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Within e DNA

When Does Missing DNA Matter?

A missing DNA signal can weaken a monster claim, but its meaning depends on sampling coverage, biology and detection limits.

On this page

  • Why non detection is not perfect absence
  • When a negative result is strongest
  • How rare visitors complicate the answer
Preview for When Does Missing DNA Matter?

Introduction

A negative environmental DNA (eDNA) result is often presented as evidence that a lake monster is not there. In reality, non-detection is more nuanced. eDNA is a powerful way to look for traces of life in water, and the absence of a DNA signal can substantially weaken some monster hypotheses. However, a negative result rarely proves absolute absence. Its meaning depends on how thoroughly the lake was sampled, how much DNA the animal would be expected to shed, how long DNA persists in the environment, and how likely the laboratory methods were to detect it if it were present. Scientific eDNA studies therefore treat non-detection as a probability statement rather than a simple yes-or-no verdict.[PLOS+2PubMed]journals.plos.orgEnvironmental DNA (eDNA) Detection Probability Is…by LS de Souza · 2016 · Cited by 261 — Detection probability is inferred through…Negative Results illustration 1 For cryptozoology, this distinction matters. A well-designed eDNA survey may strongly challenge claims of a resident population of large unknown animals, while still leaving open the possibility of an exceptionally rare visitor, a transient animal, or a creature that was simply missed.

Why Non-Detection Is Not Perfect Absence

Neil Gemmell - Environmental DNA for Biodiversity, Biosecurity, Global Health and Monster Hunting

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When a Negative Result Is Strongest

The evidential value of missing DNA increases dramatically when the claim being tested implies a large, permanent biological presence.

Consider a hypothetical lake monster described as a breeding population of large aquatic animals living year-round in a lake. Such animals would be expected to shed skin cells, mucus, waste products and other biological material continuously. If researchers collect samples from multiple depths, locations and seasons and repeatedly fail to find any trace of the expected DNA, the monster hypothesis becomes increasingly difficult to sustain.[National Park Service+2Biodiversity and Evolution]nps.govNational Park ServiceEnvironmental DNA: An Emerging Tool for Understanding…29 May 2024 — Environmental DNA (eDNA) can be used to deter…Published: May 2024

A negative result is especially persuasive when:<div class="content-enhancement content-enhancement--metric" markdown="1">

  • Sampling covers much of the habitat rather than a single location.
  • Multiple independent samples are collected.
  • Detection methods have already been shown to find rare species in similar environments.
  • Known resident species are detected successfully, demonstrating that the survey worked.
  • Statistical analysis indicates a high probability that a target species would have been found if present.[PMC+3Nature+3PMC]nature.comOptimising sampling and analysis protocols in…by A Buxton · 2021 · Cited by 89 — Here we analyse a large qPCR based eDNA data se…</div>

In practice, this means eDNA is often strongest against claims of hidden populations rather than against the mere possibility of a single unusual animal.Negative Results illustration 2

Loch Ness as a Case Study

The Loch Ness survey led by geneticist Neil Gemmell illustrates how scientists interpret a negative result. The project collected hundreds of samples from different locations and depths and identified thousands of DNA signatures from organisms living in the loch. Yet researchers found no evidence supporting popular theories involving surviving plesiosaurs, large sharks, sturgeon or giant catfish.[University of Otago+2Science Focus]otago.ac.nzfirst edna study of loch ness points to something fishyWe can't find any evidence of sturgeon either,” Professor Gemmell says…

Importantly, the researchers did not claim to have proved that no unknown animal could ever be present. Their conclusion was narrower and more scientifically defensible: the survey found no DNA evidence for several specific monster candidates despite extensive sampling. The absence of reptile DNA, in particular, strongly undermined the idea of a resident population of large prehistoric reptiles inhabiting the loch.[oldsaltblog.com+2Science Focus]oldsaltblog.comusing edna to search for nessie in scotland and angel sharks off corsicaUsing eDNA to Search for Nessie in Scotland and Angel…2 Oct 2023 — Geneticist Neil Gemmell of Otago University, who led the survey, s…

The Loch Ness work therefore demonstrates what negative eDNA results do best. They eliminate or weaken particular biological explanations rather than resolving every possible mystery.

Loch Ness monster might just be a giant eel

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How Rare Visitors Complicate the Answer

The greatest limitation of negative eDNA evidence appears when the claimed animal is extremely rare.

Imagine a large creature entering a lake only occasionally, spending little time near the sampled areas, or existing as a single individual rather than a population. Such an animal would leave far less DNA behind than a resident breeding population. In that situation, a survey could realistically miss it even if it existed.[Methods Blog+2Springer]methodsblog.comFor instance, a water sample may fail to …Read moreMethods BlogUncertainties in Species Occurrence Data: How to deal …17 Aug 2017 — In fact, eDNA surveys present the added challenge that…

Environmental conditions also matter. DNA degrades over time and can be diluted, transported or concentrated by water movement. Detection therefore depends not only on the animal itself but on where, when and how sampling occurred. Studies of eDNA detection routinely account for these uncertainties because imperfect detection is a recognised feature of the method.[Nature+3ResearchGate+3Biodiversity and Evolution]researchgate.netResearchGate(PDF) Environmental DNA reveals quantitative patterns of…Comparisons with long-term electrofishing surveys demonstrated th…

For cryptozoological claims, this creates an asymmetry. The more elusive and infrequent a creature is claimed to be, the harder it becomes for eDNA to rule it out completely. At the same time, those same claims become harder to reconcile with decades of sightings that supposedly indicate a substantial, recurring presence.Negative Results illustration 3

What Missing DNA Really Tells Us

DNA Sequencing Exposed Loch Ness’ Secret — Nessie Was Never What We Thought

Channel: Galaxy Vault

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Endnotes

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<summary>Source snippet</summary><p>Using eDNA to Search for Nessie in Scotland and Angel…2 Oct 2023 — Geneticist Neil Gemmell of Otago University, who led the survey, s…</p>

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<summary>Source snippet</summary><p>ResearchGate(PDF) Environmental DNA reveals quantitative patterns of…Comparisons with long-term electrofishing surveys demonstrated th…</p>

12. Source: researchgate.net
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<summary>Source snippet</summary><p>d false-positive rates, and their performance increased with the number of…Read more…</p>

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<summary>Source snippet</summary><p>ially zero; therefore, eels probably do not account for sightings of larger animals.Read more…</p>

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<summary>Source snippet</summary><p>We review statistical methods to account for such errors in the…Read more…</p>

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<summary>Source snippet</summary><p>Loch Ness Monster DNA study reveals 'plausible'…5 Sept 2019 — The findings quickly debunked one of the most popular theories: that the…</p>

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<summary>Source snippet</summary><p>in Traditional ChineseApr 29, 2026 — relating to the environment 自然環境的;有關環境的 People are becoming far more aware of environmental issues…</p>

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<summary>Source snippet</summary><p>Otago scientist reveals Loch Ness Monster could be…Sep 6, 2019 — An Otago scientist has cast major doubt on the existence of a monster…</p>

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<summary>Source snippet</summary><p>Now, by seeking out monster DNA from the loch's waters, scientists think they know what's down there.Read more…</p>

Additional References

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<summary>Source snippet</summary><p>Loch Ness monster might just be a giant eelScotland's fabled Loch Ness monster could possibly be a giant eel scientist said on Thursday a…</p>

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<summary>Source snippet</summary><p>eDNA IndexNeil Gemmell was introduced to the gathered press by Adrian Shine. Neil announced that there was no unexpected DNA in the loch…</p>

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<summary>Source snippet</summary><p>Long-range PCR via Illumina sequencing can generate DNA sequence fragments between…Read more…</p>

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<summary>Source snippet</summary><p>Professor Neil Gemmell from the University of Otago International is sequencing environmental DNA to find out. All animals leave behind m…</p>

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<summary>Source snippet</summary><p>Loch Ness monster could be a giant eel, say scientistsSep 5, 2019 — Loch Ness monster could be a giant eel, say scientists · The Loch Nes…</p>

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