add time.
Do I need a chain of custody form?
Not strictly, but in most cases it's highly recommended. Including one helps our sample-receipt team quickly match your samples to the right job number. A chain of custody form is emailed to you after you submit your samples online.
It's a regulatory form, mainly needed when you're doing work for someone else, such as sampling for a council, or if the results could be used as evidence in environment court.
Can I use a sampling kit for marine testing?
Yes. Our kits are designed for freshwater, but they can be used in marine environments. Reach out with your requirements and we'll help you sort it out.
Why is there no human DNA in my sample results?
We remove all human DNA as the first step when processing samples, and it's impossible for us to detect individual people.
When should I use passive samplers instead of syringe samplers?
We recommend passive samplers for flowing sites with very high sediment load, post-rainfall sampling, and pest mammal monitoring.
What's the difference between a 1.2 µm and a 5.0 µm filter?
Standard kits use a 1.2 µm filter, suitable for most applications. Turbid-water kits use a 5.0 µm filter that's less prone to clogging in high-sediment or turbid environments.
How long do samples last?
Samples last at room temperature for up to 6 months once the preservative has been added (included in every sampling kit). For long-term storage, freeze the sample.
Source: https://wilderlab.co/