Evaluation of sample collection and storage protocols for surface eDNA surveys of an invasive terrestrial insect

Environmental DNA surveys have revolutionized monitoring of rare or cryptic species and species inhabiting areas where conventional sampling is difficult or dangerous. Recent advancements within terrestrial environments include the capture of eDNA deposited by animals on surfaces such as tree bark and foliage, hereafter “surface eDNA.” Notably, a technique which uses commercial paint rollers to aggregate surface eDNA has been deployed with success to detect the presence of forest insect pests providing a potentially powerful new management tool. However, before widespread adoption is feasible, the efficiency and logistics of roller sample collection and study design, especially relative to realistic survey conditions, must be evaluated. We compared the performance of two DNA preservation treatments—cold and ethanol—on their ability to reduce the loss of captured eDNA on rollers over time. Additionally, we evaluated how the detection probability of our target species, the spotted lanternfly (Lycorma delicatula), varied with sampling effort (time spent rolling per sample) and the initial quantity of eDNA present. Finally, we evaluated how the number of trees sampled per roller influenced the final concentrations of lanternfly eDNA remaining on the roller. We found storing rollers with ethanol or cold temperatures resulted in 3–10-fold greater concentrations of experimentally controlled eDNA relative to no treatment after 24 h. Detection probability declined as the amount of lanternfly eDNA decreased, but did not change in response to sampling effort over sample time (10–80 s/tree). Finally, recovered lanternfly eDNA decreased as more trees were sampled by a single roller—a 91% reduction after 7 trees—potentially due to captured DNA being transferred back from the roller onto the bark. Our results provide improved guidance for deploying roller surface eDNA methods for spotted lanternfly surveys, and for invasive insect pest surveillance and monitoring programs generally

Differences in Energy Expenditures and Growth Dilution Explain Higher PCB Concentrations in Male Summer Flounder

<div><p>Comparison of polychlorinated biphenyl (PCB) concentrations between the sexes of mature fish may reveal important behavioral and physiological differences between the sexes. We determined whole-fish PCB concentrations in 23 female summer flounder <i>Paralichthys dentatus</i> and 27 male summer flounder from New Jersey coastal waters. To investigate the potential for differences in diet or habitat utilization between the sexes, carbon and nitrogen stable isotope ratios were also determined. In 5 of the 23 female summer flounder, PCB concentrations in the somatic tissue and ovaries were determined. In addition, we used bioenergetics modeling to assess the contribution of the growth dilution effect to the observed difference in PCB concentrations between the sexes. Whole-fish PCB concentrations for females and males averaged 87 and 124 ng/g, respectively; thus males were 43% higher in PCB concentration compared with females. Carbon and nitrogen stable isotope ratios did not significantly differ between the sexes, suggesting that diet composition and habitat utilization did not vary between the sexes. Based on PCB determinations in the somatic tissue and ovaries, we predicted that PCB concentration of females would increase by 0.6%, on average, immediately after spawning due to release of eggs. Thus, the change in PCB concentration due to release of eggs did not explain the higher PCB concentrations observed in males. Bioenergetics modeling results indicated that the growth dilution effect could account for males being 19% higher in PCB concentration compared with females. Thus, the bulk of the observed difference in PCB concentrations between the sexes was not explained by growth dilution. We concluded that a higher rate of energy expenditure in males, stemming from greater activity and a greater resting metabolic rate, was most likely the primary driver for the observed difference in PCB concentrations between the sexes.</p></div

Whole-fish ƩPCB as a function of lipid concentration for summer flounder from New Jersey coastal waters, November 2013.

<p>Displayed lines are from the fitted ANCOVA model.</p

Principal component 2 versus principal component 1, based on application of principal component analysis to proportions of ƩPCB in 10 homolog groups.

<p>The PCB congener determinations were for summer flounder from New Jersey coastal waters, November 2013.</p