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

View Article: PubMed Central - PubMed

ABSTRACT

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.

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Seasonal variations in eDNA concentration, in relation to adult and larval population size, adult body condition and temperature.(a) Shows Log10 (x + 0.0001) of the mean eDNA concentration (ngμL−1), per pond (black line, solid circles collected using glass-microfiber filters, solid squares collected using precipitation in ethanol) with 95% confidence intervals (grey) across the eight ponds. (b) Shows the mean estimated population size per pond black (adults - solid line, larvae - broken line) with 95% confidence intervals (grey). (c) Shows mean body condition (males – solid line, females – dashed line) using the scaled mass index of adults caught each week throughout a survey season with 95% confidence intervals (grey). (d) Shows mean weekly temperatures in degrees Celsius through the study period. The vertical dotted line represents the end of the breeding season and the start of the post-breeding season, as related to the models described in Tables 1, 2.
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f1: Seasonal variations in eDNA concentration, in relation to adult and larval population size, adult body condition and temperature.(a) Shows Log10 (x + 0.0001) of the mean eDNA concentration (ngμL−1), per pond (black line, solid circles collected using glass-microfiber filters, solid squares collected using precipitation in ethanol) with 95% confidence intervals (grey) across the eight ponds. (b) Shows the mean estimated population size per pond black (adults - solid line, larvae - broken line) with 95% confidence intervals (grey). (c) Shows mean body condition (males – solid line, females – dashed line) using the scaled mass index of adults caught each week throughout a survey season with 95% confidence intervals (grey). (d) Shows mean weekly temperatures in degrees Celsius through the study period. The vertical dotted line represents the end of the breeding season and the start of the post-breeding season, as related to the models described in Tables 1, 2.

Mentions: Two distinct peaks were seen in eDNA concentration (Fig. 1). The first peak corresponded to the end of the adult breeding season in early June. The second peak was observed from mid-July to mid-August and corresponded with the peak in larval numbers. The influences on eDNA concentration over the breeding season (26 February to 18 June) were identified using the first set of models. The change in body condition measured by the Scaled Mass Index (SMI)34 fell from a peak on 6 March through the breeding season and continued to fall into the post-breeding season, with most of the decline occurring from 9 April through to 4 June. Both sexes showed declines in SMI score with females showing a slightly greater decrease than males (Fig. 1). The sharpest decline in body condition for both males and females occurred in the key breeding months of April and May. During the same core period of April and May the mean eDNA concentration rose considerably but adult population changed very little, and larvae were first identified in the ponds at the beginning of June. As would be expected, temperature and UV both increased as the breeding season progressed, from early spring into early summer. This resulted in the model with the greatest AIC support (∆AIC to second model = 0.5) comprising adult abundance, larval abundance, temperature, and male and female body condition as predictors of eDNA concentration (Table 1). Three other models were shown to have strong support (∆AIC ≤ 2) also detailed in Table 1.


Seasonal variation in environmental DNA in relation to population size and environmental factors
Seasonal variations in eDNA concentration, in relation to adult and larval population size, adult body condition and temperature.(a) Shows Log10 (x + 0.0001) of the mean eDNA concentration (ngμL−1), per pond (black line, solid circles collected using glass-microfiber filters, solid squares collected using precipitation in ethanol) with 95% confidence intervals (grey) across the eight ponds. (b) Shows the mean estimated population size per pond black (adults - solid line, larvae - broken line) with 95% confidence intervals (grey). (c) Shows mean body condition (males – solid line, females – dashed line) using the scaled mass index of adults caught each week throughout a survey season with 95% confidence intervals (grey). (d) Shows mean weekly temperatures in degrees Celsius through the study period. The vertical dotted line represents the end of the breeding season and the start of the post-breeding season, as related to the models described in Tables 1, 2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5385492&req=5

f1: Seasonal variations in eDNA concentration, in relation to adult and larval population size, adult body condition and temperature.(a) Shows Log10 (x + 0.0001) of the mean eDNA concentration (ngμL−1), per pond (black line, solid circles collected using glass-microfiber filters, solid squares collected using precipitation in ethanol) with 95% confidence intervals (grey) across the eight ponds. (b) Shows the mean estimated population size per pond black (adults - solid line, larvae - broken line) with 95% confidence intervals (grey). (c) Shows mean body condition (males – solid line, females – dashed line) using the scaled mass index of adults caught each week throughout a survey season with 95% confidence intervals (grey). (d) Shows mean weekly temperatures in degrees Celsius through the study period. The vertical dotted line represents the end of the breeding season and the start of the post-breeding season, as related to the models described in Tables 1, 2.
Mentions: Two distinct peaks were seen in eDNA concentration (Fig. 1). The first peak corresponded to the end of the adult breeding season in early June. The second peak was observed from mid-July to mid-August and corresponded with the peak in larval numbers. The influences on eDNA concentration over the breeding season (26 February to 18 June) were identified using the first set of models. The change in body condition measured by the Scaled Mass Index (SMI)34 fell from a peak on 6 March through the breeding season and continued to fall into the post-breeding season, with most of the decline occurring from 9 April through to 4 June. Both sexes showed declines in SMI score with females showing a slightly greater decrease than males (Fig. 1). The sharpest decline in body condition for both males and females occurred in the key breeding months of April and May. During the same core period of April and May the mean eDNA concentration rose considerably but adult population changed very little, and larvae were first identified in the ponds at the beginning of June. As would be expected, temperature and UV both increased as the breeding season progressed, from early spring into early summer. This resulted in the model with the greatest AIC support (∆AIC to second model = 0.5) comprising adult abundance, larval abundance, temperature, and male and female body condition as predictors of eDNA concentration (Table 1). Three other models were shown to have strong support (∆AIC ≤ 2) also detailed in Table 1.

View Article: PubMed Central - PubMed

ABSTRACT

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.

No MeSH data available.


Related in: MedlinePlus