Seasonal variation in environmental DNA in relation to population size and environmental factors

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Analysing DNA that organisms release into the environment (environmental DNA, or eDNA) has

enormous potential for assessing rare and cryptic species. At present the method is only reliably used

to assess the presence-absence of species in natural environments, as seasonal influences on eDNA in

relation to presence, abundance, life stages and seasonal behaviours are poorly understood. A naturally

colonised, replicated pond system was used to show how seasonal changes in eDNA were influenced

by abundance of adults and larvae of great crested newts (Triturus cristatus). Peaks in eDNA were

observed in early June when adult breeding was coming to an end, and between mid-July and mid-

August corresponding to a peak in newt larval abundance. Changes in adult body condition associated

with reproduction also influenced eDNA concentrations, as did temperature (but not rainfall or UV).

eDNA concentration fell rapidly as larvae metamorphosed and left the ponds. eDNA concentration

may therefore reflect relative abundance in different ponds, although environmental factors can affect

the concentrations observed. Nevertheless, eDNA surveys may still represent an improvement over

unadjusted counts which are widely used in population assessments but have unreliable relationships

with population size.